fix(sync): detect changes when the project lives in a subdirectory of its git repo

[innoxxicide]

No matching issue — found while using CodeGraph on a repository whose project
lives one directory down. I couldn't find an existing report for it, so the
repro is written out in full below.

codegraph status printed Index is up to date no matter how many files had
changed, whenever the indexed project sat below its repository root — a
monorepo package, an app/ folder beside a server/ one. codegraph sync run
a second later found the same files and reindexed them, so the two commands
flatly contradicted each other, and anything trusting the status count (the
staleness reminder, a scripted check) read the index as clean forever.

Reproduced both ways on the released build before touching anything:

layout	edit	codegraph status
project is the repo root	1 file modified	Modified: 1 files
project in app/ of the repo	1 file modified	Index is up to date

What was wrong

getGitChangedFiles runs git status --porcelain with cwd set to the
project root. Porcelain is indifferent to cwd in both directions: it
prints repository-relative paths (the format deliberately ignores
status.relativePaths) and it reports the whole repository, not just cwd.
Those paths went straight into path.join(projectRoot, filePath), producing
<repo>/<sub>/<sub>/… — a path that cannot exist. fs.readFileSync threw, and
the entry was swallowed by the logDebug('Skipping unreadable file while detecting changes') guard, so added and modified came back empty for
every edit. The failure was silent and total, not partial.

getGitVisibleFiles — the scan/index path — was never affected, because
git ls-files is both cwd-relative and cwd-scoped. That asymmetry between the
two git fast paths is exactly why status and sync disagreed, and it is now
pinned by a test so it stays deliberate.

What this does

• collectGitStatus resolves where its directory sits inside the repository
  (git rev-parse --show-prefix), scopes the report to that subtree with a
  -- . pathspec, strips the prefix from every reported path, and drops anything
  outside it — so a sibling package's edits are no longer counted as this
  project's. A project that is the repository root runs the byte-identical
  command it ran before and skips the prefix logic entirely.
• The prefix is resolved per recursion level rather than threaded down from
  the caller, so the embedded-repo recursion (codegraph sync silently skips all untracked files #1213, Allow opting out of embedded git repo discovery in gitignored directories #970, [BUG] Currently, it is impossible to turn off the indexing of nested repositories #976) keeps working
  unchanged: those calls land on real repo roots and resolve an empty prefix.
• The ignore matchers (Incremental sync (git-status fast path) bypasses the ignore matcher — tracked files in excluded dirs leak back into the index #766) now compare against a genuinely relative path —
  relative to the directory whose .gitignore built them. Before this, a
  subdirectory project matched its own rules against repository-relative paths,
  so its .gitignore silently didn't apply.
• A project inside a directory its parent repository gitignores now declines
  the git fast path instead of reading git's silence as "nothing changed".
  getGitVisibleFiles already made that call; the extracted gitScopeIsIgnored
  helper (lifted verbatim out of it, not reimplemented) makes both paths make it
  identically. That shared invariant is the one this bug violated, so it
  seemed worth enforcing structurally rather than fixing the one symptom.

Detection is fully automatic — no codegraph.json option added, nothing for a
user to opt into. Scoping git status to the subtree is also strictly cheaper in
a large monorepo than reporting the whole repository and discarding most of it.

Tests

New __tests__/git-changed-subdir-project.test.ts, 11 cases. 8 of them
fail on unmodified main (expected [ 'app/src/index.js' ] to include 'src/index.js', and expected [] to include 'src/index.js' through the public
CodeGraph.getChangedFiles) and pass here; the other 3 are regression guards for
behaviour that already worked.

Modified / added / deleted reported with project-relative paths · sibling-package
edits ignored · status agreeing with sync end to end through the public
API · the embedded-repo recursion below a subdirectory project (#1213) · the
project's own .gitignore (#766) · the gitignored-project fallback · project ==
repository root · a project not in git at all.

npx vitest run __tests__/git-changed-subdir-project.test.ts
     Tests  11 passed (11)

npx vitest run __tests__/git-changed-untracked-dir.test.ts __tests__/git-hooks.test.ts \
              __tests__/include-ignored-config.test.ts __tests__/sync.test.ts \
              __tests__/sync-rebuild-convergence.test.ts
     Tests  69 passed (69)

Full suite (Windows): 3004 passed / 27 failed / 219 skipped. Those 27 failures
reproduce test-for-test on unmodified HEAD — 26 are the documented Windows
EPERM temp-dir-cleanup quirk, the rest the explore-* budget gates — so none is
introduced here. tsc --noEmit clean.

Also

A user-facing CHANGELOG.md entry under [Unreleased] → Fixes, per the
CHANGELOG rules in CLAUDE.md. No version bump.

🤖 Generated with Claude Code