fix(web): PR code tab no longer reloads when turns finish or the PR updates

[Gigioxx]

Problem

Fixes #14483. The PR panel's Code tab threw away every loaded diff page and showed "Loading pull request diff..." whenever a turn finished anywhere in the environment, or when the pull request's updatedAt moved (comments, reviews, pushes). Both background signals reused the Refresh button's token. A reader lost the diff and their scroll position mid-review even when nothing in it changed.

Change

The Code tab now takes two tokens:

• refreshToken: the Refresh button only. Same hard reset as before.
• backgroundRefreshToken: finished turns plus new updatedAt revisions. Every loaded page stays on screen. The tab re-reads them in order from the first page, and only accepts answers fetched after the refresh began, so a cached page cannot vouch for itself. An unchanged page moves the walk to the next one. A changed page replaces itself and drops the pages after it, since their cursors pointed into the old diff. Loading the next page waits until the walk catches up.

The slice reconcile step moved into reconcileDiffSlices in pullRequestDiff.logic.ts so it can be tested on its own.

This supersedes the turn-only part of #13835 and also covers the updatedAt path described in the triage.

Verification

Isolated Playwright browser against a worktree dev server with fresh .t3 state. A second tab sent a one-line prompt in an unrelated thread, so a turn completed in the same environment while the Code tab was open.

Multi-page: #14215, 476 files across 5 diff pages, all loaded, scrolled near the bottom.

	Files in Code tab	Diff scroll position	Loading state
Before (main)	476 to 100+	13732 to 0	pages dropped
After	476 throughout	13732 throughout	never shown

• Recording, before: multipage-before.mp4
• Recording, after: multipage-after.mp4

Before, after the turn	After, after the turn

A temporary console trace (removed before commit) confirmed the walk in the after run. Each of pages 1 through 5 first saw its cached answer, refreshed it, then advanced once the fresh answer matched.

Single page: #14497. Before, the diff unmounted to the loading skeleton with "0 files". After, it stayed mounted with no loading state, across repeated turns.

Before	After

Tests and checks:

• vp test run apps/web/src/components/pullRequest/pullRequestDiff.logic.test.ts: 17 passed. The new cases cover appending a page, walking forward through unchanged pages, and replacing a changed later page while dropping the pages after it.
• Web typecheck is clean. Lint shows no new warnings in the changed files.
• A Codex review of the branch found no actionable issues.

Not checked live:

• The updatedAt path. It needs a pull request that changes while open, and it uses the same token as the turn path.
• A later page whose content actually changes.

Unrelated, seen on main too: the first diff read sometimes fails with a 503 when an earlier request is aborted (499) while a shared fetch is in flight. Reloading recovers.

Made with Claude Opus 5.5 in Claude Code (via T3 Code).

[macroscopeapp]

Approvability

Verdict: Approved at 5588b4a

Macroscope's review found this PR approvable — This is a focused two-file bug fix that separates explicit refreshes from background updates and preserves the loaded pull-request diff while refreshing its data. The runtime impact is localized to existing diff-query caching and rendering, with no schema, default, static-analysis, security, or infrastructure changes.

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📝 Walkthrough

Walkthrough

The PR detail panel now sends background refreshes separately from manual refreshes. When the background token changes, the code tab refreshes diff and viewed-file data, discards later loaded slices, and resets the cursor while retaining the first slice until updated data arrives.

Changes

PR code tab background refresh

Layer / File(s)	Summary
Separate refresh tokens and update diff data apps/web/src/components/pullRequest/PullRequestDetailPanel.tsx, apps/web/src/components/pullRequest/PullRequestCodeTab.tsx	The detail panel separates revision and turn refreshes from manual refreshes and passes the background token to the code tab. The code tab refreshes cached diff queries for later slices, removes those slices, resets the cursor, and refreshes the first diff page and viewed-file state.

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

Change: Bug fix · Severity of issue fixed: Low

Suggested reviewers: juliusmarminge

🚥 Pre-merge checks | ✅ 3 | ❌ 2

❌ Failed checks (2 warnings)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description explains the problem, implementation, verification steps, screenshots, limitations, and agent usage. It does not provide the required Scope and approval information, such as maintainer…	Add a Scope and approval section. Link the triaged issue with explicit maintainer approval and the approval comment, or explain why this is a small, focused, obvious bug fix that does not require prior approval.
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main fix: preventing the PR Code tab from reloading after turns finish or the pull request updates.
Linked Issues check	✅ Passed	The changes satisfy issue #14483. PullRequestDetailPanel now separates manual refresh state from background refresh state. PullRequestCodeTab keeps the first diff slice mounted while it rereads da…
Out of Scope Changes check	✅ Passed	The changes remain within issue #14483. The new backgroundRefreshToken and slice-refresh logic directly support incremental PR diff updates. The separate token preserves the existing manual Refresh …

Full details: Description check

Explanation

The description explains the problem, implementation, verification steps, screenshots, limitations, and agent usage. It does not provide the required Scope and approval information, such as maintainer approval or an explanation of why this focused bug fix qualifies for an exemption.

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Actionable comments posted: 1

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Inline comments:
Review comments at @apps/web/src/components/pullRequest/PullRequestCodeTab.tsx:
- Line 470: Update the refresh handling that assigns `previous.slices.slice(0,
1)` so background token changes retain all currently loaded slices and keep
files and comment editors visible. Replace or remove stale slices only after
refreshed data confirms the diff changed.

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ℹ️ Review info

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Run ID: 37bc4dc8-1245-4d7a-b0c7-c3bdd4b634ff

📥 Commits

Reviewing files that changed from the base of the PR and between 0cf482b and 5588b4a.

📒 Files selected for processing (2)

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

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[juliusmarminge]

Note

This comment is posted by Julius' dot

Closing for incomplete UI verification. The screenshots show loading and loaded states, but this fix needs a recording showing the diff staying visible and preserving the reader's place during a background refresh. The new later-page invalidation is also explicitly untested.

Please add matching before/after recordings and a focused multi-page check showing later pages refresh without losing the reader's place, then request reconsideration.

[Gigioxx]

[claude-opus-5-5] Responding on behalf of Guille

Thanks. This PR can't be reopened after the force-push, so the fix continues in #14539. It adds before/after recordings on a 476-file, 5-page PR, a focused test for the page reconciliation, and a fix for the CodeRabbit finding (later pages now stay mounted and are revalidated in place). Requesting reconsideration there.