From 23c3a1461c27dc31141e3b372f569afc8ad642aa Mon Sep 17 00:00:00 2001
From: Kit Langton <kit.langton@gmail.com>
Date: Mon, 24 Aug 2026 12:09:00 -0400
Subject: [PATCH] fix(merman): harden responsive diagram layouts (#44714)

---
 packages/merman/package.json                  |   1 +
 packages/merman/script/layout-audit.ts        |  98 ++++
 packages/merman/src/flowchart/drawing.ts      |  16 +-
 .../merman/src/flowchart/flowchart.test.ts    | 388 ++++++++++++-
 packages/merman/src/flowchart/labels.ts       |   6 +
 packages/merman/src/flowchart/layout.ts       | 294 ++++++++--
 packages/merman/src/flowchart/options.ts      |   2 +-
 packages/merman/src/flowchart/routing.ts      | 244 +++++++-
 packages/merman/src/flowchart/style.ts        |  12 +-
 packages/merman/src/layout-audit.test.ts      |  81 +++
 packages/merman/src/markdown.ts               |   8 +-
 packages/merman/src/state/diagram.test.ts     | 274 ++++++++-
 packages/merman/src/state/drawing.ts          | 109 ++--
 packages/merman/src/state/layout.test.ts      |  73 ++-
 packages/merman/src/state/layout.ts           | 204 +++++--
 packages/merman/src/state/parser.ts           |   4 +-
 packages/merman/src/state/render-grid.ts      |   3 +-
 packages/merman/src/state/routing.test.ts     | 158 +++++-
 packages/merman/src/state/routing.ts          | 342 ++++++++++--
 packages/merman/src/state/types.ts            |   4 +-
 .../merman/src/test/layout-audit/fixtures.ts  | 493 +++++++++++++++++
 .../merman/src/test/layout-audit/harness.ts   | 521 ++++++++++++++++++
 packages/merman/src/test/markdown.test.ts     |  48 ++
 .../system/storybook/index.tsx                |   3 +-
 .../system/storybook/merman-layouts.tsx       | 201 +++++++
 25 files changed, 3343 insertions(+), 244 deletions(-)
 create mode 100644 packages/merman/script/layout-audit.ts
 create mode 100644 packages/merman/src/layout-audit.test.ts
 create mode 100644 packages/merman/src/test/layout-audit/fixtures.ts
 create mode 100644 packages/merman/src/test/layout-audit/harness.ts
 create mode 100644 packages/tui/src/feature-plugins/system/storybook/merman-layouts.tsx

diff --git a/packages/merman/package.json b/packages/merman/package.json
index d65fe8783b6..66877df294e 100644
--- a/packages/merman/package.json
+++ b/packages/merman/package.json
@@ -10,6 +10,7 @@
     "./plugin": "./src/plugin.ts"
   },
   "scripts": {
+    "audit:layouts": "bun run script/layout-audit.ts",
     "test": "bun test --timeout 30000 --only-failures",
     "typecheck": "tsgo --noEmit"
   },
diff --git a/packages/merman/script/layout-audit.ts b/packages/merman/script/layout-audit.ts
new file mode 100644
index 00000000000..e6085ce518e
--- /dev/null
+++ b/packages/merman/script/layout-audit.ts
@@ -0,0 +1,98 @@
+import { mkdir } from "node:fs/promises"
+import { dirname, resolve } from "node:path"
+import {
+  auditAllFixtures,
+  summarizeAudits,
+  worstAudits,
+  type LayoutAudit,
+  type LayoutMetrics,
+} from "../src/test/layout-audit/harness.js"
+
+const outputPath = resolve(import.meta.dir, "../../../tmp/merman-layout-audit.md")
+const startedAt = performance.now()
+const audits = auditAllFixtures()
+const elapsedMs = performance.now() - startedAt
+const summary = summarizeAudits(audits)
+
+function label(audit: LayoutAudit): string {
+  return `${audit.fixture.id} @${audit.viewport}`
+}
+
+function metricTable(items: readonly LayoutAudit[]): string {
+  return [
+    "| Fixture | Viewport | Size | Area | Route length | Bends | Crossings | Shared cells | Overflow |",
+    "| --- | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: |",
+    ...items.map(
+      (audit) =>
+        `| \`${audit.fixture.id}\` | ${audit.viewport} | ${audit.metrics.width}x${audit.metrics.height} | ${audit.metrics.area} | ${audit.metrics.routeLength} | ${audit.metrics.bends} | ${audit.metrics.crossings} | ${audit.metrics.sharedRouteCells} | ${audit.metrics.overflow} |`,
+    ),
+  ].join("\n")
+}
+
+function worstSection(metric: keyof LayoutMetrics): string {
+  const worst = worstAudits(audits, metric)
+  return [`### ${metric}`, "", metricTable(worst)].join("\n")
+}
+
+function fixtureSection(audit: LayoutAudit): string {
+  return [
+    `<details${audit.fixture.curated || audit.violations.length > 0 ? " open" : ""}>`,
+    `<summary><code>${label(audit)}</code> · ${audit.metrics.width}x${audit.metrics.height} · area ${audit.metrics.area} · bends ${audit.metrics.bends} · crossings ${audit.metrics.crossings} · overflow ${audit.metrics.overflow}</summary>`,
+    "",
+    ...(audit.violations.length > 0 ? ["Violations:", "", ...audit.violations.map((item) => `- ${item}`), ""] : []),
+    "Source:",
+    "",
+    "```mermaid",
+    audit.fixture.source,
+    "```",
+    "",
+    "Rendered output:",
+    "",
+    "```text",
+    audit.output,
+    "```",
+    "",
+    "</details>",
+  ].join("\n")
+}
+
+const grouped = Map.groupBy(audits, (audit) => `${audit.fixture.kind}/${audit.fixture.family}`)
+const violations = audits.flatMap((audit) => audit.violations.map((violation) => `${label(audit)}: ${violation}`))
+const markdown = [
+  "# Merman Layout Audit",
+  "",
+  `Generated from ${new Set(audits.map((audit) => audit.fixture.id)).size} sources and ${audits.length} layout runs.`,
+  "",
+  `Structural violations: **${violations.length}**`,
+  "",
+  "## Aggregate Metrics",
+  "",
+  "```json",
+  JSON.stringify(summary, null, 2),
+  "```",
+  "",
+  "## Worst Offenders",
+  "",
+  ...(["area", "bends", "crossings", "sharedRouteCells", "overflow"] as const).flatMap((metric) => [
+    worstSection(metric),
+    "",
+  ]),
+  "## Fixtures",
+  "",
+  ...[...grouped.entries()].flatMap(([family, items]) => [
+    `### ${family}`,
+    "",
+    metricTable(items),
+    "",
+    ...items.flatMap((audit) => [fixtureSection(audit), ""]),
+  ]),
+].join("\n")
+
+await mkdir(dirname(outputPath), { recursive: true })
+await Bun.write(outputPath, markdown)
+
+console.log(`Wrote ${audits.length} layout runs to ${outputPath} in ${elapsedMs.toFixed(0)}ms`)
+if (violations.length > 0) {
+  console.error(violations.join("\n"))
+  process.exitCode = 1
+}
diff --git a/packages/merman/src/flowchart/drawing.ts b/packages/merman/src/flowchart/drawing.ts
index 1582ad5a463..96bc54d7333 100644
--- a/packages/merman/src/flowchart/drawing.ts
+++ b/packages/merman/src/flowchart/drawing.ts
@@ -43,8 +43,9 @@ function mergeFlowchartCell(
   if (incoming.style !== "edge") return incoming
   if (existing.style === "label") return existing
   if (incoming.char === " ") return existing
-  if ((existing.style !== "edge" && existing.style !== "group") || existing.char === " ") return incoming
-  if (DIAGRAM_ARROW_HEADS.has(existing.char) || DIAGRAM_ARROW_HEADS.has(incoming.char)) return incoming
+  if (existing.style !== "edge" || existing.char === " ") return incoming
+  if (DIAGRAM_ARROW_HEADS.has(existing.char)) return existing
+  if (DIAGRAM_ARROW_HEADS.has(incoming.char)) return incoming
 
   return {
     ...incoming,
@@ -75,22 +76,23 @@ function drawNode(
 ): void {
   const chars = BorderChars[borderStyle]
   const style: FlowchartCellStyle = node.shape === "database" ? "database" : "node"
+  const border: FlowchartCellStyle = node.shape === "database" ? "databaseBorder" : "nodeBorder"
 
   if (node.shape === "decision") {
     drawDiagramDiamond(
       bounds,
-      (x, y, char) => grid.setCell(x, y, char, style),
+      (x, y, char) => grid.setCell(x, y, char, border),
       diagramDiamondCharactersFromBorder(chars),
     )
   } else if (node.shape === "subroutine") {
     fillDiagramFrameInterior(bounds, (x, y) => grid.setCell(x, y, " ", style))
-    drawSubroutineNode(grid, bounds, chars, style)
+    drawSubroutineNode(grid, bounds, chars, border)
   } else if (node.shape === "database") {
     fillDiagramFrameInterior(bounds, (x, y) => grid.setCell(x, y, " ", style))
-    drawDatabaseNode(grid, bounds, chars, style)
+    drawDatabaseNode(grid, bounds, chars, border)
   } else {
     fillDiagramFrameInterior(bounds, (x, y) => grid.setCell(x, y, " ", style))
-    drawDiagramFrame(bounds, chars, (x, y, char) => grid.setCell(x, y, char, style))
+    drawDiagramFrame(bounds, chars, (x, y, char) => grid.setCell(x, y, char, border))
   }
 
   const textTop =
@@ -270,7 +272,7 @@ function drawSourceConnectors(
     const connectorDirection = flowchartDirectionBetween(sourcePoint, connector)
     if (routeDirection && connectorDirection) {
       const cell = grid.getCell(sourcePoint.x, sourcePoint.y)
-      if (cell && cell.style !== "label") {
+      if (cell && cell.style !== "label" && !DIAGRAM_ARROW_HEADS.has(cell.char)) {
         grid.replaceCell(
           sourcePoint.x,
           sourcePoint.y,
diff --git a/packages/merman/src/flowchart/flowchart.test.ts b/packages/merman/src/flowchart/flowchart.test.ts
index 99c8229f495..ac3eb86f1bc 100644
--- a/packages/merman/src/flowchart/flowchart.test.ts
+++ b/packages/merman/src/flowchart/flowchart.test.ts
@@ -1,7 +1,10 @@
 import { describe, expect, test } from "bun:test"
 import { parseColor, TextAttributes } from "@opentui/core"
 import stringWidth from "string-width"
+import { diagramArrowHeadBetween } from "../core/drawing.js"
+import { orthogonalPathPoints } from "../core/geometry.js"
 import { expectDiagram } from "../test/diagram.js"
+import { deploymentArchitectureSource } from "../test/layout-audit/fixtures.js"
 import { drawFlowchartDiagramGrid as drawParsedFlowchartDiagramGrid } from "./drawing.js"
 import {
   DEFAULT_MIN_RANK_GAP,
@@ -35,7 +38,7 @@ function routeRunsAlongHorizontalBorder(
     const from = route.points[index - 1]!
     const to = route.points[index]!
     if (from.y !== to.y || !borderYs.has(from.y)) continue
-    if (Math.max(from.x, to.x) >= left && Math.min(from.x, to.x) <= right) return true
+    if (Math.min(Math.max(from.x, to.x), right) > Math.max(Math.min(from.x, to.x), left)) return true
   }
   return false
 }
@@ -52,7 +55,7 @@ function routeRunsAlongVerticalBorder(
     const from = route.points[index - 1]!
     const to = route.points[index]!
     if (from.x !== to.x || !borderXs.has(from.x)) continue
-    if (Math.max(from.y, to.y) >= top && Math.min(from.y, to.y) <= bottom) return true
+    if (Math.min(Math.max(from.y, to.y), bottom) > Math.max(Math.min(from.y, to.y), top)) return true
   }
   return false
 }
@@ -114,6 +117,111 @@ function boundsIntersect(
   )
 }
 
+function boundsContains(
+  outer: { left: number; top: number; width: number; height: number },
+  inner: { left: number; top: number; width: number; height: number },
+): boolean {
+  return (
+    inner.left >= outer.left &&
+    inner.top >= outer.top &&
+    inner.left + inner.width <= outer.left + outer.width &&
+    inner.top + inner.height <= outer.top + outer.height
+  )
+}
+
+function routesIntersect(
+  left: { points: readonly { x: number; y: number }[] },
+  right: { points: readonly { x: number; y: number }[] },
+): boolean {
+  const occupied = new Set(orthogonalPathPoints(left.points).map((point) => `${point.x}:${point.y}`))
+  return orthogonalPathPoints(right.points).some((point) => occupied.has(`${point.x}:${point.y}`))
+}
+
+function renderedDimensions(output: string): { width: number; height: number } {
+  const lines = output.split("\n")
+  return { width: Math.max(...lines.map((line) => stringWidth(line))), height: lines.length }
+}
+
+function expectResponsiveFlowchartValid(content: string, layoutMaxWidth: number) {
+  const diagram = parseMermaidFlowchartDiagram(content)
+  const options = { compact: true, layoutMaxWidth }
+  const layout = layoutParsedFlowchartDiagram(diagram, options)
+  const grid = drawParsedFlowchartDiagramGrid(diagram, options)
+  const output = renderFlowchartDiagram(content, options)
+  const nodes = [...layout.bounds.values()]
+
+  expect(layout.diagram.direction).toBe("TD")
+  for (let left = 0; left < nodes.length; left++) {
+    for (let right = left + 1; right < nodes.length; right++) {
+      expect(boundsIntersect(nodes[left]!, nodes[right]!)).toBe(false)
+    }
+  }
+  for (const route of layout.routes) {
+    expect(route.points.length).toBeGreaterThanOrEqual(2)
+    for (let index = 1; index < route.points.length; index++) {
+      const from = route.points[index - 1]!
+      const to = route.points[index]!
+      expect(from.x === to.x || from.y === to.y).toBe(true)
+    }
+    expect(terminalPointsTowardBounds(route, layout.bounds.get(route.edge.to)!)).toBe(true)
+    const end = route.points.at(-1)!
+    expect(grid.getCell(end.x, end.y)?.char).toBe(diagramArrowHeadBetween(route.points.at(-2)!, end))
+    if (route.edge.label) expect(output).toContain(route.edge.label)
+  }
+  expectFlowchartRoutesAvoidUnrelatedNodes(layout)
+
+  for (const subgraph of diagram.subgraphs ?? []) {
+    const frame = layout.subgraphBounds.get(subgraph.id)!
+    for (const nodeId of subgraph.nodeIds) expect(boundsContains(frame, layout.bounds.get(nodeId)!)).toBe(true)
+    expect(output).toContain(subgraph.label)
+  }
+  for (const node of layout.bounds.values()) {
+    for (const line of node.lines) expect(output).toContain(line)
+  }
+
+  const widestContent = Math.max(
+    ...nodes.map((node) => node.width),
+    ...layout.routes.flatMap((route) =>
+      route.edge.label ? [flowchartRouteLabelLayout(route, visualLength).width] : [],
+    ),
+  )
+  const dimensions = renderedDimensions(output)
+  expect(Math.max(...output.split("\n").map((line) => stringWidth(line)))).toBeLessThanOrEqual(
+    layoutMaxWidth + widestContent + 4,
+  )
+  return { dimensions, layout, output }
+}
+
+function generatedWideRankFlowchart(count: number): string {
+  const labels = [
+    "地域 gateway Ω",
+    "界面 worker λ",
+    "Long-running synchronization service",
+    "Cache café 🚀",
+    "Audit and observability pipeline",
+    "Provider μ endpoint",
+    "Fallback Ж service",
+    "Archive 数据 lake",
+    "Terminal résumé queue",
+  ]
+  const branches = labels
+    .slice(0, count)
+    .flatMap((label, index) => [
+      `    Hub ${index === 0 ? "-->|dispatch across regions and providers|" : "-->"} N${index}[${label}]`,
+      `    N${index} --> Join`,
+    ])
+  return [
+    "flowchart LR",
+    "  Start[Client α] --> Hub",
+    "  subgraph Services [地域 services Ω]",
+    "    Hub[Dispatch hub]",
+    ...branches,
+    "    Join[Join results]",
+    "  end",
+    "  Join --> Done[Complete ✓]",
+  ].join("\n")
+}
+
 function expectFlowchartRoutesAvoidUnrelatedNodes(layout: ReturnType<typeof layoutFlowchartDiagram>): void {
   for (const route of layout.routes) {
     for (const [id, bounds] of layout.bounds) {
@@ -327,6 +435,52 @@ describe("FlowchartDiagram", () => {
     `)
   })
 
+  test.each(
+    (["LR", "RL", "TD", "TB", "BT"] as const).flatMap((direction) =>
+      [false, true].map((compact) => ({ direction, compact })),
+    ),
+  )(
+    "preserves every target arrowhead after painting $direction routes with compact=$compact",
+    ({ direction, compact }) => {
+      const content = `flowchart ${direction}
+  A[A]
+  B[B]
+  C[C]
+  D[D]
+  A --> A
+  A --> C
+  C --> B`
+      const diagram = parseMermaidFlowchartDiagram(content)
+      const layout = layoutParsedFlowchartDiagram(diagram, { compact })
+      const grid = drawParsedFlowchartDiagramGrid(diagram, { compact })
+
+      for (const route of layout.routes) {
+        const end = route.points.at(-1)!
+        expect(grid.getCell(end.x, end.y)?.char).toBe(diagramArrowHeadBetween(route.points.at(-2)!, end))
+      }
+    },
+  )
+
+  test.each(
+    (["LR", "RL", "TD", "TB", "BT"] as const).flatMap((direction) =>
+      [false, true].map((compact) => ({ direction, compact })),
+    ),
+  )("keeps crossed endpoint-disjoint $direction routes separate with compact=$compact", ({ direction, compact }) => {
+    const layout = layoutFlowchartDiagram(
+      `flowchart ${direction}
+  A[A]
+  B[B]
+  C[C]
+  D[D]
+  A --> C
+  D --> B`,
+      { compact },
+    )
+
+    expect(layout.routes).toHaveLength(2)
+    expect(routesIntersect(layout.routes[0]!, layout.routes[1]!)).toBe(false)
+  })
+
   test("keeps vertical feedback labels clear of unrelated nodes", () => {
     const content = `flowchart TD
   S[Source] --> A[Alpha]
@@ -613,6 +767,7 @@ describe("FlowchartDiagram", () => {
       const loops = layout.routes.filter((route) => route.edge.from === "B" && route.edge.to === "B")
 
       expect(loops).toHaveLength(3)
+      expect(new Set(loops.map((route) => JSON.stringify(route.points))).size).toBe(3)
     },
   )
 
@@ -811,6 +966,119 @@ describe("FlowchartDiagram", () => {
     `)
   })
 
+  test("wraps the real deployment chart responsively without losing content or geometry", () => {
+    const expected = new Map([
+      [60, { width: 82, height: 108 }],
+      [80, { width: 97, height: 85 }],
+      [120, { width: 143, height: 77 }],
+      [160, { width: 163, height: 69 }],
+    ])
+    const results = [...expected].map(([budget, dimensions]) => {
+      const result = expectResponsiveFlowchartValid(deploymentArchitectureSource, budget)
+      expect(result.dimensions).toEqual(dimensions)
+      for (const frame of result.layout.subgraphBounds.values()) {
+        for (const other of result.layout.subgraphBounds.values()) {
+          if (frame !== other) expect(boundsIntersect(frame, other)).toBe(false)
+        }
+      }
+      return result.dimensions
+    })
+
+    for (let index = 1; index < results.length; index++) {
+      expect(results[index - 1]!.width).toBeLessThan(results[index]!.width)
+    }
+  })
+
+  test.each([7, 9])("wraps generated %s-node Unicode subgraph ranks across width targets", (count) => {
+    const results = [60, 80, 120].map(
+      (budget) => expectResponsiveFlowchartValid(generatedWideRankFlowchart(count), budget).dimensions,
+    )
+
+    for (let index = 1; index < results.length; index++) {
+      expect(results[index - 1]!.width).toBeLessThan(results[index]!.width)
+      expect(results[index - 1]!.height).toBeGreaterThanOrEqual(results[index]!.height)
+    }
+  })
+
+  test("keeps responsive local-direction subgraphs clear of sibling nodes", () => {
+    const layout = layoutFlowchartDiagram(
+      `flowchart BT
+  N0[Outside zero]
+  subgraph Outer
+    N2[Two]
+    subgraph Inner
+      direction LR
+      N3[Three]
+      N4[Four]
+    end
+    N5[X]
+  end
+  N7[Outside seven]
+  N7 --> N2
+  N2 -->|label 6| N5
+  N5 --> N4
+  N0 --> N7`,
+      { compact: true, layoutMaxWidth: 35 },
+    )
+    const nodes = [...layout.bounds.values()]
+
+    for (let left = 0; left < nodes.length; left++) {
+      for (let right = left + 1; right < nodes.length; right++) {
+        expect(boundsIntersect(nodes[left]!, nodes[right]!)).toBe(false)
+      }
+    }
+  })
+
+  test("keeps responsive sibling subgraph frames and long titles disjoint", () => {
+    const layout = layoutFlowchartDiagram(
+      `flowchart TD
+  subgraph Parent
+    direction LR
+    subgraph Left [A deliberately long left group title]
+      direction LR
+      A1[One] --> A2[Two]
+    end
+    subgraph Right [A deliberately long right group title]
+      direction LR
+      B1[Three] --> B2[Four]
+    end
+    A2 --> B1
+  end`,
+      { compact: true, layoutMaxWidth: 35 },
+    )
+
+    expect(boundsIntersect(layout.subgraphBounds.get("Left")!, layout.subgraphBounds.get("Right")!)).toBe(false)
+  })
+
+  test("does not change parallel routes for a non-binding width target", () => {
+    const diagram = parseMermaidFlowchartDiagram(`flowchart TD
+  A[A] -->|one| B[B]
+  A -->|two| B`)
+    const unconstrained = layoutParsedFlowchartDiagram(diagram, { compact: true })
+    const nonBinding = layoutParsedFlowchartDiagram(diagram, { compact: true, layoutMaxWidth: 1_000 })
+
+    expect(nonBinding.routes.map((route) => route.points)).toEqual(unconstrained.routes.map((route) => route.points))
+  })
+
+  test("keeps responsive fan-out labels inside the width target", () => {
+    const content = `flowchart TD
+  subgraph Group
+    S[Source]
+    S -->|route 0 detail| N0[Node 0]
+    S -->|route 1 detail| N1[Node 1]
+    S -->|route 2 detail| N2[Node 2]
+    S -->|route 3 detail| N3[Node 3]
+  end`
+    const layout = layoutFlowchartDiagram(content, { compact: true, layoutMaxWidth: 30 })
+    const output = renderFlowchartDiagram(content, { compact: true, layoutMaxWidth: 30 })
+
+    for (const route of layout.routes) {
+      const label = flowchartRouteLabelLayout(route, visualLength)
+      expect(label.point.x + label.width).toBeLessThanOrEqual(30)
+    }
+    expect(Math.max(...output.split("\n").map((line) => stringWidth(line)))).toBeLessThanOrEqual(34)
+  })
+
   test("parses Mermaid flowchart nodes and standard arrows", () => {
     const diagram = parseMermaidFlowchartDiagram(`
 flowchart TD
@@ -1349,6 +1617,22 @@ flowchart LR
     expect(output).not.toContain("<br")
   })
 
+  test.each(
+    (["TD", "BT"] as const).flatMap((direction) =>
+      [false, true].flatMap((compact) => [2, 4].map((lines) => ({ direction, compact, lines }))),
+    ),
+  )(
+    "keeps $lines-line $direction labels off both terminal rows with compact=$compact",
+    ({ direction, compact, lines }) => {
+      const label = Array.from({ length: lines }, (_, index) => `line ${index + 1}`).join("<br/>")
+      const route = layoutFlowchartDiagram(`flowchart ${direction}\n  A[A] -->|${label}| B[B]`, { compact }).routes[0]!
+      const layout = flowchartRouteLabelLayout(route, visualLength)
+      const terminals = new Set([route.points[0]!.y, route.points.at(-1)!.y])
+
+      for (let y = layout.point.y; y < layout.point.y + layout.height; y++) expect(terminals.has(y)).toBe(false)
+    },
+  )
+
   test("expands canvas for multiline back-edge labels", () => {
     const output = renderFlowchartDiagram(`flowchart TD
   A --> B
@@ -1393,10 +1677,10 @@ graph LR
     expect(output).toContain("API")
     expect(output).toContain("DB")
     expect(output).toContain("╭─ Web App ")
-    expect(output.split("\n").find((line) => line.includes("API") && line.includes("DB"))).toContain("┼")
+    expect(output.split("\n").find((line) => line.includes("API") && line.includes("DB"))).not.toContain("┼")
   })
 
-  test("merges horizontal routes through vertical subgraph borders", () => {
+  test("breaks vertical subgraph borders where horizontal routes pass through", () => {
     const content = `flowchart LR
   Outside[Outside] --> Inside
   subgraph Group
@@ -1408,13 +1692,14 @@ graph LR
     const group = layout.subgraphBounds.get("Group")!
     const crossing = { x: group.left, y: layout.routes[0]!.points.at(-1)!.y }
 
-    expect(grid.getCell(crossing.x, crossing.y)?.char).toBe("┼")
+    expect(grid.getCell(crossing.x, crossing.y)?.char).toBe("─")
+    expect(grid.getCell(crossing.x, crossing.y)?.style).not.toBe("group")
     expect(grid.getCell(crossing.x - 1, crossing.y)?.char).toBe("─")
     expect(grid.getCell(crossing.x, crossing.y - 1)?.char).toBe("│")
     expect(grid.getCell(crossing.x, crossing.y + 1)?.char).toBe("│")
   })
 
-  test("merges vertical routes through horizontal subgraph borders", () => {
+  test("breaks horizontal subgraph borders where vertical routes pass through", () => {
     const content = `flowchart TD
   Outside[Outside] --> Inside
   subgraph Outer [O]
@@ -1428,7 +1713,8 @@ graph LR
     const outer = layout.subgraphBounds.get("Outer")!
     const crossing = { x: layout.routes[0]!.points[0]!.x, y: outer.top }
 
-    expect(grid.getCell(crossing.x, crossing.y)?.char).toBe("┼")
+    expect(grid.getCell(crossing.x, crossing.y)?.char).toBe("│")
+    expect(grid.getCell(crossing.x, crossing.y)?.style).not.toBe("group")
     expect(grid.getCell(crossing.x - 1, crossing.y)?.char).toBe("─")
     expect(grid.getCell(crossing.x + 1, crossing.y)?.char).toBe("─")
     expect(grid.getCell(crossing.x, crossing.y - 1)?.char).toBe("│")
@@ -1466,21 +1752,20 @@ graph LR
     expect(output).not.toContain("<br")
   })
 
-  test("merges transition lines through subgraph frame borders", () => {
-    const output = renderFlowchartDiagram(`
-flowchart TD
-  subgraph Verse [verse]
-    direction LR
-    A[A] --> B[B]
-    C[C] --> D[D]
+  test("keeps long Unicode subgraph titles from replacing entering arrowheads", () => {
+    const content = `flowchart TD
+  U[Up] --> A
+  subgraph G [界界界界界界]
+    A[A]
   end
-  B --> Join
-  D --> Join
-`)
-    const crossingLines = output.split("\n").filter((line) => line.includes("Join") || line.includes("├"))
+  A --> D[Down]`
+    const diagram = parseMermaidFlowchartDiagram(content)
+    const layout = layoutParsedFlowchartDiagram(diagram, { compact: true })
+    const grid = drawParsedFlowchartDiagramGrid(diagram, { compact: true })
+    const entry = layout.routes.find((route) => route.edge.from === "U")!
+    const end = entry.points.at(-1)!
 
