fix(server): fall back when new worktrees are unavailable

[tris203]

Problem

When New threads defaults to New worktree, the first message can carry one atomic bootstrap request containing both createThread and prepareWorktree.

Two project states cannot satisfy that request:

1. A directory that is not a Git repository has no worktree source.
2. A freshly initialized Git repository has an unborn HEAD: Git reports a branch name, but no commit exists for git worktree add to branch from.

The server previously persisted thread.create before attempting git worktree add. When worktree creation failed, cleanup deleted the new thread, but event sourcing intentionally retained its ID as a tombstone. The client draft retained that same ID for retry. This produced a confusing sequence:

• First send: worktree creation fails, sometimes without a useful visible error.
• Second send: Orchestration command invariant failed (thread.create): Thread '<id>' already exists and cannot be created twice.

This could depend on client-side Git status timing, and server bootstrap requests from every client trusted the requested worktree mode without an authoritative preflight.

Fix

The server now preflights worktree bootstrap before persisting the thread:

• Detect whether the target directory is a Git repository.
• Resolve the requested local or origin base ref.
• Verify that the resolved ref names a commit with git rev-parse --verify <ref>^{commit}.
• Fall back to the project checkout when the directory is not a repository or the base has no commit.
• Preserve the existing worktree creation and setup-script path when a valid base commit exists.

Running the preflight before thread.create prevents deterministic repository/base-ref failures from leaving a thread tombstone behind.

Behavior

Project state	Requested mode	Result
Non-Git directory	New worktree	Thread starts in the project checkout
Git repository with unborn HEAD	New worktree	Thread starts in the project checkout
Git repository with a committed base ref	New worktree	A new worktree is created
Git repository with a resolvable origin base	New worktree + Start from origin	Origin is fetched and the worktree is based on the resolved commit

Reproduction

1. Set Settings → General → New threads to New worktree.
2. Add either a plain directory or a directory containing only git init with no commits.
3. Create a new thread and send its first message.
4. Before this change, the worktree command failed; retrying the same draft then hit the duplicate-thread invariant.

Verification

• pnpm exec vp test run apps/server/src/server.test.ts — 126 tests passed.
• pnpm --filter t3 typecheck — passed.
• Manual isolated-app verification covered:
  • a non-Git directory;
  • a Git repository with no commits;
  • a Git repository with an initial commit, confirming the positive worktree path remains intact.

Generated with GPT-5.6 Sol in T3 Code using the Codex harness.

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Note

Medium Risk
Changes first-message thread bootstrap and Git preflight behavior on the server; mistakes could skip worktrees or mis-route cwd, but fallbacks are narrow and covered by new integration tests.

Overview
Bootstrap worktree creation is now preflighted before thread.create, so failed worktree setup no longer leaves a thread tombstone that blocks retries with “cannot be created twice.”

GitWorkflowService gains isRepository (VCS detect → Git only) and hasCommit (git rev-parse --verify <ref>^{commit} with non-zero exit treated as false). In the WebSocket bootstrap path, origin/base resolution still runs when applicable, but createWorktree runs only when the project cwd is a Git repo and the resolved base ref points at a commit. Otherwise the flow creates the thread and starts the turn against the project checkout (no worktree meta update / setup on a missing worktree path).

Tests cover the new Git workflow helpers and two server integration cases: non-repository project cwd and unborn-head / missing base commit, plus stubs so existing bootstrap tests satisfy the new execute / work-tree checks.

^{Reviewed by Cursor Bugbot for commit 4c83fbf. Bugbot is set up for automated code reviews on this repo. Configure here.}

Note

Skip worktree creation in bootstrapProgram for non-Git repos and missing commits

• Adds GitWorkflowService.isRepository and GitWorkflowService.hasCommit to detect whether a path is a Git repository and whether a ref resolves to a commit.
• makeWsRpcLayer.bootstrapProgram in ws.ts now runs these checks before worktree preparation. For non-Git projects or base refs with no commit, it skips origin lookup, remote-base resolution, and worktree creation, then still dispatches the thread and turn.
• Adds server-router integration tests covering the non-repository and no-commit fallback paths, plus a successful Git execution fixture.
• Behavioral Change: bootstrap for non-Git projects or invalid base refs no longer attempts worktree creation; Git repositories with a valid base are unaffected.

^{Macroscope summarized 4c83fbf.}

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[cursor]

Cursor Bugbot has reviewed your changes using high effort and found 1 potential issue.

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^{Reviewed by Cursor Bugbot for commit 4c9498be6eeb2e6f47537752478757871168173c. Configure here.}

[macroscopeapp]

Approvability

Verdict: Approved at 4c83fbf

Macroscope's review found this PR approvable — This is a localized server bug fix that preflights repository and commit availability before creating a thread, preventing failed worktree setup from leaving unusable thread state. Valid worktree flows remain intact, and the fallback cases are covered by integration tests.

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