Agentic Review [2]: Remove baseline / side-by-side compare subsystem

[yannbf]

What I did

Removes the entire latest-vs-baseline side-by-side compare subsystem from the review addon (decision Q5). This is PR2 of a 5-PR stack integrating the review feature into core. It telescopes on PR1 (#35218) — review bottom-up.

Compare is an unreleased sub-feature (it lives on next via #34837), so this is maintenance, not a breaking change.

• Deleted files: ReviewCompareTool.tsx, ReviewPreviewWrapper.tsx, screens/useBaselineComparison.ts.
• De-baselined: removed the compare menu (Latest/Baseline/Split), hasBaseline, CompareMode/DEFAULT_COMPARE_MODE, PREVIEW_MODE_SESSION_KEY, the baselineStoryIds fetch + diff, and the compareMode/showCompare/setCompareMode store surface.
• Server: removed the dev-server baseline proxy (experimental_devServer, STORYBOOK_REVIEW_BASELINE, BASELINE_PROXY_PATH) and dropped the http-proxy-middleware dependency; sirv is no longer used by the review addon. experimental_serverChannel (the review cache + module-graph staleness) is kept — it moves to core-server in PR4.
• "Newly added" now derives solely from change detection's new status (previously it was change-new OR absent-from-baseline).

Incidentally resolves the Pane/LatestPane styled-component duplication, the dead latestPaneRef, and useBaselineComparison's unused return surface.

Stack position

Base: review-core/01-standalone-fixes (PR1, #35218) → yann/agentic-review-mcp-integration (#34837).

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

For a maintainer to verify compare is gone and review still works:

1. Run a sandbox (yarn task sandbox --template react-vite/default-ts --start-from auto) or cd code && yarn storybook:ui.
2. Push a review (via the display-review MCP tool / scripts/display-review.ts) and open one of the curated stories.
3. Expected: the canvas shows a single normal preview — no split/compare panes, and the review toolbar header has no "Compare mode" (Latest/Baseline/Split) menu.
4. Confirm the rest of the review flow is intact: summary ↔ story navigation, prev/next, the "New" badge on stories that change detection reports as new, and dismiss.
5. Confirm there are no console errors and that setting STORYBOOK_REVIEW_BASELINE now has no effect.

Documentation

• Add or update documentation reflecting your changes (removed the "Baseline comparison" section from the addon README)
• If you are deprecating/removing a feature, make sure to update MIGRATION.MD — N/A, feature is unreleased

Checklist for Maintainers

• ci:normal
• qa:needed
• One changelog label: maintenance

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🤖 AI note (Claude Code), not written by Yann — needs sign-off:

This removes a user-facing capability (latest-vs-baseline compare) and needs product sign-off before merge (handoff Cost #1). The stacked plan treats this as already decided (Q5 = "delete compare entirely"), but I'm flagging it explicitly since I executed it autonomously while you were away. If latest/baseline/split is a committed requirement, this PR should be held.

Decision I made: the newlyAddedStoryIds set previously unioned change-detection new with "absent from the baseline index". With baseline gone, the second source no longer exists, so newness is now purely change-detection new. The NewStory test was updated to seed a change-detection new status (it previously relied on baseline-absence). This is the only behavior nuance in the deletion.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Features Removed
  • Removed baseline comparison and compare-mode UI from the review addon, including the related compare/preview tools and wrappers.
  • Disabled baseline serving/proxying and removed baseline routing support.
• Documentation
  • Removed the “Baseline comparison” setup section for baseline configuration.
• Bug Fixes
  • Improved review state handling by deferring updates when only the review timestamp changes.
  • Enhanced universal store readiness behavior for isolated instances.
• Chores
  • Updated Storybook review test harnesses/mocks to drop baseline-fetch behavior.
  • Refreshed React/React-DOM dev dependency versions.

[storybook-app-bot]

Package Benchmarks

^{Commit: 867db42, ran on 19 June 2026 at 15:40:28 UTC}

The following packages have significant changes to their size or dependencies:

@storybook/addon-review

	Before	After	Difference
Dependency count	1	1	0
Self size	252 KB	73 KB	🎉 -179 KB 🎉
Dependency size	669 KB	669 KB	0 B
Bundle Size Analyzer	Link	Link

[yannbf]

Seems like the stories for ReviewPage stopped having a "new" badge, can you fix that?

[yannbf]

🤖 AI note (Claude Code), not written by Yann: Fixed. The "New" badge previously came from the (now-removed) baseline-absence check, so I restored it by seeding a change-detection new status for manager-settings-checklist--default in the ReviewPage stories beforeEach (matching how ReviewChangesButton.stories seeds statuses). Newness is now sourced purely from change detection.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 6d34eb1a-06c3-476f-bba0-9b64074d3ad7

📥 Commits

Reviewing files that changed from the base of the PR and between f26f113 and 867db42.