-    expect(output).toContain(" verse ")
-    expect(crossingLines.join("\n").match(/┼/g)).toHaveLength(2)
+    expect(grid.getCell(end.x, end.y)?.char).toBe(diagramArrowHeadBetween(entry.points.at(-2)!, end))
   })
 
   test("lays out subgraph-local directions independently from the outer flow", () => {
@@ -1612,6 +1897,65 @@ flowchart TD
     }
   })
 
+  test("keeps nested local-direction layouts rigid across direction and compact matrices", () => {
+    const directions = ["LR", "RL", "TD", "BT"] as const
+    for (const global of directions) {
+      for (const outer of directions) {
+        for (const inner of directions) {
+          for (const compact of [false, true]) {
+            const layout = layoutFlowchartDiagram(
+              `flowchart ${global}
+  X[X] --> A
+  subgraph Outer [Outer]
+    direction ${outer}
+    subgraph Inner [Inner]
+      direction ${inner}
+      A[A] --> B[B]
+    end
+    B --> C[C]
+  end
+  C --> Y[Y]`,
+              { compact },
+            )
+            const nodes = [...layout.bounds.values()]
+            const innerFrame = layout.subgraphBounds.get("Inner")!
+            const outerFrame = layout.subgraphBounds.get("Outer")!
+            const a = layout.bounds.get("A")!
+            const b = layout.bounds.get("B")!
+            const c = layout.bounds.get("C")!
+
+            for (let left = 0; left < nodes.length; left++) {
+              for (let right = left + 1; right < nodes.length; right++) {
+                expect(boundsIntersect(nodes[left]!, nodes[right]!)).toBe(false)
+              }
+            }
+            expect(boundsContains(innerFrame, a)).toBe(true)
+            expect(boundsContains(innerFrame, b)).toBe(true)
+            expect(boundsContains(outerFrame, innerFrame)).toBe(true)
+            expect(boundsContains(outerFrame, c)).toBe(true)
+            expect(layout.routes.every((route) => route.points.length >= 2)).toBe(true)
+            expectFlowchartRoutesAvoidUnrelatedNodes(layout)
+            for (const frame of layout.subgraphBounds.values()) {
+              for (const route of layout.routes) {
+                expect(routeRunsAlongHorizontalBorder(route, frame)).toBe(false)
+                expect(routeRunsAlongVerticalBorder(route, frame)).toBe(false)
+              }
+            }
+
+            if (inner === "LR") expect(b.left).toBeGreaterThan(a.left)
+            if (inner === "RL") expect(b.left).toBeLessThan(a.left)
+            if (inner === "TD") expect(b.top).toBeGreaterThan(a.top)
+            if (inner === "BT") expect(b.top).toBeLessThan(a.top)
+            if (outer === "LR") expect(c.centerX).toBeGreaterThan(b.centerX)
+            if (outer === "RL") expect(c.centerX).toBeLessThan(b.centerX)
+            if (outer === "TD") expect(c.centerY).toBeGreaterThan(b.centerY)
+            if (outer === "BT") expect(c.centerY).toBeLessThan(b.centerY)
+          }
+        }
+      }
+    }
+  })
+
   test("compacts stacked subgraph-local direction rows", () => {
     const layout = layoutFlowchartDiagram(`
 flowchart TD
@@ -2037,8 +2381,10 @@ flowchart LR
   test("applies the global flowchart StyledText theme", () => {
     const grid = drawFlowchartDiagramGrid("flowchart LR\n  A[Alpha] --> B[Beta]")
     const node = parseColor("#ff0000")
-    const styled = renderGridStyledText(grid, resolveFlowchartStyleColors({ node }))
+    const nodeBorder = parseColor("#0000ff")
+    const styled = renderGridStyledText(grid, resolveFlowchartStyleColors({ node, nodeBorder }))
 
     expect(styled.chunks.some((chunk) => chunk.text.includes("Alpha") && chunk.fg?.equals(node))).toBe(true)
+    expect(styled.chunks.some((chunk) => chunk.text.includes("╭") && chunk.fg?.equals(nodeBorder))).toBe(true)
   })
 })
diff --git a/packages/merman/src/flowchart/labels.ts b/packages/merman/src/flowchart/labels.ts
index 270e475bb41..d07ddbc669c 100644
--- a/packages/merman/src/flowchart/labels.ts
+++ b/packages/merman/src/flowchart/labels.ts
@@ -18,6 +18,7 @@ const LABEL_BUS_CLEARANCE = 3
 const LABEL_NODE_CLEARANCE = 2
 const LABEL_LINE_CLEARANCE = 2
 const LABEL_PADDING = 1
+const LABEL_TERMINAL_CLEARANCE = 1
 
 export interface FlowchartEdgeLabelLayout {
   lines: string[]
@@ -63,6 +64,11 @@ function segmentLabelPoint(segment: DiagramSegment, labelWidth: number, labelHei
     return clampPoint(shiftPoint(shiftPoint(segment.from, segment.direction, LABEL_LINE_CLEARANCE), "up", labelHeight))
   }
 
+  const slot = insetSpan(segmentSpan(segment), LABEL_TERMINAL_CLEARANCE)
+  if (spanCapacity(slot) >= labelHeight) {
+    return clampPoint(point(segment.from.x + 1, centeredSpanStart(slot, labelHeight)))
+  }
+
   const center = shiftPoint(pointOnSegment(segment, midpoint(segmentSpan(segment))), "right")
   return clampPoint(shiftPoint(center, "up", Math.floor((labelHeight - 1) / 2)))
 }
diff --git a/packages/merman/src/flowchart/layout.ts b/packages/merman/src/flowchart/layout.ts
index b3836dc5fc3..50e69b9c737 100644
--- a/packages/merman/src/flowchart/layout.ts
+++ b/packages/merman/src/flowchart/layout.ts
@@ -14,7 +14,7 @@ import {
   flowchartVerticalBranchLabelGap,
 } from "./labels.js"
 import type { FlowchartDiagramRenderOptions } from "./options.js"
-import { routeFlowchartEdges } from "./routing.js"
+import { avoidFlowchartFrameBorders, routeFlowchartEdges } from "./routing.js"
 import type {
   FlowchartDiagram,
   FlowchartDirection,
@@ -23,6 +23,7 @@ import type {
   FlowchartNode,
   FlowchartNodeBounds,
   FlowchartNodeSize,
+  FlowchartPoint,
   FlowchartSubgraphBounds,
 } from "./types.js"
 
@@ -364,7 +365,8 @@ function layoutRankedNodes(
   sizes: ReadonlyMap<string, FlowchartNodeSize>,
   minNodeGap: number,
   requestedMinRankGap: number,
-): Map<string, FlowchartNodeBounds> {
+  targetWidth?: number,
+): { bounds: Map<string, FlowchartNodeBounds>; wrapped: boolean } {
   const horizontal = isHorizontalDirection(direction)
   const ranks = rankNodes(diagram)
   const maxRank = Math.max(0, ...ranks.values())
@@ -406,6 +408,7 @@ function layoutRankedNodes(
   const horizontalGaps = horizontal ? horizontalRankGaps(diagram, normalizedRanks, rankKeys, requestedMinRankGap) : []
   const verticalGaps = horizontal ? [] : verticalRankGaps(diagram, normalizedRanks, rankKeys, requestedMinRankGap)
   const bounds = new Map<string, FlowchartNodeBounds>()
+  let wrapped = false
 
   if (horizontal) {
     const columnWidths = rankKeys.map((rank) =>
@@ -442,68 +445,141 @@ function layoutRankedNodes(
       x += columnWidth + (horizontalGaps[rankIndex] ?? 0)
     }
   } else {
-    const rowHeights = rankKeys.map((rank) =>
-      Math.max(...ranksByIndex.get(rank)!.map((node) => sizes.get(node.id)!.height)),
-    )
-    const rowWidths = rankKeys.map((rank) => {
+    const rankBands = rankKeys.map((rank) => {
       const nodes = ranksByIndex.get(rank)!
-      return (
+      const roomyNodeGap = verticalNodeGap(rank)
+      const naturalWidth =
         nodes.reduce((total, node) => total + sizes.get(node.id)!.width, 0) +
-        Math.max(0, nodes.length - 1) * verticalNodeGap(rank)
+        Math.max(0, nodes.length - 1) * roomyNodeGap
+      const labeledEdges = diagram.edges.filter(
+        (edge) => edge.label && (normalizedRanks.get(edge.from) === rank || normalizedRanks.get(edge.to) === rank),
       )
-    })
-    const canvasWidth = Math.max(1, ...rowWidths)
-    let y = 0
-    for (let rankIndex = 0; rankIndex < rankKeys.length; rankIndex++) {
-      const rank = rankKeys[rankIndex]!
-      const nodes = ranksByIndex.get(rank)!
-      const rowHeight = rowHeights[rankIndex]!
-      const nodeGap = verticalNodeGap(rank)
-      let x = Math.floor((canvasWidth - rowWidths[rankIndex]!) / 2)
+      const needsLabelLanes =
+        labeledEdges.length > 1 &&
+        labeledEdges.some((edge) => {
+          const targets = new Set(
+            labeledEdges.filter((candidate) => candidate.from === edge.from).map((candidate) => candidate.to),
+          )
+          const sources = new Set(
+            labeledEdges.filter((candidate) => candidate.to === edge.to).map((candidate) => candidate.from),
+          )
+          const grouped = (ids: readonly string[]) =>
+            !diagram.subgraphs?.length ||
+            diagram.subgraphs.some((subgraph) => ids.every((id) => subgraph.nodeIds.includes(id)))
+          return (
+            (targets.size > 1 && grouped([edge.from, ...targets])) ||
+            (sources.size > 1 && grouped([edge.to, ...sources]))
+          )
+        })
+      const nodeGap =
+        targetWidth !== undefined && naturalWidth > targetWidth && !needsLabelLanes ? minNodeGap : roomyNodeGap
+      const bands: { nodes: FlowchartNode[]; width: number; height: number }[] = []
       for (const node of nodes) {
         const size = sizes.get(node.id)!
-        const top = y + Math.floor((rowHeight - size.height) / 2)
-        bounds.set(node.id, {
-          id: node.id,
-          ...size,
-          left: x,
-          top,
-          centerX: x + Math.floor(size.width / 2),
-          centerY: top + Math.floor(size.height / 2),
-        })
-        x += size.width + nodeGap
+        const current = bands.at(-1)
+        const width = current ? current.width + nodeGap + size.width : size.width
+        if (current && targetWidth !== undefined && width > targetWidth) {
+          wrapped = true
+          bands.push({ nodes: [node], width: size.width, height: size.height })
+          continue
+        }
+        if (!current) {
+          bands.push({ nodes: [node], width: size.width, height: size.height })
+          continue
+        }
+        current.nodes.push(node)
+        current.width = width
+        current.height = Math.max(current.height, size.height)
       }
-      y += rowHeight + (verticalGaps[rankIndex] ?? 0)
+      return { bands, nodeGap }
+    })
+    const canvasWidth = Math.max(1, ...rankBands.flatMap((rank) => rank.bands.map((band) => band.width)))
+    let y = 0
+    for (let rankIndex = 0; rankIndex < rankKeys.length; rankIndex++) {
+      const rank = rankBands[rankIndex]!
+      for (const [bandIndex, band] of rank.bands.entries()) {
+        let x = Math.floor((canvasWidth - band.width) / 2)
+        for (const node of band.nodes) {
+          const size = sizes.get(node.id)!
+          const top = y + Math.floor((band.height - size.height) / 2)
+          bounds.set(node.id, {
+            id: node.id,
+            ...size,
+            left: x,
+            top,
+            centerX: x + Math.floor(size.width / 2),
+            centerY: top + Math.floor(size.height / 2),
+          })
+          x += size.width + rank.nodeGap
+        }
+        y += band.height + (bandIndex < rank.bands.length - 1 ? minNodeGap : 0)
+      }
+      y += verticalGaps[rankIndex] ?? 0
     }
   }
 
-  return bounds
+  return { bounds, wrapped }
 }
 
 function layoutLocalSubgraphDirections(
   diagram: FlowchartDiagram,
   nodeBounds: Map<string, FlowchartNodeBounds>,
-  sizes: ReadonlyMap<string, FlowchartNodeSize>,
   minNodeGap: number,
   requestedMinRankGap: number,
-): void {
+  targetWidth?: number,
+): boolean {
+  let wrapped = false
   for (const subgraph of [...(diagram.subgraphs ?? [])].reverse()) {
     if (!subgraph.direction || subgraph.direction === diagram.direction) continue
-    const nodeIds = new Set(subgraph.nodeIds)
-    const nodes = diagram.nodes.filter((node) => nodeIds.has(node.id))
-    if (nodes.length === 0) continue
+    const childSubgraphs = (diagram.subgraphs ?? []).filter((child) => child.parentId === subgraph.id)
+    const coveredNodeIds = new Set(childSubgraphs.flatMap((child) => [...collectSubgraphNodeIds(diagram, child.id)]))
+    const items = [
+      ...childSubgraphs.flatMap((child) => {
+        const nodeIds = [...collectSubgraphNodeIds(diagram, child.id)]
+        const content = boundsFromChildren(nodeIds.flatMap((id) => nodeBounds.get(id) ?? []))
+        const bounds = content ? subgraphBoundFromChildren(child.id, child.label, [content]) : undefined
+        return bounds ? [{ id: `subgraph:${child.id}`, nodeIds, bounds, childId: child.id }] : []
+      }),
+      ...subgraph.nodeIds.flatMap((id) => {
+        if (coveredNodeIds.has(id)) return []
+        const bounds = nodeBounds.get(id)
+        return bounds ? [{ id, nodeIds: [id], bounds, childId: undefined }] : []
+      }),
+    ]
+    if (items.length === 0) continue
 
-    const currentBounds = boundsFromChildren(nodes.flatMap((node) => nodeBounds.get(node.id) ?? []))
+    const currentBounds = boundsFromChildren(items.map((item) => item.bounds))
     if (!currentBounds) continue
 
+    const itemByEndpoint = new Map<string, string>()
+    for (const item of items) {
+      for (const nodeId of item.nodeIds) itemByEndpoint.set(nodeId, item.id)
+      if (item.childId) itemByEndpoint.set(item.childId, item.id)
+    }
+    const nodes = items.map((item): FlowchartNode => ({ id: item.id, label: item.id, shape: "box" }))
     const localDiagram: FlowchartDiagram = {
       direction: subgraph.direction,
       nodes,
-      edges: diagram.edges.filter((edge) => nodeIds.has(edge.from) && nodeIds.has(edge.to)),
+      edges: diagram.edges.flatMap((edge) => {
+        const from = itemByEndpoint.get(edge.from)
+        const to = itemByEndpoint.get(edge.to)
+        return from && to && from !== to ? [{ ...edge, from, to }] : []
+      }),
       subgraphs: [],
     }
-    const localNodeGap = isHorizontalDirection(subgraph.direction) ? Math.max(4, minNodeGap - 1) : minNodeGap
-    const localBounds = layoutRankedNodes(localDiagram, subgraph.direction, sizes, localNodeGap, requestedMinRankGap)
+    const itemSizes = new Map(
+      items.map((item) => [item.id, { width: item.bounds.width, height: item.bounds.height, lines: [item.id] }]),
+    )
+    const localLayout = layoutRankedNodes(
+      localDiagram,
+      subgraph.direction,
+      itemSizes,
+      Math.max(minNodeGap, SUBGRAPH_PADDING_X * 2 + 1),
+      requestedMinRankGap,
+      targetWidth,
+    )
+    const localBounds = localLayout.bounds
+    wrapped ||= localLayout.wrapped
     const localExtent = boundsFromChildren([...localBounds.values()])
     if (!localExtent) continue
 
@@ -512,11 +588,66 @@ function layoutLocalSubgraphDirections(
     const dx = targetLeft - localExtent.left
     const dy = targetTop - localExtent.top
 
-    for (const [nodeId, bound] of localBounds) {
-      translateBounds(bound, dx, dy)
-      nodeBounds.set(nodeId, bound)
+    const translations = new Map<string, { dx: number; dy: number }>()
+    for (const item of items) {
+      const bound = localBounds.get(item.id)!
+      const itemDx = bound.left + dx - item.bounds.left
+      const itemDy = bound.top + dy - item.bounds.top
+      for (const nodeId of item.nodeIds) translations.set(nodeId, { dx: itemDx, dy: itemDy })
+    }
+
+    let groupOffset = { x: 0, y: 0 }
+    if (targetWidth !== undefined) {
+      const localNodeIds = new Set(translations.keys())
+      const external = [...nodeBounds.entries()].filter(([id]) => !localNodeIds.has(id)).map(([, bound]) => bound)
+      const overlaps = (offset: FlowchartPoint) =>
+        [...translations].some(([id, translation]) => {
+          const bound = nodeBounds.get(id)!
+          const left = bound.left + translation.dx + offset.x
+          const top = bound.top + translation.dy + offset.y
+          return external.some(
+            (other) =>
+              left < other.left + other.width + minNodeGap &&
+              left + bound.width + minNodeGap > other.left &&
+              top < other.top + other.height + minNodeGap &&
+              top + bound.height + minNodeGap > other.top,
+          )
+        })
+      if (overlaps(groupOffset)) {
+        const vertical = !isHorizontalDirection(diagram.direction)
+        const sign = diagram.direction === "RL" || diagram.direction === "BT" ? -1 : 1
+        let found = false
+        search: for (let distance = 1; distance < 1_000; distance++) {
+          const candidates = vertical
+            ? [
+                { x: 0, y: sign * distance },
+                { x: 0, y: -sign * distance },
+                { x: distance, y: 0 },
+                { x: -distance, y: 0 },
+              ]
+            : [
+                { x: sign * distance, y: 0 },
+                { x: -sign * distance, y: 0 },
+                { x: 0, y: distance },
+                { x: 0, y: -distance },
+              ]
+          for (const candidate of candidates) {
+            if (overlaps(candidate)) continue
+            groupOffset = candidate
+            found = true
+            break search
+          }
+        }
+        if (!found) throw new Error(`Subgraph ${subgraph.id} has no collision-free responsive position`)
+      }
+    }
+
+    for (const [nodeId, translation] of translations) {
+      const nodeBound = nodeBounds.get(nodeId)
+      if (nodeBound) translateBounds(nodeBound, translation.dx + groupOffset.x, translation.dy + groupOffset.y)
     }
   }
+  return wrapped
 }
 
 function edgeDirection(diagram: FlowchartDiagram, edge: FlowchartEdge): FlowchartDirection {
@@ -601,6 +732,7 @@ function separateTopLevelItems(
   nodeBounds: Map<string, FlowchartNodeBounds>,
   subgraphBounds: ReadonlyMap<string, FlowchartSubgraphBounds>,
   gap: number,
+  targetWidth?: number,
 ): boolean {
   const hasLocalDirection = (diagram.subgraphs ?? []).some(
     (subgraph) => subgraph.direction && subgraph.direction !== diagram.direction,
@@ -734,6 +866,35 @@ function separateTopLevelItems(
       crossCursor = start + shift + size + gap
     }
   }
+  if (targetWidth !== undefined && !horizontal) {
+    const intersects = (left: (typeof items)[number], right: (typeof items)[number]): boolean =>
+      [...left.nodeIds].some((leftId) => {
+        const leftBounds = nodeBounds.get(leftId)!
+        return [...right.nodeIds].some((rightId) => {
+          const rightBounds = nodeBounds.get(rightId)!
+          return (
+            leftBounds.left <= rightBounds.left + rightBounds.width - 1 &&
+            leftBounds.left + leftBounds.width - 1 >= rightBounds.left &&
+            leftBounds.top <= rightBounds.top + rightBounds.height - 1 &&
+            leftBounds.top + leftBounds.height - 1 >= rightBounds.top
+          )
+        })
+      })
+    for (let rightIndex = 1; rightIndex < items.length; rightIndex++) {
+      const right = items[rightIndex]!
+      for (let leftIndex = 0; leftIndex < rightIndex; leftIndex++) {
+        const left = items[leftIndex]!
+        if (!intersects(left, right)) continue
+        const leftBounds = boundsFromChildren([...left.nodeIds].map((id) => nodeBounds.get(id)!))!
+        const rightBounds = boundsFromChildren([...right.nodeIds].map((id) => nodeBounds.get(id)!))!
+        const shift = reversed
+          ? leftBounds.top - gap - (rightBounds.top + rightBounds.height)
+          : leftBounds.top + leftBounds.height + gap - rightBounds.top
+        moved ||= shift !== 0
+        moveItem(right, 0, shift)
+      }
+    }
+  }
   return moved
 }
 
@@ -771,6 +932,7 @@ function layoutFlowchartWithDirection(
   sourceDiagram: FlowchartDiagram,
   options: FlowchartDiagramRenderOptions,
   direction: FlowchartDirection,
+  responsiveFallback = false,
 ): FlowchartLayout {
   const diagram = direction === sourceDiagram.direction ? sourceDiagram : { ...sourceDiagram, direction }
   const horizontal = isHorizontalDirection(direction)
@@ -786,29 +948,65 @@ function layoutFlowchartWithDirection(
         : DEFAULT_MIN_VERTICAL_RANK_GAP,
   )
   const sizes = new Map(diagram.nodes.map((node) => [node.id, nodeSize(node)]))
-  const bounds = layoutRankedNodes(diagram, direction, sizes, minNodeGap, requestedMinRankGap)
-  layoutLocalSubgraphDirections(diagram, bounds, sizes, minNodeGap, requestedMinRankGap)
+  const targetWidth =
+    !horizontal && options.layoutMaxWidth !== undefined && Number.isFinite(options.layoutMaxWidth)
+      ? Math.max(1, Math.trunc(options.layoutMaxWidth))
+      : undefined
+  const ranked = layoutRankedNodes(diagram, direction, sizes, minNodeGap, requestedMinRankGap, targetWidth)
+  const bounds = ranked.bounds
+  const responsive = layoutLocalSubgraphDirections(diagram, bounds, minNodeGap, requestedMinRankGap, targetWidth)
+  const directionAligned = responsiveFallback || responsive || ranked.wrapped
 
   const subgraphs = diagram.subgraphs ?? []
   let subgraphBounds = new Map<string, FlowchartSubgraphBounds>()
   let routes: FlowchartEdgeRoute[]
   if (subgraphs.length === 0) {
-    routes = routeFlowchartEdges(diagram, bounds, (edge) => edgeDirection(diagram, edge))
+    routes = routeFlowchartEdges(
+      diagram,
+      bounds,
+      (edge) => edgeDirection(diagram, edge),
+      undefined,
+      targetWidth,
+      directionAligned,
+    )
   } else {
-    routes = routeFlowchartEdges(diagram, bounds, (edge) => edgeDirection(diagram, edge))
+    routes = routeFlowchartEdges(
+      diagram,
+      bounds,
+      (edge) => edgeDirection(diagram, edge),
+      undefined,
+      targetWidth,
+      directionAligned,
+    )
     subgraphBounds = layoutSubgraphs(diagram, bounds, routes)
     const moved = separateTopLevelItems(
       diagram,
       bounds,
       subgraphBounds,
       Math.max(1, Math.floor(requestedMinRankGap / 2)),
+      targetWidth,
     )
     if (moved) {
-      routes = routeFlowchartEdges(diagram, bounds, (edge) => edgeDirection(diagram, edge))
+      routes = routeFlowchartEdges(
+        diagram,
+        bounds,
+        (edge) => edgeDirection(diagram, edge),
+        undefined,
+        targetWidth,
+        directionAligned,
+      )
       subgraphBounds = layoutSubgraphs(diagram, bounds, routes)
     }
-    routes = routeFlowchartEdges(diagram, bounds, (edge) => edgeDirection(diagram, edge), subgraphBounds)
+    routes = routeFlowchartEdges(
+      diagram,
+      bounds,
+      (edge) => edgeDirection(diagram, edge),
+      subgraphBounds,
+      targetWidth,
+      directionAligned,
+    )
     subgraphBounds = layoutSubgraphs(diagram, bounds, routes)
+    avoidFlowchartFrameBorders(routes, bounds, subgraphBounds)
   }
   freezeRouteLabelPoints(routes)
   const allBounds = [...bounds.values(), ...subgraphBounds.values(), ...routeRenderBounds(routes)]
@@ -834,5 +1032,5 @@ export function layoutFlowchartDiagram(
   if (!isHorizontalDirection(direction) || maxWidth === undefined || !Number.isFinite(maxWidth)) return layout
   if (layout.width <= Math.max(1, Math.trunc(maxWidth))) return layout
 
