[NathanGlasby]

Problem

Choosing a comparison base with no common commit hides the diff panel's base selector. The choice is saved per thread, so reloading leaves the panel stuck with no way to select a valid base.

Change

Keep the existing comparison controls and branch choices available when the preview fails, using the thread's checkout and current Git status as fallbacks. Users can recover by choosing Automatic or another branch.

Scope and approval

Fixes #27547.

This is a small, focused fix for an obvious bug: the existing recovery controls disappear when a branch comparison fails. The change is limited to the shared web/desktop diff panel and its regression coverage.

Verification

• Both browser regression cases failed before the fix and pass afterward: a saved unrelated branch can be reset to Automatic, and a failing automatic base can be replaced with an explicit branch. The tests also check that the recovered choice is saved.
• vp test run --project browser src/components/DiffPanel.browser.test.tsx passed from apps/web, 2 tests.
• vp run check:changed --concurrency 1 passed.
• In the built-in Browser panel against an isolated development server, reproduced the error with an unrelated Git branch, reloaded with the invalid choice saved, and recovered the real file diff by selecting Automatic. The Electron shell was not tested separately.

Before	After, with the same error

After choosing Automatic:

Created with gpt-6.1-sol in Codex.

[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	⚠️ Failed 2026-10-30T14:27:07.407885Z We couldn’t complete this review. Comment @codex review to try again.	be5e194	PR opened

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[macroscopeapp]

Approvability

Verdict: Approved at be5e194

Macroscope's review found this PR approvable — The branch comparison selector remains available after preview errors, allowing users to choose another base. The change preserves existing comparison defaults and access gates and does not mutate repository contents.

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[coderabbitai]

Important

Review skipped

Review was skipped as selected files did not have any reviewable changes.

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Recent review info

Run configuration

• Source mode: Auto
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• Branch: main
• File: .coderabbit.config.ts
• Commit: 6575ce3
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Reviewing files that changed from the base of the PR and between be5e194 and 133af66.

Files selected for processing: 1

• apps/web/src/components/DiffPanel.browser.test.tsx

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Walkthrough

DiffPanel now derives fallback comparison refs and keeps branch-base selection available when eligible. Browser tests verify that users can recover from preview errors caused by unrelated branch histories.

Changes: Diff comparison recovery

Layer / File(s)	Summary
Comparison refs and branch-base eligibility apps/web/src/components/DiffPanel.tsx	DiffPanel derives fallback head and base refs. Local and remote ref queries use the preview cwd or active cwd, and local choices exclude the derived head.
Comparison controls and recovery tests apps/web/src/components/DiffPanel.tsx, apps/web/src/components/DiffPanel.browser.test.tsx	The comparison controls use the derived refs and appear when branch-base selection is eligible. Browser tests verify recovery after an unrelated saved branch or an automatic base produces an initial error.

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: t3dotgg

Merge Risk: Minimal · previous review 133af

The recovery controls remain available after preview errors, with no actionable merge-blocking risk identified.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title clearly and concisely describes the main change: keeping the web diff base selector available after comparison errors.
Description check		The description includes the required Problem, Change, Scope and approval, and Verification sections. It explains the bug, implementation, linked issue, tests, manual validation, screenshots, and the …
Linked Issues check		Issue #27547 requires recovery controls after a branch comparison has no common commit. DiffPanel.tsx keeps the comparison selector available for branch selection and derives fallback head and base …
Out of Scope Changes check		The changes stay within issue #27547. Production changes are limited to the shared diff panel. The added browser tests cover the reported comparison failure, recovery controls, and per-thread persiste…

Full details: Description check

Explanation

The description includes the required Problem, Change, Scope and approval, and Verification sections. It explains the bug, implementation, linked issue, tests, manual validation, screenshots, and the untested Electron shell.

Full details: Linked Issues check

Explanation

Issue #27547 requires recovery controls after a branch comparison has no common commit. DiffPanel.tsx keeps the comparison selector available for branch selection and derives fallback head and base refs from Git status, the stored selection, or Automatic. It also uses the active checkout when preview data lacks cwd. DiffPanel.browser.test.tsx covers recovery from a saved unrelated branch and from a failing automatic base. The tests verify that the recovered selection is persisted.

