fix(web): Current checkout keeps a worktree base ref's existing worktree

[evolveperformance]

What Changed

On a new-thread draft, switching the workspace from New worktree to Current checkout now moves the draft into the selected branch's existing worktree ("Current worktree") when that branch is already checked out in another worktree. This matches what the branch picker does when you use it in the other order.

• BranchToolbar.logic.ts: new resolveExistingWorktreeForBaseRef helper, with unit tests.
• BranchToolbarBranchSelector.tsx: the handle exposes getBaseRefWorktree(), which returns the existing worktree for the selected base ref.
• BranchToolbar.tsx: handleEnvModeChange wraps onEnvModeChange for both the desktop and narrow workspace selectors. It sets the draft context the same way "Previous worktree" does.

Refs that live in the project checkout, or aren't checked out in any worktree, work as before. Server threads and multi-model drafts are unaffected.

Why

The result depended on which control you used first:

1. Current checkout → pick a branch that lives in a worktree: the draft moves into that worktree ("Current worktree"). ✅
2. New worktree → pick the same branch → Current checkout: in worktree mode the pick is stored only as the base ref (From <branch>, worktreePath: null). Switching to Current checkout just flipped envMode, so the draft fell back to the project checkout's branch. ❌

Both orders now end in the same state.

UI Changes

The only change is which workspace the selector ends on in scenario 2 ("Current worktree" instead of "Current checkout"). No visual changes.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for any UI changes
• I included a video for animation/interaction changes

Checked with BranchToolbar.logic.test.ts (75/75 passing) and tsc --noEmit for apps/web. There are no new lint warnings.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • When switching an eligible draft from a new worktree to the local workspace, the app can now reuse the selected base branch’s existing worktree and focus the composer there.
  • If no suitable existing worktree is available, the app continues with the standard environment-mode change.

[macroscopeapp]

Approvability

Verdict: Approved at d58e3f4

Macroscope's review found this PR approvable — This focused web bug fix preserves a selected base ref’s existing worktree when a draft switches workspace modes, while retaining prior fallback behavior and adding targeted unit coverage. It does not change product defaults, schemas, static-analysis settings, or sensitive/deployment code.

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📝 Walkthrough

Walkthrough

The branch selector now exposes the existing worktree for a selected base ref. When an eligible draft switches to local mode, the toolbar can use that worktree and request composer focus.

Changes

Base-ref worktree reuse

Layer / File(s)	Summary
Resolve and expose the selected base-ref worktree apps/web/src/components/BranchToolbar.logic.ts, apps/web/src/components/BranchToolbarBranchSelector.tsx, apps/web/src/components/BranchToolbar.logic.test.ts	The helper returns a secondary worktree path when the ref is checked out outside the active project. The selector exposes the selected base ref’s matching worktree. Tests cover secondary, active-project, missing-worktree, and null-ref cases.
Use the existing worktree during mode changes apps/web/src/components/BranchToolbar.tsx	For an eligible draft switching to local mode while its effective mode is worktree, the handler uses the selected base ref’s existing worktree when available and requests composer focus. Both mobile and desktop selectors use the handler.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~12 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant BranchToolbar
  participant BranchToolbarBranchSelector
  participant DraftContext
  BranchToolbar->>BranchToolbarBranchSelector: getBaseRefWorktree()
  BranchToolbarBranchSelector-->>BranchToolbar: selected branch and worktree path
  BranchToolbar->>DraftContext: set context to worktree and request composer focus

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Suggested reviewers: t3dotgg

Merge Risk: 🟡 Moderate · up to d58e3

Switching to Current checkout during a branch-search refresh can move a draft to the project checkout instead of the selected branch’s existing worktree. Preserve the selected worktree before merging.

Security Architecture Review

Security architecture risk: 🔵 Low · up to d58e3

The change reuses an existing worktree-selection path and is limited to eligible drafts. No new security issue was established, but validation of worktree ownership during later use was not verified.

Retained concerns
No architecture-level concerns identified.

Security review details

Security Blast Radius

• inferred — The immediate changed outcome is the workspace recorded for an eligible draft, not a new checkout operation or server-thread mutation. Later use of that workspace was not traced to an enforcement boundary.

Trust Boundaries and Controls

• observed — The selector obtains ref metadata through a query using the active environment and project/worktree directory, matches the selected branch name, and returns its path with that branch. The existing branch-picker flow already reuses VCS ref worktree paths; independent backend path-ownership validation was not verified.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 4 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 summarizes the main fix: preserving an existing worktree when switching to the current checkout.
Description check	✅ Passed	The description includes the required What Changed, Why, UI Changes, and Checklist sections. It explains the behavior, scope, testing, and absence of visual changes.
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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Actionable comments posted: 1

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🤖 Prompt to fix review comments

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only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
In `@apps/web/src/components/BranchToolbarBranchSelector.tsx`:
- Around line 568-570: Update the selected-base-ref worktree lookup around
resolveExistingWorktreeForBaseRef to retain the worktree path when the base ref
is selected. If listedActiveBranch and queriedActiveBranch are both unavailable
during a branch-search reset, use the cached path for the selected base ref
instead of passing a null refName; keep the existing lookup behavior when either
branch result is available.

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ℹ️ Review info

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Run ID: 6a316853-b5c7-46b3-bfe6-942a86050467

📥 Commits

Reviewing files that changed from the base of the PR and between e5a46d6 and d58e3f4.

📒 Files selected for processing (4)

• apps/web/src/components/BranchToolbar.logic.test.ts
• apps/web/src/components/BranchToolbar.logic.ts
• apps/web/src/components/BranchToolbar.tsx
• apps/web/src/components/BranchToolbarBranchSelector.tsx

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