-  return layoutFlowchartWithDirection(sourceDiagram, options, direction === "RL" ? "BT" : "TD")
+  return layoutFlowchartWithDirection(sourceDiagram, options, direction === "RL" ? "BT" : "TD", true)
 }
diff --git a/packages/merman/src/flowchart/options.ts b/packages/merman/src/flowchart/options.ts
index 23a0964ee96..b1ec05e6d0a 100644
--- a/packages/merman/src/flowchart/options.ts
+++ b/packages/merman/src/flowchart/options.ts
@@ -7,6 +7,6 @@ export interface FlowchartDiagramRenderOptions {
   borderStyle?: BorderStyle
   minNodeGap?: number
   minRankGap?: number
-  /** Fold oversized horizontal layouts vertically when their rendered width exceeds this limit. */
+  /** Target rendered width. Oversized horizontal layouts fold vertically and broad vertical ranks wrap. */
   layoutMaxWidth?: number
 }
diff --git a/packages/merman/src/flowchart/routing.ts b/packages/merman/src/flowchart/routing.ts
index 3c053c088d4..0ef1d320d3a 100644
--- a/packages/merman/src/flowchart/routing.ts
+++ b/packages/merman/src/flowchart/routing.ts
@@ -11,9 +11,11 @@ import {
   lane,
   oppositeSide,
   orthogonalPath,
+  orthogonalPathPoints,
   pathThrough,
   pathViaLane,
   segmentBetween,
+  segmentSpan,
   sideForDirection,
   snapCoordinate,
   shiftPoint,
@@ -138,11 +140,11 @@ function horizontalEdgePath(
   })
 }
 
-function selfEdgePath(bounds: FlowchartNodeBounds): FlowchartPoint[] {
+function selfEdgePath(bounds: FlowchartNodeBounds, laneOffset = 0): FlowchartPoint[] {
   const start = boundsSidePoint(bounds, "right")
   const end = boundsSidePoint(bounds, "bottom")
-  const rightLaneX = bounds.left + bounds.width + BUS_CLEARANCE
-  const bottomLaneY = bounds.top + bounds.height + 1
+  const rightLaneX = bounds.left + bounds.width + BUS_CLEARANCE + laneOffset
+  const bottomLaneY = bounds.top + bounds.height + 1 + laneOffset
   return [start, { x: rightLaneX, y: start.y }, { x: rightLaneX, y: bottomLaneY }, { x: end.x, y: bottomLaneY }, end]
 }
 
@@ -522,6 +524,8 @@ function routeVerticalFanIn(
 function routeParallelEdges(
   diagram: FlowchartDiagram,
   bounds: Map<string, FlowchartNodeBounds>,
+  directionForEdge: (edge: FlowchartEdge) => FlowchartDirection,
+  directionAligned: boolean,
   handled: Set<FlowchartEdge>,
   routes: FlowchartEdgeRoute[],
 ): void {
@@ -530,8 +534,18 @@ function routeParallelEdges(
     if (edges.length < 2) continue
     const from = bounds.get(edges[0]!.from)
     const to = bounds.get(edges[0]!.to)
-    if (!from || !to || from.id === to.id) continue
-    const parallelAxis = parallelLaneAxis(from, to)
+    if (!from || !to) continue
+    if (from.id === to.id) {
+      let laneOffset = 0
+      for (const edge of edges) {
+        routes.push({ edge, points: selfEdgePath(from, laneOffset) })
+        handled.add(edge)
+        laneOffset++
+      }
+      continue
+    }
+    const parallelAxis =
+      directionAligned && isVerticalDirection(directionForEdge(edges[0]!)) ? "x" : parallelLaneAxis(from, to)
     let previousRoute: FlowchartEdgeRoute | undefined
     for (const edge of edges) {
       const height = labelHeight(edge)
@@ -539,7 +553,7 @@ function routeParallelEdges(
         parallelAxis === "x"
           ? previousRoute
             ? rightRenderExtent(previousRoute) + NODE_CLEARANCE
-            : Math.max(boundsSidePoint(from, "right").x, boundsSidePoint(to, "right").x)
+            : Math.max(boundsSidePoint(from, "right").x, boundsSidePoint(to, "right").x) + (directionAligned ? 1 : 0)
           : previousRoute
             ? Math.max(...previousRoute.points.map((point) => point.y)) + (height > 1 ? height + 1 : 1)
             : Math.max(boundsSidePoint(from, "bottom").y, boundsSidePoint(to, "bottom").y) + (height > 1 ? height : 0)
@@ -795,6 +809,69 @@ function routeIntersectsLabels(route: FlowchartEdgeRoute, labels: readonly Flowc
   )
 }
 
+function pathsIntersect(left: readonly FlowchartPoint[], right: readonly FlowchartPoint[]): boolean {
+  const occupied = new Set(orthogonalPathPoints(left).map((point) => `${point.x}:${point.y}`))
+  return orthogonalPathPoints(right).some((point) => occupied.has(`${point.x}:${point.y}`))
+}
+
+function endpointDisjoint(left: FlowchartEdge, right: FlowchartEdge): boolean {
+  return left.from !== right.from && left.from !== right.to && left.to !== right.from && left.to !== right.to
+}
+
+function endpointConflictsWithRoutes(route: FlowchartEdgeRoute, otherRoutes: readonly FlowchartEdgeRoute[]): boolean {
+  const source = route.points[0]
+  const target = route.points.at(-1)
+  if (!source || !target) return false
+  return otherRoutes.some((other) => {
+    const otherSource = other.points[0]
+    const otherTarget = other.points.at(-1)
+    return (
+      (otherSource && target.x === otherSource.x && target.y === otherSource.y) ||
+      (otherTarget && source.x === otherTarget.x && source.y === otherTarget.y)
+    )
+  })
+}
+
+function pathRunsAlongFrame(points: readonly FlowchartPoint[], bounds: FlowchartSubgraphBounds): boolean {
+  const right = bounds.left + bounds.width - 1
+  const bottom = bounds.top + bounds.height - 1
+  for (let index = 1; index < points.length; index++) {
+    const segment = segmentBetween(points[index - 1]!, points[index]!)
+    if (!segment) continue
+    const span = segmentSpan(segment)
+    if (
+      segment.axis === "x" &&
+      (segment.from.y === bounds.top || segment.from.y === bottom) &&
+      Math.min(span.end, right) > Math.max(span.start, bounds.left)
+    ) {
+      return true
+    }
+    if (
+      segment.axis === "y" &&
+      (segment.from.x === bounds.left || segment.from.x === right) &&
+      Math.min(span.end, bottom) > Math.max(span.start, bounds.top)
+    ) {
+      return true
+    }
+  }
+  return false
+}
+
+function subgraphTitleBounds(bounds: FlowchartSubgraphBounds): {
+  left: number
+  top: number
+  width: number
+  height: number
+} {
+  const lines = splitDiagramLines(bounds.label)
+  return {
+    left: bounds.left + 2,
+    top: bounds.labelSide === "top" ? bounds.top : bounds.top + bounds.height - lines.length,
+    width: Math.max(...lines.map((line) => diagramTextWidth(` ${line} `))),
+    height: lines.length,
+  }
+}
+
 function avoidNodeObstacles(
   route: FlowchartEdgeRoute,
   routes: readonly FlowchartEdgeRoute[],
@@ -815,10 +892,23 @@ function avoidNodeObstacles(
       const allowedContact = isSource && isTarget ? "both" : isSource ? "source" : isTarget ? "target" : undefined
       return pathIntersectsBounds(candidate.points, bound, allowedContact)
     })
+  const intersectsStructuralObstacle = (candidate: FlowchartEdgeRoute): boolean =>
+    intersectsNode(candidate) ||
+    allSubgraphBounds.some(
+      (bound) =>
+        pathRunsAlongFrame(candidate.points, bound) ||
+        (bound.label.length > 0 && pathIntersectsBounds(candidate.points, subgraphTitleBounds(bound))),
+    )
+  const intersectsRoutingObstacle = (candidate: FlowchartEdgeRoute): boolean =>
+    intersectsStructuralObstacle(candidate) ||
+    endpointConflictsWithRoutes(candidate, otherRoutes) ||
+    otherRoutes.some(
+      (other) => endpointDisjoint(candidate.edge, other.edge) && pathsIntersect(candidate.points, other.points),
+    )
   const intersectsObstacle = (candidate: FlowchartEdgeRoute): boolean => {
     const label = candidate.edge.label ? flowchartRouteLabelLayout(candidate, diagramTextWidth) : undefined
     return (
-      intersectsNode(candidate) ||
+      intersectsRoutingObstacle(candidate) ||
       allNodeBounds.some((bound) => labelIntersectsBounds(label, bound)) ||
       allSubgraphBounds.some((bound) => labelIntersectsSubgraphFrame(label, bound)) ||
       labelIntersectsLabels(label, otherLabels) ||
@@ -839,19 +929,19 @@ function avoidNodeObstacles(
   const rightBusXs = [
     ...new Set([
       rightBusX,
-      ...otherLabels.map((label) => Math.max(rightBusX, label.point.x + label.width - 1 + BUS_CLEARANCE)),
+      ...otherLabels.map((label) => Math.max(rightBusX, label.point.x + label.width - 1 + NODE_CLEARANCE)),
     ]),
   ].sort((left, right) => left - right)
   const leftBusXs = [
-    ...new Set([leftBusX, ...otherLabels.map((label) => Math.min(leftBusX, label.point.x - BUS_CLEARANCE))]),
+    ...new Set([leftBusX, ...otherLabels.map((label) => Math.min(leftBusX, label.point.x - NODE_CLEARANCE))]),
   ].sort((left, right) => right - left)
   const topBusYs = [
-    ...new Set([topBusY, ...otherLabels.map((label) => Math.min(topBusY, label.point.y - BUS_CLEARANCE))]),
+    ...new Set([topBusY, ...otherLabels.map((label) => Math.min(topBusY, label.point.y - NODE_CLEARANCE))]),
   ].sort((left, right) => right - left)
   const bottomBusYs = [
     ...new Set([
       bottomBusY,
-      ...otherLabels.map((label) => Math.max(bottomBusY, label.point.y + label.height - 1 + BUS_CLEARANCE)),
+      ...otherLabels.map((label) => Math.max(bottomBusY, label.point.y + label.height - 1 + NODE_CLEARANCE)),
     ]),
   ].sort((left, right) => left - right)
   const busLimit = Math.max(1, Math.floor(Math.sqrt(ROUTING_CANDIDATE_BUDGET / 4)))
@@ -953,7 +1043,7 @@ function avoidNodeObstacles(
   if (from.id === to.id)
     return (
       shortest(selfLoops, (candidate) => !intersectsObstacle(candidate)) ??
-      shortest(selfLoops, (candidate) => !intersectsNode(candidate)) ??
+      shortest(selfLoops, (candidate) => !intersectsStructuralObstacle(candidate)) ??
       route
     )
   const currentTargetSide = sideForOutsidePoint(to, route.points.at(-1)!)
@@ -1002,8 +1092,8 @@ function avoidNodeObstacles(
       shortest(sameSides, (candidate) => !intersectsObstacle(candidate)) ??
       shortest(preservedSources, (candidate) => !intersectsObstacle(candidate)) ??
       shortest(attachments, (candidate) => !intersectsObstacle(candidate)) ??
-      shortest(preservedSources, (candidate) => !intersectsNode(candidate)) ??
-      shortest(attachments, (candidate) => !intersectsNode(candidate)) ??
+      shortest(preservedSources, (candidate) => !intersectsStructuralObstacle(candidate)) ??
+      shortest(attachments, (candidate) => !intersectsStructuralObstacle(candidate)) ??
       route
     )
   }
@@ -1012,8 +1102,8 @@ function avoidNodeObstacles(
     shortest(preservedTargets, (candidate) => !intersectsObstacle(candidate)) ??
     attachments.find((candidate) => !intersectsObstacle(candidate)) ??
     shortest(preservedSources, (candidate) => !intersectsObstacle(candidate)) ??
-    shortest(attachments, (candidate) => !intersectsNode(candidate)) ??
-    shortest(preservedSources, (candidate) => !intersectsNode(candidate)) ??
+    shortest(attachments, (candidate) => !intersectsStructuralObstacle(candidate)) ??
+    shortest(preservedSources, (candidate) => !intersectsStructuralObstacle(candidate)) ??
     route
   )
 }
@@ -1023,6 +1113,8 @@ function avoidLabelOverlap(
   otherRoutes: readonly FlowchartEdgeRoute[],
   bounds: ReadonlyMap<string, FlowchartNodeBounds>,
   subgraphBounds: ReadonlyMap<string, FlowchartSubgraphBounds> | undefined,
+  targetWidth?: number,
+  includeLabelWidth = true,
 ): FlowchartEdgeRoute {
   if (!route.edge.label) return route
   const nodeBounds = [...bounds.values()]
@@ -1040,7 +1132,14 @@ function avoidLabelOverlap(
       { left: sourcePoint.x, top: sourcePoint.y, width: 1, height: 1 },
     ]
   })
+  const hasParallelRoute = otherRoutes.some(
+    (other) => other.edge.from === route.edge.from && other.edge.to === route.edge.to,
+  )
   const intersectsObstacle = (label: FlowchartEdgeLabelLayout): boolean =>
+    (targetWidth !== undefined &&
+      (hasParallelRoute || !includeLabelWidth
+        ? label.point.x > targetWidth
+        : label.point.x + label.width > targetWidth)) ||
     nodeBounds.some((bound) => labelIntersectsBounds(label, bound)) ||
     frameBounds.some((bound) => labelIntersectsSubgraphFrame(label, bound)) ||
     labelIntersectsLabels(label, otherLabels) ||
@@ -1094,6 +1193,15 @@ function avoidLabelOverlap(
       }
     }
   }
+  if (targetWidth !== undefined && includeLabelWidth && current.point.x + current.width > targetWidth) {
+    const x = Math.max(0, targetWidth - current.width)
+    for (let distance = 0; distance < 100; distance++) {
+      for (const y of distance === 0 ? [current.point.y] : [current.point.y - distance, current.point.y + distance]) {
+        if (y < 0 || intersectsObstacle({ ...current, point: { x, y } })) continue
+        return { ...route, labelPoint: { x, y } }
+      }
+    }
+  }
   return route
 }
 
@@ -1102,6 +1210,8 @@ export function routeFlowchartEdges(
   bounds: Map<string, FlowchartNodeBounds>,
   directionForEdge: (edge: FlowchartEdge) => FlowchartDirection = () => diagram.direction,
   subgraphBounds?: ReadonlyMap<string, FlowchartSubgraphBounds>,
+  targetWidth?: number,
+  directionAligned = false,
 ): FlowchartEdgeRoute[] {
   const routedDiagram = { ...diagram, edges: diagram.edges.filter((edge) => !edge.orderOnly) }
   const handled = new Set<FlowchartEdge>()
@@ -1110,7 +1220,7 @@ export function routeFlowchartEdges(
     ? Math.min(...[...bounds.values(), ...subgraphBounds.values()].map((bound) => bound.left))
     : undefined
 
-  routeParallelEdges(routedDiagram, bounds, handled, routes)
+  routeParallelEdges(routedDiagram, bounds, directionForEdge, directionAligned, handled, routes)
 
   for (const direction of ["LR", "RL"] satisfies FlowchartDirection[]) {
     const horizontalEdges = routedDiagram.edges.filter(
@@ -1145,11 +1255,109 @@ export function routeFlowchartEdges(
   for (let index = routes.length - 1; index >= 0; index--) {
     routes[index] = avoidNodeObstacles(routes[index]!, routes, bounds, subgraphBounds, index)
   }
+  const subgraphs = diagram.subgraphs ?? []
+  const subgraphById = new Map(subgraphs.map((subgraph) => [subgraph.id, subgraph]))
+  const containers = (id: string) => {
+    const ids = new Set<string>()
+    let current = subgraphs.find((subgraph) => subgraph.nodeIds.includes(id))
+    while (current) {
+      ids.add(current.id)
+      current = current.parentId ? subgraphById.get(current.parentId) : undefined
+    }
+    return ids
+  }
+  const groupedLabelEdge = (edge: FlowchartEdge) => {
+    const fromContainers = containers(edge.from)
+    if (![...containers(edge.to)].some((id) => fromContainers.has(id))) return false
+    const targets = new Set(
+      routedDiagram.edges
+        .filter((candidate) => candidate.label && candidate.from === edge.from)
+        .map((candidate) => candidate.to),
+    )
+    const sources = new Set(
+      routedDiagram.edges
+        .filter((candidate) => candidate.label && candidate.to === edge.to)
+        .map((candidate) => candidate.from),
+    )
+    return targets.size > 1 || sources.size > 1
+  }
   return routes.reduce<FlowchartEdgeRoute[]>((resolved, route, index) => {
-    return [...resolved, avoidLabelOverlap(route, [...resolved, ...routes.slice(index + 1)], bounds, subgraphBounds)]
+    const grouped = groupedLabelEdge(route.edge)
+    return [
+      ...resolved,
+      avoidLabelOverlap(
+        route,
+        [...resolved, ...routes.slice(index + 1)],
+        bounds,
+        subgraphBounds,
+        targetWidth !== undefined && subgraphs.length > 0 && grouped ? Math.max(1, targetWidth - 5) : targetWidth,
+        subgraphs.length === 0 || grouped,
+      ),
+    ]
   }, [])
 }
 
+export function avoidFlowchartFrameBorders(
+  routes: readonly FlowchartEdgeRoute[],
+  bounds: ReadonlyMap<string, FlowchartNodeBounds>,
+  subgraphBounds: ReadonlyMap<string, FlowchartSubgraphBounds>,
+): void {
+  const inside = (node: FlowchartNodeBounds, frame: FlowchartSubgraphBounds) =>
+    node.left >= frame.left &&
+    node.top >= frame.top &&
+    node.left + node.width <= frame.left + frame.width &&
+    node.top + node.height <= frame.top + frame.height
+
+  for (const route of routes) {
+    const source = bounds.get(route.edge.from)
+    const target = bounds.get(route.edge.to)
+    for (const frame of subgraphBounds.values()) {
+      const inward = Boolean(source && target && inside(source, frame) && inside(target, frame))
+      const right = frame.left + frame.width - 1
+      const bottom = frame.top + frame.height - 1
+      const points: FlowchartPoint[] = [route.points[0]!]
+      for (let index = 1; index < route.points.length; index++) {
+        const from = route.points[index - 1]!
+        const to = route.points[index]!
+        const segment = segmentBetween(from, to)
+        if (!segment) continue
+        const span = segmentSpan(segment)
+        const horizontalSide =
+          segment.axis === "x" && Math.min(span.end, right) > Math.max(span.start, frame.left)
+            ? segment.from.y === frame.top
+              ? "top"
+              : segment.from.y === bottom
+                ? "bottom"
+                : undefined
+            : undefined
+        const verticalSide =
+          segment.axis === "y" && Math.min(span.end, bottom) > Math.max(span.start, frame.top)
+            ? segment.from.x === frame.left
+              ? "left"
+              : segment.from.x === right
+                ? "right"
+                : undefined
+            : undefined
+        if (!horizontalSide && !verticalSide) {
+          points.push(to)
+          continue
+        }
+
+        const offset = horizontalSide
+          ? horizontalSide === "top"
+            ? frame.top + (inward ? 1 : -1)
+            : bottom + (inward ? -1 : 1)
+          : verticalSide === "left"
+            ? frame.left + (inward ? 1 : -1)
+            : right + (inward ? -1 : 1)
+        if (horizontalSide) points.push({ x: from.x, y: offset }, { x: to.x, y: offset }, to)
+        else points.push({ x: offset, y: from.y }, { x: offset, y: to.y }, to)
+      }
+      route.points = pathThrough(points)
+    }
+  }
+}
+
 function sideForOutsidePoint(bounds: FlowchartNodeBounds, sourcePoint: FlowchartPoint): DiagramSide {
   if (sourcePoint.x < bounds.left) return "left"
   if (sourcePoint.x >= bounds.left + bounds.width) return "right"
diff --git a/packages/merman/src/flowchart/style.ts b/packages/merman/src/flowchart/style.ts
index 40a90e8bd32..f4dae9bf270 100644
--- a/packages/merman/src/flowchart/style.ts
+++ b/packages/merman/src/flowchart/style.ts
@@ -10,7 +10,7 @@ import {
   type DiagramRgb,
 } from "../core/color/style.js"
 
-export type FlowchartBaseCellStyle = "node" | "database" | "edge" | "label" | "group"
+export type FlowchartBaseCellStyle = "node" | "nodeBorder" | "database" | "databaseBorder" | "edge" | "label" | "group"
 export type FlowchartNodeEdgeFadeStyle = `nodeEdgeFade${DiagramFadeStep}`
 export type FlowchartDatabaseEdgeFadeStyle = `databaseEdgeFade${DiagramFadeStep}`
 export type FlowchartEdgeFadeStyle = FlowchartNodeEdgeFadeStyle | FlowchartDatabaseEdgeFadeStyle
@@ -22,7 +22,9 @@ export type FlowchartGrid = DiagramCanvas<FlowchartCellStyle, FlowchartCellMetad
 export type FlowchartStyleColors = Required<Record<FlowchartCellStyle, RGBA>>
 export const DEFAULT_THEME_RGB = {
   node: [228, 239, 232],
+  nodeBorder: [141, 163, 151],
   database: [228, 239, 232],
+  databaseBorder: [141, 163, 151],
   edge: [134, 225, 200],
   label: [134, 225, 200],
   group: [76, 99, 89],
@@ -35,16 +37,20 @@ export function resolveFlowchartStyleColors(
   colors: Partial<Record<FlowchartCellStyle, RGBA | undefined>> = {},
 ): FlowchartStyleColors {
   const node = colors.node ?? rgba(DEFAULT_THEME_RGB.node)
+  const nodeBorder = colors.nodeBorder ?? rgba(DEFAULT_THEME_RGB.nodeBorder)
   const database = colors.database ?? rgba(DEFAULT_THEME_RGB.database)
+  const databaseBorder = colors.databaseBorder ?? rgba(DEFAULT_THEME_RGB.databaseBorder)
   const edge = colors.edge ?? rgba(DEFAULT_THEME_RGB.edge)
   return {
     node,
+    nodeBorder,
     database,
+    databaseBorder,
     edge,
     label: colors.label ?? rgba(DEFAULT_THEME_RGB.label),
     group: colors.group ?? rgba(DEFAULT_THEME_RGB.group),
-    ...createColorRampTheme(NODE_EDGE_FADE_STYLES, node, edge),
-    ...createColorRampTheme(DATABASE_EDGE_FADE_STYLES, database, edge),
+    ...createColorRampTheme(NODE_EDGE_FADE_STYLES, nodeBorder, edge),
+    ...createColorRampTheme(DATABASE_EDGE_FADE_STYLES, databaseBorder, edge),
   }
 }
 
diff --git a/packages/merman/src/layout-audit.test.ts b/packages/merman/src/layout-audit.test.ts
new file mode 100644
index 00000000000..d56187a457d
--- /dev/null
+++ b/packages/merman/src/layout-audit.test.ts
@@ -0,0 +1,81 @@
+import { expect, test } from "bun:test"
+import { auditAllFixtures, auditFixture, summarizeAudits, worstAudits } from "./test/layout-audit/harness.js"
+import { layoutFixtures } from "./test/layout-audit/fixtures.js"
+
+test("audits deterministic flowchart and state layout families", () => {
+  const fixtures = layoutFixtures()
+  const flowcharts = fixtures.filter((fixture) => fixture.kind === "flowchart")
+  const states = fixtures.filter((fixture) => fixture.kind === "state")
+  expect(flowcharts.length).toBeGreaterThanOrEqual(100)
+  expect(states.length).toBeGreaterThanOrEqual(100)
+  expect(new Set(fixtures.map((fixture) => fixture.id)).size).toBe(fixtures.length)
+
+  const startedAt = performance.now()
+  const audits = auditAllFixtures()
+  const elapsedMs = performance.now() - startedAt
+  const violations = audits.flatMap((audit) =>
+    audit.violations.map((violation) => `${audit.fixture.id} @${audit.viewport}: ${violation}`),
+  )
+  const summary = summarizeAudits(audits)
+
+  expect(audits.length).toBeGreaterThanOrEqual(fixtures.length)
+  expect(violations).toEqual([])
+  expect(elapsedMs).toBeLessThan(35_000)
+  for (const audit of audits.filter((audit) => audit.fixture.kind === "state")) {
+    expect(audit.viewport).toBe(audit.fixture.profile === "short" ? 60 : audit.fixture.profile === "unicode" ? 80 : 120)
+  }
+  for (const id of ["state/chain/lr-long", "state/chain/rl-long"]) {
+    const audit = audits.find((candidate) => candidate.fixture.id === id)!
+    expect(audit.viewport).toBe(120)
+    expect([audit.metrics.width, audit.metrics.height, audit.metrics.overflow]).toEqual([84, 41, 0])
+  }
+  expect(
+    audits
+      .filter((audit) => audit.fixture.id === "flowchart/deployment-architecture/curated")
+      .map((audit) => audit.viewport),
+  ).toEqual([60, 80, 120])
+  expect(summary.total.area.max).toBeLessThanOrEqual(11_011)
+  expect(summary.total.area.p95).toBeLessThanOrEqual(5_313)
+  expect(summary.total.bends.max).toBeLessThanOrEqual(30)
+  expect(summary.total.bends.p95).toBeLessThanOrEqual(11)
+  expect(summary.total.crossings.total).toBeLessThanOrEqual(40)
+  expect(summary.total.crossings.max).toBeLessThanOrEqual(3)
+  expect(summary.total.routeLength.max).toBeLessThanOrEqual(930)
+  expect(summary.total.routeLength.p95).toBeLessThanOrEqual(364)
+  expect(summary.total.sharedRouteCells.max).toBeLessThanOrEqual(547)
+  expect(summary.total.sharedRouteCells.p95).toBeLessThanOrEqual(122)
+  expect(summary.total.overflow.max).toBeLessThanOrEqual(170)
+  expect(summary.total.overflow.p95).toBeLessThanOrEqual(99)
+  expect(summary.state.crossings.total).toBe(0)
+
+  for (const fixture of [...Map.groupBy(fixtures, (candidate) => `${candidate.kind}/${candidate.family}`).values()].map(
+    (family) => family[0]!,
+  )) {
+    const first = auditFixture(fixture, 80)
+    const second = auditFixture(fixture, 80)
+    expect(second.output).toBe(first.output)
+    expect(second.metrics).toEqual(first.metrics)
+    expect(second.violations).toEqual(first.violations)
+  }
+
+  console.log(
+    `[layout-audit] ${fixtures.length} sources, ${audits.length} runs, ${elapsedMs.toFixed(0)}ms`,
+    JSON.stringify({
+      summary,
+      worst: {
+        area: worstAudits(audits, "area", 3).map((audit) => [audit.fixture.id, audit.viewport, audit.metrics.area]),
+        bends: worstAudits(audits, "bends", 3).map((audit) => [audit.fixture.id, audit.viewport, audit.metrics.bends]),
+        crossings: worstAudits(audits, "crossings", 3).map((audit) => [
+          audit.fixture.id,
+          audit.viewport,
+          audit.metrics.crossings,
+        ]),
+        overflow: worstAudits(audits, "overflow", 3).map((audit) => [
+          audit.fixture.id,
+          audit.viewport,
+          audit.metrics.overflow,
+        ]),
+      },
+    }),
+  )
+}, 40_000)
diff --git a/packages/merman/src/markdown.ts b/packages/merman/src/markdown.ts
index c94db60a6a4..9b7cc390278 100644
--- a/packages/merman/src/markdown.ts
+++ b/packages/merman/src/markdown.ts
@@ -51,7 +51,7 @@ interface PreparedDiagram {
 export interface MermaidMarkdownRendererOptions {
   /** Use terminal-optimized diagram spacing. Defaults to true. */
   compact?: boolean
-  /** Fold horizontal flowcharts that exceed this width. Defaults to 120 columns. */
+  /** Fold responsive horizontal diagrams that exceed this width. Defaults to 120 columns. */
   layoutMaxWidth?: number
   /** Gantt-specific terminal rendering options. */
   gantt?: Omit<GanttDiagramRenderOptions, "layoutMaxWidth">
@@ -141,7 +141,9 @@ function prepareDiagram(
           grid,
           resolveFlowchartStyleColors({
             node: color(colors.primary),
+            nodeBorder: color(colors.muted),
             database: color(colors.primary),
+            databaseBorder: color(colors.muted),
             edge: color(colors.secondary),
             label: color(colors.text),
             group: color(colors.muted),
@@ -215,8 +217,8 @@ function prepareDiagram(
       }
     }
     case "state": {
-      const grid = drawStateDiagramGrid(parseMermaidStateDiagram(source))
-      const size = grid.getTextSize({ trimBottom: true })
+      const grid = drawStateDiagramGrid(parseMermaidStateDiagram(source), { layoutMaxWidth })
+      const size = grid.getTextSize({ trimTop: true, trimBottom: true })
       return {
         kind,
         source,
diff --git a/packages/merman/src/state/diagram.test.ts b/packages/merman/src/state/diagram.test.ts
index abff6bc541a..7c1f5af1f27 100644
--- a/packages/merman/src/state/diagram.test.ts
+++ b/packages/merman/src/state/diagram.test.ts
@@ -3,7 +3,7 @@ import stringWidth from "string-width"
 import { spatialPathClaim } from "../core/spatial.js"
 import { expectDiagram } from "../test/diagram.js"
 import { renderStateDiagram } from "./diagram.js"
-import { drawStateDiagramGrid } from "./drawing.js"
+import { createStateDiagramDrawing, drawStateDiagramGrid } from "./drawing.js"
 import { createStateDiagramLayout } from "./layout.js"
 import { parseMermaidStateDiagram } from "./parser.js"
 import { prepareVisibleStateDiagram } from "./visible-model.js"
@@ -60,6 +60,35 @@ function expectCompleteStateDiagram(source: string, output = renderStateDiagram(
   }
 }
 
