fix(server): support local-only worktree bases

[frankleng]

Starting a thread from a local-only branch fails when the saved Start from origin preference makes bootstrap resolve a remote-tracking ref that does not exist. The valid local branch is never used, and the user only sees a generic GitVcsDriver.resolveRemoteTrackingCommit error.

After fetching origin, fall back to the selected local base branch when its remote-tracking commit cannot be resolved. Existing behavior is unchanged when the remote branch exists, and fetch failures still abort bootstrap. The server regression test now covers both a missing origin and a branch that exists only locally.

Tests:

• vp test run apps/server/src/server.test.ts -t "bootstraps first-send worktree turns|falls back to the local base branch"
• vp lint apps/server/src/ws.ts apps/server/src/server.test.ts --report-unused-disable-directives
• vp run --filter t3 typecheck
• git diff --check

Model: GPT-5.6 sol (medium)
Harness: T3 Code / Codex

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Note

Low Risk
Narrows bootstrap failure to fetch errors only; remote resolution success path is unchanged and covered by expanded regression tests.

Overview
Thread bootstrap with Start from origin no longer fails when the chosen base branch has no remote-tracking ref on origin. After a successful origin fetch, resolveRemoteTrackingCommit failures are treated as a miss and worktree creation keeps using the local base branch; when resolution succeeds, behavior is unchanged.

The integration test for this fallback is parameterized to cover both a missing origin remote and an existing origin where the base branch only exists locally, with expectations for fetch/resolve calls adjusted per scenario.

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Note

Fall back to local base branch in makeWsRpcLayer when remote tracking commit fails to resolve

When startFromOrigin is enabled and the origin remote exists, worktree bootstrap now wraps resolveRemoteTrackingCommit in a recovery path so that a missing remote branch silently falls back to the local base branch instead of propagating an error. The test in server.test.ts is parameterized to cover both scenarios: origin missing entirely, and origin present but the base branch absent on it.

^{Macroscope summarized 3388d31.}

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[Copilot]

Pull request overview

Fixes thread bootstrap when the Start from origin preference is enabled but the selected base branch has no remote-tracking ref (e.g., branch exists only locally). Instead of failing bootstrap with a generic GitVcsDriver.resolveRemoteTrackingCommit error, the server now falls back to using the local base branch after a successful origin fetch.

Changes:

• In worktree bootstrap, treat remote-tracking commit resolution failures as a miss and keep using the local base branch.
• Expand/parameterize the server regression test to cover both: missing origin, and origin present but base branch missing on origin.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
apps/server/src/ws.ts	Adds fallback behavior when resolveRemoteTrackingCommit fails during bootstrap with “Start from origin”.
apps/server/src/server.test.ts	Updates regression test to cover both missing-remote and missing-remote-branch scenarios.

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[macroscopeapp]

Approvability

Verdict: Approved at 3388d31

Macroscope's review found this PR approvable — This is a localized server bug fix that preserves existing remote-based worktree behavior while allowing local-only branches to fall back to the selected local base. The accompanying changes are focused tests with no production impact, and no schema, security, billing, or deployment surfaces are involved.

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