fix(web): branch picker no longer interrupts a running turn

[ScottN-PV]

Problem

Picking a ref that lives in another worktree while a turn runs moves the thread there and ends the run. The picker stops the provider session, and the server detaches it on any worktree change. The timeline reads "Run interrupted by user", and nothing links that to the branch pick. Picking the main checkout's ref from a worktree thread does the same.

Change

While Stop is offered for the thread, the picker disables every ref that would move the thread to another worktree. The list footer reads "Stop the current turn to switch worktrees." The guard reuses the rule that shows Stop (deriveCanInterruptRunningThread), so it also covers preparing, waiting, and a queued run behind an active one.

• Refs that keep the thread in its worktree stay selectable, and so does creating a ref.
• Enter on a disabled row does nothing. Handlers read the thread's latest runtime and worktree path from the store when they act, so a run or a move from another client counts before the picker re-renders.
• If a run is active when a checkout or a ref creation returns, and finishing the pick would move the thread to another worktree, the thread stays where it is. A warning toast says the ref was checked out or created. The picker's own session stop reads the same state.

Once the run ends, the picker behaves as before.

Scope and approval

Closes #14245. Maintainer triage there (comment) asked that the picker "either disable selections that change worktreePath, or confirm that the turn will be interrupted." This PR disables them.

This rebuilds #14289 on V2's run state. That PR was closed after the V2 merge because it used the removed session model (closure comment).

The server still accepts the move, because V2's MCP worktree handoff moves its own thread mid-run. This picker checks the latest state the client has received. Entry points without this guard, such as mobile's Create worktree, and a run or move that has not reached this client yet, can still interrupt a run.

Verification

An agent ran these checks in the web client on a Linux dev box, with an isolated home and Codex gpt-6-astra. The fixture has a main checkout on main and a worktree on repro-wt.

Before, on 43bd6677: with a turn running sleep 90, repro-wt is selectable. Picking it moved the thread, and the server marked the run interrupted in the same second.

before-select.mp4

After, captured on f827e4ae: repro-wt is disabled and the footer shows the notice. A click and Enter on the row left the run running on the server. After Stop, the row was selectable, the thread moved, and the next turn's pwd printed the worktree path. From the worktree, main is disabled the same way. On 371f9026, a worktree thread gave the same results: main was disabled with the notice, a click on it left the run running, and after Stop the thread moved to the main checkout.

after-blocked-stop-select.mp4

Second client during a checkout: from an idle thread in the worktree, the web client picked a ref that has no worktree, and a post-checkout hook held the checkout for 8 s. During the hold, a scripted second client (WebSocket RPC) moved the thread to the main checkout and started a sleep 30 turn there.

• Before, on f827e4ae: when the checkout returned, the picker moved the thread back to the worktree. The server detached the session and marked the run interrupted 48 ms later. No toast appeared.

  
  x-v2-before.mp4

• After, on 76525dcd: the warning toast appeared, the client sent no metadata update and no stop, and the run completed in the main checkout. The details panel covers part of the toast in the recording.

  
  x-v2-after.mp4

Second client during a ref creation: the same setup, but the web client created a new ref, which the hook also held for 8 s.

• Before, on 76525dcd: when the creation returned, the picker stopped the session, interrupting the run, and moved the thread back to the worktree.

  

• After, on 371f9026: the toast "Created x-v4-after, but this thread stayed in its current worktree." appeared, the client sent no stop and no metadata update, and the run completed in the main checkout. Without a second client, creating a ref kept the thread in its worktree on the new ref, as before. The details panel covers part of the toast in the frame and the recording. The text comes from the client's DOM log.

  
  x-v4-after.mp4

When the picked ref is main and the second client has already moved the thread there, f827e4ae let the run continue but showed the toast although the thread was already there. 76525dcd showed no toast and sent no stop, and the run completed.

• vp test run src/components/BranchToolbar.logic.test.ts in apps/web: 90 of 90 pass, 14 new. With the guard returning false, the 7 blocking cases fail and the other 83 pass. These tests cover the blocking rule. The captures above cover which thread state the handlers read.

• On 371f9026, vp run --filter @t3tools/web typecheck exits 0. vp lint and vp fmt --check on the four changed files report no warnings, errors, or format changes.

• Rebased onto 09c5e7a (refactor: prune narration and history comments #19559 comment pruning); 88 focused tests and package typecheck pass on MSI-DEV-BOX. Revert limitation: The guard is a new export, so restoring current-main production files makes the added cases fail with a missing-function TypeError. Raw current-main revert is recorded separately with source confirmation that selectBranch directly retargets an existing worktree without a runtime guard; existing real-client captures in the PR prove handler wiring.

• Rebased onto 16e6a6ab50 (perf(web): the branch toolbar selector compiles without manual memoization #20567 React Compiler branch selector): 94 focused tests pass, the revert check fails as expected, and typecheck passes on MSI-DEV-BOX.

