fix(yield): group commit attribution by canonical repo, not launch path

Sessions launched from monorepo subdirectories or separate worktrees
of one repository formed independent attribution groups, each awarding
the same commit (double-counted productive sessions; the duplicate
owner was not even flagged ambiguous). Groups now key on the realpath
of git-common-dir, so all subdirs and worktrees of a repo collapse
into one group while distinct repos stay separate; ambiguity semantics
unchanged, now correctly spanning the whole repo. rev-parse results
cached per directory.

Fixes #713. Regression tests fail on the unfixed code.

src/yield.ts

@@ -1,4 +1,6 @@
 import { execFileSync } from 'child_process'
+import { realpathSync } from 'fs'
+import { resolve } from 'path'
 import { parseAllSessions } from './parser.js'
 import type { DateRange, SessionSummary } from './types.js'
 
@@ -60,8 +62,59 @@ function runGit(args: string[], cwd: string): string | null {
   }
 }
 
-function isGitRepo(dir: string): boolean {
-  return runGit(['rev-parse', '--is-inside-work-tree'], dir) === 'true'
+type RepoIdentity = {
+  /** Canonical group key: the absolute git-common-dir (shared object store). */
+  readonly key: string
+  /** A member directory to run `git log` from; --all spans the whole store. */
+  readonly gitDir: string
+}
+
+function canonicalPath(path: string): string {
+  try {
+    return realpathSync(path)
+  } catch {
+    return path
+  }
+}
+
+/**
+ * Resolve a directory to its canonical repository identity, or null when it is
+ * not inside a git work tree.
+ *
+ * The key is the absolute `git-common-dir` (the shared object store), NOT the
+ * raw path: `git rev-parse --is-inside-work-tree` is true in every subdirectory
+ * and `git log --all` returns the same repo-wide list from any of them, so
+ * keying groups on the raw path would let two monorepo subdirectories — or two
+ * worktrees of one repo — each award the same commit. All subdirectories AND
+ * all worktrees of one repo share this common-dir, so they collapse to a single
+ * group; distinct repositories keep distinct keys.
+ *
+ * Cached per directory: resolution runs once per unique path (many sessions
+ * share a path), never once per session.
+ */
+function resolveRepoIdentity(
+  dir: string,
+  cache: Map<string, RepoIdentity | null>,
+): RepoIdentity | null {
+  const cached = cache.get(dir)
+  if (cached !== undefined) return cached
+
+  let identity: RepoIdentity | null = null
+  // One fork answers both questions; line 1 is --is-inside-work-tree, line 2 the
+  // --git-common-dir (relative to `dir` for a subdir, absolute for a worktree).
+  const out = runGit(['rev-parse', '--is-inside-work-tree', '--git-common-dir'], dir)
+  if (out) {
+    const [insideWorkTree, commonDir] = out.split('\n')
+    if (insideWorkTree === 'true' && commonDir) {
+      // realpath canonicalizes symlinks: git reports a linked worktree's
+      // common-dir as a realpath but the main worktree's as ".git" relative to
+      // its (possibly symlinked) path, so both must be canonicalized to collapse
+      // to one key.
+      identity = { key: canonicalPath(resolve(dir, commonDir)), gitDir: dir }
+    }
+  }
+  cache.set(dir, identity)
+  return identity
 }
 
 function getMainBranch(cwd: string): string {
@@ -252,32 +305,42 @@ export async function computeYield(range: DateRange, cwd: string, provider: stri
     details: [],
   }
 
+  const repoIdentityCache = new Map<string, RepoIdentity | null>()
+
   // Get all commits in the date range for correlation
-  const commits = isGitRepo(cwd)
+  const cwdIdentity = resolveRepoIdentity(cwd, repoIdentityCache)
+  const cwdCommits = cwdIdentity
     ? getCommitsInRange(cwd, range.start, range.end, getMainBranch(cwd))
     : []
 
-  // Group sessions by resolved repo before attributing: every project entry
-  // whose projectPath is missing (or not a git repo) falls back to the same
-  // cwd and shares one commit list, so attribution must run once per repo or
-  // two such entries could each award the same commit to one of their sessions.
+  // Group sessions by canonical repository identity before attributing so that
+  // each commit is awarded at most once across the whole repo. Two monorepo
+  // subdirectory sessions, or two worktrees of one repo, resolve to the same
+  // git-common-dir and share ONE group; keying on the raw path would double
+  // count. A project whose path is missing or not a git repo falls back to the
+  // cwd repo (or, when cwd is not a repo either, an empty commit list) exactly
+  // as before.
   type RepoGroup = { commits: CommitInfo[]; sessions: SessionSummary[]; projectNames: string[] }
   const repoGroups = new Map<string, RepoGroup>()
   for (const project of projects) {
-    const projectCwd = project.projectPath && isGitRepo(project.projectPath)
-      ? project.projectPath
-      : cwd
+    const projectIdentity = project.projectPath
+      ? resolveRepoIdentity(project.projectPath, repoIdentityCache)
+      : null
+    const identity = projectIdentity ?? cwdIdentity
+    const groupKey = identity ? identity.key : cwd
 
