refactor(cli): factor /diff column widths into a shared helper

Audit of the colorize commit found one real DRY hazard: DiffStatsDisplay
and renderDiffModelText each independently re-derived addWidth /
remWidth / statColumnWidth from the same row list. If anyone later
changed one formula, the interactive Ink output and the non-interactive
plain text would silently fall out of column alignment.

Extract the computation into computeDiffColumnWidths() exported from
diffCommand.ts; both renderers now call it. Adds a focused unit test of
the contract (empty rows, widest non-binary row wins, binary rows are
ignored, untracked text rows count). Drop a redundant
`Omit<HistoryItemDiffStats, 'id'>` annotation since the type already has
no id field.

packages/cli/src/ui/commands/diffCommand.test.ts

@@ -6,7 +6,7 @@
 
 import type { Mock } from 'vitest';
 import { vi, describe, it, expect, beforeEach } from 'vitest';
-import { diffCommand } from './diffCommand.js';
+import { computeDiffColumnWidths, diffCommand } from './diffCommand.js';
 import { type CommandContext } from './types.js';
 import { createMockCommandContext } from '../../test-utils/mockCommandContext.js';
 import { fetchGitDiff, type GitDiffResult } from '@qwen-code/qwen-code-core';
@@ -340,6 +340,83 @@ describe('diffCommand interactive mode', () => {
   });
 });
 
+describe('computeDiffColumnWidths', () => {
+  // Direct contract test — both the Ink component and the plain-text
+  // renderer call this helper, so its output binds their column alignment.
+  // If anyone changes the formula, both paths must shift together.
+
+  it('reports min widths of 1 for an empty row list', () => {
+    expect(computeDiffColumnWidths([])).toEqual({
+      addWidth: 1,
+      remWidth: 1,
+      statColumnWidth: 5, // `+_ -_` with single-digit padding
+    });
+  });
+
+  it('sizes columns to the widest non-binary row', () => {
+    const widths = computeDiffColumnWidths([
+      {
+        filename: 'a',
+        added: 9999,
+        removed: 5,
+        isBinary: false,
+        isUntracked: false,
+        truncated: false,
+      },
+      {
+        filename: 'b',
+        added: 2,
+        removed: 100,
+        isBinary: false,
+        isUntracked: false,
+        truncated: false,
+      },
+    ]);
+    // 1 (`+`) + 4 (digits) + 1 (` `) + 1 (`-`) + 3 (digits) = 10
+    expect(widths).toEqual({ addWidth: 4, remWidth: 3, statColumnWidth: 10 });
+  });
+
+  it('ignores binary rows when computing widths', () => {
+    // A binary row must not push the numeric column wider, otherwise the
+    // `~` placeholder ends up padded to a column that no real number ever
+    // occupies.
+    const widths = computeDiffColumnWidths([
+      {
+        filename: 'a',
+        added: 1,
+        removed: 1,
+        isBinary: false,
+        isUntracked: false,
+        truncated: false,
+      },
+      {
+        filename: 'b.bin',
+        isBinary: true,
+        isUntracked: false,
+        truncated: false,
+      },
+    ]);
+    expect(widths).toEqual({ addWidth: 1, remWidth: 1, statColumnWidth: 5 });
+  });
+
+  it('counts untracked text rows in width calculation', () => {
+    // Untracked rows render as `+N -0  filename (new)`; their `added`
+    // value must be allowed to widen the column.
+    const widths = computeDiffColumnWidths([
+      {
+        filename: 'fresh.log',
+        added: 12345,
+        removed: 0,
+        isBinary: false,
+        isUntracked: true,
+        truncated: false,
+      },
+    ]);
+    expect(widths.addWidth).toBe(5);
+    expect(widths.statColumnWidth).toBe(1 + 5 + 1 + 1 + 1);
+  });
+});
+
 describe('diffCommand registration', () => {
   it('declares all execution modes so it works in non-interactive and ACP', () => {
     expect(diffCommand.supportedModes).toEqual([

packages/cli/src/ui/commands/diffCommand.ts

@@ -82,7 +82,7 @@ async function diffAction(
   // plain-text MessageActionReturn path so pipes, logs, and transports that
   // don't speak Ink still see legible output.
   if (context.executionMode === 'interactive') {
-    const item: Omit<HistoryItemDiffStats, 'id'> = {
+    const item: HistoryItemDiffStats = {
       type: MessageType.DIFF_STATS,
       model,
     };
@@ -136,6 +136,38 @@ function toRow(filename: string, s: PerFileStats): DiffRenderRow {
   };
 }
 
