[Bug]: Sidebar thread label keeps the branch stamped at thread creation after the session switches worktree and branch

[gretschann]

Before submitting

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

Area

apps/desktop

What happens

The branch label (and the linked-MR badge) on a thread row in the sidebar is the branch
the thread started on. If the session later moves to a different worktree and checks out
a different branch, the row keeps showing the original value for the rest of the thread's
life. There is no refresh, and nothing in the row hints that it is a historical value.

Steps to reproduce

1. Open a project that has several git worktrees under .claude/worktrees/.
2. Start a thread from the main checkout while it is on some branch — here
   fix/preview-uri-expiry-retry, which had a linked MR !164.
3. In the thread, have the agent switch into an existing worktree (the EnterWorktree
   tool with a path) and then git checkout main there.
4. Look at the thread's row in the sidebar.

Notes

This looks like the exact divergence PR #8126 ("fix(web): sidebar follows a worktree
thread's live branch", closed unmerged 2026-08-25) described: the sidebar renders
thread.branch from persistent storage while the thread view uses the live
gitStatus.refName. That PR's own "Deviations" section notes that other thread-level
features still key off the stamped branch — which would explain the MR badge too.

Related: #8204, #8209.

Practical impact: with several worktrees open per project, the sidebar is not a reliable
answer to "where is this session working" — it silently reports a stale location.

Environment

• T3 Code:
• macOS 15 (Darwin 25.6.0), Apple silicon
• Project hosted on a self-hosted GitLab (MRs, not GitHub PRs)

Expected behavior

The row shows the branch the session is actually on — main, in the worktree it moved
into — or at minimum stops asserting a branch it is no longer on.

Actual behavior

The row still reads fix/preview-uri-expiry-... with the #164 badge, while the session
is in .claude/worktrees/home-screen-figma-design-8d2b90 on main. Verified from inside
the thread:

$ pwd
/Users/…/ggg-app-prometheus/.claude/worktrees/home-screen-figma-design-8d2b90
$ git rev-parse --abbrev-ref HEAD
main

!164 has also been merged and its remote branch deleted since the thread started, and
the badge still shows it — possibly the same root cause, since the MR is resolved from the
same stamped branch.

Impact

Major degradation or frequent failure

Version or commit

No response

Environment

No response

Logs or stack traces

Screenshots, recordings, or supporting files

No response

Workaround

No response

[juliusmarminge]

Triage

Confirmed on current main. The sidebar is showing the creation-time stamp, not the session’s live worktree/branch. Desktop is just hosting the web UI — this is not an apps/desktop-only bug.

What the row uses

• Branch label / tooltip / search row render persisted thread.branch (apps/web/src/components/Sidebar.tsx). Same stamp is used in the command palette and the mobile thread list.
• Git status for that row is thread.worktreePath ?? project.workspaceRoot, not the provider session cwd.
• The “checked out on another branch” warning only runs for local threads and compares the stamp to the main repo (resolveLocalCheckoutBranchMismatch). An EnterWorktree into .claude/worktrees/… does not trip it, so the row never looks historical.
• The MR badge is the same stamp path: useLinkedThreadPullRequest reads persisted linkedPullRequest / branchPullRequest / pullRequests, and ThreadPullRequestReactor looks up by thread.branch. Local threads also keep a merged/closed PR after the lookup goes empty. That matches !164 surviving merge + deleted remote.

Why the existing follow-up missed this repro

followWorktreeBranchDrift (apps/server/src/orchestration/Layers/CheckpointReactor.ts) does persist a dedicated worktree’s new HEAD at turn end. It refuses when worktreePath is null, when the worktree is shared, or when HEAD is detached / a temporary t3code/<hex> branch.

This thread started on the main checkout (worktreePath === null), then the agent used Claude’s EnterWorktree into an existing .claude/worktrees/… path and checked out main. T3 has no EnterWorktree handler and does not write that cwd back onto the thread. Drift-follow therefore never runs. #5159 / #4831 fixed the dedicated-worktree case only.

Both the sidebar and the thread toolbar query the persisted cwd, so this is not the “toolbar live / sidebar stale” split #8126 described. The live location in the report is the agent shell (pwd / git rev-parse).

Not a duplicate of

• [Bug]: Worktree threads lose their PR badge once the agent switches branches inside the worktree #4831 (closed; dedicated-worktree sync only)
• fix(web): sidebar follows a worktree thread's live branch #8126 (closed unmerged; display-only, missing shared/temp guards, would desync the PR badge)
• [Bug]: Branch name in session screen is not reactive #7409 (terminal checkout not refreshing UI)
• [Bug]: Diff shows prior branch's changes as deletions after switching checked-out branch mid-thread #8204 (stale diff base)
• [Bug]: Thread shows the base branch's PR when the branch tracks a non-default base #8209 (wrong PR for a non-default upstream)

Fix direction

Do not revive #8126 as the primary fix. Persist location on the server when the session cwd moves into a dedicated worktree, with the existing shared / detached / temp-branch guards. If the session is on a shared worktree (likely here — home-screen-figma-design-8d2b90 looks like another session’s tree), do not adopt that HEAD as thread.branch; at minimum stop asserting the old branch and its MR as current.

Leaving this open as an accepted bug.