refactor: derive replay metadata platforms from the canonical selectors

[thymikee]

Follow-up to thymikee's review on #895: the replay parser hand-restated the leaf-platform allow-list a 4th time, and the type/runtime didn't agree.

Problem

src/replay/script.ts defined type ReplayScriptPlatform = Exclude<PlatformSelector, 'apple'> (which still INCLUDES 'web') while REPLAY_METADATA_PLATFORMS was a hardcoded Set(['ios','android','macos','linux']) (omits 'web'). So context platform=web lines were silently dropped even though the type permitted web — a type/runtime mismatch and a copy of the allow-list that can drift.

Fix (behaviorless)

• Narrow the type so web's exclusion is explicit: Exclude<PlatformSelector, 'apple' | 'web'>.
• Derive the runtime set from the already-exported canonical PLATFORM_SELECTORS (src/utils/device.ts) instead of hardcoding. This yields exactly ['ios','macos','android','linux'] today and auto-includes any future leaf platform except web.
• Comment that replay metadata context platform= lines do not support web.

Web stays dropped exactly as before — now intentionally, type-safe, and derived from a single source. Adding web support remains a separate feature decision and is out of scope here. This branch does not depend on #895 (it derives from PLATFORM_SELECTORS, already exported on main).

Tests

Extended src/replay/__tests__/script.test.ts:

• REPLAY_METADATA_PLATFORMS equals exactly the non-web leaf platforms.
• every concrete leaf platform (ios/android/macos/linux) is accepted in a context line.
• a context platform=web line is dropped (behaviorless).

Verified: tsc --noEmit, oxfmt, oxlint --deny-warnings, and vitest run replay (153 passed) all green.

[github-actions]

Size Report

Metric	Base	Current	Diff
JS raw	1.4 MB	1.4 MB	+49 B
JS gzip	445.2 kB	445.2 kB	+31 B
npm tarball	583.3 kB	583.3 kB	+12 B
npm unpacked	2.0 MB	2.0 MB	+49 B

Startup median (7 runs, lower is better):

Scenario	Base	Current	Diff
CLI --version	25.9 ms	26.1 ms	+0.2 ms
CLI --help	46.1 ms	45.9 ms	-0.2 ms

Top changed chunks:

Chunk	Raw diff	Gzip diff
dist/src/4428.js	+49 B	+31 B

[thymikee]

Reviewed — merge-ready. ✅

Verified

• PLATFORM_SELECTORS.filter(p => p !== 'apple' && p !== 'web') derives exactly {ios, macos, android, linux} — byte-identical to the old hardcoded set, so this is genuinely behaviorless today (checked by hand, not just CI).
• Type now matches runtime: Exclude<PlatformSelector, 'apple' | 'web'> drops the stale 'web' member the old Exclude<…, 'apple'> left in. The .has() guard at script.ts:83 still rejects web at runtime, so context platform=web stays dropped — confirmed by the new test.
• Single source of truth: no more 4th copy of the leaf-platform allow-list. The type guard in the .filter is sound.
• No accidental widening of supported runtime behavior. Tests are accurate (set membership, all 4 leaves accepted, web dropped). Typecheck/Unit/Coverage/Web Platform Smoke all green.

Residual risk (non-blocking, both out of scope per the description)

1. The derive flips the default for future leaf platforms from opt-in to opt-out: any new entry added to PLATFORM_SELECTORS is auto-accepted as a replay metadata platform unless it's hand-excluded like web. That's the documented intent, just worth keeping in mind when the next platform lands.
2. Pre-existing round-trip asymmetry (not introduced here): the write path at script.ts:461 emits context platform=${session.device.platform}, which can be web, but read-back drops it → metadata.platform undefined for web replay scripts. This is exactly the gap the PR scopes out for a separate web-support decision.

[github-actions]

PR Preview Action v1.8.1
Preview removed because the pull request was closed.
2026-06-27 12:02 UTC