fix(server): treat symlinked worktree paths as the same directory

[Mnigos]

The shared-worktree check in the branch-drift guard compares raw path strings, so on macOS /tmp/foo and /private/tmp/foo (a symlink) count as two different worktrees and a drifted checkout can be adopted while a sibling thread still points at the directory through the other spelling.

Both the session-cwd ownership check and the shared-worktree check now compare realpath results, falling back to the raw string when resolution fails. Regression tests use real symlinks (created as directory junctions, which need no symlink privilege on Windows) to cover shared siblings and a session cwd spelled differently from the recorded worktree. Dedicated worktrees follow branch drift; shared worktrees keep their recorded branch.

Validation: all 35 checkpoint reactor tests, server typecheck, and targeted lint pass. The session-cwd regression fails before its fix.

Related to #9245: this covers the branch-drift comparisons; the shared-worktree removal guard proposed in #9185 is not part of this PR, so the issue stays open for it.

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Note

Medium Risk
Changes orchestration metadata updates on turn completion when branch drift is detected; incorrect canonicalization could block legitimate drift-follow or allow unwanted updates, though fallback to raw paths limits regression risk.

Overview
Fixes branch-drift adoption when two threads reference the same worktree through different path spellings (e.g. macOS /tmp/... vs /private/tmp/..., or an explicit symlink).

In CheckpointReactor, the guard that skips adopting a drifted checkout for shared worktrees used raw string equality on worktreePath. Sibling threads with alternate spellings of one directory were treated as separate worktrees, so thread-1 could still follow checkout drift after an agent rename.

Worktree paths are now compared via realPath (Effect FileSystem), falling back to the original string if resolution fails. The shared-worktree check canonicalizes the current thread path and every other thread’s path before deciding whether to skip thread.meta.update.

Tests add harness support for a second thread with a custom worktree path and a case where thread-2 points at thread-1’s cwd through a directory symlink, asserting the recorded branch stays t3code/original-branch.

^{Reviewed by Cursor Bugbot for commit fc818fbcb74b3de3f72dd61e2966921713af0bd0. Configure here.}

Note

Fix 'CheckpointReactor' to treat symlinked worktree paths as same directory

During branch drift handling, CheckpointReactor now resolves worktree paths using realPath on the FileSystem service instead of comparing raw path strings, so symlinked paths are recognized as the same directory.

• Updates the test harness createHarness with an optional callback to set the second thread's worktree path, and adds a regression test confirming a completed turn does not overwrite a locally detected branch when the worktree is shared via symlink.
• Risk: if realPath resolution fails, the comparison falls back to the original path strings, which may cause the original branch drift bug to reoccur for symlinked paths in that edge case.

^{Macroscope summarized d3eb8bd.}

Summary by CodeRabbit

• Bug Fixes
  • Improved shared-worktree detection when equivalent paths use symlinks or alternate path spellings.
  • Prevented drifted checkouts from being incorrectly adopted when a worktree is shared.
  • Preserved the original thread branch in shared-worktree scenarios.
  • Ensured unshared drifted checkouts can still be adopted and pull requests refreshed.
  • Improved worktree path resolution across supported environments.

[macroscopeapp]

Approvability

Verdict: Approved at fc818fb

Macroscope's review found this PR approvable — This is a contained server bug fix that canonicalizes worktree paths only when deciding whether branch-drift metadata should be updated, with a safe fallback and targeted symlink regression coverage. The test harness change is isolated to development tests and existing behavior remains unchanged for normal path spellings.

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[lnieuwenhuis]

Maintainer verification: narrow and additive — realPath canonicalization applies only to the shared-worktree branch-drift guard, and resolution failures fall back to plain string equality, so the worst case is the old behavior. Symlink regression included and full CI is green. Looks merge-ready to me.

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📝 Walkthrough

Walkthrough

CheckpointReactor now canonicalizes worktree paths before shared-worktree checks. Tests cover symlinked paths and verify branch-drift behavior for shared and unshared worktrees.

Changes

Worktree identity handling

Layer / File(s)	Summary
Canonical path detection apps/server/src/orchestration/Layers/CheckpointReactor.ts	The reactor resolves worktree paths with the filesystem service and falls back to raw paths when resolution fails. Shared-worktree detection compares canonical paths.
Symlinked worktree validation apps/server/src/orchestration/Layers/CheckpointReactor.test.ts	The harness supports alternate paths for a second thread. Tests verify that shared worktrees retain t3code/original-branch, while unshared worktrees adopt the drifted branch and refresh the pull request.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix

Suggested reviewers: juliusmarminge, t3dotgg

Merge Risk: ⚪ Minimal · up to 5aaba

Canonical path handling now recognizes symlinked spellings of the same worktree while retaining raw-path behavior when resolution fails. No actionable merge risk remains.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: treating symlinked worktree paths as the same directory.
Description check	✅ Passed	The description explains what changed, why it changed, the test coverage, validation results, risk, and out-of-scope work. It is sufficiently complete despite not using the template headings or checkl…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[coderabbitai]

Actionable comments posted: 1

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Inline comments:
In `@apps/server/src/orchestration/Layers/CheckpointReactor.ts`:
- Around line 584-586: Update the ownership-check flow in the surrounding
checkpoint reactor logic to canonicalize both thread.worktreePath and input.cwd
before the existing early-return guard, using canonicalWorktreePath and
retaining raw paths when resolution fails. Compare the canonical values in that
guard, then preserve the existing canonicalWorktreePath handling for
canonicalWorktree and canonicalOthers.

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• apps/server/src/orchestration/Layers/CheckpointReactor.ts

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[shivamhwp]

Note: GPT-6 on behalf of shivam (@shivamhwp).

This fixes canonical path comparisons in checkpoint branch-drift handling. #9245 also covers the shared-worktree removal guard in #9185, which this PR does not change. Please keep the issue open for that remaining guard or split its tracking before using Fixes #9245. The new symlink tests should use a Windows-compatible directory junction or an explicit platform guard so Windows runners do not require symlink privileges.

[Mnigos]

@shivamhwp done in 8f97af2: dropped the Fixes keyword (removal guard from #9185 stays tracked in #9245) and the tests now create junctions.

[Mnigos]

Note

🤖 Claude Fable 5.1 on behalf of Mnigos

Closing for now: this touches the server layer that is being rewritten for V2, and the maintainers are not taking changes there until it lands. The fix is still needed against current main; I will reopen or resubmit it against the new code once V2 is in.