ABI: implement exception scopes and termination control

[chrisbbreuer]

Parent

• Roadmap: implement every README-declared missing runtime surface #134
• ABI: define and implement versioned Bun and Home private-JSC profiles #140
• ABI: implement the pinned Home private-JSC profile #163
• ABI: implement the pinned Bun private-JSC profile #164

Scope

Implement the 18 shared pinned exception/termination imports:

• all six TopExceptionScope__* operations;
• JSGlobalObject__clearExceptionExceptTermination, clearTerminationException, createOutOfMemoryError, requestTermination, throwOutOfMemoryError, and throwStackOverflow;
• JSC__VM__clearHasTerminationRequest, executionForbidden, hasTerminationRequest, notifyNeedTermination, setExecutionForbidden;
• JSC__JSValue__isTerminationException.

Acceptance criteria

• The caller-provided 8/56-byte, 8-aligned TopExceptionScope storage retains exact VM identity, supports pure vs trap-aware exception reads, unconditional clear, assertion checking, and safe destruction without escaping stack storage.
• Termination requests are VM-shared and thread-safe; trap-aware scope lookup materializes one stable termination exception, while pure lookup does not process a pending request.
• Normal exceptions clear through clearExceptionExceptTermination; termination remains and returns false until clearTerminationException clears both the request and thrown termination exception.
• VM request and execution-forbidden controls preserve the pinned behavior, including the source contract where setExecutionForbidden makes execution forbidden regardless of the boolean argument.
• OOM creation returns a selected-realm Error without throwing; OOM and stack-overflow throw operations publish exact Error kinds while preserving the first pending exception.
• Focused coverage includes 8- and 56-byte scope buffers, sibling realms/VM identity, normal and primitive exceptions, pending requests, materialization order, stable exception identity, classification, clearing/resumption, foreign/invalid pointers, forbidden state, OOM/stack errors, and first-exception preservation.
• Inventories, README/API evidence, and parent trackers are regenerated from checked-in results.

[chrisbbreuer]

Implemented and documented on main.

Evidence:

• 929284a6 — 18 pinned exception-scope, termination, VM-control, and native-error imports plus regenerated inventories
• 0de075b8 — README/API/Home/ABI evidence and current counts
• zig build test-home-private-abi -Doptimize=Debug — 136/136 linked runtime matrix passed
• zig build home-private-abi-audit bun-private-abi-audit — Home 137/431 (294 pending), Bun 131/421 (290 pending), zero drift/unclassified entries

Coverage includes both caller storage layouts, sibling/foreign VM isolation, normal and primitive exceptions, pure/trap-aware ordering, stable termination identity/classification, selective and explicit clearing, pinned set-only execution-forbidden behavior, selected-realm OOM/stack errors, null boundaries, and first-exception preservation. Benchmark results were intentionally not rerun or altered because this is an ABI-only slice.