+type ResponsiveStateLabelProfile = "short" | "long" | "unicode"
+
+function responsiveStateChain(direction: "LR" | "RL", profile: ResponsiveStateLabelProfile): string {
+  const stateLabel = (id: string) => {
+    if (profile === "long") return `${id} deliberate state with a long descriptive label`
+    if (profile === "unicode") return `${id} 東京<br/>résumé 🚀`
+    return `${id} node`
+  }
+  const transitionLabel = (id: string) => {
+    if (profile === "long") return `${id} transition carrying detailed context`
+    if (profile === "unicode") return `${id} 東京<br/>✓ prêt`
+    return `${id} edge`
+  }
+  const ids = ["A", "B", "C", "D", "E"]
+  return [
+    "stateDiagram-v2",
+    `direction ${direction}`,
+    ...ids.map((id) => `state "${stateLabel(id)}" as ${id}`),
+    "[*] --> A",
+    ...ids.slice(0, -1).map((id, index) => `${id} --> ${ids[index + 1]}: ${transitionLabel(`E0${index + 1}`)}`),
+    "E --> [*]",
+  ].join("\n")
+}
+
+function renderedStateDimensions(output: string) {
+  const lines = output.split("\n")
+  return { width: Math.max(...lines.map((line) => stringWidth(line))), height: lines.length }
+}
+
 describe("StateDiagram", () => {
   test("detects and parses Mermaid state diagrams", () => {
     const diagram = parseMermaidStateDiagram(`
@@ -179,6 +208,95 @@ stateDiagram-v2
     expect(output).toContain("◀")
   })
 
+  test("renders reverse vertical direction from bottom to top", () => {
+    const source = `stateDiagram-v2
+  direction BT
+  A --> B`
+    const drawing = createStateDiagramDrawing(parseMermaidStateDiagram(source))
+
+    expect(drawing.layout.bounds.get("A")!.top).toBeGreaterThan(drawing.layout.bounds.get("B")!.top)
+    expect(drawing.grid.toString({ trimTop: true, trimBottom: true })).toContain("▲")
+  })
+
+  test.each(
+    (["LR", "RL"] as const).flatMap((direction) =>
+      (["short", "long", "unicode"] as const).flatMap((profile) =>
+        ([60, 80, 120] as const).map((layoutMaxWidth) => [direction, profile, layoutMaxWidth] as const),
+      ),
+    ),
+  )("folds responsive %s %s chains at %d columns", (direction, profile, layoutMaxWidth) => {
+    const source = responsiveStateChain(direction, profile)
+    const horizontal = renderStateDiagram(source)
+    const responsive = renderStateDiagram(source, { layoutMaxWidth })
+    const vertical = renderStateDiagram(source, { direction: direction === "RL" ? "BT" : "TB" })
+
+    expect(renderedStateDimensions(horizontal).width).toBeGreaterThan(layoutMaxWidth)
+    expect(responsive).toBe(vertical)
+    expect(renderedStateDimensions(responsive).width).toBeLessThan(renderedStateDimensions(horizontal).width)
+    for (const content of ["A", "B", "C", "D", "E", "E01", "E02", "E03", "E04"]) {
+      expect(responsive).toContain(content)
+    }
+  })
+
+  test.each(["LR", "RL"] as const)("keeps the narrower %s orientation for broad ranks", (direction) => {
+    const source = `stateDiagram-v2
+  direction ${direction}
+${Array.from({ length: 8 }, (_, index) => `  A --> B${index}`).join("\n")}`
+    const horizontal = renderStateDiagram(source)
+    const vertical = renderStateDiagram(source, { direction: direction === "RL" ? "BT" : "TB" })
+    const responsive = renderStateDiagram(source, { layoutMaxWidth: 60 })
+
+    expect(renderedStateDimensions(horizontal).width).toBeLessThan(renderedStateDimensions(vertical).width)
+    expect(responsive).toBe(horizontal)
+  })
+
+  test("falls back before allocating an oversized horizontal canvas", () => {
+    const ids = Array.from({ length: 301 }, (_, index) => `S${index}`)
+    const label = "transition label carrying enough context to make the horizontal canvas too large"
+    const source = `stateDiagram-v2
+  direction LR
+${ids
+  .slice(0, -1)
+  .map((id, index) => `  ${id} --> ${ids[index + 1]}: ${label}`)
+  .join("\n")}`
+    const output = renderStateDiagram(source, { layoutMaxWidth: 80 })
+
+    expect(output).toContain("S0")
+    expect(output).toContain("S300")
+    expect(renderedStateDimensions(output).width).toBeLessThanOrEqual(stringWidth(label) + 8)
+  })
+
+  test.each(["TB", "TD", "BT"] as const)("preserves explicit %s layouts under a narrow width target", (direction) => {
+    const source = `stateDiagram-v2
+  direction ${direction}
+  A --> B: next`
+
+    expect(renderStateDiagram(source, { layoutMaxWidth: 1 })).toBe(renderStateDiagram(source))
+  })
+
+  test("preserves horizontal layouts that fit or have no finite width target", () => {
+    const source = `stateDiagram-v2
+  direction LR
+  A --> B`
+    const output = renderStateDiagram(source)
+
+    expect(renderStateDiagram(source, { layoutMaxWidth: 120 })).toBe(output)
+    expect(renderStateDiagram(source, { layoutMaxWidth: Number.POSITIVE_INFINITY })).toBe(output)
+  })
+
+  test("treats a single irreducibly wide state as soft overflow", () => {
+    const label = "界".repeat(40)
+    const output = renderStateDiagram(
+      `stateDiagram-v2
+  direction LR
+  state "${label}" as Wide`,
+      { layoutMaxWidth: 60 },
+    )
+
+    expect(renderedStateDimensions(output).width).toBeGreaterThan(60)
+    expect(output).toContain(label)
+  })
+
   test("does not mutate a parsed diagram when rendering with a direction override", () => {
     const diagram = parseMermaidStateDiagram(`stateDiagram-v2
   direction LR
@@ -249,24 +367,21 @@ stateDiagram-v2
 
     for (const line of labelLines) expect(output.split(line)).toHaveLength(2)
     expect(output).toMatchInlineSnapshot(`
-      "
-        create from base image ╭─────────╮
+      "  create from base image ╭─────────╮
       ●───────────────────────▶│ Running │
-                               ╰──┬──────╯ 💥 sandbox dies BEFORE hook fires
-                                ▲ │   ▲    (crash, our bug, race)
-                       ╭────────┼─┴───┼───────╮
+                               ╰──┬──────╯
+                                ▲ │   ▲        💥 sandbox dies BEFORE hook fires
+                       ╭────────┼─┴───┼───────╮(crash, our bug, race)
                        ▼   ╭────┼─────╯       ▼
                     ╭──────┴──╮ │           ╭──────╮
                     │ Dormant │ │           │ Lost │
                     ╰─────────╯ │           ╰───┬──╯
                                 │               │
-       📸 suspend hook fires    │               │
-       (WE must call it on idle)│               │
+       📸 suspend hook fires    │               │ wake from LAST snapshot
+       (WE must call it on idle)│               │ ⚠ files since then GONE
                                 ╰───────────────╯
                             wake from snapshot image
-                            (apt installs restored!)
-                                  wake from LAST snapshot
-                                  ⚠ files since then GONE"
+                            (apt installs restored!)"
     `)
   })
 
@@ -505,6 +620,14 @@ stateDiagram-v2
     expect(output.split("\n").filter((line) => line.trim())).toHaveLength(3)
   })
 
+  test.each(["LR", "RL"] as const)("trims leading rows from standalone %s choices", (direction) => {
+    const output = renderStateDiagram(`stateDiagram-v2
+  direction ${direction}
+  state Decision <<choice>>`)
+
+    expect(output).toBe("◆")
+  })
+
   test("renders parallel transitions without losing labels", () => {
     const horizontal = renderStateDiagram(`stateDiagram-v2
   direction LR
@@ -683,6 +806,135 @@ stateDiagram-v2
     }
   })
 
+  test("grows parallel vertical diagrams by the maximum label width rather than their sum", () => {
+    const render = (labels: readonly string[]) =>
+      renderStateDiagram(`stateDiagram-v2
+  direction TB
+${labels.map((label) => `  A --> B: ${label}`).join("\n")}`)
+    const shortLabels = ["one", "two", "three"]
+    const longLabels = [
+      "alpha route label that is deliberately long",
+      "beta route label that is deliberately long",
+      "gamma route label that is deliberately long",
+    ]
+    const width = (output: string) => Math.max(...output.split("\n").map((line) => stringWidth(line)))
+    const labelGrowth =
+      Math.max(...longLabels.map((label) => stringWidth(label))) -
+      Math.max(...shortLabels.map((label) => stringWidth(label)))
+
+    expect(width(render(longLabels)) - width(render(shortLabels))).toBeLessThanOrEqual(labelGrowth + 2)
+  })
+
+  test("keeps audited parallel labels clear of frames and rails", () => {
+    const output = renderStateDiagram(`stateDiagram-v2
+  direction TB
+  A --> B: alpha route label that is deliberately long
+  A --> B: beta route label that is deliberately long
+  A --> B: gamma route label that is deliberately long`)
+
+    expect(output).toMatchInlineSnapshot(`
+      "╭───╮ alpha route label that is deliberately long
+      │ A ├───┬──╮
+      ╰─┬─╯   │  │
+        │     │  │ gamma route label that is deliberately long
+        │     │  │ beta route label that is deliberately long
+        │     │  │
+        ▼     │  │
+      ╭───╮   │  │
+      │ B │◀──┴──╯
+      ╰───╯"
+    `)
+  })
+
+  test("keeps audited repeated self-transition lanes distinct and readable", () => {
+    const output = renderStateDiagram(`stateDiagram-v2
+  direction LR
+  A --> A: one
+  A --> A: two
+  A --> A: three`)
+
+    expect(output).toMatchInlineSnapshot(`
+      "╭───╮
+      │ A │
+      ╰─┬─╯
+        │  ▲   ▲   ▲
+        ├──╯   │   │
+        │      │   │
+        │ one  │   │
+        ├──────╯   │
+        │          │
+        │     two  │ three
+        ╰──────────╯"
+    `)
+  })
+
+  test("expands composites around self-transition labels without engulfing external states", () => {
+    const source = `stateDiagram-v2
+  direction LR
+  state Outer {
+    A --> A: loop-0
+    A --> A: loop-1
+    A --> A: loop-2
+  }
+  A --> C`
+    const drawing = createStateDiagramDrawing(parseMermaidStateDiagram(source))
+    const outer = drawing.layout.compositeBounds.get("Outer")!
+    const external = drawing.layout.bounds.get("C")!
+    const output = drawing.grid.toString({ trimTop: true, trimBottom: true })
+
+    expect(
+      external.left < outer.left + outer.width &&
+        external.left + external.width > outer.left &&
+        external.top < outer.top + outer.height &&
+        external.top + external.height > outer.top,
+    ).toBe(false)
+    for (const plan of drawing.transitionPlans.filter(
+      (plan) => plan.route.transition.from === plan.route.transition.to,
+    )) {
+      expect(plan.label).toBeDefined()
+      expect(plan.label!.x).toBeGreaterThan(outer.left)
+      expect(plan.label!.y).toBeGreaterThan(outer.top)
+      expect(plan.label!.x + Math.max(...plan.label!.lines.map((line) => stringWidth(line)))).toBeLessThan(
+        outer.left + outer.width,
+      )
+      expect(plan.label!.y + plan.label!.lines.length).toBeLessThan(outer.top + outer.height)
+    }
+    for (const label of ["loop-0", "loop-1", "loop-2"]) expect(output.match(new RegExp(label, "g"))).toHaveLength(1)
+  })
+
+  test("keeps audited nested note connectors direct and inside every frame", () => {
+    const output = renderStateDiagram(`stateDiagram-v2
+  direction TB
+  state Outer {
+    state Inner {
+      A --> B: down
+      B --> A: up
+      note right of B: note
+    }
+  }`)
+
+    expect(output).toMatchInlineSnapshot(`
+      "╭─ Outer ───────────────╮
+      │                       │
+      │ ╭─ Inner ───────────╮ │
+      │ │                   │ │
+      │ │ ╭───╮             │ │
+      │ │▶│ A │             │ │
+      │ ││╰─┬─╯             │ │
+      │ ││  │               │ │
+      │ ││  │ down          │ │
+      │ ││  │               │ │
+      │ ││  ▼               │ │
+      │ ││╭───╮    ╔══════╗ │ │
+      │ │╰┤ B │════╣ note ║ │ │
+      │ │ ╰───╯    ╚══════╝ │ │
+      │ │up                 │ │
+      │ ╰───────────────────╯ │
+      │                       │
+      ╰───────────────────────╯"
+    `)
+  })
+
   test("keeps explicit choices visible in choice-only cycles", () => {
     const output = renderStateDiagram(`stateDiagram-v2
   direction TB
diff --git a/packages/merman/src/state/drawing.ts b/packages/merman/src/state/drawing.ts
index cafc57fc992..a6ba41a426d 100644
--- a/packages/merman/src/state/drawing.ts
+++ b/packages/merman/src/state/drawing.ts
@@ -1,5 +1,5 @@
 import { BorderChars, type BorderCharacters, type BorderStyle } from "@opentui/core"
-import { DiagramCanvas, type DiagramCanvasCell } from "../core/canvas.js"
+import { DiagramCanvas, DiagramCanvasSizeError, type DiagramCanvasCell } from "../core/canvas.js"
 import { directionBetween, orthogonalPathPoints, type DiagramDirection } from "../core/geometry.js"
 import {
   diagramArrowHead,
@@ -12,6 +12,7 @@ import {
   createStateDiagramLayout,
   expandCompositeBoundsForFeedback,
   expandCompositeBoundsForInternalTransitions,
+  separateExternalBoundsFromComposites,
   translateStateDiagramLayout,
   type StateDiagramBoxBounds as BoxBounds,
   type StateDiagramNoteBounds as StateNoteBounds,
@@ -67,23 +68,11 @@ function makeGrid(width: number, height: number): StateGrid {
   })
 }
 
-function setCell(
-  grid: StateGrid,
-  x: number,
-  y: number,
-  char: string,
-  style?: StateCellStyle,
-): void {
+function setCell(grid: StateGrid, x: number, y: number, char: string, style?: StateCellStyle): void {
   grid.setCell(x, y, char, style)
 }
 
-function setText(
-  grid: StateGrid,
-  x: number,
-  y: number,
-  text: string,
-  style?: StateCellStyle,
-): void {
+function setText(grid: StateGrid, x: number, y: number, text: string, style?: StateCellStyle): void {
   grid.setText(x, y, text, style)
 }
 
@@ -108,12 +97,7 @@ function drawBox(
   })
 }
 
-function drawStateFrame(
-  grid: StateGrid,
-  bounds: BoxBounds,
-  chars: BorderCharacters,
-  style: StateCellStyle,
-): void {
+function drawStateFrame(grid: StateGrid, bounds: BoxBounds, chars: BorderCharacters, style: StateCellStyle): void {
   drawDiagramFrame(bounds, chars, (x, y, char) => setCell(grid, x, y, char, style))
 }
 
@@ -125,6 +109,10 @@ function drawContainerFrame(
   style: StateCellStyle,
 ): void {
   drawDiagramFrame(bounds, chars, (x, y, char) => setCell(grid, x, y, char, style))
+  drawContainerLabel(grid, bounds, label, style)
+}
+
+function drawContainerLabel(grid: StateGrid, bounds: BoxBounds, label: string, style: StateCellStyle): void {
   if (label) setText(grid, bounds.left + 2, bounds.top, ` ${label} `, style)
 }
 
@@ -190,9 +178,7 @@ function drawTransitionRenderPlan(
     setCell(grid, cell.x, cell.y, char, departure.get(`${cell.x}:${cell.y}`) ?? "transition")
   }
   if (plan.label) {
-    plan.label.lines.forEach((line, index) =>
-      setText(grid, plan.label!.x, plan.label!.y + index, line, "label"),
-    )
+    plan.label.lines.forEach((line, index) => setText(grid, plan.label!.x, plan.label!.y + index, line, "label"))
   }
 }
 
@@ -210,8 +196,49 @@ function drawTransitionJunctionPlans(
 }
 
 export function drawStateDiagramGrid(sourceDiagram: StateDiagram, options: StateDiagramRenderOptions = {}): StateGrid {
-  const directedDiagram = options.direction ? { ...sourceDiagram, direction: options.direction } : sourceDiagram
-  const diagram = prepareVisibleStateDiagram(directedDiagram)
+  return createStateDiagramDrawing(sourceDiagram, options).grid
+}
+
+export function createStateDiagramDrawing(sourceDiagram: StateDiagram, options: StateDiagramRenderOptions = {}) {
+  const direction = options.direction ?? sourceDiagram.direction
+  if (direction !== "LR" && direction !== "RL") {
+    return createStateDiagramDrawingWithDirection(sourceDiagram, options, direction)
+  }
+  if (options.layoutMaxWidth === undefined || !Number.isFinite(options.layoutMaxWidth)) {
+    return createStateDiagramDrawingWithDirection(sourceDiagram, options, direction)
+  }
+  const fallbackDirection = direction === "RL" ? "BT" : "TB"
+  const maxWidth = Math.max(1, Math.trunc(options.layoutMaxWidth))
+  const drawing = (() => {
+    try {
+      return createStateDiagramDrawingWithDirection(sourceDiagram, options, direction)
+    } catch (error) {
+      if (error instanceof DiagramCanvasSizeError) return undefined
+      throw error
+    }
+  })()
+  if (!drawing) return createStateDiagramDrawingWithDirection(sourceDiagram, options, fallbackDirection)
+  if (drawing.grid.getTextSize({ trimTop: true, trimBottom: true }).width <= maxWidth) {
+    return drawing
+  }
+  const fallback = createStateDiagramDrawingWithDirection(sourceDiagram, options, fallbackDirection)
+  if (
+    fallback.grid.getTextSize({ trimTop: true, trimBottom: true }).width >=
+    drawing.grid.getTextSize({ trimTop: true, trimBottom: true }).width
+  ) {
+    return drawing
+  }
+  return fallback
+}
+
+function createStateDiagramDrawingWithDirection(
+  sourceDiagram: StateDiagram,
+  options: StateDiagramRenderOptions,
+  direction: StateDiagram["direction"],
+) {
+  const diagram = prepareVisibleStateDiagram(
+    direction === sourceDiagram.direction ? sourceDiagram : { ...sourceDiagram, direction },
+  )
   const borderStyle = options.borderStyle ?? DEFAULT_STATE_BORDER_STYLE
   const arrowHeadStyle = options.arrowHeadStyle ?? DEFAULT_STATE_ARROW_HEAD_STYLE
   const minStateGap = normalizeStateMinStateGap(options.minStateGap)
@@ -226,21 +253,24 @@ export function drawStateDiagramGrid(sourceDiagram: StateDiagram, options: State
   const feedbackLaneY = maxY + 3
   const feedbackTopY = Math.min(0, ...allBounds.map((bound) => bound.top)) - 3
   expandCompositeBoundsForFeedback(diagram, bounds, compositeBounds, feedbackLaneY)
-  let transitionPlans = createStateTransitionRenderPlans(diagram, bounds, feedbackLaneY, {
-    feedbackTopY,
-    noteBounds,
-    searchBudget,
-  })
-  expandCompositeBoundsForInternalTransitions(diagram, compositeBounds, transitionPlans)
+  let transitionPlans: StateTransitionRenderPlan[] = []
+  const separationAttempts = diagram.states.length + diagram.composites.length + 1
+  for (let attempt = 0; attempt < separationAttempts; attempt++) {
+    transitionPlans = createStateTransitionRenderPlans(diagram, bounds, feedbackLaneY, {
+      feedbackTopY,
+      noteBounds,
+      searchBudget,
+    })
+    expandCompositeBoundsForInternalTransitions(diagram, compositeBounds, transitionPlans)
+    if (!separateExternalBoundsFromComposites(diagram, layout)) break
+    if (attempt === separationAttempts - 1) throw new Error("State composite separation did not converge")
+  }
   const connectorPoints = noteBounds.flatMap((bound) => bound.connector?.points ?? [])
   const contentLeft = Math.min(
     0,
     ...[...bounds.values(), ...noteBounds].map((bound) => bound.left),
     ...connectorPoints.map((point) => point.x),
-    ...transitionPlans.flatMap((plan) => [
-      ...plan.cells.map((cell) => cell.x),
-      ...(plan.label ? [plan.label.x] : []),
-    ]),
+    ...transitionPlans.flatMap((plan) => [...plan.cells.map((cell) => cell.x), ...(plan.label ? [plan.label.x] : [])]),
   )
   const contentTop = Math.min(
     0,
@@ -305,10 +335,15 @@ export function drawStateDiagramGrid(sourceDiagram: StateDiagram, options: State
 
   drawTransitionJunctionPlans(grid, diagram, bounds, transitionPlans)
 
+  for (const composite of diagram.composites) {
+    const bound = compositeBounds.get(composite.id)
+    if (bound) drawContainerLabel(grid, bound, composite.label, "composite")
+  }
+
   for (const noteBound of noteBounds) {
     const target = bounds.get(noteBound.note.target)
     if (target) drawNote(grid, noteBound, target)
   }
 
