chore(server): port upstream git, Windows and speed fixes (2026-10-08)

[TheDarkPhantom]

The fork has not merged upstream since 2026-07-30. This PR hand-ports four upstream git fixes onto the fork's GitVcsDriverCore: index lock contention, Windows long paths, untracked-file CPU cost, and a worktree data-loss bug.

Ported

• fix(server): status polling no longer locks the git index pingdotgg/t3code#14718 status polling no longer locks the git index. Every git subprocess gets GIT_OPTIONAL_LOCKS=0. Numstat now uses the diff-index -M / diff-files plumbing commands. Unborn HEAD detection also recognises diff-index's bad revision 'HEAD'.
• fix(server): status refresh no longer pegs CPU in repos with thousands of untracked files pingdotgg/t3code#16771 (re-expressed) the review diff no longer pegs the CPU when a repo has thousands of untracked files. The fork's status refresh has no Changes totals, so upstream's literal fix has nothing to patch here. The fork's cost was in readUntrackedReviewDiffs, which spawned one git diff --no-index per untracked file: about 100ms each on Windows, and 5,001 files ran past a 60s timeout. Untracked files are now added as intent-to-add entries to an empty temporary index and diffed with a single git diff, the same technique upstream uses. Upstream's 5,000-file cap marks the untracked diff as truncated beyond that. The real index is never touched, and a test asserts this.
• fix(server): worktree cleanup no longer deletes files hidden by showUntrackedFiles=no pingdotgg/t3code#15834 worktree removal no longer deletes files hidden by status.showUntrackedFiles=no. git worktree remove now runs with -c status.showUntrackedFiles=normal. Avi Code addition: the fork's WorktreeCleanup had the same hole, in a worse form. Its isDirty flag came from git status, which hides those files. The cleanup dialog pre-selects "clean" dead worktrees, and the health monitor auto-removes them by deleting the directory outright. isDirty now comes from a new hasWorktreeChanges driver op that runs git status --porcelain --untracked-files=normal.
• Avi Code addition: WorktreeCleanup now fails closed. If the hasWorktreeChanges dirty check errors, the worktree is treated as dirty, so the health monitor never auto-removes it and the dialog does not pre-select it. Before, a failed check counted as clean. A test covers a failing check.
• fix(server): Windows worktrees with long paths no longer fail or strand pingdotgg/t3code#14917 Windows worktrees with long paths no longer fail or get stranded. On win32, core.longpaths=true is appended to each git subprocess via GIT_CONFIG_COUNT/KEY/VALUE, keeping any inherited entries.

Skipped

• fix(server): stop the startup project sync from delaying the app window pingdotgg/t3code#14912 (stop the startup project sync from delaying the app window): the fork has no startup auto-pull. That came from upstream feat(projects): automatically pull clean default branches pingdotgg/t3code#9277 (2026-09-02), which the fork has not merged, so there is no project sync to move off the startup path.

Verification

• vp test run (before the fail-closed commit) on GitVcsDriverCore, GitWorkflowService, WorktreeCleanup, WorktreeCleanupExecute, WorktreeHealthMonitor, ReviewService and VcsStatusBroadcaster tests: 101 passed, 1 failed. The failure is preserves newline characters in worktree paths when listing refs, which also fails on unmodified origin/main on Windows because Windows cannot create a path containing a newline.
• With each fix reverted, its new test fails: the index bytes change; the uncapped untracked diff contains bulk/; the hidden worktree file gets deleted.
• Fail-closed commit: WorktreeCleanup, WorktreeCleanupExecute and WorktreeHealthMonitor tests pass (29/29), and the new test fails with the old fail-open behaviour.
• vp lint and vp fmt --check pass on the changed files. tsgo --noEmit -p apps/server/tsconfig.json reports no errors. vp run check:avicode and vp run test:avicode (7/7) pass.

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