perf: reduce cold iOS runner startup latency

[thymikee]

Summary

Reduce cold iOS simulator startup latency without changing snapshot backends.

• reuse the existing bounded fresh-boot observation instead of immediately paying for a duplicate simctl list devices -j; stale booleans and memo failures still fall back to native discovery
• wake one runner connection retry from the runner's authoritative NWListener-ready marker, while keeping the HTTP probe authoritative
• extract xcodebuild process launch/output ownership from the oversized runner session module and make retry wakeups cancellation- and resource-safe

On the same existing iPhone 17 Pro simulator, cold open plus the first interactive snapshot improved from 5.45s to 3.83s. Retained runner preparation remained effectively instant (14ms internally), and a warm snapshot measured 185ms.

This does not make private AX the default. The current private-AX backend still runs inside XCTest, so it cannot remove XCTest startup.

Validation

• pnpm check:affected --run — 342 files / 2,533 tests passed, plus format, lint, typecheck, layering, fallow, and build
• live isolated cold/retained/adopted startup matrix on the existing iPhone 17 Pro simulator
• verified no simulator was created or deleted and the isolated runner/daemon were stopped

[github-actions]

Size Report

Metric	Base	Current	Diff
JS raw	2.34 MB	2.34 MB	+1.5 kB
JS gzip	769.6 kB	770.2 kB	+548 B
npm tarball	895.4 kB	895.9 kB	+532 B
npm unpacked	3.12 MB	3.12 MB	+1.5 kB

Startup median (7 runs, lower is better):

Scenario	Base	Current	Diff
CLI --version	20.2 ms	21.7 ms	+1.5 ms
CLI --help	44.8 ms	49.8 ms	+4.9 ms

Top changed chunks:

Chunk	Raw diff	Gzip diff
dist/src/runner-client.js	+627 B	+238 B
dist/src/runtime4.js	+144 B	+46 B
dist/src/runner-disposal.js	+64 B	+25 B
dist/src/internal/daemon.js	0 B	+2 B

[thymikee]

Reviewed 6a6efce66c8d8f7031fc771ac2dd69c6a5caace4: clean. The readiness memo preserves native fallback, and the NWListener marker only shortens one retry while the HTTP probe remains authoritative. The launch extraction also gives xcodebuild ownership a clearer seam. Remaining CI evidence: iOS Smoke is in progress.

[github-actions]

PR Preview Action v1.8.1
Preview removed because the pull request was closed.
2026-08-20 19:47 UTC