fix(project): prevent cross-repo project_id cache collisions for bare repos

[StevenTCramer]

Issue for this PR

Closes #18045

Type of change

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

What does this PR do?

Project.fromDirectory was caching the project id at worktree/.git/opencode.
For bare repos (for example .../org/repo.git), worktree was computed from path.dirname(git-common-dir), which resolves to the parent org directory instead of the repo git dir.
That made unrelated repos under the same parent share one cache file and sometimes the same project_id.

This change reads/writes the cache directly in git-common-dir (<common>/opencode) so each repo gets its own cache file.
It also keeps the existing fallback behavior when --git-common-dir resolves to sandbox/empty output.

Added regression coverage for two different bare repos under the same parent directory to assert they do not share project ids.

How did you verify your code works?

• Ran: bun test --timeout 30000 test/project/project.test.ts
• Result: 20 pass, 0 fail
• Also validated regression behavior manually:
  • reverted src/project/project.ts to previous commit and reran test -> new regression test failed as expected
  • restored fixed src/project/project.ts and reran test -> all tests passed

Screenshots / recordings

If this is a UI change, please include a screenshot or recording.

N/A (non-UI change)

Checklist

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

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Found 2 related PRs that may be duplicates or related to PR #18044:

1. PR fix(project): use path-aware project identity to prevent clone collisions #17943: fix(project): use path-aware project identity to prevent clone collisions

   • fix(project): use path-aware project identity to prevent clone collisions #17943
   • Related: Also addresses project ID collision prevention, potentially overlapping with the cache isolation fix

2. PR fix(project): repair split project IDs across worktrees #14287: fix(project): repair split project IDs across worktrees

   • fix(project): repair split project IDs across worktrees #14287
   • Related: Addresses project ID handling across different repo contexts (worktrees), which may relate to the bare repo cache isolation

These PRs appear to be in the same problem domain (project ID uniqueness and collision prevention), so there may be overlap or related fixes.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[StevenTCramer]

Closing this PR. The upstream code has been completely refactored to Effect, so this fix needs to be reimplemented against the new codebase. Will revisit when time permits.