⛔ Files ignored due to path filters (1)

• yarn.lock is excluded by !**/yarn.lock, !**/*.lock

📒 Files selected for processing (14)

• code/addons/review/README.md
• code/addons/review/package.json
• code/addons/review/src/ReviewCompareTool.tsx
• code/addons/review/src/ReviewPage.stories.tsx
• code/addons/review/src/ReviewPreviewWrapper.tsx
• code/addons/review/src/ReviewProvider.tsx
• code/addons/review/src/ReviewToolbarHeader.stories.tsx
• code/addons/review/src/constants.ts
• code/addons/review/src/manager.tsx
• code/addons/review/src/preset.ts
• code/addons/review/src/review-state.ts
• code/addons/review/src/review-store.ts
• code/addons/review/src/screens/useBaselineComparison.ts
• code/core/src/shared/universal-store/index.ts

💤 Files with no reviewable changes (9)

• code/addons/review/src/ReviewCompareTool.tsx
• code/addons/review/src/manager.tsx
• code/addons/review/README.md
• code/addons/review/src/review-state.ts
• code/addons/review/src/constants.ts
• code/addons/review/src/ReviewPreviewWrapper.tsx
• code/addons/review/src/review-store.ts
• code/addons/review/package.json
• code/addons/review/src/screens/useBaselineComparison.ts

✅ Files skipped from review due to trivial changes (1)

• code/addons/review/src/ReviewPage.stories.tsx

🚧 Files skipped from review as they are similar to previous changes (4)

• code/addons/review/src/ReviewToolbarHeader.stories.tsx
• code/addons/review/src/preset.ts
• code/core/src/shared/universal-store/index.ts
• code/addons/review/src/ReviewProvider.tsx

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📝 Walkthrough

Walkthrough

Removes the baseline comparison feature from the review addon end-to-end: deletes the experimental_devServer preset hook, ReviewCompareTool, ReviewPreviewWrapper, compare-mode constants/types, and related ReviewProvider state. ReviewProvider gains a deferred-update helper and simplifies new-story detection to use isChangeDetectedNew. UniversalStore is fixed so isolated instances with environmentOverrides do not resolve or wait on the shared preparation promise.

Changes

Remove baseline/compare-mode from review addon

Layer / File(s)	Summary
Remove compare-mode types and constants code/addons/review/src/constants.ts, code/addons/review/src/review-state.ts, code/addons/review/src/review-store.ts	Removes BASELINE_PROXY_PATH, BASELINE_INDEX_URL, PREVIEW_MODE_SESSION_KEY, CompareMode, DEFAULT_COMPARE_MODE, hasBaseline from ReviewState, and compareMode/showCompare/setCompareMode from ReviewStoreState and emptyStore.
Remove baseline dev server hook from preset code/addons/review/src/preset.ts	Strips filesystem, proxy, sirv, and logger imports and deletes the exported experimental_devServer hook that served/proxied STORYBOOK_REVIEW_BASELINE; module-graph review channel logic is unchanged.
Remove compare and preview addon registrations code/addons/review/src/manager.tsx	Removes reviewCompareTool and reviewPreviewWrapper imports and their addons.add registrations, leaving only ReviewProvider.
Simplify ReviewProvider: remove baseline/compare state, add deferred update code/addons/review/src/ReviewProvider.tsx	Deletes baselineStoryIds, compareMode, setCompareMode, baseline-fetch effect, and showCompare derivation; adds isDeferredReviewUpdate for deferred DISPLAY_REVIEW handling; reworks newlyAddedStoryIds via isChangeDetectedNew; strips removed fields from reviewStore value and useMemo deps.
Update story test harnesses, docs, and package.json code/addons/review/src/ReviewPage.stories.tsx, code/addons/review/src/ReviewToolbarHeader.stories.tsx, code/addons/review/README.md, code/addons/review/package.json	Removes hasBaseline from fixtures, strips all fetch-mock scaffolding, updates beforeEach/cleanup to seed internal_fullStatusStore with change-detection status, removes Baseline comparison section from README.

Fix UniversalStore isolated instance readiness

Layer / File(s)	Summary
UniversalStore: isolated instance readiness isolation code/core/src/shared/universal-store/index.ts	untilReady() short-circuits the shared preparation wait when channel and environment are already present; constructor gates UniversalStore.preparation.resolve() to non-environmentOverrides instances only.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• storybookjs/storybook#35110: Directly related — adds the ReviewCompareTool.tsx and ReviewPreviewWrapper.tsx components plus baseline routing constants that this PR removes.
• storybookjs/storybook#35059: Related — introduces the session-mapped compare mode and compare-mode UI logic in DetailsScreen that overlaps with the compareMode/showCompare infrastructure being removed here.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

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