Vectorize exact MP3 PCM quantization in audio WASM

[Hona]

Summary

• Quantize independent MP3 synthesis samples with standard 128-bit WASM SIMD, preserving the special scalar pair, nearest-even rounding, signed saturation and bounded tails.
• Enable SIMD only for the separately built audio module. Gameplay compilation features, shared memory, TLS and binding contracts are unchanged; gameplay SIMD expansion is excluded.
• Preserve native scalar behavior, PCM buffer capacity, build identities, unshared audio memory, and pre-instantiation browser capability checks.

Verification

• Native and actual scalar/SIMD WASM tests cover mono/stereo groups, short/unaligned tails, infinities, NaNs, signed zero and subnormals.
• Five decoder inputs totaling 2,108,160 samples match the public decoder reference exactly. Configured Windows input is read from its pinned local archive, not transferred test media.
• Retained complete audio WASM comparisons preserve Float32 paint bytes for six master gains, including signed zero and subnormal values.
• Existing real headed Windows x64 Edge 152 evidence measured 1.6934 → 1.4959 ms per decode (median of 32-call batches), an approximately 11.7% reduction, with identical initial/final PCM hashes and linear-memory sizes. This is decoder-kernel evidence, not end-to-end loading, gameplay FPS or a fix for one-second freezes.
• After integrating current main, 26 focused tests / 226 assertions passed locally, including configured native and actual scalar/SIMD WASM PCM tests, audio lifecycle/worklet tests, compiler flags/remaps and unsupported-target admission.

Headed decoder evidence

This retained screenshot reports 32-call batch means, not individual-call tail percentiles. The profiler now supports individual durations and explicit sample age; no additional results from that instrumentation are claimed here.

Evidence limits

The reported performance evidence is the existing headed x64 PCM/batch measurement; current-main verification uses focused exact-audio and build checks. New individual-call browser tail distributions, ARM headed performance, live-device capture completion and a full 90-second gameplay campaign remain unmeasured. The pending remote task has not been relaunched; its prior unknown outcome/teardown is not treated as successful acceptance.

No graphics, bot work, simulation cadence, networking or production changes. The abandoned live-gameplay profiling extension was removed from this narrow change.

[Copilot]

🔵 Needs a closer look

It changes correctness-sensitive MP3 PCM quantization and introduces new SIMD/fixture workflows that warrant final human verification despite strong test/evidence additions.

Pull request overview

This PR adds a WebAssembly-SIMD128 vectorized quantization path for MP3 PCM output while preserving exact scalar behavior for the special “first pair” lanes, and wires up build/test/profile infrastructure so SIMD is enabled only for the separately built audio/decoder module (not gameplay).

Changes:

• Vectorize MP3 float→i16 quantization on wasm32 with simd128, preserving scalar-pair rounding and exact tail handling.
• Add an explicit audio WASM Rust-flag path (-Ctarget-feature=+simd128) distinct from threaded/gameplay flags, plus tests asserting the separation.
• Add configured parity evidence generation and a headed Playwright profile (simd-decoder) for scalar vs SIMD decoder comparison.

File summaries

File	Description
tools/playsrc/tests/tf2-wasm-build.test.ts	Adds coverage ensuring gameplay/threaded flags do not pick up SIMD, and audio flags do.
tools/playsrc/tests/simd-configured.test.ts	Adds opt-in configured parity test that produces retained scalar/SIMD WASM artifacts + PCM hashes.
tools/playsrc/src/tf2-wasm-build.ts	Factors remap flags and introduces audioWasmRustFlags() to enable SIMD only for audio WASM builds.
tools/playsrc/src/profile-runner.ts	Registers a new simd-decoder profile runner entry (with Windows Edge channel override).
tools/playsrc/profile/simd-decoder.profile.ts	Adds headed-browser scalar vs SIMD decoder execution + timing/hash evidence capture.
tools/playsrc/local-jobs.md	Documents how to prepare and run the new simd-decoder workflow.
playwright.simd-profile.config.ts	Adds a dedicated Playwright config for the SIMD decoder profile.
packages/presentation/audio/tests/wasm.test.ts	Adds tests for preflight SIMD support checks and “no compile if unsupported” behavior.
packages/presentation/audio/src/wasm.ts	Introduces compileAudioModule() which bounds size and rejects unsupported SIMD targets early.
packages/presentation/audio/src/playback.ts	Routes audio module compilation through compileAudioModule() to enforce SIMD/capacity checks.
packages/formats/mp3/rust/tests/configured.rs	Updates configured test to read pinned local TF2 archive input and retain cow1.mp3 evidence.
packages/formats/mp3/rust/src/lib.rs	Reworks decode output fill to a bulk quantize step with a SIMD128 fast-path on wasm.
packages/formats/mp3/rust/Cargo.toml	Adds dev-dependencies needed by the configured evidence test.
Cargo.lock	Locks new dev-dependency resolution for the mp3 crate.

Review details

• Files reviewed: 13/14 changed files
• Comments generated: 1
• Review effort level: Lite

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