fix(web): viewed PR files stay folded when the Code tab is reopened

[Mnigos]

Fixes #13279.

Problem

Marking a changed file as Viewed folds it. The mark is persisted (host / environment store), but the folded-file set (toggledFiles) is local to PullRequestCodeTab and starts empty when the tab remounts, so whenever the tab mounts again (the panel is closed and reopened, another right-panel surface is shown and Code is returned to, or the commit scope changes and resets the fold set) every viewed file was expanded again while its tick stayed on. Switching among Summary, Timeline and Code does not remount the tab and was never affected, as the triage notes.

Fix

Folding stays what it is today, the reader's difference from the toolbar default rather than something derived from the ticks (so "fold all" still ticks nothing off). What changes is the start of a mount:

• usePullRequestFilesViewed exposes ready (the host has answered at least once; the marks query yields null until then, and that is not ready).
• foldViewedFilesOnce (pure, pullRequestDiff.logic.ts) takes the files on screen with their viewed state, the set of file keys already considered for this mount, the fold default and the current fold set. For every file it has not seen yet it records it by path (the diff's fileKey changes with the whitespace toggle, the path does not), and if that file is viewed (and not stale) folds it through the same toggleFileDiffFoldForViewed a tick uses. Files it has seen are left alone, so a file the reader unfolds by hand, or ticks later, is not touched again; every fold or tick the reader makes also marks the file as read for this mount, so a choice made before the marks arrive is kept too.
• The Code tab runs it in an effect once the marks are ready, per file as diff slices load, and resets the seen set together with the fold set when the scope (PR / commit) changes.

Tests

pullRequestDiff.logic.test.ts covers the helper: folds only the already-ticked files under an expanded default, changes nothing under a folded default, leaves a file it has already seen to the reader even if it is ticked now, recognises a file by its path after a whitespace toggle re-keys the diff, and folds only files that arrived since the last pass (23 tests pass across the diff logic and the viewed-files hook). Web typecheck and targeted lint are clean; the six lint warnings in PullRequestCodeTab.tsx are pre-existing and none is on a changed line.

Evidence

Captured in the web client on macOS 15.7.5 (Playwright, headless Chromium 1400×900, light appearance, "Default diff file state: Expanded") against isolated seeded servers, on main at 5cc99e1 and on this branch at 39a78e7. The fixture is a temporary four-file draft PR on my fork. On each build: open the PR's Code tab, mark the first two files Viewed, close the PR panel with its tab's close control, reopen the same PR and select Code. The marks were reset between the two runs.

	before (main @ 5cc99e1)	after (PR @ 39a78e7)
right after marking two files Viewed
after closing and reopening the panel

Recording, main first and then this branch: before-then-after.mp4.

Observed: on main both Viewed ticks survive the reopen but all four diffs are expanded again. On this branch the two viewed files stay folded and the two unviewed ones stay expanded. The captures are from 39a78e7; the one commit after it only makes an explicit Expand all or Collapse all outrank this fold (for ticks and files that load afterwards too) and does not change the path shown here. Not exercised in the client: that Expand all case, folds made before the marks finish loading and the whitespace toggle (both covered by pullRequestDiff.logic.test.ts), and the desktop and mobile clients.

Implemented with Claude Code (Claude Fable 5.1).

Summary by CodeRabbit

• New Features
  • Viewed files are automatically folded once their viewed status is ready. Files that are unviewed or already handled are left unchanged.
  • Your individual fold choices are preserved, and using Expand all or Collapse all prevents later automatic folding—including for files loaded afterward.
  • Automatic folding recognizes files by path even if their display key changes.

[macroscopeapp]

Approvability

Verdict: Approved at 7eb382a

Macroscope's review found this PR approvable — This is a focused, tested web bug fix that preserves viewed-file fold state without changing schemas, defaults, or sensitive production paths. A remaining medium-severity asynchronous fold-order finding represents a correctness risk, although the current head includes a guard intended to cover that case.

Notes:

• This verdict was updated automatically after the outstanding correctness findings were resolved. Macroscope did not re-review the code.