-  return grid
+  return { grid, diagram, layout, transitionPlans }
 }
diff --git a/packages/merman/src/state/layout.test.ts b/packages/merman/src/state/layout.test.ts
index fc226c73be7..fcbb5b4f678 100644
--- a/packages/merman/src/state/layout.test.ts
+++ b/packages/merman/src/state/layout.test.ts
@@ -2,7 +2,7 @@ import { describe, expect, test } from "bun:test"
 import { spatialPathClaim } from "../core/spatial.js"
 import { diagramTextWidth } from "../core/text.js"
 import type { StateDiagram } from "./types.js"
-import { createStateDiagramLayout } from "./layout.js"
+import { createStateDiagramLayout, expandCompositeBoundsForInternalTransitions } from "./layout.js"
 import { stateDiagramNoteConnector } from "./note.js"
 import { parseMermaidStateDiagram } from "./parser.js"
 import { createStateTransitionRenderPlans } from "./routing.js"
@@ -192,4 +192,75 @@ describe("StateDiagramLayout", () => {
     )
     expect(plans.every((plan) => plan.path.every(([x, y]) => !noteCells.has(`${x}:${y}`)))).toBe(true)
   })
+
+  test.each([
+    ["LR", -1],
+    ["RL", 1],
+  ] as const)("keeps a reciprocal pair on the %s axis", (direction, expectedSign) => {
+    const diagram = prepareVisibleStateDiagram(
+      parseMermaidStateDiagram(`stateDiagram-v2
+  direction ${direction}
+  A --> B: forward
+  B --> A: backward`),
+    )
+    const layout = createStateDiagramLayout(diagram, { minStateGap: 5 })
+    const a = layout.bounds.get("A")!
+    const b = layout.bounds.get("B")!
+
+    expect(a.centerY).toBe(b.centerY)
+    expect(Math.sign(a.centerX - b.centerX)).toBe(expectedSign)
+  })
+
+  test.each(["TB", "TD"] as const)(
+    "contains nested internal feedback with strict margins in %s diagrams",
+    (direction) => {
+      const diagram = prepareVisibleStateDiagram(
+        parseMermaidStateDiagram(`stateDiagram-v2
+  direction ${direction}
+  state Outer {
+    state Inner {
+      A --> B: down
+      B --> A: up
+      note right of B: nested note
+    }
+  }`),
+      )
+      const layout = createStateDiagramLayout(diagram, { minStateGap: 5 })
+      const plans = createStateTransitionRenderPlans(diagram, layout.bounds, 30, { noteBounds: layout.noteBounds })
+      expandCompositeBoundsForInternalTransitions(diagram, layout.compositeBounds, plans)
+      const inner = layout.compositeBounds.get("Inner")!
+      const outer = layout.compositeBounds.get("Outer")!
+      const note = layout.noteBounds[0]!
+
+      for (const composite of [inner, outer]) {
+        for (const plan of plans) {
+          expect(
+            plan.path.every(
+              ([x, y]) =>
+                x > composite.left &&
+                x < composite.left + composite.width - 1 &&
+                y > composite.top &&
+                y < composite.top + composite.height - 1,
+            ),
+          ).toBe(true)
+        }
+        expect(
+          note.connector!.points.every(
+            (point) =>
+              point.x > composite.left &&
+              point.x < composite.left + composite.width - 1 &&
+              point.y > composite.top &&
+              point.y < composite.top + composite.height - 1,
+          ),
+        ).toBe(true)
+      }
+      expect(new Set(note.connector!.points.map((point) => point.y))).toEqual(
+        new Set([layout.bounds.get("B")!.centerY]),
+      )
+      expect(inner.left - outer.left).toBeGreaterThanOrEqual(2)
+      expect(inner.top - outer.top).toBeGreaterThanOrEqual(2)
+      expect(outer.left + outer.width - (inner.left + inner.width)).toBeGreaterThanOrEqual(2)
+      expect(outer.top + outer.height - (inner.top + inner.height)).toBeGreaterThanOrEqual(2)
+    },
+  )
 })
diff --git a/packages/merman/src/state/layout.ts b/packages/merman/src/state/layout.ts
index 7c6bf497d7c..188e958ef59 100644
--- a/packages/merman/src/state/layout.ts
+++ b/packages/merman/src/state/layout.ts
@@ -131,7 +131,8 @@ function computeMainPath(diagram: StateDiagram): string[] {
         const fromParent = statesById.get(current)?.parentId
         const toParent = statesById.get(transition.to)?.parentId
         return Boolean(fromParent && toParent && fromParent !== toParent)
-      })
+      }) ??
+      (path.length === 1 && candidates.length === 1 ? candidates[0] : undefined)
     if (!next) break
     path.push(next.to)
     visited.add(next.to)
@@ -319,7 +320,12 @@ function findNoteConnector(
   const isFree = (point: DiagramPoint): boolean =>
     point.x >= 0 &&
     !search.blocked.has(`${point.x}:${point.y}`) &&
-    !(point.x >= bounds.left && point.x < bounds.left + bounds.width && point.y >= bounds.top && point.y < bounds.top + bounds.height)
+    !(
+      point.x >= bounds.left &&
+      point.x < bounds.left + bounds.width &&
+      point.y >= bounds.top &&
+      point.y < bounds.top + bounds.height
+    )
   if (!isFree(end) || !isFree(goal)) return undefined
 
   for (const start of starts.filter(isFree)) {
@@ -335,14 +341,7 @@ function findNoteConnector(
   const minY = Math.min(target.top, bounds.top, search.minY) - margin
   const maxX = Math.max(target.left + target.width, bounds.left + bounds.width, search.maxX) + margin
   const maxY = Math.max(target.top + target.height, bounds.top + bounds.height, search.maxY) + margin
-  const path = findStateManhattanPath(
-    starts,
-    goal,
-    search,
-    { minX: 0, minY, maxX, maxY },
-    budget,
-    isFree,
-  )
+  const path = findStateManhattanPath(starts, goal, search, { minX: 0, minY, maxX, maxY }, budget, isFree)
   return path ? { connectorY, points: [...path, end] } : undefined
 }
 
@@ -375,13 +374,27 @@ function expandCompositeBoundsForNotes(diagram: StateDiagram, layout: StateDiagr
     )
     if (descendantNotes.length === 0) continue
 
-    const childBounds = [bound, ...descendantNotes]
-    const noteTop = Math.min(...childBounds.map((child) => child.top), bound.top)
-    const noteBottom = Math.max(...childBounds.map((child) => child.top + child.height), bound.top + bound.height)
-    const left = Math.min(...childBounds.map((child) => child.left)) - 2
-    const top = noteTop < bound.top ? noteTop - 1 : bound.top
-    const right = Math.max(...childBounds.map((child) => child.left + child.width)) + 2
-    const bottom = noteBottom > bound.top + bound.height ? noteBottom + 1 : bound.top + bound.height
+    const connectorPoints = descendantNotes.flatMap((note) => note.connector?.points ?? [])
+    const left = Math.min(
+      bound.left,
+      ...descendantNotes.map((note) => note.left - 2),
+      ...connectorPoints.map((point) => point.x - 1),
+    )
+    const top = Math.min(
+      bound.top,
+      ...descendantNotes.map((note) => note.top - 1),
+      ...connectorPoints.map((point) => point.y - 1),
+    )
+    const right = Math.max(
+      bound.left + bound.width,
+      ...descendantNotes.map((note) => note.left + note.width + 2),
+      ...connectorPoints.map((point) => point.x + 2),
+    )
+    const bottom = Math.max(
+      bound.top + bound.height,
+      ...descendantNotes.map((note) => note.top + note.height + 1),
+      ...connectorPoints.map((point) => point.y + 2),
+    )
 
     bound.left = left
     bound.top = top
@@ -392,13 +405,112 @@ function expandCompositeBoundsForNotes(diagram: StateDiagram, layout: StateDiagr
   }
 }
 
+function expandCompositeBoundsForInternalRouting(diagram: StateDiagram, layout: StateDiagramLayout): void {
+  if (diagram.direction === "LR" || diagram.direction === "RL") return
+  const statesById = new Map(diagram.states.map((state) => [state.id, state]))
+  const compositesById = new Map(diagram.composites.map((composite) => [composite.id, composite]))
+
+  for (const composite of [...diagram.composites].reverse()) {
+    const bound = layout.compositeBounds.get(composite.id)
+    if (!bound) continue
+    const internal = diagram.transitions.filter(
+      (transition) =>
+        transition.from !== transition.to &&
+        innermostCommonCompositeId(transition, statesById, compositesById) === composite.id,
+    )
+    const endpointOccurrences = new Map<string, number>()
+    const sideRoutes = internal.filter((transition) => {
+      const from = layout.bounds.get(transition.from)
+      const to = layout.bounds.get(transition.to)
+      if (!from || !to) return false
+      const key = `${transition.from}\u0000${transition.to}`
+      const occurrence = endpointOccurrences.get(key) ?? 0
+      endpointOccurrences.set(key, occurrence + 1)
+      const fromParent = statesById.get(transition.from)?.parentId
+      const toParent = statesById.get(transition.to)?.parentId
+      return occurrence > 0 || from.centerY > to.centerY || fromParent !== toParent
+    })
+    if (sideRoutes.length === 0) continue
+    const childRight = Math.max(
+      ...diagram.states.flatMap((state) => {
+        if (!belongsToComposite(state.id, composite.id, statesById, compositesById)) return []
+        const child = layout.bounds.get(state.id)
+        return child ? [child.left + child.width] : []
+      }),
+      ...diagram.composites.flatMap((childComposite) => {
+        if (childComposite.parentId !== composite.id) return []
+        const child = layout.compositeBounds.get(childComposite.id)
+        return child ? [child.left + child.width] : []
+      }),
+    )
+    const labelWidth = Math.max(...sideRoutes.map((transition) => measureStateTransitionLabel(transition.label).width))
+    const right = childRight + labelWidth + sideRoutes.length * 3 + 6
+    if (right <= bound.left + bound.width) continue
+    bound.width = right - bound.left
+    bound.centerX = bound.left + Math.floor(bound.width / 2)
+  }
+
+  enforceCompositeMargins(diagram, layout.compositeBounds)
+}
+
+function innermostCommonCompositeId(
+  transition: StateDiagramTransition,
+  statesById: Map<string, StateDiagramState>,
+  compositesById: Map<string, StateDiagramCompositeState>,
+): string | undefined {
+  const containers = (id: string) => {
+    const ids: string[] = []
+    let parentId = statesById.get(id)?.parentId ?? compositesById.get(id)?.parentId
+    while (parentId) {
+      ids.push(parentId)
+      parentId = compositesById.get(parentId)?.parentId
+    }
+    return ids
+  }
+  const target = new Set(containers(transition.to))
+  return containers(transition.from).find((id) => target.has(id))
+}
+
+function enforceCompositeMargins(diagram: StateDiagram, compositeBounds: Map<string, StateDiagramBoxBounds>): void {
+  const compositesByParent = new Map<string, StateDiagramCompositeState[]>()
+  for (const composite of diagram.composites) {
+    if (!composite.parentId) continue
+    const children = compositesByParent.get(composite.parentId) ?? []
+    children.push(composite)
+    compositesByParent.set(composite.parentId, children)
+  }
+
+  const expand = (composite: StateDiagramCompositeState): StateDiagramBoxBounds | undefined => {
+    const bound = compositeBounds.get(composite.id)
+    if (!bound) return undefined
+    const children = (compositesByParent.get(composite.id) ?? [])
+      .map(expand)
+      .filter((child): child is StateDiagramBoxBounds => Boolean(child))
+    if (children.length === 0) return bound
+    const left = Math.min(bound.left, ...children.map((child) => child.left - 2))
+    const top = Math.min(bound.top, ...children.map((child) => child.top - 2))
+    const right = Math.max(bound.left + bound.width, ...children.map((child) => child.left + child.width + 2))
+    const bottom = Math.max(bound.top + bound.height, ...children.map((child) => child.top + child.height + 2))
+    bound.left = left
+    bound.top = top
+    bound.width = right - left
+    bound.height = bottom - top
+    bound.centerX = left + Math.floor(bound.width / 2)
+    bound.centerY = top + Math.floor(bound.height / 2)
+    return bound
+  }
+
+  for (const composite of diagram.composites.filter((candidate) => !candidate.parentId)) expand(composite)
+}
+
 function boundsIntersect(left: StateDiagramBoxBounds, right: StateDiagramBoxBounds): boolean {
   return intersects(left.left, left.top, left.width, left.height, right, 0)
 }
 
-function separateExternalBoundsFromComposites(diagram: StateDiagram, layout: StateDiagramLayout): void {
+export function separateExternalBoundsFromComposites(diagram: StateDiagram, layout: StateDiagramLayout): boolean {
   const statesById = new Map(diagram.states.map((state) => [state.id, state]))
   const compositesById = new Map(diagram.composites.map((composite) => [composite.id, composite]))
+  let shifted = false
 
   for (const composite of diagram.composites) {
     const compositeBound = layout.compositeBounds.get(composite.id)
@@ -433,8 +545,10 @@ function separateExternalBoundsFromComposites(diagram: StateDiagram, layout: Sta
       }
 
       shiftBounds(uniqueBounds(boundsToShift), dx, 0)
+      shifted = true
     }
   }
+  return shifted
 }
 
 function finalizeLayout(
@@ -445,6 +559,7 @@ function finalizeLayout(
   if (diagram.composites.length === 0 && diagram.notes.length === 0) return layout
   addCompositeBounds(diagram, layout)
   normalizeLayout(layout)
+  expandCompositeBoundsForInternalRouting(diagram, layout)
   if (diagram.notes.length > 0) {
     const allBounds = [...layout.bounds.values()]
     placeStateDiagramNotesAroundTransitions(
@@ -464,6 +579,7 @@ function finalizeLayout(
     )
   }
   expandCompositeBoundsForNotes(diagram, layout)
+  expandCompositeBoundsForInternalRouting(diagram, layout)
   separateExternalBoundsFromComposites(diagram, layout)
   normalizeLayout(layout)
   return layout
@@ -479,9 +595,10 @@ export function createStateDiagramLayout(
   }
 
   const ranks = computeRanks(diagram)
+  const maxRank = Math.max(0, ...ranks.values())
   const byRank = new Map<number, StateDiagramState[]>()
   for (const state of diagram.states) {
-    const rank = ranks.get(state.id) ?? 0
+    const rank = diagram.direction === "BT" ? maxRank - (ranks.get(state.id) ?? 0) : (ranks.get(state.id) ?? 0)
     const list = byRank.get(rank) ?? []
     list.push(state)
     byRank.set(rank, list)
@@ -491,9 +608,13 @@ export function createStateDiagramLayout(
   const sizes = new Map(diagram.states.map((state) => [state.id, stateSize(state)]))
   const bounds = new Map<string, StateDiagramBoxBounds>()
   const outgoingLabelRows = new Map<string, number>()
+  const selfTransitionCounts = new Map<string, number>()
   for (const transition of diagram.transitions) {
     const rows = measureStateTransitionLabel(transition.label).height
     outgoingLabelRows.set(transition.from, Math.max(outgoingLabelRows.get(transition.from) ?? 0, rows))
+    if (transition.from === transition.to) {
+      selfTransitionCounts.set(transition.from, (selfTransitionCounts.get(transition.from) ?? 0) + 1)
+    }
   }
 
   const singleColumnCenter = Math.max(
@@ -524,8 +645,12 @@ export function createStateDiagramLayout(
       x += size.width + options.minStateGap + 8
     }
     const labelRows = states.reduce((rows, state) => Math.max(rows, outgoingLabelRows.get(state.id) ?? 0), 0)
+    const selfTransitionRows = states.reduce(
+      (rows, state) => Math.max(rows, (selfTransitionCounts.get(state.id) ?? 0) * 3 + 1),
+      0,
+    )
     const pseudoStateApproachClearance = states.some((state) => state.kind === "choice") ? 2 : 0
-    y += rowHeight + Math.max(4, labelRows + 3) + pseudoStateApproachClearance
+    y += rowHeight + Math.max(4, labelRows + 3, selfTransitionRows) + pseudoStateApproachClearance
   }
 
   return finalizeLayout(diagram, emptyLayout(bounds, sizes), budget)
@@ -805,21 +930,21 @@ function placeStateDiagramNotesAroundTransitions(
           size,
         ),
       ),
-    )
-      .flat()
+    ).flat()
     const findPlacement = (candidateSpace: SpatialIndex, limit: number) => {
       const connectorSearch = createStateSearchSpace(candidateSpace, (role) => (role === "label" ? 1 : 0))
       for (const bound of candidateBounds.slice(0, limit)) {
         if (bound.left < 0) continue
         const owner = `note:${index}`
-        if (!candidateSpace.isFree(spatialRectClaim(`${owner}:body`, owner, "body", bound), { clearance: 1 }))
-          continue
+        if (!candidateSpace.isFree(spatialRectClaim(`${owner}:body`, owner, "body", bound), { clearance: 1 })) continue
         const connector = findNoteConnector(connectorSearch, bound, target, budget)
         if (connector) return { bound: { ...bound, connector }, connector }
       }
       return undefined
     }
     const placement =
+      findPlacement(space, 1) ??
+      findPlacement(noteSpace, 1) ??
       findPlacement(space, MAX_STRICT_NOTE_PLACEMENTS) ??
       findPlacement(reserved, candidateBounds.length) ??
       outsideNotePlacement(noteSpace, note, index, target, size)
@@ -857,10 +982,7 @@ function outsideNotePlacement(
       size,
     )
     const alignedNoteX = position === "left" ? aligned.left + aligned.width : aligned.left - 1
-    const alignedConnectorY = Math.max(
-      aligned.top + 1,
-      Math.min(target.centerY, aligned.top + aligned.height - 2),
-    )
+    const alignedConnectorY = Math.max(aligned.top + 1, Math.min(target.centerY, aligned.top + aligned.height - 2))
     const alignedTargetX = position === "left" ? target.left - 1 : target.left + target.width
     const alignedConnector = {
       connectorY: alignedConnectorY,
@@ -975,16 +1097,30 @@ export function expandCompositeBoundsForInternalTransitions(
         belongsToComposite(plan.route.transition.from, composite.id, statesById, compositesById) &&
         belongsToComposite(plan.route.transition.to, composite.id, statesById, compositesById),
     )
-    const occupiedYs = internalPlans.flatMap((plan) => [
-      ...plan.cells.map((cell) => cell.y),
-      ...(plan.label ? plan.label.lines.map((_, index) => plan.label!.y + index) : []),
+    const occupied = internalPlans.flatMap((plan) => [
+      ...plan.cells.map((cell) => ({ x: cell.x, y: cell.y })),
+      ...(plan.label
+        ? plan.label.lines.flatMap((line, row) =>
+            Array.from({ length: diagramTextWidth(line) }, (_, column) => ({
+              x: plan.label!.x + column,
+              y: plan.label!.y + row,
+            })),
+          )
+        : []),
     ])
-    if (occupiedYs.length === 0) continue
+    if (occupied.length === 0) continue
 
-    const top = Math.min(bound.top, Math.min(...occupiedYs) - 1)
-    const bottom = Math.max(bound.top + bound.height, Math.max(...occupiedYs) + 2)
+    const left = Math.min(bound.left, Math.min(...occupied.map((point) => point.x)) - 1)
+    const top = Math.min(bound.top, Math.min(...occupied.map((point) => point.y)) - 1)
+    const right = Math.max(bound.left + bound.width, Math.max(...occupied.map((point) => point.x)) + 2)
+    const bottom = Math.max(bound.top + bound.height, Math.max(...occupied.map((point) => point.y)) + 2)
+    bound.left = left
     bound.top = top
+    bound.width = right - left
     bound.height = bottom - top
+    bound.centerX = bound.left + Math.floor(bound.width / 2)
     bound.centerY = bound.top + Math.floor(bound.height / 2)
   }
+
+  enforceCompositeMargins(diagram, compositeBounds)
 }
diff --git a/packages/merman/src/state/parser.ts b/packages/merman/src/state/parser.ts
index fa2521b993b..c02a5af881a 100644
--- a/packages/merman/src/state/parser.ts
+++ b/packages/merman/src/state/parser.ts
@@ -16,14 +16,14 @@ const STATE_RE = /^state\s+"([^"]+)"\s+as\s+(\S+)$/i
 const COMPOSITE_STATE_RE = /^state\s+(?:"([^"]+)"\s+as\s+)?(\S+)\s*\{$/i
 const CHOICE_STATE_RE = /^state\s+(\S+)\s+<<choice>>$/i
 const TRANSITION_RE = /^(\[\*\]|[^\s:]+)\s*-->\s*(\[\*\]|[^\s:]+)(?:\s*:\s*(.*))?$/
-const DIRECTION_RE = /^direction\s+(TB|TD|LR|RL)$/i
+const DIRECTION_RE = /^direction\s+(TB|TD|BT|LR|RL)$/i
 const NOTE_INLINE_RE = /^note\s+(left|right)\s+of\s+(\S+)\s*:\s*(.*)$/i
 const NOTE_START_RE = /^note\s+(left|right)\s+of\s+(\S+)\s*$/i
 const NOTE_END_RE = /^end\s+note$/i
 
 function normalizeDirection(value?: string): StateDiagramDirection {
   const upper = value?.toUpperCase()
-  if (upper === "TB" || upper === "TD" || upper === "LR" || upper === "RL") return upper
+  if (upper === "TB" || upper === "TD" || upper === "BT" || upper === "LR" || upper === "RL") return upper
   return DEFAULT_DIRECTION
 }
 
diff --git a/packages/merman/src/state/render-grid.ts b/packages/merman/src/state/render-grid.ts
index 50a0fb186cf..687d1aba2a0 100644
--- a/packages/merman/src/state/render-grid.ts
+++ b/packages/merman/src/state/render-grid.ts
@@ -7,11 +7,12 @@ import type { StateCellStyle } from "./types.js"
 export type StateGrid = DiagramCanvas<StateCellStyle>
 
 export function renderStateGridText(grid: StateGrid): string {
-  return grid.toString({ trimBottom: true })
+  return grid.toString({ trimTop: true, trimBottom: true })
 }
 
 export function renderStateGridStyledText(grid: StateGrid, colors: StateStyleColors): StyledText {
   return renderDiagramGridStyledText(grid, (run) => (run.style ? colors[run.style] : undefined), undefined, {
+    trimTop: true,
     trimBottom: true,
   })
 }
diff --git a/packages/merman/src/state/routing.test.ts b/packages/merman/src/state/routing.test.ts
index ce6088b20b3..fa8f351fdb7 100644
--- a/packages/merman/src/state/routing.test.ts
+++ b/packages/merman/src/state/routing.test.ts
@@ -1,4 +1,5 @@
 import { describe, expect, test } from "bun:test"
+import { diagramTextWidth } from "../core/text.js"
 import type { StateDiagramBoxBounds } from "./layout.js"
 import { createStateDiagramLayout } from "./layout.js"
 import { parseMermaidStateDiagram } from "./parser.js"
@@ -286,10 +287,7 @@ describe("createStateTransitionRenderPlans", () => {
     expect(
       plan.path.some(
         ([x, y]) =>
-          x >= sibling.left &&
-          x < sibling.left + sibling.width &&
-          y >= sibling.top &&
-          y < sibling.top + sibling.height,
+          x >= sibling.left && x < sibling.left + sibling.width && y >= sibling.top && y < sibling.top + sibling.height,
       ),
     ).toBe(false)
   })
@@ -348,6 +346,158 @@ describe("createStateTransitionRenderPlans", () => {
       }),
     ).toBe(true)
   })
+
+  test.each(["LR", "RL", "TB", "TD"] as const)(
+    "keeps endpoint-disjoint %s transitions on separate cells when a detour exists",
+    (direction) => {
+      const diagram = prepareVisibleStateDiagram(
+        parseMermaidStateDiagram(`stateDiagram-v2
+  direction ${direction}
+  state "A" as A
+  state "B" as B
+  state "C" as C
+  state "D" as D
+  B --> D: e0
+  C --> A: e1`),
+      )
+      const layout = createStateDiagramLayout(diagram, { minStateGap: 5 })
+      const plans = createStateTransitionRenderPlans(diagram, layout.bounds, 30)
+      const first = new Set(plans[0]!.path.map(([x, y]) => `${x}:${y}`))
+
+      expect(plans[1]!.path.every(([x, y]) => !first.has(`${x}:${y}`))).toBe(true)
+    },
+  )
+
+  test("anchors labels to final repaired transition geometry", () => {
+    const diagram = prepareVisibleStateDiagram(
+      parseMermaidStateDiagram(`stateDiagram-v2
+  direction TB
+  state "A" as A
+  state "B" as B
+  state "C" as C
+  A --> B: e0
+  A --> C: e1
+  B --> A: e2`),
+    )
+    const layout = createStateDiagramLayout(diagram, { minStateGap: 5 })
+    const plan = createStateTransitionRenderPlans(diagram, layout.bounds, 30).find(
+      (candidate) => candidate.route.transition.label === "e2",
+    )!
+    const width = Math.max(...plan.label!.lines.map(diagramTextWidth))
+    const distance = Math.min(
+      ...plan.path.map(([pathX, pathY]) => {
+        const dx =
+          pathX < plan.label!.x
+            ? plan.label!.x - pathX
+            : pathX >= plan.label!.x + width
+              ? pathX - (plan.label!.x + width - 1)
+              : 0
+        const dy =
+          pathY < plan.label!.y
+            ? plan.label!.y - pathY
+            : pathY >= plan.label!.y + plan.label!.lines.length
+              ? pathY - (plan.label!.y + plan.label!.lines.length - 1)
+              : 0
+        return dx + dy
+      }),
+    )
+
+    expect(plan.pathRepaired).toBe(true)
+    expect(distance).toBeLessThanOrEqual(4)
+  })
+
+  test.each(["LR", "RL", "TB", "TD"] as const)(
+    "allocates distinct connected self-transition lanes in %s diagrams",
+    (direction) => {
+      for (const count of [2, 3, 4]) {
+        const diagram = prepareVisibleStateDiagram(
+          parseMermaidStateDiagram(`stateDiagram-v2
+  direction ${direction}
+${Array.from({ length: count }, (_, index) => `  A --> A: loop-${index}`).join("\n")}`),
+        )
+        const layout = createStateDiagramLayout(diagram, { minStateGap: 5 })
+        const plans = createStateTransitionRenderPlans(diagram, layout.bounds, 30)
+
+        expect(new Set(plans.map((plan) => plan.path.map(([x, y]) => `${x}:${y}`).join("|"))).size).toBe(count)
+        for (const plan of plans) {
+          expect(
+            plan.path.slice(1).every(([x, y], index) => {
+              const previous = plan.path[index]!
+              return Math.abs(x - previous[0]) + Math.abs(y - previous[1]) === 1
+            }),
+          ).toBe(true)
+        }
+      }
+    },
+  )
+
+  test("uses fixed-width side lanes for long parallel vertical labels", () => {
+    const diagram = prepareVisibleStateDiagram(
+      parseMermaidStateDiagram(`stateDiagram-v2
+  direction TB
+  A --> B: alpha route label that is deliberately long
+  A --> B: beta route label that is deliberately long
+  A --> B: gamma route label that is deliberately long`),
+    )
+    const layout = createStateDiagramLayout(diagram, { minStateGap: 5 })
+    const rails = createStateTransitionRoutePlans(diagram, layout.bounds, 30)
+      .filter((plan) => plan.kind === "side-parallel")
+      .map((plan) => plan.railX)
+
+    expect(rails).toHaveLength(2)
+    expect(rails[1]! - rails[0]!).toBe(3)
+  })
+
+  test.each([
+    [
+      "parallel",
+      `stateDiagram-v2
+  direction TB
+  A --> B: alpha route label that is deliberately long
+  A --> B: beta route label that is deliberately long
+  A --> B: gamma route label that is deliberately long`,
+      3,
+    ],
+    [
+      "self",
+      `stateDiagram-v2
+  direction LR
+  A --> A: one
+  A --> A: two
+  A --> A: three`,
+      3,
+    ],
+  ] as const)("keeps %s labels one column clear of frames and route rails", (_, source, count) => {
+    const diagram = prepareVisibleStateDiagram(parseMermaidStateDiagram(source))
+    const layout = createStateDiagramLayout(diagram, { minStateGap: 5 })
+    const plans = createStateTransitionRenderPlans(diagram, layout.bounds, 30)
+    const routeCells = plans.flatMap((plan) => plan.path)
+
+    expect(plans).toHaveLength(count)
+    for (const plan of plans) {
+      const width = Math.max(...plan.label!.lines.map(diagramTextWidth))
+      for (const [row, line] of plan.label!.lines.entries()) {
+        const lineWidth = diagramTextWidth(line)
+        const y = plan.label!.y + row
+        expect(
+          routeCells
+            .filter(([, routeY]) => routeY === y)
+            .every(([routeX]) => routeX < plan.label!.x - 1 || routeX > plan.label!.x + lineWidth),
+        ).toBe(true)
+        for (const bound of layout.bounds.values()) {
+          if (y < bound.top || y >= bound.top + bound.height) continue
+          expect(bound.left + bound.width <= plan.label!.x - 1 || bound.left >= plan.label!.x + width + 1).toBe(true)
+        }
+      }
+    }
+
+    if (source.includes("A --> A")) {
+      const arrowXs = plans
+        .flatMap((plan) => plan.cells.filter((cell) => cell.arrowDirection).map((cell) => cell.x))
+        .sort((left, right) => left - right)
+      expect(arrowXs.slice(1).every((x, index) => x - arrowXs[index]! >= 4)).toBe(true)
+    }
+  })
 })
 
 describe("createStateTransitionJunctionPlans", () => {
diff --git a/packages/merman/src/state/routing.ts b/packages/merman/src/state/routing.ts
index 4e4b7df48b1..16d742ff4ad 100644
--- a/packages/merman/src/state/routing.ts
+++ b/packages/merman/src/state/routing.ts
@@ -1,6 +1,6 @@
 import { BorderChars } from "@opentui/core"
 import { diagramLineGlyph } from "../core/drawing.js"
-import type { DiagramDirection } from "../core/geometry.js"
+import { orthogonalPathPoints, type DiagramDirection } from "../core/geometry.js"
 import { SpatialIndex, spatialPathClaim, spatialRectClaim } from "../core/spatial.js"
 import { diagramTextWidth, splitDiagramLines } from "../core/text.js"
 import type { StateDiagramBoxBounds as BoxBounds, StateDiagramNoteBounds } from "./layout.js"
@@ -24,7 +24,7 @@ interface StateTransitionRoutePlanBase {
 }
 
 export type StateTransitionRoutePlan =
-  | (StateTransitionRoutePlanBase & { kind: "self" })
+  | (StateTransitionRoutePlanBase & { kind: "self"; lane: number })
   | (StateTransitionRoutePlanBase & { kind: "horizontal-forward"; leftToRight: boolean })
   | (StateTransitionRoutePlanBase & { kind: "bottom-feedback"; railY: number; approachX: number })
   | (StateTransitionRoutePlanBase & { kind: "top-feedback"; railY: number })
@@ -58,6 +58,7 @@ export interface StateTransitionRenderPlan {
   cells: readonly StateTransitionRenderCell[]
   path: readonly StateTransitionPathPoint[]
   label?: StateTransitionRenderLabel
+  pathRepaired?: boolean
 }
 
 export interface StateTransitionRenderOptions {
@@ -350,6 +351,26 @@ function sideParallelTargetApproach(
   })
 }
 
