Platform: support Windows and restricted-JIT Darwin profiles

[chrisbbreuer]

Parent: #459
Depends on: #483, #484, #498, #499
Related: #485

Goal

Declare and implement Windows x86-64/ARM64 plus restricted-JIT Darwin profiles with explicit native, AOT, or fast-VM performance contracts.

Current boundary

docs/platforms.md explicitly claims no Windows release platform. The optimizer inventory rejects iOS AArch64 publication. #484/#485 cover macOS/Linux native backends but leave Windows and platforms where executable-memory policy forbids normal JIT publication undefined.

Scope

• Add versioned platform profiles for Windows x86-64, Windows ARM64, iOS/tvOS/visionOS as appropriate, and macOS deployments with JIT disabled by policy.
• Implement Windows executable-memory allocation/protection/cache synchronization, ABI/calling conventions, unwind tables, exception/trap integration, thread-local/runtime primitives, and artifact retirement through JIT: unify backend-neutral codegen and W^X memory contracts #483.
• Extend owned x86-64/AArch64 encoders and backend tests to Windows ABIs; never depend on an external assembler/JIT/runtime.
• Define entitlement/policy detection for Darwin-family restricted hosts and select VM: build a fast no-JIT execution tier for restricted hosts #498/Runtime: add versioned bytecode, realm snapshots, and AOT artifacts #499 exact no-JIT/AOT paths without attempting forbidden mappings.
• Gate portable engine, C API, private/public ABI where applicable, Workers/threads, GC, Wasm, modules, filesystem/provider boundaries, and packaging.
• Collect correctness and performance evidence on real supported hardware; cross-build/emulation proves buildability only.

No-workaround rules

• No RWX, writable published code, disabled platform mitigations, emulation-only performance claim, undocumented feature loss, external JIT/compiler, or platform marked native when optimizer publication remains zero.

Acceptance

• Platform inventory names OS versions, architectures, ABI, native/no-JIT/AOT mode, executable policy, sanitizer support, CI/evidence host, and explicit unsupported cases.
• Windows native profiles pass forced-tier, unwind, GC relocation, no-GIL, debugger/termination, OOM/fault, artifact-lifetime, test262, Wasm, ABI, and embedding gates.
• Restricted profiles pass the complete VM: build a fast no-JIT execution tier for restricted hosts #498/Runtime: add versioned bytecode, realm snapshots, and AOT artifacts #499 contract without executable mapping attempts.
• Real-hardware Bench: define the representative dependency-free performance matrix #460/Perf: add causal attribution and exact-parent regression infrastructure #461 evidence records cold/warm throughput, compile/load cost, code/metadata/RSS, and tier attribution.
• Owned dependency/offline gates remain green.

Foundation

Current declared matrix: docs/platforms.md and docs/.data/optimizer-release-inventory.json.