-    let group = repoGroups.get(projectCwd)
+    let group = repoGroups.get(groupKey)
     if (!group) {
       group = {
-        commits: projectCwd === cwd
-          ? commits
-          : getCommitsInRange(projectCwd, range.start, range.end, getMainBranch(projectCwd)),
+        commits: !identity
+          ? []
+          : cwdIdentity && identity.key === cwdIdentity.key
+            ? cwdCommits
+            : getCommitsInRange(identity.gitDir, range.start, range.end, getMainBranch(identity.gitDir)),
         sessions: [],
         projectNames: [],
       }
-      repoGroups.set(projectCwd, group)
+      repoGroups.set(groupKey, group)
     }
     for (const session of project.sessions) {
       group.sessions.push(session)

tests/yield-repo-grouping.test.ts

@@ -0,0 +1,188 @@
+import { execFileSync } from 'node:child_process'
+import { mkdir, mkdtemp, rm, writeFile } from 'node:fs/promises'
+import { tmpdir } from 'node:os'
+import { join } from 'node:path'
+
+import { afterAll, beforeAll, describe, expect, it, vi } from 'vitest'
+
+import type { ProjectSummary, SessionSummary } from '../src/types.js'
+import { computeYield } from '../src/yield.js'
+
+const { parseAllSessionsMock } = vi.hoisted(() => ({
+  parseAllSessionsMock: vi.fn(),
+}))
+
+vi.mock('../src/parser.js', () => ({
+  parseAllSessions: parseAllSessionsMock,
+}))
+
+function git(cwd: string, args: string[], env: Record<string, string> = {}): string {
+  return execFileSync('git', args, {
+    cwd,
+    encoding: 'utf-8',
+    env: { ...process.env, ...env },
+  }).trim()
+}
+
+function initRepo(dir: string): void {
+  git(dir, ['init', '-b', 'main'])
+  git(dir, ['config', 'user.email', 'test@example.com'])
+  git(dir, ['config', 'user.name', 'Test'])
+}
+
+function commitAt(dir: string, message: string, iso: string): void {
+  git(dir, ['add', '.'])
+  git(dir, ['commit', '-m', message], {
+    GIT_AUTHOR_DATE: iso,
+    GIT_COMMITTER_DATE: iso,
+  })
+}
+
+function makeSession(overrides: Partial<SessionSummary>): SessionSummary {
+  return {
+    sessionId: 'session',
+    project: 'app',
+    firstTimestamp: '2026-01-01T10:00:00.000Z',
+    lastTimestamp: '2026-01-01T11:00:00.000Z',
+    totalCostUSD: 1,
+    totalSavingsUSD: 0,
+    totalInputTokens: 0,
+    totalOutputTokens: 0,
+    totalReasoningTokens: 0,
+    totalCacheReadTokens: 0,
+    totalCacheWriteTokens: 0,
+    apiCalls: 1,
+    turns: [],
+    modelBreakdown: {},
+    toolBreakdown: {},
+    mcpBreakdown: {},
+    bashBreakdown: {},
+    categoryBreakdown: {} as SessionSummary['categoryBreakdown'],
+    skillBreakdown: {},
+    subagentBreakdown: {},
+    ...overrides,
+  }
+}
+
+const range = {
+  start: new Date('2026-01-01T00:00:00.000Z'),
+  end: new Date('2026-01-02T00:00:00.000Z'),
+}
+
+// Tighter window (span 1.5h): 10:15 -> 10:45 (+1h = 11:45). Wins any commit it shares.
+const tightWindow = {
+  firstTimestamp: '2026-01-01T10:15:00.000Z',
+  lastTimestamp: '2026-01-01T10:45:00.000Z',
+}
+// Broader window (span 2h): 10:00 -> 11:00 (+1h = 12:00). Loses the shared commit.
+const broadWindow = {
+  firstTimestamp: '2026-01-01T10:00:00.000Z',
+  lastTimestamp: '2026-01-01T11:00:00.000Z',
+}
+
+describe('yield repo grouping by canonical repository identity (issue #713)', () => {
+  it('credits one commit once across two monorepo subdirectory sessions', async () => {
+    const repoDir = await mkdtemp(join(tmpdir(), 'codeburn-yield-monorepo-'))
+    try {
+      initRepo(repoDir)
+      // Two package subdirectories of ONE repo. `git rev-parse --is-inside-work-tree`
+      // is true in both, and `git log --all` returns the same repo-wide commit
+      // list from either, so keying groups by the raw subdir path double-credits.
+      await writeFile(join(repoDir, 'a.txt'), 'a\n')
+      await writeFile(join(repoDir, 'b.txt'), 'b\n')
+      commitAt(repoDir, 'feat: shipped once', '2026-01-01T10:30:00Z')
+
+      const subA = join(repoDir, 'packages', 'a')
+      const subB = join(repoDir, 'packages', 'b')
+      await mkdir(subA, { recursive: true })
+      await mkdir(subB, { recursive: true })
+
+      const sessionA = makeSession({ sessionId: 'sub-a', project: 'pkg-a', ...tightWindow, totalCostUSD: 5 })
