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[Bug]: Forking a Claude thread fails after its project's workspace root changes#22796

opened19d agobyUurjitc

Before submitting

  • I searched existing issues and did not find a duplicate.
  • I included enough detail to reproduce or investigate the problem.

Area

apps/server

Steps to reproduce

  1. Create a project at /work/app and run at least one turn in a Claude thread.
  2. Move the repository to /work/app/platform and point the project at it (t3_project_update with the new workspaceRoot, which records a project.meta-updated event).
  3. Continue the thread. This still works.
  4. Fork the thread from any response and send a message in the fork.

Expected behavior

The fork starts from the parent's Claude session, the same way continuing the parent still does.

Actual behavior

The fork's turn fails to start with "Provider turn failed to start: Claude Agent SDK query failed." The server trace shows:

1ProviderAdapterForkThreadError: Failed to fork claudeAgent provider thread …
2 [cause]: ClaudeAgentSdkQueryRunnerError: Claude Agent SDK query failed.
3 [cause]: Error: Session <id> not found in project directory for /work/app/platform

Claude files a transcript under the directory the session started in (~/.claude/projects/-work-app/<id>.jsonl). forkThread passes the thread's current cwd as dir (ClaudeAdapterV2.ts, forkOptions). With dir, the SDK only checks that directory's project folder and its git worktrees, so it never finds -work-app. Without dir, forkSession searches every project, which is how resume finds the same session.

The subagent launch lookup (subagentLaunchToolUseId, called with dir: runtimePolicy.cwd) has the same cwd pinning after a root change. Open PR #17596 is rewriting that call for custom Claude homes, so I left it out of the fix for this report.

Not a duplicate of #18260 (custom homePath, fixed in #18662): there the transcript was in a different Claude home. Here it is in the right home, but under an earlier project directory.

Impact

Major degradation or frequent failure

Version or commit

0.1.2-nightly.20261021.3457 (desktop, nightly)

Environment

macOS (Darwin 27), T3 Code desktop nightly, Claude Agent SDK 0.3.276, Claude provider on the default home.

Workaround

Symlink the transcript into the current directory's project folder: ln -s ~/.claude/projects/<old-slug>/<id>.jsonl ~/.claude/projects/<new-slug>/.