fix: keep failed checkouts accurate and speed up branch switches

[Blankeos]

Summary

• Stop optimistically changing HEAD before checkout succeeds, so rejected checkouts keep the actual branch visible after dismissing the error.
• Make successful switches fast without speculation: read the confirmed HEAD hash/ref on the checkout worker and apply it before the next paint, without waiting for a full model reload.
• Start post-checkout refresh immediately instead of waiting through an idle 50ms/200ms input poll. Pending refreshes keep the input loop on its 16ms async cadence.
• Discard pre-checkout model/files-refresh results so stale data cannot overwrite confirmed HEAD. A failed metadata read falls back to the immediate background refresh without falsely reporting checkout failure.
• Preserve the busy-operation guard and normal push/pull/fetch refresh behavior.

Measured latency

Headless event-loop benchmark on a local two-branch fixture, 10 successful switches per mode; measures request to both displayed branch marker and HEAD identity updating (not total full-panel refresh or terminal rendering):

Auto-refresh	Before	After
Enabled	110.6ms median	36.8ms median
Disabled	258.4ms median	35.6ms median

Timing is machine/repository dependent. Git's checkout command and hooks are unchanged; the improvement removes application-side waiting after checkout.

Run the manual benchmark with cargo test checkout_visibility_latency -- --ignored --nocapture.

Regression coverage

• Rejected checkout due to conflicting local changes, error dismissal, retry, and preservation of edits via Space, previous branch (-), and ref picker (c).
• Confirmed HEAD updates before the full refresh for branch and detached tag checkouts.
• Stale in-flight refresh invalidation, metadata-read fallback, missing-ref branch creation, busy-operation handling, and normal remote-operation behavior.
• Nested branch names, annotated tags, and unborn HEAD metadata.

Validation

• cargo fmt --check
• cargo test — 295 passed, 1 manual benchmark ignored
• Manual checkout visibility benchmark — passed
• cargo clippy --all-targets — completed with warnings

Implemented in a separate worktree branched from origin/main; no edits made to the original worktree.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-06T17:25:20.138822Z	66fc823	PR opened

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[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 66fc823b16

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[chatgpt-codex-connector]

Refresh HEAD when checkout reports a post-hook error

When a repository has a post-checkout hook that exits nonzero, Git has already switched branches but propagates the hook's exit status; the official documentation confirms that the hook cannot affect the checkout outcome and only changes the command's exit status (Git githooks documentation). Here the closure consequently returns Err, while receive_remote_op_results does not request a refresh on errors; after removing the optimistic updates, the model therefore continues showing the old branch and hash even though the real HEAD moved. Refresh the model—or explicitly re-read HEAD—after a checkout error before deciding which branch to display.

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