🤖 fix: delete local branch on workspace delete

[ThomasK33]

This changes workspace deletion for local worktree workspaces to also delete the associated local git branch.

• Normal delete uses git branch -d (safe; only deletes if merged)
• Force delete uses git branch -D
• Adds guardrails to avoid deleting protected branches (e.g. main) or branches still checked out elsewhere

UI copy is updated (desktop + mobile) so users understand that deleting a workspace also deletes the branch.

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📋 Implementation Plan

Plan: Delete workspace also deletes its git branch

Summary (what will change)

• Archive remains non-destructive (metadata timestamp only).
• Delete workspace will remove:
  1. the git worktree directory (existing)
  2. the associated local git branch by default (new)

Behavior details (per decisions captured):

• Safe by default: normal delete uses git branch -d <branch> (only deletes if git considers it merged).
• Force delete uses git branch -D <branch> (matches existing force: true semantics).
• No remote deletion: we will not delete origin/<branch>.
• SSH runtimes: keep simplest safe behavior (directory removal only; no explicit remote branch deletion).

Net LoC estimate (prod code): ~80–140 LoC (mostly WorktreeRuntime + UI copy).

Current behavior (confirmed in repo)

• Delete call flow:
  • WorkspaceContext.removeWorkspace() → api.workspace.remove() → workspaceService.remove() → runtime.deleteWorkspace()
• WorktreeRuntime.deleteWorkspace() already does best-effort branch deletion, but only when the workspace name starts with agent_.
• SSHRuntime.deleteWorkspace() deletes the remote directory only (no explicit git branch -d/-D).

Recommended approach

1) Backend: generalize branch deletion in WorktreeRuntime.deleteWorkspace

Files:

• src/node/runtime/WorktreeRuntime.ts
• (optional helper) src/node/git.ts

Steps:

1. Change the branch-deletion gate

   • Today:
     • shouldDeleteBranch = !isInPlace && workspaceName.startsWith("agent_")
   • Proposed:
     • shouldDeleteBranch = !isInPlace (delete branch for all worktree workspaces, not just agent_*).

2. Add safety checks before deleting the branch (defensive, and errs on “skip deletion” rather than “delete the wrong thing”):

   • If branch does not exist locally (await listLocalBranches(projectPath)): skip.
   • If branch is the repo’s detected trunk (detectDefaultTrunkBranch(projectPath)) or the current branch in the main worktree (getCurrentBranch(projectPath)): skip.
   • If branch is still checked out by another worktree (parse git -C <projectPath> worktree list --porcelain and see if any remaining worktree reports branch refs/heads/<name>): skip.

3. Deletion command

   • Keep existing deleteFlag behavior:
     • force=false → git branch -d "<branch>"
     • force=true → git branch -D "<branch>"

4. Keep deletion best-effort

   • Continue treating branch cleanup as non-blocking (never fail workspace delete just because git branch -d failed).
   • Upgrade logging so it’s clear whether we skipped due to guardrails vs git failure.

2) UI: update delete UX copy to reflect branch deletion

Goal: make it obvious that “Delete” now also targets the branch.

Files / call sites to update:

• Desktop command palette: src/browser/utils/commands/sources.ts (confirm("Remove current workspace…"))
• Archived view:
  • src/browser/components/ArchivedWorkspaces.tsx tooltip/copy around “Delete permanently”
  • src/browser/components/ForceDeleteModal.tsx warning text (“Force delete” should mention branch deletion too)
• Mobile: mobile/src/screens/ProjectsScreen.tsx delete confirmation + force delete wording

Copy guidance:

• Mention local branch by name where feasible.
• Mention that normal delete is “safe” (may not delete branch if unmerged) and that Force Delete is destructive.

3) Tests

1. Unit tests (src/node/runtime/WorktreeRuntime.test.ts)

   • Add coverage for a non-agent_ branch:
     • Force delete (force=true) removes the branch.
   • Add coverage for safe delete (force=false) on a merged branch:
     • Create branch → commit → merge into main → delete workspace → branch removed with -d.
   • Add a guardrail test:
     • Workspace on main can be deleted as a worktree, but main branch must not be deleted.

2. Integration test (optional but valuable)

   • Extend tests/ipc/removeWorkspace.test.ts for local runtime:
     • Create workspace branch, then remove with { options: { force: true } }, assert git branch --list <branch> is empty in the main repo.

Alternatives considered (not recommended for this iteration)

• Add a “keep branch” checkbox / option to workspace.remove

  • Pros: avoids deleting user-provided existing branches.
  • Cons: requires API/schema changes, UI affordances across desktop + mobile, and new persistence semantics.

• Delete only “Mux-created” branches (e.g. track whether branch existed at creation time)

  • Pros: safest.
  • Cons: needs new metadata field + backfill semantics for existing workspaces.

Given the explicit desire for “delete means delete” now that archiving exists, the simplest consistent behavior is: delete branch by default, with strong guardrails and clear UI copy.

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Generated with mux • Model: openai:gpt-5.2 • Thinking: xhigh