^{You can add or adjust custom eligibility rules. Learn more.}

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• apps/web/src/components/pullRequest/PullRequestCodeTab.tsx

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📝 Walkthrough

Walkthrough

The Code tab folds newly observed files marked as viewed after viewed-file tracking is ready. It tracks paths across file-key changes and stops automatic folding after the reader uses Expand all or Collapse all.

Changes

Viewed-file folding

Layer / File(s)	Summary
Fold-once logic apps/web/src/components/pullRequest/pullRequestDiff.logic.ts, apps/web/src/components/pullRequest/pullRequestDiff.logic.test.ts	Adds foldViewedFilesOnce to track paths and fold newly observed viewed files. Tests cover folded and expanded states, previously seen paths, path changes to file keys, and new arrivals.
Ready-gated Code tab integration apps/web/src/components/pullRequest/usePullRequestFilesViewed.ts, apps/web/src/components/pullRequest/PullRequestCodeTab.tsx	Exposes whether viewed-file tracking is ready. The Code tab calls the helper when tracking is ready, resets its seen-path and all-fold tracking when the diff scope changes, and marks paths seen when the reader toggles a file or changes its viewed state. Expand all and Collapse all prevent later automatic folding.

Priority: ⬇️ Low

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

Change: Bug fix · Severity of issue fixed: Low

Suggested reviewers: yordis

Merge Risk: 🔵 Low · up to 7eb38

After switching environments for the same PR, some viewed files may remain expanded instead of folding automatically. This is a bounded UI issue with a manual workaround, so the change is mergeable with follow-up.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Issue #13279 requires viewed files to remain folded after the Code tab reopens and to expand when the Viewed mark is cleared. PullRequestCodeTab.tsx waits for filesViewed.ready, folds current view…
Out of Scope Changes check	✅ Passed	The changes remain within issue #13279. PullRequestCodeTab.tsx, pullRequestDiff.logic.ts, and usePullRequestFilesViewed.ts implement readiness, viewed-file folding, path tracking, and scope rese…
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 4 functions across 4 files.
Title check	✅ Passed	The title clearly and concisely describes the main fix: viewed pull request files remain folded when the Code tab is reopened.
Description check	✅ Passed	The description is mostly complete. It explains the problem, fix, testing, observed results, screenshots, recording, limitations, and implementation model. The issue reference provides scope context, …

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Inline comments:
In `@apps/web/src/components/pullRequest/PullRequestCodeTab.tsx`:
- Line 273: Update the reset scope in PullRequestCodeTab so seen viewed paths
are cleared when environmentId changes, even if the PR and commit stay the same;
align it with the environment-aware scope used by usePullRequestFilesViewed.
- Around line 656-657: Update the viewed-file folding flow around
`foldViewedFilesOnce` to preserve explicit per-file reader actions made before
`filesViewed.ready`. Track those actions separately from parity-based
`toggleFile` state, and skip explicitly expanded files during automatic folding
while leaving other viewed-file folding behavior unchanged.

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• apps/web/src/components/pullRequest/PullRequestCodeTab.tsx
• apps/web/src/components/pullRequest/pullRequestDiff.logic.test.ts
• apps/web/src/components/pullRequest/pullRequestDiff.logic.ts
• apps/web/src/components/pullRequest/usePullRequestFilesViewed.ts

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[otavio]

Hit this independently on main @ ab099178a7: I marked files Viewed, closed the PR panel, and reopened it. The ticks stayed but the diffs were expanded again.

I wrote a local fix before I found this PR, and it came out almost the same: expose whether the marks have loaded (states !== null), then fold each viewed file once through toggleFileDiffFoldForViewed the first time it shows up, and clear the seen set when the scope changes. This PR goes further than mine. It keys the seen set by path, so the whitespace toggle doesn't re-fold files, and it keeps folds made before the marks load. So I'm dropping mine in favour of this.

I read through the diff (39a78e7) and found no blocking issues. +1 to merging.

Comment posted by Claude Opus 5.5 (Claude Code) on behalf of @otavio.