BridgeJS: Add opt-in TypedArray bridging for numeric arrays

[krodak]

Overview

Optimize numeric array bridging with bulk TypedArray memory transfer. When a Swift function passes or receives a numeric array ([Int], [UInt8], [Float], [Double], etc.), BridgeJS now uses bulk memory copy instead of element-by-element stack serialization. TypeScript types remain number[] / bigint[] — no user-facing API change.

This is a transparent performance optimization following the same pattern as bridgeJSStackPopAsOptional — the ABI changes internally but the type contract is unchanged.

How it works

Swift → JS (return values): withUnsafeBufferPointer → swift_js_push_typed_array(ptr, count, kind) → JS copies bytes into a TypedArray → pre-allocated for-loop converts to number[].

JS → Swift (parameters): JS converts the input array to a TypedArray → retains in JS heap → passes (id, count) as WASM params → Swift allocates via Array(unsafeUninitializedCapacity:) → calls back to JS via swift_js_init_typed_array_memory to bulk copy.

Non-numeric arrays ([String], [MyStruct], etc.) are unaffected — they continue using the existing element-by-element stack protocol.

What changed

• BridgeJSSkeleton.swift — isNumericScalar and typedArrayKind helpers on BridgeType
• BridgeJSIntrinsics.swift — _BridgeJSTypedArrayElement protocol, conformances for 12 numeric types, _bridgeJS_typedArrayPush and _bridgeJS_typedArrayLiftParameter bulk transfer functions, WASM externs for swift_js_push_typed_array and swift_js_init_typed_array_memory
• JSGlueGen.swift — numericArrayLift, numericArrayLower, numericArrayLowerReturn JS fragment generators; routing in lowerParameter, liftReturn, liftParameter, lowerReturn to detect numeric arrays
• BridgeJSLink.swift — taStack, typedArrayConstructors, swift_js_push_typed_array, swift_js_init_typed_array_memory handlers
• ExportSwift.swift — Numeric array parameters use (sourceId, count) WASM params + _bridgeJS_typedArrayLiftParameter; returns use _bridgeJS_typedArrayPush
• ImportTS.swift — Numeric array parameters use _bridgeJS_typedArrayPush; returns use _bridgeJS_typedArrayLiftParameter
• ClosureCodegen.swift — Numeric array closure parameters use bulk path

Benchmark results

Release build, 10K iterations × 5 runs, --filter=ArrayRoundtrip:

JS → Swift (take*)

Test	Before	After	Speedup
takeIntArray (1K)	758 ms	13 ms	58× faster
takeDoubleArray (1K)	791 ms	13 ms	61× faster

Swift → JS (make*)

Test	Before	After	Speedup
makeIntArray (1K)	221 ms	18 ms	12× faster
makeIntArrayLarge (10K)	2160 ms	146 ms	15× faster
makeDoubleArray (1K)	271 ms	36 ms	7.5× faster

Roundtrips

Test	Before	After	Speedup
roundtripIntArray (1K)	964 ms	29 ms	33× faster
roundtripDoubleArray (1K)	1065 ms	29 ms	37× faster

Non-numeric — zero impact

Test	Before	After
takeStringArray	23 ms	25 ms
makeStringArray	7 ms	7 ms
takePointArray	6 ms	6 ms

Follow-up

For users who want actual Uint8Array / Float32Array in their JS API (e.g., for fetch body, WebGPU), a separate PR can add JSTypedArray<T> as a recognized BridgeJS type — per maintainer guidance. This would return TypedArrays directly without the Array conversion step.