+function containingCompositeIds(diagram: StateVisibleDiagram, id: string): string[] {
+  const statesById = new Map(diagram.states.map((state) => [state.id, state]))
+  const compositesById = new Map(diagram.composites.map((composite) => [composite.id, composite]))
+  const ids: string[] = []
+  let parentId = statesById.get(id)?.parentId ?? compositesById.get(id)?.parentId
+  while (parentId) {
+    ids.push(parentId)
+    parentId = compositesById.get(parentId)?.parentId
+  }
+  return ids
+}
+
+function innermostCommonComposite(
+  diagram: StateVisibleDiagram,
+  transition: StateVisibleTransition,
+): string | undefined {
+  const target = new Set(containingCompositeIds(diagram, transition.to))
+  return containingCompositeIds(diagram, transition.from).find((id) => target.has(id))
+}
+
 export function createStateTransitionRoutePlans(
   diagram: StateVisibleDiagram,
   bounds: ReadonlyMap<string, BoxBounds>,
@@ -358,11 +379,13 @@ export function createStateTransitionRoutePlans(
 ): StateTransitionRoutePlan[] {
   const statesById = new Map(diagram.states.map((state) => [state.id, state]))
   const endpointOccurrences = new Map<string, number>()
+  const selfOccurrences = new Map<string, number>()
   const parallelLaneGap = Math.max(
     3,
     ...diagram.transitions.map((transition) => measureStateTransitionLabel(transition.label).height + 2),
   )
   let nextSideRailX = Math.max(0, ...[...bounds.values()].map((bound) => bound.left + bound.width)) + 3
+  const sideRailLanes = new Map<string, number>()
   const feedbackAllocations = createFeedbackAllocations(diagram, bounds, feedbackLaneY, parallelLaneGap, feedbackTopY)
   let nextBottomRailY =
     Math.max(
@@ -371,9 +394,24 @@ export function createStateTransitionRoutePlans(
         .filter((allocation) => allocation.side === "bottom")
         .map((allocation) => allocation.railY),
     ) + parallelLaneGap
-  const allocateSideRail = (label: string): number => {
+  const allocateSideRail = (transition: StateVisibleTransition): number => {
+    const compositeId = innermostCommonComposite(diagram, transition)
+    const composite = compositeId ? bounds.get(compositeId) : undefined
+    if (compositeId && composite) {
+      const lane = sideRailLanes.get(compositeId) ?? 0
+      sideRailLanes.set(compositeId, lane + 1)
+      const descendantRight = Math.max(
+        composite.left + 1,
+        ...diagram.states.flatMap((state) => {
+          if (!containingCompositeIds(diagram, state.id).includes(compositeId)) return []
+          const bound = bounds.get(state.id)
+          return bound ? [bound.left + bound.width] : []
+        }),
+      )
+      return Math.min(descendantRight + 2 + lane * 3, composite.left + composite.width - 2)
+    }
     const railX = nextSideRailX
-    nextSideRailX += Math.max(3, measureStateTransitionLabel(label).width + 2)
+    nextSideRailX += 3
     return railX
   }
   const allocateBottomRail = (): number => {
@@ -392,7 +430,7 @@ export function createStateTransitionRoutePlans(
     const targetIsHiddenMarker = isHiddenCompositeMarker(targetState)
     const base = { transition, from, to, targetIsChoice, targetIsHiddenMarker }
     const sideParallel = (): StateTransitionRoutePlan => {
-      const railX = allocateSideRail(transition.label)
+      const railX = allocateSideRail(transition)
       return {
         ...base,
         kind: "side-parallel",
@@ -400,7 +438,11 @@ export function createStateTransitionRoutePlans(
         targetApproach: sideParallelTargetApproach(diagram, transition, from, to, bounds, railX),
       }
     }
-    if (transition.from === transition.to) return [{ ...base, kind: "self" }]
+    if (transition.from === transition.to) {
+      const lane = selfOccurrences.get(transition.from) ?? 0
+      selfOccurrences.set(transition.from, lane + 1)
+      return [{ ...base, kind: "self", lane }]
+    }
     const endpointKey = `${transition.from}\u0000${transition.to}`
     const parallelIndex = endpointOccurrences.get(endpointKey) ?? 0
     endpointOccurrences.set(endpointKey, parallelIndex + 1)
@@ -449,7 +491,8 @@ export function createStateTransitionRoutePlans(
       if (verticalCorridorCrossesUnrelatedState(diagram, transition, from, to, bounds)) {
         return [sideParallel()]
       }
-      if (from.centerY > to.centerY) {
+      const verticalFeedback = diagram.direction === "BT" ? from.centerY < to.centerY : from.centerY > to.centerY
+      if (verticalFeedback) {
         return [sideParallel()]
       }
       if (from.centerY === to.centerY) {
@@ -612,33 +655,36 @@ function addHorizontalForward(builder: StateTransitionRenderBuilder): void {
 }
 
 function addSelfTransition(builder: StateTransitionRenderBuilder): void {
-  const { from: bounds, transition } = builder.route
+  const { from: bounds, transition, lane } = builder.route as Extract<StateTransitionRoutePlan, { kind: "self" }>
   if (bounds.width <= 1 || bounds.height <= 1) {
-    const railX = bounds.left + 4
-    const railY = bounds.top + 2
+    const railX = bounds.left + 4 + lane * 4
+    const railY = bounds.top + 2 + lane * 2
     addHorizontalLine(builder, bounds.left + 1, railX - 1, bounds.top, 1)
     addCell(builder, { x: railX, y: bounds.top, char: "╮" })
-    addCell(builder, { x: railX, y: bounds.top + 1, char: "│" })
+    addVerticalLine(builder, railX, bounds.top + 1, railY - 1, 1)
     addCell(builder, { x: railX, y: railY, char: "╯" })
     addHorizontalLine(builder, railX - 1, bounds.left + 1, railY, -1)
     addCell(builder, { x: bounds.left, y: railY, char: "╰" })
+    for (let y = railY - 1; y > bounds.top + 1; y--) addCell(builder, { x: bounds.left, y, char: "│" })
     addCell(builder, { x: bounds.left, y: bounds.top + 1, arrowDirection: "up" })
     addPathPoint(builder, bounds.left, bounds.top)
-    if (transition.label) addLabel(builder, railX + 2, bounds.top + 1, transition.label)
+    if (transition.label) addLabel(builder, railX + 2, lane === 0 ? bounds.top + 1 : railY - 1, transition.label)
     return
   }
   const sourceX = bounds.left + Math.max(2, Math.floor(bounds.width / 3))
   const bottomY = bounds.top + bounds.height - 1
-  const railY = bottomY + 2
-  const targetX = Math.max(sourceX + 3, bounds.left + Math.min(bounds.width - 3, Math.ceil((bounds.width * 2) / 3)))
+  const railY = bottomY + 2 + lane * 3
+  const targetX =
+    Math.max(sourceX + 3, bounds.left + Math.min(bounds.width - 3, Math.ceil((bounds.width * 2) / 3))) + lane * 4
 
   addBottomDeparture(builder, bounds, sourceX)
-  addCell(builder, { x: sourceX, y: bottomY + 1, char: "│" })
+  addVerticalLine(builder, sourceX, bottomY + 1, railY - 1, 1)
   addCell(builder, { x: sourceX, y: railY, char: "╰" })
   for (let x = sourceX + 1; x < targetX; x++) addCell(builder, { x, y: railY, char: "─" })
   addCell(builder, { x: targetX, y: railY, char: "╯" })
+  for (let y = railY - 1; y > bottomY + 1; y--) addCell(builder, { x: targetX, y, char: "│" })
   addCell(builder, { x: targetX, y: bottomY + 1, arrowDirection: "up" })
-  if (transition.label) addLabel(builder, targetX + 2, bottomY + 1, transition.label)
+  if (transition.label) addLabel(builder, targetX + 2, lane === 0 ? bottomY + 1 : railY - 1, transition.label)
 }
 
 function outsideBottomY(bounds: BoxBounds): number {
@@ -732,10 +778,8 @@ function addTopFeedbackTransition(builder: StateTransitionRenderBuilder): void {
 }
 
 function addSideParallelTransition(builder: StateTransitionRenderBuilder): void {
-  const { from, to, targetIsChoice, targetIsHiddenMarker, transition, railX, targetApproach } = builder.route as Extract<
-    StateTransitionRoutePlan,
-    { kind: "side-parallel" }
-  >
+  const { from, to, targetIsChoice, targetIsHiddenMarker, transition, railX, targetApproach } =
+    builder.route as Extract<StateTransitionRoutePlan, { kind: "side-parallel" }>
   const startX = from.left + from.width
   const startY = from.centerY
   const endY = targetApproach === "top" ? to.top - 2 : targetApproach === "bottom" ? to.top + to.height + 1 : to.centerY
@@ -757,7 +801,12 @@ function addSideParallelTransition(builder: StateTransitionRenderBuilder): void
     if (targetIsChoice || targetIsHiddenMarker) addPathPoint(builder, to.left, to.top)
     if (transition.label) {
       const metrics = measureStateTransitionLabel(transition.label)
-      addLabel(builder, railX + 2, Math.max(0, Math.floor((startY + to.centerY - metrics.height + 1) / 2)), transition.label)
+      addLabel(
+        builder,
+        railX + 2,
+        Math.max(0, Math.floor((startY + to.centerY - metrics.height + 1) / 2)),
+        transition.label,
+      )
     }
     return
   }
@@ -938,31 +987,62 @@ function routeIntersectsUnrelatedState(
       "boundary",
       stateDiagramNoteConnector(noteBound, target).points,
     )
-    return plan.path.some(([x, y]) =>
-      connector.spans.some((span) => span.y === y && x >= span.fromX && x <= span.toX),
-    )
+    return plan.path.some(([x, y]) => connector.spans.some((span) => span.y === y && x >= span.fromX && x <= span.toX))
   })
 }
 
 function findBodySafePath(
   start: StateTransitionPathPoint,
   end: StateTransitionPathPoint,
+  diagram: StateVisibleDiagram,
   bounds: ReadonlyMap<string, BoxBounds>,
   plan: StateTransitionRenderPlan,
   search: StateSearchSpace,
   budget: StateSearchBudget,
 ): StateTransitionPathPoint[] | undefined {
   const margin = Math.max(8, bounds.size * 2)
+  const compositeId = innermostCommonComposite(diagram, plan.route.transition)
+  const composite = compositeId ? bounds.get(compositeId) : undefined
+  const searchBounds = {
+    minX: composite ? composite.left + 1 : search.minX - margin,
+    minY: composite ? composite.top + 1 : Math.min(search.minY, ...plan.path.map((point) => point[1])) - margin,
+    maxX: composite
+      ? composite.left + composite.width - 2
+      : Math.max(search.maxX, ...plan.path.map((point) => point[0])) + margin,
+    maxY: composite
+      ? composite.top + composite.height - 2
+      : Math.max(search.maxY, ...plan.path.map((point) => point[1])) + margin,
+  }
+  const isFree = ([x, y]: StateTransitionPathPoint) =>
+    x >= searchBounds.minX &&
+    x <= searchBounds.maxX &&
+    y >= searchBounds.minY &&
+    y <= searchBounds.maxY &&
+    !search.blocked.has(`${x}:${y}`)
+  const pathMinX = Math.min(...plan.path.map((point) => point[0]))
+  const pathMinY = Math.min(...plan.path.map((point) => point[1]))
+  const pathMaxX = Math.max(...plan.path.map((point) => point[0]))
+  const pathMaxY = Math.max(...plan.path.map((point) => point[1]))
+  const directCandidates: StateTransitionPathPoint[][] = [
+    [start, [start[0], end[1]] as const, end],
+    [start, [end[0], start[1]] as const, end],
+    ...Array.from({ length: 4 }, (_, index) => index + 1).flatMap((offset): StateTransitionPathPoint[][] => [
+      [start, [start[0], pathMinY - offset], [end[0], pathMinY - offset], end],
+      [start, [start[0], pathMaxY + offset], [end[0], pathMaxY + offset], end],
+      [start, [pathMinX - offset, start[1]], [pathMinX - offset, end[1]], end],
+      [start, [pathMaxX + offset, start[1]], [pathMaxX + offset, end[1]], end],
+    ]),
+  ]
+  const direct = directCandidates
+    .map((points) => orthogonalPathPoints(points.map(([x, y]) => ({ x, y }))).map(({ x, y }) => [x, y] as const))
+    .filter((points) => points.every(isFree))
+    .sort((left, right) => left.length - right.length)[0]
+  if (direct) return direct
   const path = findStateManhattanPath(
     [{ x: start[0], y: start[1] }],
     { x: end[0], y: end[1] },
     search,
-    {
-      minX: search.minX - margin,
-      minY: Math.min(search.minY, ...plan.path.map((point) => point[1])) - margin,
-      maxX: Math.max(search.maxX, ...plan.path.map((point) => point[0])) + margin,
-      maxY: Math.max(search.maxY, ...plan.path.map((point) => point[1])) + margin,
-    },
+    searchBounds,
     budget,
   )
   return path?.map((point) => [point.x, point.y] as const)
@@ -975,17 +1055,29 @@ function bodySafeTransitionPlan(
   noteBounds: readonly StateDiagramNoteBounds[],
   search: StateSearchSpace,
   budget: StateSearchBudget,
+  forceRepair = false,
 ): StateTransitionRenderPlan {
-  if (!routeIntersectsUnrelatedState(plan, diagram, bounds, noteBounds)) return plan
+  if (!forceRepair && !routeIntersectsUnrelatedState(plan, diagram, bounds, noteBounds)) return plan
   const sourceOutsideIndex = plan.path.findIndex((point) => !pointIsInsideBounds(point, plan.route.from))
   const targetOutsideIndex = plan.path.findLastIndex((point) => !pointIsInsideBounds(point, plan.route.to))
   if (sourceOutsideIndex < 0 || targetOutsideIndex < sourceOutsideIndex) return plan
-  const safePath = findBodySafePath(plan.path[sourceOutsideIndex]!, plan.path[targetOutsideIndex]!, bounds, plan, search, budget)
+  const safePath = findBodySafePath(
+    plan.path[sourceOutsideIndex]!,
+    plan.path[targetOutsideIndex]!,
+    diagram,
+    bounds,
+    plan,
+    search,
+    budget,
+  )
   if (!safePath) return alternateBodySafeTransitionPlan(plan, diagram, bounds, noteBounds, search, budget)
 
   const prefix = plan.path.slice(0, sourceOutsideIndex)
   const suffix = plan.path.slice(targetOutsideIndex + 1)
-  return renderBodySafeTransitionPlan(plan, safePath, prefix, suffix)
+  const repaired = renderBodySafeTransitionPlan(plan, safePath, prefix, suffix)
+  if (safePath.length <= plan.path.length + 4) return repaired
+  const alternate = alternateBodySafeTransitionPlan(plan, diagram, bounds, noteBounds, search, budget)
+  return alternate !== plan && alternate.path.length < repaired.path.length ? alternate : repaired
 }
 
 function alternateBodySafeTransitionPlan(
@@ -996,9 +1088,10 @@ function alternateBodySafeTransitionPlan(
   search: StateSearchSpace,
   budget: StateSearchBudget,
 ): StateTransitionRenderPlan {
+  const candidates: StateTransitionRenderPlan[] = []
   for (const source of stateRoutePorts(plan.route.from)) {
     for (const target of stateRoutePorts(plan.route.to)) {
-      const safePath = findBodySafePath(source.outside, target.outside, bounds, plan, search, budget)
+      const safePath = findBodySafePath(source.outside, target.outside, diagram, bounds, plan, search, budget)
       if (!safePath) continue
       const prefix = plan.route.from.width > 1 && plan.route.from.height > 1 ? [source.border] : []
       const suffix =
@@ -1006,10 +1099,10 @@ function alternateBodySafeTransitionPlan(
           ? ([[plan.route.to.left, plan.route.to.top]] as const)
           : []
       const repaired = renderBodySafeTransitionPlan(plan, safePath, prefix, suffix, source.char)
-      if (!routeIntersectsUnrelatedState(repaired, diagram, bounds, noteBounds)) return repaired
+      if (!routeIntersectsUnrelatedState(repaired, diagram, bounds, noteBounds)) candidates.push(repaired)
     }
   }
-  return plan
+  return candidates.sort((left, right) => left.path.length - right.path.length)[0] ?? plan
 }
 
 function stateRoutePorts(bounds: BoxBounds): Array<{
@@ -1072,7 +1165,50 @@ function renderBodySafeTransitionPlan(
     cells.push({ x: point[0], y: point[1], char: diagramLineGlyph(connections, "rounded") })
   }
 
-  return { ...plan, cells, path: fullPath }
+  return { ...plan, cells, path: fullPath, pathRepaired: true }
+}
+
+function labelDistanceToPath(
+  x: number,
+  y: number,
+  width: number,
+  height: number,
+  path: readonly StateTransitionPathPoint[],
+): number {
+  return Math.min(
+    ...path.map(([pathX, pathY]) => {
+      const dx = pathX < x ? x - pathX : pathX >= x + width ? pathX - (x + width - 1) : 0
+      const dy = pathY < y ? y - pathY : pathY >= y + height ? pathY - (y + height - 1) : 0
+      return dx + dy
+    }),
+  )
+}
+
+function stateTransitionLabelCandidates(
+  plan: StateTransitionRenderPlan,
+  width: number,
+  height: number,
+): Array<{ x: number; y: number }> {
+  const candidates = new Map<string, { x: number; y: number }>()
+  const add = (x: number, y: number) => candidates.set(`${x}:${y}`, { x, y })
+  if (
+    plan.label &&
+    (!plan.pathRepaired || labelDistanceToPath(plan.label.x, plan.label.y, width, height, plan.path) <= 4)
+  ) {
+    add(plan.label.x, plan.label.y)
+  }
+  for (const [x, y] of plan.path) {
+    add(x + 2, y - Math.floor(height / 2))
+    add(x - width - 2, y - Math.floor(height / 2))
+    add(x - Math.floor(width / 2), y - height - 1)
+    add(x - Math.floor(width / 2), y + 2)
+  }
+  const preferred = plan.label ?? { x: plan.path[0]?.[0] ?? 0, y: plan.path[0]?.[1] ?? 0 }
+  return [...candidates.values()].sort((left, right) => {
+    const leftDistance = Math.abs(left.x - preferred.x) + Math.abs(left.y - preferred.y)
+    const rightDistance = Math.abs(right.x - preferred.x) + Math.abs(right.y - preferred.y)
+    return leftDistance - rightDistance
+  })
 }
 
 function placeStateTransitionLabels(
@@ -1096,6 +1232,19 @@ function placeStateTransitionLabels(
         plan.path.map(([x, y]) => ({ x, y })),
       ),
     ),
+    ...diagram.composites.flatMap((composite) => {
+      const bound = bounds.get(composite.id)
+      if (!bound) return []
+      return [
+        spatialPathClaim(`composite:${composite.id}`, `composite:${composite.id}`, "boundary", [
+          { x: bound.left, y: bound.top },
+          { x: bound.left + bound.width - 1, y: bound.top },
+          { x: bound.left + bound.width - 1, y: bound.top + bound.height - 1 },
+          { x: bound.left, y: bound.top + bound.height - 1 },
+          { x: bound.left, y: bound.top },
+        ]),
+      ]
+    }),
     ...noteBounds.flatMap((noteBound) => {
       const target = bounds.get(noteBound.note.target)
       return [
@@ -1114,10 +1263,25 @@ function placeStateTransitionLabels(
     }),
   )
 
-  return plans.map((plan, planIndex) => {
-    if (!plan.label) return plan
+  const placed = new Map<number, StateTransitionRenderPlan>()
+  const endpointCounts = new Map<string, number>()
+  for (const plan of plans) {
+    const key = `${plan.route.transition.from}\u0000${plan.route.transition.to}`
+    endpointCounts.set(key, (endpointCounts.get(key) ?? 0) + 1)
+  }
+  const placementOrder = [...plans.keys()].sort(
+    (left, right) => Number(Boolean(plans[left]!.pathRepaired)) - Number(Boolean(plans[right]!.pathRepaired)),
+  )
+  for (const planIndex of placementOrder) {
+    const plan = plans[planIndex]!
+    if (!plan.label) {
+      placed.set(planIndex, plan)
+      continue
+    }
     const width = Math.max(...plan.label.lines.map(diagramTextWidth))
-    const statePadding = plan.label.lines.length === 1 ? 0 : 1
+    const endpointKey = `${plan.route.transition.from}\u0000${plan.route.transition.to}`
+    const needsLaneClearance = (endpointCounts.get(endpointKey) ?? 0) > 1
+    const statePadding = needsLaneClearance || plan.label.lines.length > 1 ? 1 : 0
     const labelClaim = (x: number, y: number) =>
       spatialRectClaim(`label:${planIndex}`, `label:${planIndex}`, "label", {
         left: x,
@@ -1131,19 +1295,35 @@ function placeStateTransitionLabels(
         clearance: {
           body: statePadding,
           label: { x: 1, y: 0 },
+          route:
+            plan.pathRepaired || plan.route.kind === "side-parallel" || needsLaneClearance
+              ? {
+                  x: 1,
+                  y: 0,
+                }
+              : 0,
         },
       })
     }
 
-    let x = plan.label.x
-    let y = plan.label.y
-    if (!isClear(x, y)) {
+    const candidates = stateTransitionLabelCandidates(plan, width, plan.label.lines.length)
+    const nearby = candidates.find(
+      (candidate) =>
+        (!(plan.pathRepaired || plan.route.kind === "side-parallel" || needsLaneClearance) ||
+          labelDistanceToPath(candidate.x, candidate.y, width, plan.label!.lines.length, plan.path) >= 2) &&
+        isClear(candidate.x, candidate.y),
+    )
+    let x = nearby?.x ?? candidates[0]?.x ?? plan.label.x
+    let y = nearby?.y ?? candidates[0]?.y ?? plan.label.y
+    if (!nearby) {
       search: for (let distance = 1; distance < 500; distance++) {
         for (let dx = -distance; dx <= distance; dx++) {
           const dy = distance - Math.abs(dx)
           for (const candidateY of dy === 0 ? [y] : [y - dy, y + dy]) {
             const candidateX = x + dx
             if (!isClear(candidateX, candidateY)) continue
+            const pathDistance = labelDistanceToPath(candidateX, candidateY, width, plan.label!.lines.length, plan.path)
+            if (pathDistance < 2 || pathDistance > 8) continue
             x = candidateX
             y = candidateY
             break search
@@ -1151,10 +1331,26 @@ function placeStateTransitionLabels(
         }
       }
     }
+    if (!isClear(x, y)) {
+      fallback: for (let distance = 1; distance < 500; distance++) {
+        for (let dx = -distance; dx <= distance; dx++) {
+          const dy = distance - Math.abs(dx)
+          for (const candidateY of dy === 0 ? [y] : [y - dy, y + dy]) {
+            const candidateX = x + dx
+            if (!isClear(candidateX, candidateY)) continue
+            x = candidateX
+            y = candidateY
+            break fallback
+          }
+        }
+      }
+    }
+    if (!isClear(x, y)) throw new Error(`Transition ${endpointKey} has no clear label position`)
 
     space = space.add(labelClaim(x, y))
-    return { ...plan, label: { ...plan.label, x, y } }
-  })
+    placed.set(planIndex, { ...plan, label: { ...plan.label, x, y } })
+  }
+  return plans.map((plan, index) => placed.get(index) ?? plan)
 }
 
 export function createStateTransitionRenderPlans(
@@ -1169,15 +1365,59 @@ export function createStateTransitionRenderPlans(
     createStateTransitionRenderPlan,
   )
   if (options.repairRoutes === false) return placeStateTransitionLabels(plans, diagram, bounds, noteBounds)
-  const routeSpace = createStateSearchSpace(transitionObstacles(diagram, bounds, noteBounds))
-  return placeStateTransitionLabels(
-    plans.map((plan) => bodySafeTransitionPlan(plan, diagram, bounds, noteBounds, routeSpace, budget)),
-    diagram,
-    bounds,
-    noteBounds,
+  const baseObstacles = transitionObstacles(diagram, bounds, noteBounds)
+  const repaired: StateTransitionRenderPlan[] = []
+  for (const [index, plan] of plans.entries()) {
+    const disjoint = repaired.filter((previous) => transitionsHaveDisjointEndpoints(previous, plan))
+    const routeObstacles = repaired.filter(
+      (previous) => disjoint.includes(previous) || transitionsAreReciprocal(previous, plan),
+    )
+    const routeSpace = createStateSearchSpace(
+      baseObstacles.add(
+        ...routeObstacles.map((previous, previousIndex) =>
+          spatialPathClaim(
+            `transition:${index}:obstacle:${previousIndex}`,
+            `transition:${index}:obstacle:${previousIndex}`,
+            "route",
+            previous.path.map(([x, y]) => ({ x, y })),
+          ),
+        ),
+      ),
+    )
+    repaired.push(
+      bodySafeTransitionPlan(
+        plan,
+        diagram,
+        bounds,
+        noteBounds,
+        routeSpace,
+        budget,
+        disjoint.some((previous) => pathsIntersect(previous.path, plan.path)),
+      ),
+    )
+  }
+  return placeStateTransitionLabels(repaired, diagram, bounds, noteBounds)
+}
+
+function transitionsHaveDisjointEndpoints(left: StateTransitionRenderPlan, right: StateTransitionRenderPlan): boolean {
+  const leftEndpoints = new Set([left.route.transition.from, left.route.transition.to])
+  return !leftEndpoints.has(right.route.transition.from) && !leftEndpoints.has(right.route.transition.to)
+}
+
+function transitionsAreReciprocal(left: StateTransitionRenderPlan, right: StateTransitionRenderPlan): boolean {
+  return (
+    left.route.transition.from === right.route.transition.to && left.route.transition.to === right.route.transition.from
   )
 }
 