• Rebased onto 4b1024dafe (refactor(web): the branch selector keeps its caching without "use memo" #20822/perf(web): the open thread's chat chrome no longer re-renders on every streaming tick #20860 branch selector): 100 focused tests pass, the revert check fails as expected, and typecheck passes on MSI-DEV-BOX.

• BranchToolbarBranchSelector.test.tsx (jsdom) opens the picker in both layouts with a running thread on the main checkout and a leftover worktree draft. main stays selectable, and picking it updates the thread without a stop. Both cases fail without 4e4e8fb5's selector change. The client removes that draft once the thread starts, so this state has no capture. On 4e4e8fb5, vp test run src/components/BranchToolbar.logic.test.ts src/components/BranchToolbarBranchSelector.test.tsx src/components/BranchToolbar.panel.test.tsx in apps/web passes all 94 tests. Restoring the parent selector makes exactly these two enabled-row assertions fail; the other 92 tests pass.

• On 2c31ea5bbb, six new jsdom cases in BranchToolbarBranchSelector.test.tsx simulate a thread store ahead of the rendered state, as if another client had moved the thread to a worktree and started a run. They cover a pick of the default ref and of a non-default ref from the base list, and the automatic base-branch default, in both layouts. In each case the picker sends no stop, checkout or metadata update. All 100 focused tests, format, lint and web typecheck pass on MSI-DEV-BOX. With the selector restored from 24eb554680, all six cases fail because the picker calls the mocked session-stop command. This change was not run in a live client.

Not checked: Claude and the other providers, the desktop app, and mobile. The guard reads only the thread's run status and does not depend on the provider.

Not reproduced: a click on a stale row right after another client moves the thread. On both f827e4ae and 76525dcd the client re-rendered about 0.4 s after the server accepted the move, and the list reloaded with the row disabled. The handler change for that moment is checked by reading the code only.

Model: Claude Opus 5.5, Claude Fable 5.1 (review), GPT-6-Astra (review), GPT-6.1-Sol. Harness: Claude Code, Codex.

[macroscopeapp]

Approvability

Verdict: Approved at d4d3df7

Macroscope's review found this PR approvable — This is a focused web bug fix that prevents existing branch-picker actions from detaching active runs, including stale-state races during checkout and ref creation. The production change is localized and supported by targeted logic and component tests, with no schema, deployment, security, or static-analysis configuration impact.

^{You can add or adjust custom eligibility rules. Learn more.}

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📝 Walkthrough

The branch picker now blocks worktree changes during active runs. It checks the latest thread state before selection and after checkout or ref creation. It disables affected branch rows and displays a warning when a change is blocked.

Changes: Worktree change guard

Layer / File(s)	Summary
Define and test the worktree change predicate apps/web/src/components/BranchToolbar.logic.ts, apps/web/src/components/BranchToolbar.logic.test.ts	isWorktreeChangeBlocked blocks changes to a different worktree when the runtime indicates an interruptible running thread. Tests cover active and inactive statuses, queued runs, same-worktree selections, and returns to the main checkout.
Guard branch selection and show blocked state apps/web/src/components/BranchToolbarBranchSelector.tsx, apps/web/src/components/BranchPicker.tsx, apps/web/src/components/BranchToolbarBranchSelector.test.tsx	The selector reads the latest thread state before selection and rechecks it after checkout or ref creation. If a change is blocked, it skips the thread update, restores the optimistic branch when needed, and displays a warning. The picker disables affected rows and supports notices and extra data for row updates. Tests cover toolbar and panel selection, including a null server worktree path.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix · Severity of issue fixed: Medium

Sequence Diagram(s)

sequenceDiagram
  participant BranchToolbarBranchSelector
  participant ThreadEntityStore
  participant BranchCheckout
  participant ThreadMetadata
  participant BranchPicker
  BranchToolbarBranchSelector->>ThreadEntityStore: Read latest runtime and worktree path
  BranchToolbarBranchSelector->>BranchCheckout: Checkout selected branch
  BranchToolbarBranchSelector->>ThreadEntityStore: Recheck runtime and worktree path
  BranchToolbarBranchSelector->>ThreadMetadata: Update branch when worktree change is allowed
  BranchToolbarBranchSelector->>BranchPicker: Provide blocked-row state and notice

Loading

Suggested reviewers: juliusmarminge

Merge Risk: 🔵 Low · up to d4d3d

Branch selection is intended to keep an active turn from being interrupted by a worktree change. The code contains post-checkout and post-creation guards, but the new tests do not cover a run starting while either operation is pending, leaving a regression-coverage gap. The change is mergeable with a focused test follow-up.