Full details: Out of Scope Changes check

Explanation

The changes stay within issue #27547. Production changes are limited to the shared diff panel. The added browser tests cover the reported comparison failure, recovery controls, and per-thread persistence. No unrelated production behavior is demonstrated.

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Additional comments: 1

apps/web/src/components/DiffPanel.browser.test.tsx: 1

209-210: Trivial · Maintainability & Code Quality · Quick win

Unverified finding
Verification ran but could not confirm this finding. It is shown for review, not as a verified issue.

Use vi.waitFor for the store assertions.

These plain expect calls do not follow the browser-test assertion rule. Wrap both store assertions in vi.waitFor.

As per coding guidelines, “Browser tests assert through expect.element or vi.waitFor.”

Source: Coding guidelines

---

Review info

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• Source mode: Auto
• Repository: pingdotgg/t3code
• Branch: main
• File: .coderabbit.config.ts
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Reviewing files that changed from the base of the PR and between 6575ce3 and be5e194.

Files selected for processing: 2

• apps/web/src/components/DiffPanel.browser.test.tsx
• apps/web/src/components/DiffPanel.tsx

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[maria-rcks]

Note

Written by gpt-6.1-sol on behalf of Maria

kept NathanGlasby's implementation and both regression cases. the fallback refs and checkout path are already the smallest correct fix i found. merged current main without rebasing; no product or test changes were needed. head: 3e833383f5c1183a7e7650e2fc36a61d49b5cda2.

verification:

• both existing browser cases fail on current main because the comparison selector disappears, then pass with this fix.
• blacksmith vp run check:changed github/main passes: format, lint, knip, affected typechecks, both browser cases, and react compiler checks.
• system chrome against the real dev server and a repository with unrelated history: the saved bad base survives reload, the selector stays available, choosing Automatic restores the real patch, and reload retains the recovered base. replay supplied the chat only; git supplied the diff.
• all 29 ci checks pass. two independent source reviews approve this head without findings. the old failed codex review produced no actionable finding; the latest automatic review reports no new changes to review.
• unverified: electron shell, native mobile, remote/relay/tunnel, and other providers. this change is confined to the shared web/desktop diff panel.

before on main:

after, same error and repository:

[maria-rcks]

Note

Written by gpt-6.1-sol on behalf of Maria

Verified in a real dev environment

verified as-is at 3e833383f5c1183a7e7650e2fc36a61d49b5cda2 on this linux vm. no code changes or pushes.

• ran github/main (6d46336476) in a separate worktree, then stopped it before installing and running the exact pr head. drove the real web client with repository playwright and system chrome.
• added a project through the app. a real codex gpt-6.1-sol turn initialized git, created main, feature/recovery and an unrelated orphan branch, committed changes, and left a working-tree edit. no replay, mocks or database fixtures.
• main: selected unrelated. git reported no common commit, the comparison selector disappeared, and reload preserved the trapped state.
• pr, same repository and saved selection: the selector remained available. selecting automatic restored the actual patch; reload retained the recovered selection.
• a second real codex turn appended a line and configured an unrelated automatic base. after reload, automatic failed. selecting explicit main restored the patch and survived reload.
• nearby behavior: uncommitted scope showed the expected working-tree line. latest-turn scope after the second turn showed exactly the new provider followup line, with no branch selector. the initial setup turn began outside git and had no usable initial checkpoint; the subsequent turn in the initialized repository produced a working checkpoint diff.
• blacksmith: installed dependencies and chromium, then ran cd apps/web && vp test run --project browser src/components/DiffPanel.browser.test.tsx: both cases passed. current head has 29 successful ci checks, zero failing or pending.

runtime transcript:

main dev: server 16733, web 8693
codex setup: completed; feature/recovery, main, unrelated; example.txt modified
main unrelated comparison: selector count 0, including after reload
pr dev: server 13773, web 5733
pr same error: selector count 1
automatic recovery: baseRef null persisted after reload; error count 0
failing automatic recovery: explicit main persisted after reload
latest turn: +1 -0, provider followup
blacksmith: 1 test file passed, 2 tests passed

Not verified

native electron, ios/android, macos/windows, remote/relay/tunnel, other providers, and permission-restricted sessions were not exercised. this pass verified local web and real codex. no product changes required a new check:changed run; focused browser regressions passed remotely. captures were inspected and uploaded video playback and seeking passed in chrome.