[colbymchenry]

Summary

codegraph sync no longer says "Already up to date" on an index an older engine built. It syncs changed files as before, then warns that a full codegraph index is what picks up the new engine. It still exits 0, and --quiet stays silent.

Root cause

Sync re-reads changed files only and never advances the extraction stamp, so an index from an older engine stays out of date however little changed. codegraph status already said so; sync said the opposite.

What came from the contributor, and what changed

The PR's detection and its test matrix stand: old stamp and missing stamp, unchanged and changed files, quiet and not, a current index, and the rebuild clearing the condition.

Its behaviour changed, by the maintainer's decision. The PR refused the sync with exit 1. The installed git hooks run sync in the background with output discarded, so a refusal would quietly stop every hooked index from following commits on the next upgrade, with nothing to tell the user why. So:

• sync warns and still runs, with exit 0;
• the stale case says "No files changed" in place of "Already up to date";
• --quiet prints nothing, as cli-sync.test.ts already pins. The PR's stderr line existed to explain a failed exit, and there is no failure now.

No automatic rebuild here. That stays #1798.

Validation

• Red→green: cli-sync-stale-index.test.ts, 6 cases. 3 fail on main (the warning cases), the 3 that pin unchanged behaviour pass on both, and all 6 pass here.
• Real run against a private home: a repo with the installed post-commit hook and a stale stamp. A real git commit put the new file in the index in about a second, and a manual sync printed the warning and exited 0.
• Suite: one full Vitest 4 run with 4 workers on a stack of this PR with feat(mcp): warn when project indexes need rebuilding #1853, fix(cli): require full rebuild for stale extraction indexes #1256 and feat(cli): expose test-file classification #1960: top c8652154 on main d494e43, 845 files, 10307 tests, 10219 passed, 1 failed, 87 skipped. The one failure was owning-package.test.ts, which pins the files --json keys and needed the new field from feat(cli): expose test-file classification #1960; that fix is in feat(cli): expose test-file classification #1960's commit. This commit also ran alone at f9b7997b on Vitest 2: 839 files, 9966 tests, 9879 passed, 0 failed, 87 skipped.
• After rebasing the stack onto 446d08c (top fc42f83b): 8 affected test files, 174 passed, 1 skipped, kernel expected. Main's new commits share only CHANGELOG.md and README.md with the stack, in other hunks.

Lands #1842 by @bompus

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