perf(mobile): device preview compiles with the React Compiler

[juliusmarminge]

The React Compiler skipped DevicePreviewRouteScreen because shutting down a device wrapped an await in try/finally.

Stacked on #20970. Part of the React Compiler ratchet from #20967.

The pending flag is now cleared with .finally() on the shutdown command. All 6 useMemo/useCallback calls in features/devices are gone, and the file is removed from KNOWN_BAILOUTS (85 to 84).

Verified with vp test run src/reactCompilerCoverage.test.ts plus the feature's own tests, mobile typecheck, and lint on the changed files. Measured on an Android emulator below.

Measurement

Scenario: --route /threads/<environment>/<thread>/devices on a seeded thread. Device: Android emulator, Pixel 9 API 36, on nucbox-1, with Metro and an isolated seeded server on cups; dev client rebuilt from #20967 today. Harness: --route scenario from #21001 at 4dee0fbead. Each run reloads the app on Home, starts the counter, opens the route with an app link and records 6 s covering mount and data settling. Median of 3. Both sides sit on the same base, main 13aa882c22 plus the stack below; "before" is the parent PR head, "after" is this PR head. Before: #20970 at e620e9c4e2. After: 2aa9623a2e.

No device host: the isolated server has no simulators or emulators to stream, so this measures the screen with no devices. It mounts, loads device state, finds no preview for the thread and closes itself, which is the empty path. DeviceStreamWebView never mounts, so the stream half of this PR isn't covered.

Runs (renders/commits): before 923/20, 3017/18, 931/18. After 862/19, 929/18, 929/17. Before run 2 is an outlier the median drops; I didn't trace it.

	before	after	Δ
renders	931	929	-2
commits	18	18	0
renders per commit	52	52	0

Device components, one probe run per side with the same window:

Component	before	after
DevicePreviewScreen	3	4
DeviceOptionsMenu	3	4
DevicePreviewRouteScreen	1	1

Cause	before	after
DeviceOptionsMenu props:items	2	3
DevicePreviewScreen state#3	1	1
DevicePreviewScreen state#10	1	1
DevicePreviewScreen context	0	1
DevicePreviewScreen mount	1	1

What it means: no measurable change on the empty path. The screen renders 3–4 times before it closes, and the one-render difference follows when device state arrives, not the code. Measuring the stream needs a device host on the server.

Claude Opus 5.5 via Claude Code.

🤖 Generated with Claude Code

[github-actions]

Thread transfer impact

⚠️ The latest CI run did not produce a thread transfer result for 2aa9623.

This comment will update automatically after the next completed run.

[macroscopeapp]

Approvability

Verdict: Approved at 5dd228e

Macroscope's review found this PR approvable — This is a localized React Compiler compatibility cleanup that removes redundant manual memoization while preserving the existing device-preview behavior and shutdown cleanup. The accompanying test only updates compiler bailout coverage, with no schema, default, deployment, security, or static-analysis suppression changes.

No code changes detected at 2aa9623. Prior analysis still applies.

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📥 Commits

Reviewing files that changed from the base of the PR and between 044079d and 5dd228e.

📒 Files selected for processing: 3

• apps/mobile/src/features/devices/DevicePreviewRouteScreen.tsx
• apps/mobile/src/features/devices/DeviceStreamWebView.tsx
• apps/mobile/src/reactCompilerCoverage.test.ts

💤 Files with no reviewable changes: 1

• apps/mobile/src/reactCompilerCoverage.test.ts

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📝 Walkthrough

The device preview route now creates callbacks and derives preview data during render. Shutdown state resets in a promise finally block. The stream view constructs its WebView source during render. The coverage test no longer lists the route as a compiler bailout.

Changes: Device Preview

Layer / File(s)	Summary
Render-time values and compiler coverage apps/mobile/src/features/devices/DevicePreviewRouteScreen.tsx, apps/mobile/src/features/devices/DeviceStreamWebView.tsx, apps/mobile/src/reactCompilerCoverage.test.ts	The route creates callbacks and derives preview data during render. Shutdown state resets in a promise finally block. The stream view constructs its source directly, and the coverage test removes the route from KNOWN_BAILOUTS.

Priority: ⬇️ Low

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

Change: Refactor

Suggested reviewers: maria-rcks

Merge Risk: ⚪ Minimal · up to 5dd22

No confirmed device-preview regression currently blocks merging; complete normal checks before release.

Pre-merge checks: 4

Check name	Status	Explanation
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.
Title check		The title clearly identifies the primary change: enabling React Compiler compilation for the mobile device preview.
Description check		The description explains the problem, implementation, scope, verification, measurements, limitations, and agent attribution. It provides relevant issue references, although it does not include an expl…

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Explanation

The description explains the problem, implementation, scope, verification, measurements, limitations, and agent attribution. It provides relevant issue references, although it does not include an explicit maintainer approval comment.

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