Security architecture risk: 🔵 Low · up to d4d3d

The change reduces accidental interruption of running turns without adding permissions or broader access. Protection still depends on client-visible state rather than an atomic server-side rule, so concurrent actions remain a limitation.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The changed behavior operates on existing branch actions, worktrees, and thread metadata within the selected environment. The comparison adds no server endpoint, credential authority, or deployment change; no expansion of attacker-controlled reachability was established.

Trust Boundaries and Controls

• observed — Git actions continue to recheck source-control write permission and, for server threads, orchestration-operate permission. Metadata application also rechecks orchestration permission. Runtime-based row disabling supplements these controls rather than replacing them.

Resilience and Maintainability Implications

• inferred — Residual stale-update and run-start races predate this PR. The server supports optional expected-worktree and expected-branch checks, but this client command does not forward those conditions. A latest-state read is therefore not an atomic ownership guarantee, although the new checks reduce previously unguarded transitions.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title clearly and concisely describes the primary web change: preventing the branch picker from interrupting a running turn.
Description check		The description includes all required sections. It explains the problem, implementation, scope approval, verification results, limitations, screenshots, and agent details. It is detailed and directly …
Linked Issues check		[#14245] The web branch picker blocks refs that change the thread worktree while deriveCanInterruptRunningThread reports an interruptible run. The rule covers preparing, starting, running, waiting, …
Out of Scope Changes check		The changes in BranchToolbar.logic.ts, BranchToolbarBranchSelector.tsx, and BranchPicker.tsx implement the worktree-change guard, current-state checks, notices, and row refresh required by [#142…

Full details: Description check

Explanation

The description includes all required sections. It explains the problem, implementation, scope approval, verification results, limitations, screenshots, and agent details. It is detailed and directly related to the changes.

Full details: Linked Issues check

Explanation

[#14245] The web branch picker blocks refs that change the thread worktree while deriveCanInterruptRunningThread reports an interruptible run. The rule covers preparing, starting, running, waiting, and queued runs. Same-worktree refs and ref creation remain available. BranchToolbarBranchSelector reads current thread state when actions execute and rechecks state after asynchronous checkout or ref creation. It preserves the current worktree and shows a warning when a newer run or worktree move appears. The supplied logic and selector tests cover blocked refs, allowed refs, stale store state, and both picker layouts.

Full details: Out of Scope Changes check

Explanation

The changes in BranchToolbar.logic.ts, BranchToolbarBranchSelector.tsx, and BranchPicker.tsx implement the worktree-change guard, current-state checks, notices, and row refresh required by [#14245]. The added logic and tests support branch selection behavior. No unrelated change is evident in the supplied whole-PR summary.

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Inline comments:
Review comments at @apps/web/src/components/BranchToolbarBranchSelector.tsx:
- Line 468: Update currentWorktreePath in resolveBranchSelectionTarget to use
latestThread.worktreePath whenever latestThread exists, including when that path
is null; fall back to activeWorktreePath only when latestThread is absent.
- Around line 427-431: Update the selection handler around readThreadShell and
isWorktreeChangeBlockedForRef to resolve the current worktree path from the
latest thread state, then use that path for both the guard and selection target
instead of the stale render-time path. Preserve the existing behavior when no
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Review comments at @apps/web/src/components/BranchToolbarBranchSelector.tsx:
- Around line 538-557: Update the post-create guard in the branch selector to
read the latest thread shell path for currentWorktreePath, falling back to
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- Line 748: Update the `extraData` value in the `BranchToolbarBranchSelector`
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🧹 Nitpick comments: 1

apps/web/src/components/BranchToolbarBranchSelector.test.tsx: 1

128-250: 🎯 Functional Correctness | 🔵 Trivial | ⚡ Quick win

Exercise the post-await guard in the selector tests.

The added cases change latestStarted and latestWorktreePath before the click. The selection then exits at the pre-action guard and never awaits checkout or ref creation. Add deferred switchRef and createRefMutation cases that change the latest thread state while the promise is pending, then assert that neither stopSession nor metadata update runs. Otherwise, removing the post-checkout or post-create guard can pass these tests.

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Review comment at @apps/web/src/components/BranchToolbarBranchSelector.test.tsx
around lines 128 - 250:
Update the tests for the selection flow in BranchToolbarBranchSelector to cover
both deferred switchRef and createRefMutation operations. Change latestStarted
and latestWorktreePath while each operation is pending, then resolve it and
assert that neither stopSession nor updateMetadata runs; ensure the selection
passes the pre-action guard so the post-await guard is exercised.

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Review comments at
@apps/web/src/components/BranchToolbarBranchSelector.test.tsx:
- Around line 128-250: Update the tests for the selection flow in
BranchToolbarBranchSelector to cover both deferred switchRef and
createRefMutation operations. Change latestStarted and latestWorktreePath while
each operation is pending, then resolve it and assert that neither stopSession
nor updateMetadata runs; ensure the selection passes the pre-action guard so the
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