Embedding: optimize Zig, C, private ABI, and Objective-C boundaries

[chrisbbreuer]

Parent: #459
Depends on: #460, #461, #463, #473, #479

Goal

Make Zig, public C, private ABI, and Objective-C host boundaries low-overhead for realistic embedding patterns while preserving all handle/lifetime/exception/affinity contracts.

Scope

• Add symmetric host-boundary benchmarks for evaluate/compile, direct function/method/constructor calls, native callbacks, property/index access, strings UTF-8/UTF-16, typed arrays/no-copy buffers, protect/unprotect, context groups/realms, promises/jobs, modules, inspector, and ObjC/Foundation conversion.
• Attribute boxing/handle lookup, context/realm validation, string conversion/copy, argument marshalling, callbacks/reentrancy, exception projection, locks, GC protection/barriers, and allocator traffic.
• Add borrowed/owned views, batched operations, cached descriptors, or direct native stubs only when lifetime, mutation, relocation, and ABI behavior remain exact.
• Keep public/private profile layouts and version pins immutable unless an intentional versioned contract change is made.
• Compare system JSC only for exact public/ObjC API-equivalent calls; report zig-js extensions separately.

No-workaround rules

• No raw internal pointer leak, skipped affinity/realm validation, unrooted borrowed value, elided exception, mutable buffer alias beyond contract, or benchmark-only unsafe API.

Acceptance

• Bench: define the representative dependency-free performance matrix #460 contains cold/warm, scalar/batch, small/large, callback/reentrant, GC-moving, and 1/8-context host rows with exact transcripts/checksums.
• Public C, private Home/Bun, and ObjC inventory/audit fixtures remain exact in Debug/ReleaseSafe/TSan.
• ObjC: replace libffi with an owned native ABI dispatcher #463 removes libffi without regressing the owned bridge path.
• Profiles prove reduced marshalling/copy/handle/lock cost with bounded memory and exact teardown.
• Every directly comparable accepted host-boundary row meets Roadmap: broad performance leadership with owned dependencies and no workarounds #459 gates.

Foundation

Completed public/private/ObjC profiles under #135/#138/#140 and their linked inventories; stable embedding docs in docs/api.md.

[chrisbbreuer]

String private-ABI child #622 is complete via 287550f8. JSC__JSValue__stringIncludes now shares the bounded-linear exact UTF-16 matcher and maps scratch OOM into the pending-exception channel. Home private ABI audit was 447/447 with 0 pending/unclassified; the 392/392 runtime matrix passed normal and TSan.

[chrisbbreuer]

Child #654 is complete and closed. Every private-ABI Zig build now carries the pinned checked-out Home runtime in build-graph identity, and the fresh complete Linux private-ABI boundary leg passed. Closure evidence: #654 (comment)

[chrisbbreuer]

Opened #672 to audit and correct private ABI String-value egress into semantic byte consumers. Scope is canonical property keys/atoms, URL and form parsing, module/time-zone source, and Error text, with unchanged symbols/layouts and full private/public ABI fixtures.

[chrisbbreuer]

Child #672 is complete in df57cd7e. Private decoded-string egress is canonical across keys/atoms, names, error text, URL/form/DOMURL, time-zone, and property paths; Home/Bun ABI audits and affected runtime fixtures are green with zero symbol or layout changes.

[chrisbbreuer]

Opened #674 for the remaining public C value-key boundary. JSObject*PropertyForKey currently routes String Values through the physical asStr() image; the child will make all four entry points consume canonical WTF-8, preserve allocation-free ASCII/canonical borrowing and public exception semantics, and verify the pinned C ABI with no symbol/layout change.

[chrisbbreuer]

Public value-key child #674 is complete in d56dbb80. JSObject*PropertyForKey now canonicalizes String Values representation-aware after ToPropertyKey, borrowing ASCII/canonical storage and preserving public OOM exceptions for future flat Latin-1 conversion. Public audit 117/117, Home ABI 50/50, all public host fixtures, TSan, ReleaseSafe, and 1767-pass full units are green with no ABI change.