feat: cache iOS runner artifacts during prepare

[thymikee]

Summary

prepare ios-runner now owns iOS runner artifact restore/build/health behavior: cache hits launch from the restored .xctestrun, misses build through prepare, and bad restored artifacts are cleaned and rebuilt once.

The prepare path is now a dedicated prepareIosRunner API instead of prepare-only flags on generic runner commands, so normal runner execution does not carry cache recovery or diagnostics assumptions. Request-scoped provider tests still route prepare health through the provider seam.

The iOS CI and nightly iOS replay workflows now dogfood this path by restoring/saving the runner cache without prebuilding on cache miss, then running prepare ios-runner --timeout 300000 --json as the single build-or-health gate.

Added unit stress coverage for exact cache hits, bad-artifact marking, cleanup, rebuild, timeout propagation, metadata parity, prepare timeout option plumbing, and runner-client prepare recovery/double-failure orchestration.

Touched files: 14. Scope expanded from runner runtime to CI workflow/action wiring so this repo uses the new prepare-owned cache path.

Validation

pnpm check:quick passed.

pnpm check:fallow --base origin/main passed.

Targeted runner/prepare tests passed: pnpm exec vitest run src/platforms/ios/__tests__/runner-client.test.ts src/platforms/ios/__tests__/runner-session.test.ts src/platforms/ios/__tests__/runner-xctestrun.test.ts src/daemon/handlers/__tests__/session.test.ts --project unit.

Recovery-focused runner tests passed: pnpm exec vitest run src/platforms/ios/__tests__/runner-command-retry.test.ts src/platforms/ios/__tests__/runner-xctestrun.test.ts src/daemon/handlers/__tests__/session.test.ts --project unit.

Provider integration passed: pnpm test:integration:provider.

Coverage passed outside the sandbox: pnpm test:coverage with 2106 passed tests and 1 skipped.

Smoke validation passed separately: pnpm test:smoke.

pnpm check:unit was attempted after the simplification but local full-suite runs hit unrelated 5s Android/iOS timing flakes; each failed test passed when rerun in isolation. CI has restarted on this PR.

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Size Report

Metric	Base	Current	Diff
JS raw	1.1 MB	1.1 MB	+4.1 kB
JS gzip	367.5 kB	368.7 kB	+1.2 kB
npm tarball	473.5 kB	474.9 kB	+1.4 kB
npm unpacked	1.6 MB	1.6 MB	+4.1 kB

Startup median (7 runs, lower is better):

Scenario	Base	Current	Diff
CLI --version	27.5 ms	27.7 ms	+0.2 ms
CLI --help	43.8 ms	42.9 ms	-1.0 ms

Top changed chunks:

Chunk	Raw diff	Gzip diff
dist/src/2415.js	+4.0 kB	+1.2 kB
dist/src/session.js	+108 B	+51 B