fix(core): the npm package no longer ships the unminified media sync runtime - #6515

What

@hyperframes/core's npm package no longer ships the unminified browser media sync (dist/runtime/media.js and three files only it imports). The package is 57 KB smaller unpacked and 17 KB smaller packed, and every published entry point still resolves.

Why

src/runtime is excluded from core's tsc build: the runtime reaches users as the minified bundles (./runtime, ./runtime-script), and a runtime file only reaches dist when a module in the build imports it. Three such imports pulled runtime/media.ts in by accident:

• runtime/timeline.ts imported two playbackRate.ts helpers through media.ts's re-exports;
• runtime/state.ts type-imported RuntimeMediaClip from media.ts (a type-only import still adds the file to the program, so it is emitted);
• runtime/clock.ts imported the MEDIA_HARD_SYNC_SECONDS constant from media.ts.

So core shipped the media sync loop as plain source next to the bundles, and every change to it counted against core's size budget about three times. A playback fix on top of this one was refused by the merge queue for exactly that: its code fit the bundles, but the extra unminified copy pushed core over its budget.

How

• timeline.ts imports readElementPlaybackRate and readMediaStart from playbackRate.ts (where they are defined).
• RuntimeMediaClip moves to runtime/types.ts; media.ts re-exports it, so every existing import keeps working.
• MEDIA_HARD_SYNC_SECONDS moves to mediaSteer.ts, beside MEDIA_SYNC_TOLERANCE_SECONDS; media.ts and clock.ts import it from there.
• mediaSteer.ts joins core's tsconfig.json files, because the published ./runtime/media-steer subpath needs it and it no longer arrives through media.ts.

No runtime behaviour changes: the bundles are built from the same sources, and only where a type and a constant are declared moves.

What I measured

npm pack --dry-run in packages/core, main against this branch, both built from clean:

Files that leave the package: dist/runtime/media, preloadMedia, timedClipHide and adapters/seek-dispatch (.js and .d.ts each). None is a published subpath, and no remaining file in the tarball references them.

• ./runtime/media-steer from the packed tarball in a clean consumer: resolves and exports MEDIA_HARD_SYNC_SECONDS, MEDIA_SYNC_TOLERANCE_SECONDS, forgetSteering, isSteering, steerMedia.
• verify:packed-manifests: 185 packed exports resolved, 175 Node exports executed, NodeNext declaration check and size budgets pass.
• check:package-subpaths, check-package-cycles, oxfmt, oxlint, comment ratchet and fallow audit clean.
• core typecheck (including the runtime config); tsc --noEmit in player, engine and studio.
• core vitest run: 249 files, 5457 tests, 3 runs in a row.

What I did NOT exercise

• A real publish to the registry: the tarball was checked through npm pack and the packed-consumer install that verify:packed-manifests does.

Test plan

• Tarball before/after with npm pack --dry-run
• Packed subpath import for ./runtime/media-steer
• verify:packed-manifests, subpath and cycle checks
• Typecheck in core, player, engine, studio; core unit tests 3x
• Documentation updated (not applicable: no public API change)