refactor(app): extract layout side effect controllers

[Astro-Han]

Summary

Extract the first non-visual side-effect controller boundary from packages/app/src/pages/layout.tsx.

• Move update polling into layout-update-polling.ts.
• Move SDK notification, permission, question, and worktree event effects into layout-sdk-event-effects.ts.
• Add focused helper tests for current/descendant suppression, question dedupe keys, terminal question reset, route-ready question notifications, and permission cooldown.

Why

layout.tsx was mixing shell composition with background update and SDK event behavior. This PR keeps the visible shell stable while making those side effects easier to review and safer to change later.

Related Issue

Refs #875

Human Review Status

Pending

Review Focus

Please focus on behavior preservation: Solid owner lifecycle, reactive accessor usage, SDK listener cleanup, update polling interval cleanup, notification dedupe/cooldown, and worktree ready/failed effects.

Risk Notes

• Platform surface touched: updater polling and desktop notifications are mechanically preserved behind explicit dependencies.
• (conditional) Visible UI/manual screenshot checklist left unticked because no visible UI, copy, DOM, aria, command, route, or storage key behavior changed.
• (conditional) Docs/release/dependencies/generated-content checklist left unticked because none of those surfaces changed.

How To Verify

Focused layout tests: 155 pass, 0 fail
Command: cd packages/app && bun test --preload ./happydom.ts ./src/pages/layout/*.test.ts ./src/pages/layout/*.test.tsx ./src/pages/update-install-flow-source.test.ts

Typecheck: 8 successful, 8 total
Command: bun run typecheck

Diff whitespace check: no errors
Command: git diff --check

Screenshots or Recordings

Not required. This PR has no visible UI change.

Checklist

How to use this checklist:

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• I linked the related issue, or stated in Summary why there is no issue.
• I described the review focus and any meaningful risks.
• I replaced the example block in How To Verify with the real verification steps and the key result for each.
• I did not introduce unrelated refactors, dependencies, generated files, or file changes beyond the stated scope.
• (conditional) I manually checked visible UI or copy changes when needed, with screenshots or recordings. Leave unticked only if no visible UI or copy changed.
• (conditional) I considered macOS and Windows impact for platform, packaging, updater, signing, paths, shell, or permissions changes. Leave unticked only if no platform/packaging surface was touched.
• (conditional) I called out docs, release notes, dependencies, permissions, credentials, deletion behavior, generated content, or local file changes when relevant. Leave unticked only if none of those surfaces was touched.
• I reviewed the final diff for unrelated changes and suspicious dependency changes.
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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: d537da95-8188-4476-a13d-37437fe75db9

📥 Commits

Reviewing files that changed from the base of the PR and between d9d052e and c8a6c13.

📒 Files selected for processing (5)

• packages/app/src/pages/layout.tsx
• packages/app/src/pages/layout/layout-sdk-event-effects.test.ts
• packages/app/src/pages/layout/layout-sdk-event-effects.ts
• packages/app/src/pages/layout/layout-update-polling.ts
• packages/app/src/pages/update-install-flow-source.test.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/i875-layout-side-effects

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[github-actions]

Suggested priority: P2 (includes user-path files (packages/app/src/pages/layout.tsx, packages/app/src/pages/layout/layout-sdk-event-effects.test.ts, packages/app/src/pages/layout/layout-sdk-event-effects.ts, packages/app/src/pages/layout/layout-update-polling.ts, packages/app/src/pages/update-install-flow-source.test.ts)).

P1/P0 are reserved for maintainer confirmation. Please relabel manually if this is a release blocker, security issue, data-loss risk, or updater/runtime failure.

[gemini-code-assist]

Code Review

This pull request refactors the main Layout component by extracting the update polling and SDK notification logic into separate, testable modules. New unit tests have been introduced for the SDK event effects. The reviewer suggested optimizing performance by deferring session lookups until they are strictly necessary and using targeted lookups to minimize memory overhead when processing events.

[github-actions]

Perf delta summary

Comparator: pass

Profile / Scenario	interaction median	interaction worst	long task max	tbt	frame gap p95	frame gap max	jank count	cls	status
default / homepage-cold	24 -> 24 (0)	48 -> 32 (-16)	112 -> 69 (-43)	62 -> 19 (-43)	33.4 -> 16.8 (-16.6)	150 -> 183.3 (+33.3)	4 -> 3 (-1)	0 -> 0 (0)	pass
default / long-session-input-lag	48 -> 48 (0)	64 -> 48 (-16)	0 -> 0 (0)	0 -> 0 (0)	16.8 -> 16.7 (-0.1)	16.8 -> 16.8 (0)	0 -> 0 (0)	0 -> 0 (0)	pass
default / session-streaming-long	40 -> 48 (+8)	80 -> 64 (-16)	0 -> 0 (0)	0 -> 0 (0)	16.7 -> 16.8 (+0.1)	16.8 -> 33.4 (+16.6)	0 -> 0 (0)	0 -> 0 (0)	pass
default / tool-call-expand	16 -> 16 (0)	24 -> 40 (+16)	0 -> 0 (0)	0 -> 0 (0)	16.7 -> 16.8 (+0.1)	16.7 -> 16.8 (+0.1)	0 -> 0 (0)	0 -> 0 (0)	pass
default / tool-default-open-heavy-bash	16 -> 16 (0)	16 -> 24 (+8)	93 -> 66 (-27)	58 -> 29 (-29)	50 -> 50 (0)	116.6 -> 116.6 (0)	3 -> 3 (0)	0 -> 0 (0)	pass
default / terminal-side-panel-open	40 -> 48 (+8)	48 -> 56 (+8)	0 -> 0 (0)	0 -> 0 (0)	33.3 -> 33.3 (0)	33.3 -> 33.4 (+0.1)	0 -> 0 (0)	0 -> 0 (0)	pass
default / session-scroll-reading	16 -> 16 (0)	48 -> 32 (-16)	0 -> 0 (0)	0 -> 0 (0)	16.7 -> 16.7 (0)	16.7 -> 16.7 (0)	0 -> 0 (0)	0 -> 0 (0)	pass