fix(web): the pull request Code tab keeps its diff after a refresh

[Brechard]

Note

🤖 Claude Sonnet 5.5 writing on behalf of Rodrigo

Problem

The pull request Code tab intermittently shows "This pull request has no file changes." and a "0 files" header for a PR that has changes. It appears a few minutes after the PR opens or after an agent turn, and clears on its own once the diff changes or the tab remounts.

The cause is in PullRequestCodeTab.tsx. A refresh (the panel's refreshToken goes up after a PR sync, an agent turn, or a manual refresh) empties the accumulated diff slices and refetches the first page. The slices were only refilled when the query returned a different data object, cursor or scope. Since #20850, an equal refetch keeps the previous data object, so after the reset data, the cursor and the scope all match what was already applied and nothing refills the slices. This happens whenever nothing beyond the first page is loaded, which is the normal case for a small or new PR.

Change

The tab now decides whether the current page is already applied by looking at the loaded slices, instead of tracking the data object's identity in a separate appliedPage state. A refresh shows the first page again right away and replaces it only if its content changed. The rule that a changed page drops the slices after it is unchanged. The existing content comparison became a small sameSlice helper used in both places.

Scope and approval

Very small, focused fix for an obvious bug, so submitted without a prior issue or discussion: a refresh of an unchanged diff leaves the tab permanently empty. It changes no setting, control or default, and no contract.

Verification

• New browser test PullRequestCodeTab.browser.test.tsx renders the real component with the real useEnvironmentQuery and useAtomRefresh, loads a one-file diff, bumps refreshToken, and has the refetch return the same page object. It expects the file to stay on screen. On upstream/main it fails with the "no file changes" message; with this change it passes.
• vp lint on both files and the apps/web typecheck are clean.
• Observed in the private build of the app: the server's diff request to GitHub returned HTTP 200 three times in eight seconds for a five-minute-old PR while the tab showed "0 files", which matches the client-side cause above.

Not checked: the fix in a live app, since the empty state cannot be staged without altering state, so there are no screenshots. The test fakes the equal refetch with a stand-in atom rather than the real environment query family. A second suspected path (selecting a commit or update range and switching back before its diff loads) is covered by the same change but has no test.

Written by Claude Opus 5.5 (fix and test) and Claude Sonnet 5.5 (PR) in Claude Code.

🤖 Generated with Claude Code

[macroscopeapp]

Approvability

Verdict: Approved at 815842c

Macroscope's review found this PR approvable — This is a focused bug fix that restores an existing pull request diff after an equivalent refresh, with the changed-page behavior preserved and a targeted browser regression test added. It introduces no new capability, schema, product default, deployment change, or static-analysis override.

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 5307c23 and 815842c.

📒 Files selected for processing: 2

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

📝 Walkthrough

PullRequestCodeTab now compares diff pages by their contents when refreshing. A changed page replaces its loaded slice and removes later slices. A browser test checks that an unchanged page keeps the file count visible after refresh.

Changes: Diff slice refresh handling

Layer / File(s)	Summary
Diff slice comparison and updates apps/web/src/components/pullRequest/PullRequestCodeTab.tsx	The code tab compares pages by cursor, patch, truncation status, next cursor, and ordered omitted-file statistics. It appends pages with new cursors, replaces changed slices and later pages, and leaves equal slices unchanged.
Refresh regression test apps/web/src/components/pullRequest/PullRequestCodeTab.browser.test.tsx	The browser test mocks a diff-page refresh with unchanged data and checks that the file count remains visible and the no-file-changes message does not appear.

Priority: ⬇️ Low

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

Change: Bug fix

Suggested reviewers: juliusmarminge

Merge Risk: ⚪ Minimal · up to 81584

The Code tab refresh fix has no identified merge-blocking issue. It is ready to merge after normal checks.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title is concise, specific, and accurately describes the main fix: preserving the pull request Code tab diff after a refresh.
Description check		The description includes all required sections. It explains the problem, fix, scope rationale, focused verification, limitations, and agent attribution. The missing screenshots are explicitly explaine…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description includes all required sections. It explains the problem, fix, scope rationale, focused verification, limitations, and agent attribution. The missing screenshots are explicitly explained because the live empty state could not be staged.

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