+function pathsIntersect(
+  left: readonly StateTransitionPathPoint[],
+  right: readonly StateTransitionPathPoint[],
+): boolean {
+  const occupied = new Set(left.map(([x, y]) => `${x}:${y}`))
+  return right.some(([x, y]) => occupied.has(`${x}:${y}`))
+}
+
 function transitionObstacles(
   diagram: StateVisibleDiagram,
   bounds: ReadonlyMap<string, BoxBounds>,
diff --git a/packages/merman/src/state/types.ts b/packages/merman/src/state/types.ts
index baca23aaff0..1cf3658abd7 100644
--- a/packages/merman/src/state/types.ts
+++ b/packages/merman/src/state/types.ts
@@ -1,6 +1,6 @@
 import type { BorderStyle } from "@opentui/core"
 
-export type StateDiagramDirection = "TB" | "TD" | "LR" | "RL"
+export type StateDiagramDirection = "TB" | "TD" | "BT" | "LR" | "RL"
 export type StateDiagramArrowHeadStyle = "filled" | "line"
 
 export interface StateDiagramState {
@@ -41,6 +41,8 @@ export interface StateDiagramRenderOptions {
   borderStyle?: BorderStyle
   arrowHeadStyle?: StateDiagramArrowHeadStyle
   minStateGap?: number
+  /** Target rendered width. Oversized horizontal layouts fold vertically. */
+  layoutMaxWidth?: number
 }
 
 export type NoteConnectorRampStyle = `noteConnectorRamp${1 | 2 | 3}`
diff --git a/packages/merman/src/test/layout-audit/fixtures.ts b/packages/merman/src/test/layout-audit/fixtures.ts
new file mode 100644
index 00000000000..d1638415214
--- /dev/null
+++ b/packages/merman/src/test/layout-audit/fixtures.ts
@@ -0,0 +1,493 @@
+import type { FlowchartDirection } from "../../flowchart/types.js"
+import type { StateDiagramDirection } from "../../state/types.js"
+
+export type LayoutFixture = {
+  id: string
+  kind: "flowchart" | "state"
+  family: string
+  profile: LabelProfile
+  source: string
+  curated?: boolean
+}
+
+type LabelProfile = "short" | "long" | "unicode"
+
+const flowVariants = [
+  ["TB", "short"],
+  ["TD", "long"],
+  ["BT", "unicode"],
+  ["LR", "short"],
+  ["RL", "long"],
+  ["TB", "unicode"],
+  ["TD", "short"],
+  ["BT", "long"],
+  ["LR", "unicode"],
+  ["RL", "short"],
+  ["LR", "long"],
+  ["TD", "unicode"],
+  ["TB", "long"],
+  ["BT", "short"],
+  ["RL", "unicode"],
+] as const satisfies readonly (readonly [FlowchartDirection, LabelProfile])[]
+
+const stateVariants = [
+  ["TB", "short"],
+  ["TD", "long"],
+  ["LR", "unicode"],
+  ["RL", "short"],
+  ["TB", "long"],
+  ["TD", "unicode"],
+  ["LR", "short"],
+  ["RL", "long"],
+  ["LR", "long"],
+  ["TD", "short"],
+  ["TB", "unicode"],
+  ["RL", "unicode"],
+  ["BT", "short"],
+  ["BT", "long"],
+  ["BT", "unicode"],
+] as const satisfies readonly (readonly [StateDiagramDirection, LabelProfile])[]
+
+function nodeLabel(id: string, profile: LabelProfile): string {
+  if (profile === "long") return `${id} deliberate deployment stage with a long descriptive label`
+  if (profile === "unicode") return `${id} 東京<br/>résumé 🚀`
+  return `${id} node`
+}
+
+function edgeLabel(id: string, profile: LabelProfile): string {
+  if (profile === "long") return `${id} transition carrying detailed deployment context`
+  if (profile === "unicode") return `${id} 東京<br/>✓ prêt`
+  return `${id} edge`
+}
+
+function flowNode(id: string, profile: LabelProfile): string {
+  return `  ${id}["${nodeLabel(id, profile)}"]`
+}
+
+function flowEdge(from: string, to: string, id: string, profile: LabelProfile): string {
+  return `  ${from} -->|"${edgeLabel(id, profile)}"| ${to}`
+}
+
+function flowSource(
+  direction: FlowchartDirection,
+  profile: LabelProfile,
+  nodes: readonly string[],
+  edges: readonly [from: string, to: string, id: string][],
+  extra: readonly string[] = [],
+): string {
+  return [
+    `flowchart ${direction}`,
+    ...nodes.map((id) => flowNode(id, profile)),
+    ...extra,
+    ...edges.map(([from, to, id]) => flowEdge(from, to, id, profile)),
+  ].join("\n")
+}
+
+const flowFamilies = {
+  chain(direction: FlowchartDirection, profile: LabelProfile) {
+    return flowSource(
+      direction,
+      profile,
+      ["A", "B", "C", "D", "E", "F"],
+      [
+        ["A", "B", "E01"],
+        ["B", "C", "E02"],
+        ["C", "D", "E03"],
+        ["D", "E", "E04"],
+        ["E", "F", "E05"],
+      ],
+    )
+  },
+  fork(direction: FlowchartDirection, profile: LabelProfile) {
+    return flowSource(
+      direction,
+      profile,
+      ["A", "B", "C", "D", "E"],
+      [
+        ["A", "B", "E01"],
+        ["A", "C", "E02"],
+        ["A", "D", "E03"],
+        ["A", "E", "E04"],
+      ],
+    )
+  },
+  join(direction: FlowchartDirection, profile: LabelProfile) {
+    return flowSource(
+      direction,
+      profile,
+      ["A", "B", "C", "D", "E"],
+      [
+        ["A", "E", "E01"],
+        ["B", "E", "E02"],
+        ["C", "E", "E03"],
+        ["D", "E", "E04"],
+      ],
+    )
+  },
+  cycle(direction: FlowchartDirection, profile: LabelProfile) {
+    return flowSource(
+      direction,
+      profile,
+      ["A", "B", "C", "D"],
+      [
+        ["A", "B", "E01"],
+        ["B", "C", "E02"],
+        ["C", "D", "E03"],
+        ["D", "A", "E04"],
+        ["C", "A", "E05"],
+      ],
+    )
+  },
+  crossing(direction: FlowchartDirection, profile: LabelProfile) {
+    return flowSource(
+      direction,
+      profile,
+      ["A", "B", "C", "D", "E", "F"],
+      [
+        ["A", "C", "E01"],
+        ["A", "D", "E02"],
+        ["B", "C", "E03"],
+        ["B", "D", "E04"],
+        ["C", "E", "E05"],
+        ["D", "F", "E06"],
+      ],
+    )
+  },
+  parallel(direction: FlowchartDirection, profile: LabelProfile) {
+    return flowSource(
+      direction,
+      profile,
+      ["A", "B", "C"],
+      [
+        ["A", "B", "E01"],
+        ["A", "B", "E02"],
+        ["A", "B", "E03"],
+        ["B", "C", "E04"],
+        ["B", "C", "E05"],
+      ],
+    )
+  },
+  self(direction: FlowchartDirection, profile: LabelProfile) {
+    return flowSource(
+      direction,
+      profile,
+      ["A", "B", "C"],
+      [
+        ["A", "A", "E01"],
+        ["A", "B", "E02"],
+        ["B", "B", "E03"],
+        ["B", "C", "E04"],
+      ],
+    )
+  },
+  subgraph(direction: FlowchartDirection, profile: LabelProfile) {
+    return [
+      `flowchart ${direction}`,
+      `  subgraph Left["Left ${nodeLabel("SG1", profile)}"]`,
+      flowNode("A", profile),
+      flowNode("B", profile),
+      "  end",
+      `  subgraph Right["Right ${nodeLabel("SG2", profile)}"]`,
+      flowNode("C", profile),
+      flowNode("D", profile),
+      "  end",
+      flowEdge("A", "B", "E01", profile),
+      flowEdge("A", "C", "E02", profile),
+      flowEdge("B", "D", "E03", profile),
+      flowEdge("C", "D", "E04", profile),
+    ].join("\n")
+  },
+  "nested-subgraph"(direction: FlowchartDirection, profile: LabelProfile) {
+    const local = direction === "LR" || direction === "RL" ? "TB" : "LR"
+    return [
+      `flowchart ${direction}`,
+      `  subgraph Outer["Outer ${nodeLabel("SG1", profile)}"]`,
+      `    direction ${local}`,
+      `    subgraph Inner["Inner ${nodeLabel("SG2", profile)}"]`,
+      flowNode("A", profile),
+      flowNode("B", profile),
+      "    end",
+      flowNode("C", profile),
+      "  end",
+      flowNode("D", profile),
+      flowEdge("A", "B", "E01", profile),
+      flowEdge("A", "C", "E02", profile),
+      flowEdge("B", "D", "E03", profile),
+      flowEdge("C", "D", "E04", profile),
+    ].join("\n")
+  },
+} satisfies Record<string, (direction: FlowchartDirection, profile: LabelProfile) => string>
+
+function stateDeclaration(id: string, profile: LabelProfile, indent = "  "): string {
+  return `${indent}state "${nodeLabel(id, profile)}" as ${id}`
+}
+
+function stateTransition(from: string, to: string, id: string, profile: LabelProfile, indent = "  "): string {
+  return `${indent}${from} --> ${to}: ${edgeLabel(id, profile)}`
+}
+
+function stateSource(
+  direction: StateDiagramDirection,
+  profile: LabelProfile,
+  states: readonly string[],
+  transitions: readonly [from: string, to: string, id: string][],
+  extra: readonly string[] = [],
+): string {
+  return [
+    "stateDiagram-v2",
+    `  direction ${direction}`,
+    ...states.map((id) => stateDeclaration(id, profile)),
+    ...extra,
+    ...transitions.map(([from, to, id]) => stateTransition(from, to, id, profile)),
+  ].join("\n")
+}
+
+const stateFamilies = {
+  chain(direction: StateDiagramDirection, profile: LabelProfile) {
+    return stateSource(
+      direction,
+      profile,
+      ["A", "B", "C", "D", "E"],
+      [
+        ["A", "B", "E01"],
+        ["B", "C", "E02"],
+        ["C", "D", "E03"],
+        ["D", "E", "E04"],
+      ],
+      ["  [*] --> A", "  E --> [*]"],
+    )
+  },
+  fork(direction: StateDiagramDirection, profile: LabelProfile) {
+    return stateSource(
+      direction,
+      profile,
+      ["A", "B", "C", "D"],
+      [
+        ["A", "B", "E01"],
+        ["A", "C", "E02"],
+        ["A", "D", "E03"],
+      ],
+    )
+  },
+  join(direction: StateDiagramDirection, profile: LabelProfile) {
+    return stateSource(
+      direction,
+      profile,
+      ["A", "B", "C", "D"],
+      [
+        ["A", "D", "E01"],
+        ["B", "D", "E02"],
+        ["C", "D", "E03"],
+      ],
+    )
+  },
+  cycle(direction: StateDiagramDirection, profile: LabelProfile) {
+    return stateSource(
+      direction,
+      profile,
+      ["A", "B", "C", "D"],
+      [
+        ["A", "B", "E01"],
+        ["B", "C", "E02"],
+        ["C", "D", "E03"],
+        ["D", "A", "E04"],
+        ["C", "A", "E05"],
+      ],
+    )
+  },
+  crossing(direction: StateDiagramDirection, profile: LabelProfile) {
+    return stateSource(
+      direction,
+      profile,
+      ["A", "B", "C", "D"],
+      [
+        ["A", "C", "E01"],
+        ["A", "D", "E02"],
+        ["B", "C", "E03"],
+        ["B", "D", "E04"],
+      ],
+    )
+  },
+  parallel(direction: StateDiagramDirection, profile: LabelProfile) {
+    return stateSource(
+      direction,
+      profile,
+      ["A", "B", "C"],
+      [
+        ["A", "B", "E01"],
+        ["A", "B", "E02"],
+        ["A", "B", "E03"],
+        ["B", "C", "E04"],
+      ],
+    )
+  },
+  self(direction: StateDiagramDirection, profile: LabelProfile) {
+    return stateSource(
+      direction,
+      profile,
+      ["A", "B", "C"],
+      [
+        ["A", "A", "E01"],
+        ["A", "B", "E02"],
+        ["B", "B", "E03"],
+        ["B", "C", "E04"],
+      ],
+    )
+  },
+  choice(direction: StateDiagramDirection, profile: LabelProfile) {
+    return stateSource(
+      direction,
+      profile,
+      ["A", "B", "C"],
+      [
+        ["A", "Choice", "E01"],
+        ["Choice", "B", "E02"],
+        ["Choice", "C", "E03"],
+        ["C", "A", "E04"],
+      ],
+      ["  state Choice <<choice>>"],
+    )
+  },
+  notes(direction: StateDiagramDirection, profile: LabelProfile) {
+    return stateSource(
+      direction,
+      profile,
+      ["A", "B", "C"],
+      [
+        ["A", "B", "E01"],
+        ["B", "C", "E02"],
+        ["C", "A", "E03"],
+      ],
+      [
+        `  note left of A: ${edgeLabel("N01", profile)}`,
+        `  note right of B: ${edgeLabel("N02", profile)}`,
+        `  note right of C: ${edgeLabel("N03", profile)}`,
+      ],
+    )
+  },
+  composite(direction: StateDiagramDirection, profile: LabelProfile) {
+    return [
+      "stateDiagram-v2",
+      `  direction ${direction}`,
+      `  state "${nodeLabel("Outer", profile)}" as Outer {`,
+      stateDeclaration("A", profile, "    "),
+      stateDeclaration("B", profile, "    "),
+      "    [*] --> A",
+      stateTransition("A", "B", "E01", profile, "    "),
+      "    B --> [*]",
+      "  }",
+      stateDeclaration("Done", profile),
+      stateTransition("Outer", "Done", "E02", profile),
+      `  note right of B: ${edgeLabel("N01", profile)}`,
+    ].join("\n")
+  },
+  "nested-composite"(direction: StateDiagramDirection, profile: LabelProfile) {
+    return [
+      "stateDiagram-v2",
+      `  direction ${direction}`,
+      `  state "${nodeLabel("Session", profile)}" as Session {`,
+      "    [*] --> Open",
+      `    state "${nodeLabel("Open", profile)}" as Open {`,
+      stateDeclaration("Clean", profile, "      "),
+      stateDeclaration("Dirty", profile, "      "),
+      "      [*] --> Clean",
+      stateTransition("Clean", "Dirty", "E01", profile, "      "),
+      stateTransition("Dirty", "Clean", "E02", profile, "      "),
+      "      Dirty --> [*]",
+      "    }",
+      "    Open --> [*]",
+      "  }",
+      stateDeclaration("Done", profile),
+      stateTransition("Session", "Done", "E03", profile),
+      `  note right of Dirty: ${edgeLabel("N01", profile)}`,
+    ].join("\n")
+  },
+} satisfies Record<string, (direction: StateDiagramDirection, profile: LabelProfile) => string>
+
+export const deploymentArchitectureSource = `flowchart LR
+    Client[OpenCode client]
+
+    subgraph CF[Cloudflare]
+      DNS[opencode.ai]
+      Web[Console frontend Worker]
+      Proxy[Console API proxy Worker]
+      Infer[inference-next Worker]
+      KV[Model registry KV]
+      Redis[Upstash Redis]
+      Logs[Axiom / Cloudflare logs]
+      Lake[Pipeline to R2 data lake]
+    end
+
+    subgraph AWS[AWS]
+      EKS[EKS cluster]
+      API[Console API pod<br/>1 replica]
+      OTEL[OTel collector]
+      ECR[ECR]
+    end
+
+    DB[(PlanetScale)]
+    Models[Anthropic / OpenAI / other providers]
+
+    Client -->|/inference/*| DNS --> Infer
+    Client -->|/console/*| DNS --> Web
+    Web -->|/console/api, /auth, etc.| Proxy
+    Proxy -->|Cloudflare VPC service| API
+
+    Infer -->|public DATABASE_URL| DB
+    Infer --> KV
+    Infer --> Redis
+    Infer --> Models
+    Infer --> Logs
+    Infer --> Lake
+
+    API -->|private DATABASE_AWS_URL| DB
+    API --> OTEL
+    ECR --> API`
+
+export function layoutFixtures(): readonly LayoutFixture[] {
+  const flowcharts = Object.entries(flowFamilies).flatMap(([family, source]) =>
+    flowVariants.map(([direction, profile]) => ({
+      id: `flowchart/${family}/${direction.toLowerCase()}-${profile}`,
+      kind: "flowchart" as const,
+      family,
+      profile,
+      source: source(direction, profile),
+    })),
+  )
+  const states = Object.entries(stateFamilies).flatMap(([family, source]) =>
+    stateVariants.map(([direction, profile]) => ({
+      id: `state/${family}/${direction.toLowerCase()}-${profile}`,
+      kind: "state" as const,
+      family,
+      profile,
+      source: source(direction, profile),
+    })),
+  )
+  return [
+    ...flowcharts,
+    {
+      id: "flowchart/deployment-architecture/curated",
+      kind: "flowchart" as const,
+      family: "deployment-architecture",
+      profile: "short" as const,
+      source: deploymentArchitectureSource,
+      curated: true,
+    },
+    {
+      id: "flowchart/grouped-fanout/curated",
+      kind: "flowchart" as const,
+      family: "grouped-fanout",
+      profile: "short" as const,
+      source: `flowchart TD
+  subgraph Group
+    S[Source]
+    S -->|route 0 detail| N0[Node 0]
+    S -->|route 1 detail| N1[Node 1]
+    S -->|route 2 detail| N2[Node 2]
+    S -->|route 3 detail| N3[Node 3]
+  end`,
+      curated: true,
+    },
+    ...states,
+  ]
+}
diff --git a/packages/merman/src/test/layout-audit/harness.ts b/packages/merman/src/test/layout-audit/harness.ts
new file mode 100644
index 00000000000..450ba4237dc
--- /dev/null
+++ b/packages/merman/src/test/layout-audit/harness.ts
@@ -0,0 +1,521 @@
+import { orthogonalPathPoints, segmentBetween, type DiagramPoint } from "../../core/geometry.js"
+import { SpatialIndex, spatialPathClaim, spatialRectClaim } from "../../core/spatial.js"
+import { diagramTextWidth } from "../../core/text.js"
+import { splitDiagramLines } from "../../core/text-lines.js"
+import { drawFlowchartDiagramGrid } from "../../flowchart/drawing.js"
+import { layoutFlowchartDiagram } from "../../flowchart/layout.js"
+import { flowchartRouteLabelLayout } from "../../flowchart/labels.js"
+import { parseMermaidFlowchartDiagram } from "../../flowchart/parser.js"
+import { createStateDiagramDrawing } from "../../state/drawing.js"
+import type { StateDiagramBoxBounds } from "../../state/layout.js"
+import { stateDiagramNoteConnector } from "../../state/note.js"
+import { parseMermaidStateDiagram } from "../../state/parser.js"
+import type { StateTransitionRenderPlan } from "../../state/routing.js"
+import { isHiddenCompositeMarker } from "../../state/visible-model.js"
+import { layoutFixtures, type LayoutFixture } from "./fixtures.js"
+
+export const auditViewports = [60, 80, 120] as const
+
+export type LayoutMetrics = {
+  width: number
+  height: number
+  area: number
+  routeLength: number
+  bends: number
+  crossings: number
+  sharedRouteCells: number
+  overflow: number
+}
+
+export type LayoutAudit = {
+  fixture: LayoutFixture
+  viewport: (typeof auditViewports)[number]
+  output: string
+  metrics: LayoutMetrics
+  violations: string[]
+}
+
+type Bounds = Pick<StateDiagramBoxBounds, "left" | "top" | "width" | "height">
+type AuditedRoute = {
+  from: string
+  to: string
+  points: readonly DiagramPoint[]
+}
+
+function finiteBounds(bounds: Bounds): boolean {
+  return (
+    [bounds.left, bounds.top, bounds.width, bounds.height].every(Number.isFinite) &&
+    bounds.width > 0 &&
+    bounds.height > 0
+  )
+}
+
+function boundsOverlap(left: Bounds, right: Bounds): boolean {
+  return (
+    left.left < right.left + right.width &&
+    left.left + left.width > right.left &&
+    left.top < right.top + right.height &&
+    left.top + left.height > right.top
+  )
+}
+
+function boundsContain(outer: Bounds, inner: Bounds): boolean {
+  return (
+    inner.left >= outer.left &&
+    inner.top >= outer.top &&
+    inner.left + inner.width <= outer.left + outer.width &&
+    inner.top + inner.height <= outer.top + outer.height
+  )
+}
+
+function pointInBounds(point: DiagramPoint, bounds: Bounds): boolean {
+  return (
+    point.x >= bounds.left &&
+    point.x < bounds.left + bounds.width &&
+    point.y >= bounds.top &&
+    point.y < bounds.top + bounds.height
+  )
+}
+
+function pointTouchesBounds(point: DiagramPoint, bounds: Bounds): boolean {
+  if (pointInBounds(point, bounds)) return true
+  return (
+    ((point.x === bounds.left - 1 || point.x === bounds.left + bounds.width) &&
+      point.y >= bounds.top &&
+      point.y < bounds.top + bounds.height) ||
+    ((point.y === bounds.top - 1 || point.y === bounds.top + bounds.height) &&
+      point.x >= bounds.left &&
+      point.x < bounds.left + bounds.width)
+  )
+}
+
+function isOrthogonal(points: readonly DiagramPoint[]): boolean {
+  return points.every((point, index) => {
+    if (
+      !Number.isFinite(point.x) ||
+      !Number.isFinite(point.y) ||
+      !Number.isInteger(point.x) ||
+      !Number.isInteger(point.y)
+    )
+      return false
+    const previous = points[index - 1]
+    return !previous || previous.x === point.x || previous.y === point.y
+  })
+}
+
+function expandedPath(points: readonly DiagramPoint[]): DiagramPoint[] {
+  if (!isOrthogonal(points)) return []
+  return orthogonalPathPoints(points)
+}
+
+function routeLength(points: readonly DiagramPoint[]): number {
+  return routeSegments(points).reduce((total, segment) => total + segment.length, 0)
+}
+
+function routeBends(points: readonly DiagramPoint[]): number {
+  const directions = points.slice(1).flatMap((point, index) => {
+    const previous = points[index]
+    if (point.x === previous.x && point.y !== previous.y) return ["y"]
+    if (point.y === previous.y && point.x !== previous.x) return ["x"]
+    return []
+  })
+  return directions.slice(1).filter((axis, index) => axis !== directions[index]).length
+}
+
+function routeSegments(points: readonly DiagramPoint[]) {
+  return points.slice(1).flatMap((point, index) => segmentBetween(points[index]!, point) ?? [])
+}
+
+function crossingCount(routes: readonly AuditedRoute[]): number {
+  let count = 0
+  for (const [index, route] of routes.entries()) {
+    for (const other of routes.slice(index + 1)) {
+      for (const segment of routeSegments(route.points)) {
+        for (const otherSegment of routeSegments(other.points)) {
+          if (segment.axis === otherSegment.axis) continue
+          const horizontal = segment.axis === "x" ? segment : otherSegment
+          const vertical = segment.axis === "y" ? segment : otherSegment
+          const x = vertical.from.x
+          const y = horizontal.from.y
+          const horizontalMin = Math.min(horizontal.from.x, horizontal.to.x)
+          const horizontalMax = Math.max(horizontal.from.x, horizontal.to.x)
+          const verticalMin = Math.min(vertical.from.y, vertical.to.y)
+          const verticalMax = Math.max(vertical.from.y, vertical.to.y)
+          if (x <= horizontalMin || x >= horizontalMax || y <= verticalMin || y >= verticalMax) continue
+          count++
+        }
+      }
+    }
+  }
+  return count
+}
+
+function sharedRouteCellCount(routes: readonly AuditedRoute[]): number {
+  let count = 0
+  const cells = routes.map((route) => new Set(expandedPath(route.points).map((point) => `${point.x}:${point.y}`)))
+  for (const [index, routeCells] of cells.entries()) {
+    for (const other of cells.slice(index + 1)) {
+      for (const cell of routeCells) if (other.has(cell)) count++
+    }
+  }
+  return count
+}
+
+function metrics(
+  width: number,
+  height: number,
+  routes: readonly AuditedRoute[],
+  viewport: (typeof auditViewports)[number],
+): LayoutMetrics {
+  return {
+    width,
+    height,
+    area: width * height,
+    routeLength: routes.reduce((total, route) => total + routeLength(route.points), 0),
+    bends: routes.reduce((total, route) => total + routeBends(route.points), 0),
+    crossings: crossingCount(routes),
+    sharedRouteCells: sharedRouteCellCount(routes),
+    overflow: Math.max(0, width - viewport),
+  }
+}
+
+function requireOutputLines(output: string, lines: readonly string[], owner: string, violations: string[]): void {
+  for (const line of lines.map((line) => line.trim()).filter(Boolean)) {
+    if (!output.includes(line)) violations.push(`${owner} content missing: ${JSON.stringify(line)}`)
+  }
+}
+
+function validateRoutes(
+  routes: readonly AuditedRoute[],
+  bounds: ReadonlyMap<string, Bounds>,
+  bodyIds: readonly string[],
+  violations: string[],
+): void {
+  for (const [index, route] of routes.entries()) {
+    if (route.points.length < 2) {
+      violations.push(`route ${index} ${route.from}->${route.to} is empty`)
+      continue
+    }
+    if (!isOrthogonal(route.points))
+      violations.push(`route ${index} ${route.from}->${route.to} is not finite and orthogonal`)
+    const from = bounds.get(route.from)
+    const to = bounds.get(route.to)
+    if (!from || !to) {
+      violations.push(`route ${index} ${route.from}->${route.to} has a missing endpoint bound`)
+      continue
+    }
+    if (!pointTouchesBounds(route.points[0], from))
+      violations.push(`route ${index} does not touch source ${route.from}`)
+    if (!pointTouchesBounds(route.points.at(-1)!, to))
+      violations.push(`route ${index} does not touch target ${route.to}`)
+    if (!isOrthogonal(route.points)) continue
+    const bodySpace = SpatialIndex.empty().add(
+      ...bodyIds.flatMap((id) => {
+        const bound = bounds.get(id)
+        return id === route.from || id === route.to || !bound
+          ? []
+          : [spatialRectClaim(`body:${id}`, `body:${id}`, "body", bound)]
+      }),
+    )
+    const conflicts = bodySpace.conflicts(spatialPathClaim(`route:${index}`, `route:${index}`, "route", route.points))
+    for (const id of new Set(conflicts.map((conflict) => conflict.existing.owner.slice("body:".length)))) {
+      violations.push(`route ${index} ${route.from}->${route.to} intersects unrelated body ${id}`)
+    }
+  }
+}
+
+function validateBodies(bounds: ReadonlyMap<string, Bounds>, ids: readonly string[], violations: string[]): void {
+  let occupied = SpatialIndex.empty()
+  for (const id of ids) {
+    const bound = bounds.get(id)
+    if (!bound) {
+      violations.push(`missing body bound ${id}`)
+      continue
+    }
+    if (!finiteBounds(bound)) {
+      violations.push(`body ${id} has invalid bounds`)
+      continue
+    }
+    const claim = spatialRectClaim(`body:${id}`, `body:${id}`, "body", bound)
+    for (const otherId of new Set(
+      occupied.conflicts(claim).map((conflict) => conflict.existing.owner.slice("body:".length)),
+    )) {
+      violations.push(`bodies ${id} and ${otherId} overlap`)
+    }
+    occupied = occupied.add(claim)
+  }
+}
+
+function auditFlowchart(fixture: LayoutFixture, viewport: (typeof auditViewports)[number]): LayoutAudit {
+  const violations: string[] = []
+  const diagram = parseMermaidFlowchartDiagram(fixture.source)
+  const layout = layoutFlowchartDiagram(diagram, { compact: true, layoutMaxWidth: viewport })
+  const grid = drawFlowchartDiagramGrid(diagram, { compact: true, layoutMaxWidth: viewport })
+  const output = grid.toString({ trimTop: true, trimBottom: true })
+  const size = grid.getTextSize({ trimTop: true, trimBottom: true })
+  const routes = layout.routes.map((route) => ({ from: route.edge.from, to: route.edge.to, points: route.points }))
+  const bodyIds = layout.diagram.nodes.map((node) => node.id)
+
+  if (!Number.isFinite(size.width) || !Number.isFinite(size.height) || size.width <= 0 || size.height <= 0)
+    violations.push("rendered grid has invalid dimensions")
+  if (!Number.isFinite(layout.width) || !Number.isFinite(layout.height) || layout.width <= 0 || layout.height <= 0)
+    violations.push("layout has invalid dimensions")
+  if (layout.routes.length !== layout.diagram.edges.filter((edge) => !edge.orderOnly).length)
+    violations.push("rendered route count does not match visible edge count")
+  validateBodies(layout.bounds, bodyIds, violations)
+  validateRoutes(routes, layout.bounds, bodyIds, violations)
+
+  for (const node of layout.diagram.nodes)
+    requireOutputLines(output, layout.bounds.get(node.id)?.lines ?? [], `node ${node.id}`, violations)
+  for (const route of layout.routes) {
+    if (!route.edge.label) continue
+    requireOutputLines(
+      output,
+      flowchartRouteLabelLayout(route, diagramTextWidth).lines,
+      `edge ${route.edge.from}->${route.edge.to}`,
+      violations,
+    )
+    const targets = new Set(
+      layout.diagram.edges.filter((edge) => edge.label && edge.from === route.edge.from).map((edge) => edge.to),
+    )
+    const sources = new Set(
+      layout.diagram.edges.filter((edge) => edge.label && edge.to === route.edge.to).map((edge) => edge.from),
+    )
+    const label = flowchartRouteLabelLayout(route, diagramTextWidth)
+    if (
+      fixture.family === "grouped-fanout" &&
+      (targets.size > 1 || sources.size > 1) &&
+      label.point.x + label.width > viewport
+    ) {
+      violations.push(`grouped edge ${route.edge.from}->${route.edge.to} label exceeds viewport`)
+    }
+  }
+  for (const subgraph of layout.diagram.subgraphs ?? []) {
+    const bound = layout.subgraphBounds.get(subgraph.id)
+    if (!bound || !finiteBounds(bound)) violations.push(`subgraph ${subgraph.id} has invalid bounds`)
+    requireOutputLines(output, splitDiagramLines(subgraph.label), `subgraph ${subgraph.id}`, violations)
+    for (const nodeId of subgraph.nodeIds) {
+      const node = layout.bounds.get(nodeId)
+      if (bound && node && !boundsContain(bound, node))
+        violations.push(`subgraph ${subgraph.id} does not contain ${nodeId}`)
+    }
+  }
+  const subgraphs = layout.diagram.subgraphs ?? []
+  const subgraphById = new Map(subgraphs.map((subgraph) => [subgraph.id, subgraph]))
+  const ancestorOf = (ancestor: string, id: string) => {
+    let parentId = subgraphById.get(id)?.parentId
+    while (parentId) {
+      if (parentId === ancestor) return true
+      parentId = subgraphById.get(parentId)?.parentId
+    }
+    return false
+  }
+  for (const [index, subgraph] of subgraphs.entries()) {
+    const bound = layout.subgraphBounds.get(subgraph.id)
+    if (!bound) continue
+    for (const other of subgraphs.slice(index + 1)) {
+      if (ancestorOf(subgraph.id, other.id) || ancestorOf(other.id, subgraph.id)) continue
+      const otherBound = layout.subgraphBounds.get(other.id)
+      if (otherBound && boundsOverlap(bound, otherBound)) {
+        violations.push(`subgraphs ${subgraph.id} and ${other.id} overlap`)
+      }
+    }
+  }
+
+  return { fixture, viewport, output, metrics: metrics(size.width, size.height, routes, viewport), violations }
+}
+
+function stateRoute(route: StateTransitionRenderPlan): AuditedRoute {
+  return {
+    from: route.route.transition.from,
+    to: route.route.transition.to,
+    points: route.path.map(([x, y]) => ({ x, y })),
+  }
+}
+
+function auditState(fixture: LayoutFixture, viewport: (typeof auditViewports)[number]): LayoutAudit {
+  const violations: string[] = []
+  const parsed = parseMermaidStateDiagram(fixture.source)
+  const drawing = createStateDiagramDrawing(parsed, { minStateGap: 5, layoutMaxWidth: viewport })
+  const diagram = drawing.diagram
+  const layout = drawing.layout
+  const plans = drawing.transitionPlans
+  const grid = drawing.grid
+  const routes = plans.map(stateRoute)
+  const output = grid.toString({ trimTop: true, trimBottom: true })
+  const size = grid.getTextSize({ trimTop: true, trimBottom: true })
+  const bodyIds = diagram.states.filter((state) => !isHiddenCompositeMarker(state)).map((state) => state.id)
+
+  if (!Number.isFinite(size.width) || !Number.isFinite(size.height) || size.width <= 0 || size.height <= 0)
+    violations.push("rendered grid has invalid dimensions")
+  if (plans.length !== diagram.transitions.length)
+    violations.push("rendered route count does not match visible transition count")
+  validateBodies(layout.bounds, bodyIds, violations)
+  validateRoutes(routes, layout.bounds, bodyIds, violations)
+  if (diagram.direction === "BT" && fixture.family === "chain") {
+    for (const transition of diagram.transitions) {
+      if (transition.from === transition.to) continue
+      const from = layout.bounds.get(transition.from)
+      const to = layout.bounds.get(transition.to)
+      if (from && to && from.centerY <= to.centerY) {
+        violations.push(`BT transition ${transition.from}->${transition.to} does not travel upward`)
+      }
+    }
+  }
+
+  for (const state of diagram.states) {
+    if (isHiddenCompositeMarker(state)) continue
+    requireOutputLines(output, layout.sizes.get(state.id)?.lines ?? [state.label], `state ${state.id}`, violations)
+  }
+  for (const plan of plans) {
+    if (!plan.route.transition.label) continue
+    if (!plan.label)
+      violations.push(`transition ${plan.route.transition.from}->${plan.route.transition.to} has no label layout`)
+    requireOutputLines(
+      output,
+      plan.label?.lines ?? [],
+      `transition ${plan.route.transition.from}->${plan.route.transition.to}`,
+      violations,
+    )
+  }
+
+  const statesById = new Map(diagram.states.map((state) => [state.id, state]))
+  const compositesById = new Map(diagram.composites.map((composite) => [composite.id, composite]))
+  const descendantOf = (id: string, compositeId: string) => {
+    let parentId = statesById.get(id)?.parentId ?? compositesById.get(id)?.parentId
+    while (parentId) {
+      if (parentId === compositeId) return true
+      parentId = compositesById.get(parentId)?.parentId
+    }
+    return false
+  }
+  for (const composite of diagram.composites) {
+    const bound = layout.compositeBounds.get(composite.id)
+    if (!bound || !finiteBounds(bound)) {
+      violations.push(`composite ${composite.id} has invalid bounds`)
+      continue
+    }
+    requireOutputLines(output, splitDiagramLines(composite.label), `composite ${composite.id}`, violations)
+    for (const state of diagram.states.filter(
+      (state) => !isHiddenCompositeMarker(state) && descendantOf(state.id, composite.id),
+    )) {
+      const stateBound = layout.bounds.get(state.id)
+      if (stateBound && !boundsContain(bound, stateBound))
+        violations.push(`composite ${composite.id} does not contain ${state.id}`)
+    }
+  }
+
+  for (const [index, note] of layout.noteBounds.entries()) {
+    if (!finiteBounds(note)) violations.push(`note ${index} has invalid bounds`)
+    requireOutputLines(output, note.lines, `note ${index}`, violations)
+    for (const id of bodyIds) {
+      const bound = layout.bounds.get(id)
+      if (bound && boundsOverlap(note, bound)) violations.push(`note ${index} overlaps state ${id}`)
+    }
+    for (const other of layout.noteBounds.slice(index + 1)) {
+      if (boundsOverlap(note, other)) violations.push(`notes ${index} and ${other.id} overlap`)
+    }
+    const target = layout.bounds.get(note.note.target)
+    if (!target) {
+      violations.push(`note ${index} has no target bound`)
+      continue
+    }
+    for (const point of expandedPath(stateDiagramNoteConnector(note, target).points)) {
+      for (const id of bodyIds) {
+        if (id === note.note.target) continue
+        const bound = layout.bounds.get(id)
+        if (bound && pointInBounds(point, bound)) violations.push(`note ${index} connector intersects state ${id}`)
+      }
+      for (const other of layout.noteBounds) {
+        if (other === note) continue
+        if (pointInBounds(point, other)) violations.push(`note ${index} connector intersects note ${other.id}`)
+      }
+    }
+  }
+
+  return { fixture, viewport, output, metrics: metrics(size.width, size.height, routes, viewport), violations }
+}
+
+export function auditFixture(fixture: LayoutFixture, viewport: (typeof auditViewports)[number] = 120): LayoutAudit {
+  return fixture.kind === "flowchart" ? auditFlowchart(fixture, viewport) : auditState(fixture, viewport)
+}
+
+export function auditAllFixtures(): LayoutAudit[] {
+  return layoutFixtures().flatMap((fixture, index) => {
+    if (fixture.curated) return auditViewports.map((viewport) => auditFixture(fixture, viewport))
+    if (fixture.kind === "flowchart") {
+      return auditFixture(fixture, auditViewports[index % auditViewports.length])
+    }
+    const viewport = fixture.profile === "short" ? 60 : fixture.profile === "unicode" ? 80 : 120
+    return auditFixture(fixture, viewport)
+  })
+}
+
+function percentile(values: readonly number[], ratio: number): number {
+  if (values.length === 0) return 0
+  return [...values].sort((left, right) => left - right)[Math.ceil(values.length * ratio) - 1] ?? 0
+}
+
+export function summarizeAudits(audits: readonly LayoutAudit[]) {
+  const summarize = (selected: readonly LayoutAudit[]) => ({
+    runs: selected.length,
+    sources: new Set(selected.map((audit) => audit.fixture.id)).size,
+    violations: selected.reduce((total, audit) => total + audit.violations.length, 0),
+    area: {
+      p50: percentile(
+        selected.map((audit) => audit.metrics.area),
+        0.5,
+      ),
+      p95: percentile(
+        selected.map((audit) => audit.metrics.area),
+        0.95,
+      ),
+      max: Math.max(0, ...selected.map((audit) => audit.metrics.area)),
+    },
+    bends: {
+      p95: percentile(
+        selected.map((audit) => audit.metrics.bends),
+        0.95,
+      ),
+      max: Math.max(0, ...selected.map((audit) => audit.metrics.bends)),
+    },
+    crossings: {
+      total: selected.reduce((total, audit) => total + audit.metrics.crossings, 0),
+      max: Math.max(0, ...selected.map((audit) => audit.metrics.crossings)),
+    },
+    routeLength: {
+      p95: percentile(
+        selected.map((audit) => audit.metrics.routeLength),
+        0.95,
+      ),
+      max: Math.max(0, ...selected.map((audit) => audit.metrics.routeLength)),
+    },
+    sharedRouteCells: {
+      p95: percentile(
+        selected.map((audit) => audit.metrics.sharedRouteCells),
+        0.95,
+      ),
+      max: Math.max(0, ...selected.map((audit) => audit.metrics.sharedRouteCells)),
+    },
+    overflow: {
+      p95: percentile(
+        selected.map((audit) => audit.metrics.overflow),
+        0.95,
+      ),
+      max: Math.max(0, ...selected.map((audit) => audit.metrics.overflow)),
+    },
+  })
+  return {
+    total: summarize(audits),
+    flowchart: summarize(audits.filter((audit) => audit.fixture.kind === "flowchart")),
+    state: summarize(audits.filter((audit) => audit.fixture.kind === "state")),
+  }
+}
+
+export function worstAudits(audits: readonly LayoutAudit[], metric: keyof LayoutMetrics, limit = 10): LayoutAudit[] {
+  return [...audits]
+    .sort(
+      (left, right) => right.metrics[metric] - left.metrics[metric] || left.fixture.id.localeCompare(right.fixture.id),
+    )
+    .slice(0, limit)
+}
diff --git a/packages/merman/src/test/markdown.test.ts b/packages/merman/src/test/markdown.test.ts
index 57a75b99f80..878a83802eb 100644
--- a/packages/merman/src/test/markdown.test.ts
+++ b/packages/merman/src/test/markdown.test.ts
@@ -334,6 +334,33 @@ flowchart LR
   expect(testRenderer.captureCharFrame()).toContain("GLOBAL registry")
 })
 