+      const sessionB = makeSession({ sessionId: 'sub-b', project: 'pkg-b', ...broadWindow, totalCostUSD: 3 })
+
+      parseAllSessionsMock.mockResolvedValue([
+        { project: 'pkg-a', projectPath: subA, sessions: [sessionA] } as ProjectSummary,
+        { project: 'pkg-b', projectPath: subB, sessions: [sessionB] } as ProjectSummary,
+      ])
+
+      const summary = await computeYield(range, repoDir)
+
+      const productive = summary.details.filter(d => d.category === 'productive')
+      expect(productive.map(d => d.sessionId)).toEqual(['sub-a'])
+      expect(productive[0]!.commitCount).toBe(1)
+
+      const detailB = summary.details.find(d => d.sessionId === 'sub-b')!
+      expect(detailB.category).toBe('ambiguous')
+      expect(detailB.commitCount).toBe(0)
+      expect(summary.ambiguous).toEqual({ cost: 3, sessions: 1 })
+    } finally {
+      await rm(repoDir, { recursive: true, force: true })
+    }
+  })
+
+  it('credits one commit once across two worktrees of one repo', async () => {
+    const repoDir = await mkdtemp(join(tmpdir(), 'codeburn-yield-worktree-'))
+    let wtDir = ''
+    try {
+      initRepo(repoDir)
+      await writeFile(join(repoDir, 'file.txt'), 'hello\n')
+      commitAt(repoDir, 'feat: shipped once', '2026-01-01T10:30:00Z')
+
+      // Linked worktree on a different branch, sharing the same object store.
+      wtDir = join(repoDir, '..', `${repoDir.split('/').pop()}-wt`)
+      git(repoDir, ['worktree', 'add', wtDir, '-b', 'feature'])
+
+      const sessionMain = makeSession({ sessionId: 'wt-main', project: 'app', ...tightWindow, totalCostUSD: 5 })
+      const sessionLinked = makeSession({ sessionId: 'wt-linked', project: 'app', ...broadWindow, totalCostUSD: 3 })
+
+      parseAllSessionsMock.mockResolvedValue([
+        { project: 'app', projectPath: repoDir, sessions: [sessionMain] } as ProjectSummary,
+        { project: 'app', projectPath: wtDir, sessions: [sessionLinked] } as ProjectSummary,
+      ])
+
+      const summary = await computeYield(range, repoDir)
+
+      const productive = summary.details.filter(d => d.category === 'productive')
+      expect(productive.map(d => d.sessionId)).toEqual(['wt-main'])
+      expect(productive[0]!.commitCount).toBe(1)
+
+      const detailLinked = summary.details.find(d => d.sessionId === 'wt-linked')!
+      expect(detailLinked.category).toBe('ambiguous')
+      expect(detailLinked.commitCount).toBe(0)
+    } finally {
+      if (wtDir) await rm(wtDir, { recursive: true, force: true })
+      await rm(repoDir, { recursive: true, force: true })
+    }
+  })
+
+  it('keeps two genuinely separate repos as independent groups (no over-merge)', async () => {
+    const repo1 = await mkdtemp(join(tmpdir(), 'codeburn-yield-sep1-'))
+    const repo2 = await mkdtemp(join(tmpdir(), 'codeburn-yield-sep2-'))
+    try {
+      for (const [dir, name] of [[repo1, 'first'], [repo2, 'second']] as const) {
+        initRepo(dir)
+        await writeFile(join(dir, 'file.txt'), `${name}\n`)
+        commitAt(dir, `feat: ${name}`, '2026-01-01T10:30:00Z')
+      }
+
+      // Identical overlapping windows: only correct because the repos are distinct.
+      const session1 = makeSession({ sessionId: 'repo1-session', project: 'r1', ...broadWindow, totalCostUSD: 4 })
+      const session2 = makeSession({ sessionId: 'repo2-session', project: 'r2', ...broadWindow, totalCostUSD: 4 })
+
+      parseAllSessionsMock.mockResolvedValue([
+        { project: 'r1', projectPath: repo1, sessions: [session1] } as ProjectSummary,
+        { project: 'r2', projectPath: repo2, sessions: [session2] } as ProjectSummary,
+      ])
+
+      const summary = await computeYield(range, repo1)
+
+      const productive = summary.details.filter(d => d.category === 'productive')
+      expect(productive.map(d => d.sessionId).sort()).toEqual(['repo1-session', 'repo2-session'])
+      expect(productive.every(d => d.commitCount === 1)).toBe(true)
+      expect(summary.ambiguous).toEqual({ cost: 0, sessions: 0 })
+    } finally {
+      await rm(repo1, { recursive: true, force: true })
+      await rm(repo2, { recursive: true, force: true })
+    }
+  })
+})