Bug: getDiff fails with 'not a git repository' when agents cd out of worktree

[that-github-user]

Summary

During thinktank runs, getDiff frequently fails with:
`fatal: not a git repository (or any of the parent directories): .git`

This happens because Claude Code agents sometimes cd into subdirectories or temp directories during execution, and when getDiff runs afterward, the current working directory is no longer the worktree.

Fix

getDiff and getDiffStats should always use the explicit worktree path as cwd, which they already do. But the issue may be that the worktree was removed by git or the OS during agent execution. Need to verify the worktree still exists before trying to diff.

Impact

Shows 0 files changed for agents that actually made changes. Reduces the effectiveness of convergence analysis.

[that-github-user]

Fixed in #142. getDiff now resolves to absolute path, verifies .git exists and git rev-parse works before running git add. Clear warning on corrupted worktrees.

[that-github-user]

Partial fix in #142. getDiff now:

• Resolves to absolute path
• Checks .git file exists before git add
• Clear diagnostic: "ENOENT: no such file or directory, access '....git'"

Root cause identified: on complex multi-minute Opus tasks, the .git file in the worktree directory is being deleted during agent execution. Simple tasks work perfectly (verified). The .git file in a worktree is a pointer file (not a directory) containing gitdir: /path/to/main/.git/worktrees/name. If the agent runs git commands that clean up or reinitialize, this file gets removed.

Remaining investigation needed: why do long-running Claude Code sessions delete the .git pointer file?

[that-github-user]

Further investigation: the .git file backup/restore approach (PR #143) didn't fully fix it. The new error reveals the deeper issue:

```
fatal: not a git repository: C:/Users/silon/.../thinktank/.git/worktrees/thinktank-agent-3-tPYIBt
```

The .git POINTER file in the worktree IS present, but the worktree METADATA directory in the main repo's .git/worktrees/ is missing. This means something is pruning or deleting the worktree registration during the agent run.

Likely cause: the cleanupBranches() call at the start of run.ts, or git worktree prune being triggered by one of the agents' git operations. When one agent's git command triggers a prune, it can remove another concurrent agent's worktree metadata.

This is fundamentally a concurrency issue with git worktrees — multiple agents running git commands simultaneously can interfere with each other's worktree registrations.

Needs dedicated investigation session.

[that-github-user]

Fixed in #144. Root cause: concurrent agents' git commit triggers gc --auto → git worktree prune → deletes other agents' worktree metadata.

Fix:

1. git worktree lock immediately after creation — locked worktrees survive prune
2. gc.auto=0 env vars on agent processes — prevents gc from triggering
3. Verify worktree metadata directory (not just .git pointer) in getDiff

Verified: locked file appears in .git/worktrees/NAME/, removeWorktree still works with locked worktrees.

[that-github-user]

Root cause fully identified

The getDiff bug has TWO layers:

1. gc pruning (fixed in Fix worktree pruning: lock worktrees + disable agent auto-gc #144) — concurrent agents' git commits trigger gc --auto → worktree prune
2. Self-referential interference (unfixable via locks) — when thinktank runs on its OWN repo, agents with Bash access find and execute thinktank's git worktree management code (removeWorktree, cleanupBranches, git worktree prune), destroying their own and sibling worktrees

Evidence:

• Simple tasks on the thinktank repo work perfectly (diff captured, tests pass)
• Complex tasks where agents deeply explore the codebase fail (agents empty their own worktree directories)
• Tasks on OTHER repos (Express testbed) always work — agents can't find thinktank infrastructure code

This is a dogfooding-specific issue. When thinktank is installed as a global npm package (#139), the tool binary runs from the global install path, not from the worktree source. Agents interact with the CODE, not the TOOL infrastructure. This cleanly separates the two.

Status

• gc pruning fixed via worktree lock (Fix worktree pruning: lock worktrees + disable agent auto-gc #144)
• .git file restoration via backup (Restore .git pointer file backup for agents that delete it #145)
• Self-referential interference — known limitation, resolved by npm publish (Publish npm package and add npx thinktank support #139)

Closing this issue. The remaining case is tracked as a known limitation in the dogfooding context, resolved by #139.