fix(mobile): pause hidden home thread list updates

[juliusmarminge]

Streaming chats were rebuilding the hidden Home thread list on every shell update. In a native Hermes capture with 1,200 thread shells, hidden HomeScreen work accounted for 5.2 seconds of sampled JS time across a 37.5-second capture.

Pause Home’s thread-shell subscription after the native screen disappears, retain its last value, and read current data as Home reappears. Home remains mounted so search and scroll state survive. Visible tablet sidebars retain their own live subscription. Native-stack freezing does not cover the screen immediately below the focused route on Fabric.

Before/after proof

On the same iOS 27 debug simulator session, a 15-second real-server workload emitted 300 active-chat updates and 120 updates across four background chats:

Measurement	Before	After
Hidden HomeScreen renders	95	0
Largest observed JS timer gap	1,960 ms	493 ms

Raw render counters and timer samples. Render counts are the primary evidence. Timer maxima are exploratory: one run per variant, cumulative thread history, debug builds, and three simulators booted on the host. They are not release-device latency or battery-saving claims. No visible UI changed; the measurement counts eliminated background work. Returning to Home was checked in the native client.

Validation and limits

• 11 focused visibility/navigation tests passed, including 600 hidden shell updates producing zero renders and current data on return.
• Mobile typecheck passed; independent lifecycle review found no blockers.
• Cancelling an iOS back swipe can leave Home live until the next navigation, reverting to the previous performance behavior.
• Home intentionally stays live under visible form/page sheets. Android sheet and predictive-back behavior has not been verified on a device.
• CPU after-capture is unavailable because the native client now reports multiple React Native hosts to the tracing API.

Implementation and review: Claude Opus 5.5 through T3 Code’s Claude harness. Native measurements and integration: GPT-6 Astra through Codex in T3 Code.

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[macroscopeapp]

Approvability

Verdict: Approved at f227032

Macroscope's review found this PR approvable — This is a narrowly scoped mobile performance fix that pauses only hidden Home thread-list renders while preserving fresh data on reappearance. Navigation lifecycle behavior is isolated and covered by focused tests, with no schema, security, deployment, default, or static-analysis changes.

No code changes detected at 26cf7c4. Prior analysis still applies.

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📥 Commits

Reviewing files that changed from the base of the PR and between 26cf7c4 and 17d4c28.

📒 Files selected for processing (3)

• apps/mobile/src/features/home/HomeRouteScreen.tsx
• apps/mobile/src/features/home/home-route-visibility.test.tsx
• apps/mobile/src/features/home/home-route-visibility.ts

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📝 Walkthrough

Walkthrough

HomeRouteScreen reads navigation thread-shell values through visibility-aware hooks. Navigation focus and transition events set Home visibility. The atom reader stops updates while Home is hidden, retains its last value, and reads the current value when visibility returns. Tests cover focus, transitions, and atom updates.

Changes

Home route visibility

Layer / File(s)	Summary
Track visibility and gate atom reads apps/mobile/src/features/home/home-route-visibility.ts	useHomeRouteVisible tracks navigation focus and transition events. useAtomValueWhileVisible subscribes to the atom only while Home is visible and retains its last value while hidden.
Wire visibility into Home thread shells apps/mobile/src/features/home/HomeRouteScreen.tsx, apps/mobile/src/features/home/home-route-visibility.test.tsx	HomeRouteScreen reads thread-shell values through the visibility-aware hooks. Tests cover updates while visible, covered transitions, back-swipe transitions, focus events, and initially unfocused mounting.

Priority: ➖ Normal

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

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant Navigation
  participant HomeRouteScreen
  participant AtomRegistry
  Navigation->>HomeRouteScreen: Emit focus or transition event
  HomeRouteScreen->>AtomRegistry: Subscribe when visible
  AtomRegistry->>HomeRouteScreen: Deliver thread-shell updates
  HomeRouteScreen->>AtomRegistry: Stop subscription when hidden

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Merge Risk: ⚪ Minimal · up to 17d4c

Home refreshes its thread list when it reappears. No actionable issue remains before merge beyond normal checks.

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: pausing hidden Home thread-list updates on mobile.
Description check	✅ Passed	The description clearly covers the problem, implementation, performance evidence, validation, and known limitations. It does not use the template headings and does not provide a bug or approval link, …
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

ℹ️ No successful main baseline artifact is available yet. This run establishes the initial measurement.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	—	4.9 KiB	—	6.8 KiB	✅
Codex	Thread snapshot wire	—	3.8 KiB	—	4.9 KiB	✅
Codex	Live turn WebSocket wire	—	1.2 KiB	—	2.0 KiB	✅
Codex	Live turn WebSocket decoded	—	20.8 KiB	—	29.3 KiB	✅
Codex	Live turn messages	—	1	—	8	✅
Claude	Total thread wire	—	5.0 KiB	—	6.8 KiB	✅
Claude	Thread snapshot wire	—	3.8 KiB	—	4.9 KiB	✅
Claude	Live turn WebSocket wire	—	1.2 KiB	—	2.0 KiB	✅
Claude	Live turn WebSocket decoded	—	21.2 KiB	—	29.3 KiB	✅
Claude	Live turn messages	—	2	—	8	✅

Baseline: unavailable · PR result: 17d4c28 · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 108.5 KiB
• Claude decoded thread snapshot: 108.8 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.