fix(server): reject requests for missing project directories

[shijiatongxue]

Issue for this PR

Fixes #39471

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

When a saved project directory has been deleted or moved, the instance HTTP middleware now checks the decoded project directory before loading the instance context.

If the directory is missing, the server returns the declared 404 NotFoundError JSON response instead of allowing the request to complete silently without an assistant response. The regression test covers GET /path and POST /session/:sessionID/prompt_async.

How did you verify your code works?

• Targeted regression test passed: bun test test/server/httpapi-instance.test.ts -t "rejects instance requests for missing project directories" — 1 pass, 0 fail.
• Full repository typecheck passed: bun run typecheck — 30 successful tasks.
• The full httpapi-instance.test.ts file had one unrelated 5-second timeout in emits a sync fence header for fixed-workspace mutations; the new regression test passed.
• Built and manually exercised the desktop dev app.
• git diff --check passed.
• Pre-push typecheck passed. Bun 1.4.0 emitted only a version-difference warning against the repository's expected 1.3.14.

Screenshots

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[Enough1122]

AI code review — automated review for reference; please use your judgment.

• packages/opencode/src/server/routes/instance/httpapi/middleware/instance-context.ts:29 — the fs.isDir pre-check adds a filesystem stat to every instance-routed request on the hot path. Alternative worth considering: let store.load fail and map its not-found error to this 404 response, keeping the happy path syscall-free. Non-blocking.
• instance-context.ts:28 — TOCTOU window between isDir and store.load: harmless today since load surfaces its own error, but the two checks can disagree (symlink swapped out between them). Fine as-is; just be aware.
• instance-context.ts:26 — make sure isDir sees the same path notion store.load uses (relative dirs, symlink resolution, Windows case-insensitivity); if load canonicalizes differently the pre-check could 404 a directory load would accept.
• Returning HttpServerResponse.jsonUnsafe(notFound(...)) manually must keep matching the declared 404 error schema exactly — the regression test pins the {name, data:{message}} body, which is good protection against schema drift.
• Test covers GET and POST prompt_async with exact-body assertions. No blocking issues found.

[shijiatongxue]

Following up on the review above. This response is also AI-generated.

I kept the fs.isDir check intentionally. InstanceStore.load may return a cached context after the directory is deleted, and a missing child can resolve through an ancestor repository rather than fail. Therefore, letting store.load handle the not-found case would not cover the regression. I added a regression test for the cached-instance/deleted-directory case and documented the reasoning. The extra stat remains a deliberate correctness trade-off on this request path.

Implemented in commit 3b364d447.