+/**
+ * Single source of truth for the per-row column layout. Used by both the
+ * Ink component and the plain-text renderer so the two paths can never
+ * silently disagree on alignment.
+ */
+export interface DiffColumnWidths {
+  /** Digits in the widest non-binary `added` value (min 1). */
+  addWidth: number;
+  /** Digits in the widest non-binary `removed` value (min 1). */
+  remWidth: number;
+  /** Visual width of the `+X -Y` stat column, used to pad the binary `~`
+   *  marker so it lines up with the numeric rows. */
+  statColumnWidth: number;
+}
+
+export function computeDiffColumnWidths(
+  rows: readonly DiffRenderRow[],
+): DiffColumnWidths {
+  let maxAdded = 0;
+  let maxRemoved = 0;
+  for (const r of rows) {
+    if (r.isBinary) continue;
+    if ((r.added ?? 0) > maxAdded) maxAdded = r.added ?? 0;
+    if ((r.removed ?? 0) > maxRemoved) maxRemoved = r.removed ?? 0;
+  }
+  const addWidth = String(maxAdded).length;
+  const remWidth = String(maxRemoved).length;
+  // `+` + addDigits + ' ' + `-` + remDigits.
+  const statColumnWidth = 1 + addWidth + 1 + 1 + remWidth;
+  return { addWidth, remWidth, statColumnWidth };
+}
+
 /**
  * Plain-text rendering of a `DiffRenderModel`. Used in non-interactive / ACP
  * modes where no Ink renderer is available, and as the source of truth for
@@ -168,16 +200,7 @@ export function renderDiffModelText(model: DiffRenderModel): string {
 
 function formatRowsText(rows: DiffRenderRow[]): string[] {
   if (rows.length === 0) return [];
-  let maxAdded = 0;
-  let maxRemoved = 0;
-  for (const r of rows) {
-    if (r.isBinary) continue;
-    if ((r.added ?? 0) > maxAdded) maxAdded = r.added ?? 0;
-    if ((r.removed ?? 0) > maxRemoved) maxRemoved = r.removed ?? 0;
-  }
-  const addWidth = String(maxAdded).length;
-  const remWidth = String(maxRemoved).length;
-  const statColumnWidth = 1 + addWidth + 1 + 1 + remWidth;
+  const { addWidth, remWidth, statColumnWidth } = computeDiffColumnWidths(rows);
 
   const out: string[] = [];
   for (const r of rows) {

packages/cli/src/ui/components/messages/DiffStatsDisplay.tsx

@@ -8,6 +8,7 @@ import type React from 'react';
 import { Box, Text } from 'ink';
 import { theme } from '../../semantic-colors.js';
 import type { DiffRenderModel, DiffRenderRow } from '../../types.js';
+import { computeDiffColumnWidths } from '../../commands/diffCommand.js';
 import { t } from '../../../i18n/index.js';
 
 interface DiffStatsDisplayProps {
@@ -24,19 +25,10 @@ export const DiffStatsDisplay: React.FC<DiffStatsDisplayProps> = ({
   model,
 }) => {
   const { filesCount, linesAdded, linesRemoved, rows, hiddenCount } = model;
-
-  // Reproduce the numeric-column alignment of the text renderer so the
-  // interactive and non-interactive outputs are visually interchangeable.
-  let maxAdded = 0;
-  let maxRemoved = 0;
-  for (const r of rows) {
-    if (r.isBinary) continue;
-    if ((r.added ?? 0) > maxAdded) maxAdded = r.added ?? 0;
-    if ((r.removed ?? 0) > maxRemoved) maxRemoved = r.removed ?? 0;
-  }
-  const addWidth = String(maxAdded).length;
-  const remWidth = String(maxRemoved).length;
-  const statColumnWidth = 1 + addWidth + 1 + 1 + remWidth;
+  // Single source of truth shared with `renderDiffModelText`, so the
+  // interactive Ink output and the non-interactive plain text never drift
+  // out of column alignment.
+  const { addWidth, remWidth, statColumnWidth } = computeDiffColumnWidths(rows);
 
   const headerLabel =
     filesCount === 1

scripts/unused-keys-only-in-locales.json

@@ -1,5 +1,5 @@
 {
-  "generatedAt": "2026-04-27T03:28:33.689Z",
+  "generatedAt": "2026-04-27T03:39:04.133Z",
   "keys": [
     "  Models: Qwen latest models\n",
     "  qwen auth qwen-oauth     - Authenticate with Qwen OAuth (discontinued)",