+test("folds a horizontal state diagram to the Markdown context width", async () => {
+  const testRenderer = await createTestRenderer({ width: 60, height: 48 })
+  renderer = testRenderer.renderer
+  const markdown = new MarkdownRenderable(renderer, {
+    id: "markdown-horizontal-state",
+    content: `\`\`\`mermaid
+stateDiagram-v2
+  direction LR
+  [*] --> A
+  A --> B: first
+  B --> C: second
+  C --> D: third
+  D --> [*]
+\`\`\``,
+    syntaxStyle,
+    renderNode: createMermaidMarkdownRenderer(renderer),
+  })
+
+  renderer.root.add(markdown)
+  await renderMarkdown(markdown, testRenderer.renderOnce)
+
+  const diagram = markdown.getChildren()[0] as CodeRenderable
+  expect(diagram.scrollWidth).toBeLessThanOrEqual(diagram.width)
+  expect(diagram.scrollWidth).toBeLessThanOrEqual(60)
+  expect(testRenderer.captureCharFrame()).toContain("third")
+})
+
 test("renders a Mermaid state fence inside MarkdownRenderable", async () => {
   const testRenderer = await createTestRenderer({ width: 80, height: 14 })
   renderer = testRenderer.renderer
@@ -357,6 +384,27 @@ stateDiagram-v2
   expect(frame).not.toContain("stateDiagram-v2")
 })
 
+test("sizes a standalone state choice after trimming leading rows", async () => {
+  const testRenderer = await createTestRenderer({ width: 80, height: 6 })
+  renderer = testRenderer.renderer
+  const markdown = new MarkdownRenderable(renderer, {
+    id: "markdown-state-choice",
+    content: `\`\`\`mermaid
+stateDiagram-v2
+  direction LR
+  state Decision <<choice>>
+\`\`\``,
+    syntaxStyle,
+    renderNode: createMermaidMarkdownRenderer(renderer),
+  })
+
+  renderer.root.add(markdown)
+  await renderMarkdown(markdown, testRenderer.renderOnce)
+
+  expect(markdown.getChildren()[0]?.height).toBe(1)
+  expect(testRenderer.captureCharFrame()).toContain("◆")
+})
+
 test("renders a Mermaid timeline fence inside MarkdownRenderable", async () => {
   const testRenderer = await createTestRenderer({ width: 80, height: 18 })
   renderer = testRenderer.renderer
diff --git a/packages/tui/src/feature-plugins/system/storybook/index.tsx b/packages/tui/src/feature-plugins/system/storybook/index.tsx
index f6c38ecfc48..c57e7f6f6e0 100644
--- a/packages/tui/src/feature-plugins/system/storybook/index.tsx
+++ b/packages/tui/src/feature-plugins/system/storybook/index.tsx
@@ -2,6 +2,7 @@ import { Plugin } from "@opencode-ai/plugin/tui"
 import { useTerminalDimensions } from "@opentui/solid"
 import { createSignal, For, type JSX } from "solid-js"
 import { StoryFooter } from "./footer"
+import { mermanLayoutsStory } from "./merman-layouts"
 import { sessionTabsStory } from "./session-tabs"
 import { sessionLocationMissingStory } from "./session-location-missing"
 
@@ -15,7 +16,7 @@ export type Story = {
   render: (context: Plugin.Context) => JSX.Element
 }
 
-const stories: Story[] = [sessionTabsStory, sessionLocationMissingStory]
+const stories: Story[] = [mermanLayoutsStory, sessionTabsStory, sessionLocationMissingStory]
 
 function Commands(props: { context: Plugin.Context }) {
   props.context.keymap.layer(() => ({
diff --git a/packages/tui/src/feature-plugins/system/storybook/merman-layouts.tsx b/packages/tui/src/feature-plugins/system/storybook/merman-layouts.tsx
new file mode 100644
index 00000000000..e2227f35685
--- /dev/null
+++ b/packages/tui/src/feature-plugins/system/storybook/merman-layouts.tsx
@@ -0,0 +1,201 @@
+import type { Plugin } from "@opencode-ai/plugin/tui"
+import { useTerminalDimensions } from "@opentui/solid"
+import { createMemo, createSignal, Show } from "solid-js"
+import { useTheme, useThemes } from "../../../context/theme"
+import { usePlugin } from "../../../plugin/context"
+import type { Story } from "./index"
+import { StoryFooter } from "./footer"
+
+const fixtures = [
+  {
+    id: "deployment",
+    title: "Deployment architecture",
+    source: `flowchart LR
+  Client[OpenCode client]
+
+  subgraph CF[Cloudflare]
+    DNS[opencode.ai]
+    Web[Console frontend Worker]
+    Proxy[Console API proxy Worker]
+    Infer[inference-next Worker]
+    KV[Model registry KV]
+    Redis[Upstash Redis]
+    Logs[Axiom / Cloudflare logs]
+    Lake[Pipeline to R2 data lake]
+  end
+
+  subgraph AWS[AWS]
+    EKS[EKS cluster]
+    API[Console API pod<br/>1 replica]
+    OTEL[OTel collector]
+    ECR[ECR]
+  end
+
+  DB[(PlanetScale)]
+  Models[Anthropic / OpenAI / other providers]
+
+  Client -->|/inference/*| DNS --> Infer
+  Client -->|/console/*| DNS --> Web
+  Web -->|/console/api, /auth, etc.| Proxy
+  Proxy -->|Cloudflare VPC service| API
+  Infer -->|public DATABASE_URL| DB
+  Infer --> KV
+  Infer --> Redis
+  Infer --> Models
+  Infer --> Logs
+  Infer --> Lake
+  API -->|private DATABASE_AWS_URL| DB
+  API --> OTEL
+  ECR --> API`,
+  },
+  {
+    id: "nested-flow",
+    title: "Nested directed groups",
+    source: `flowchart LR
+  Input([Input]) --> Parse
+  subgraph Outer[Outer orchestration]
+    direction RL
+    subgraph Inner[Inner pipeline]
+      direction TD
+      Parse[Parse request] --> Validate{Valid?}
+      Validate -->|yes| Cache[(Cache)]
+      Cache -->|stale| Validate
+    end
+    Validate --> Dispatch[[Dispatch work]]
+    Dispatch -->|requeue| Parse
+  end
+  Dispatch -. result .-> Output([Output])
+  Output -->|audit| Cache`,
+  },
+  {
+    id: "state-feedback",
+    title: "Dense state feedback",
+    source: `stateDiagram-v2
+  direction TB
+  [*] --> Root
+  Root --> Alpha: dispatch alpha
+  Root --> Beta: dispatch beta
+  Alpha --> Merge: alpha complete
+  Beta --> Merge: beta complete
+  Merge --> Alpha: retry alpha
+  Merge --> Beta: retry beta
+  Merge --> [*]: finish
+  note right of Merge
+    Retries preserve the original request
+    and remain visible after compaction
+  end note`,
+  },
+  {
+    id: "state-composite",
+    title: "Nested composite lifecycle",
+    source: `stateDiagram-v2
+  direction LR
+  state Session {
+    [*] --> Open
+    state Open {
+      [*] --> Clean
+      Clean --> Dirty: edit
+      Dirty --> Clean: save
+    }
+    Open --> Closing: request close
+    Closing --> Open: cancel
+    Closing --> [*]: closed
+    note right of Dirty: unsaved changes
+  }
+  [*] --> Session: hydrate
+  Session --> [*]: release`,
+  },
+] as const
+
+function MermanLayoutsStory(props: { context: Plugin.Context }) {
+  const dimensions = useTerminalDimensions()
+  const theme = useTheme()
+  const themes = useThemes()
+  const plugins = usePlugin()
+  const [selected, setSelected] = createSignal(0)
+  const [generation, setGeneration] = createSignal(0)
+  const fixture = createMemo(() => fixtures[selected()]!)
+  const rendered = createMemo(() => ({ fixture: fixture(), generation: generation() }))
+  const markdown = createMemo(() => `\`\`\`mermaid\n${fixture().source}\n\`\`\``)
+  const move = (offset: number) => setSelected((current) => (current + offset + fixtures.length) % fixtures.length)
+
+  props.context.keymap.layer(() => ({
+    commands: [
+      {
+        bind: "escape",
+        title: "Back to storybook",
+        group: "Storybook",
+        run: () => props.context.ui.router.navigate({ type: "plugin", name: "storybook" }),
+      },
+      {
+        bind: "left,k",
+        title: "Previous fixture",
+        group: "Storybook",
+        run: () => move(-1),
+      },
+      {
+        bind: "right,j",
+        title: "Next fixture",
+        group: "Storybook",
+        run: () => move(1),
+      },
+      {
+        bind: "r",
+        title: "Reset fixture",
+        group: "Storybook",
+        run: () => {
+          setSelected(0)
+          setGeneration((current) => current + 1)
+        },
+      },
+    ],
+  }))
+
+  return (
+    <box
+      width={dimensions().width}
+      height={dimensions().height}
+      flexDirection="column"
+      backgroundColor={theme.background.default}
+    >
+      <Show when={rendered()} keyed>
+        {(item) => (
+          <scrollbox flexGrow={1} minHeight={0} viewportOptions={{ paddingRight: 1 }}>
+            <box paddingLeft={2} paddingRight={2} paddingTop={1} flexDirection="column">
+              <text fg={theme.text.default}>{item.fixture.title}</text>
+              <text fg={theme.text.subdued}>{item.fixture.id}</text>
+              <box height={1} />
+              <markdown
+                width="100%"
+                syntaxStyle={themes.currentSyntax()}
+                content={markdown()}
+                internalBlockMode="top-level"
+                tableOptions={{ style: "grid", cellPaddingX: 1 }}
+                conceal={true}
+                fg={theme.markdown.text}
+                bg={theme.background.default}
+                renderNode={plugins.markdown()}
+              />
+            </box>
+          </scrollbox>
+        )}
+      </Show>
+      <StoryFooter
+        context={props.context}
+        title="storybook / Mermaid layouts"
+        details={[`${selected() + 1}/${fixtures.length}`, fixture().id, `${dimensions().width}x${dimensions().height}`]}
+        controls={[
+          { shortcut: "j/k or ←/→", label: "fixture" },
+          { shortcut: "r", label: "reset" },
+          { shortcut: "esc", label: "back" },
+        ]}
+      />
+    </box>
+  )
+}
+
+export const mermanLayoutsStory: Story = {
+  id: "merman-layouts",
+  title: "Mermaid layouts",
+  render: (context) => <MermanLayoutsStory context={context} />,
+}