[Patrick Kelly (pk8189)]

Description

Two things, both test-only:

1. Re-enables pctx_executor's unit tests. #[cfg(test)] mod tests; was dropped from crates/pctx_executor/src/lib.rs in 52efa39 ("execution event trace", shipped in v0.7.0), so nothing under src/tests/ has compiled or run since — including concurrent_v8_stress, our guard against the multi-threaded V8 isolate crash. All 51 existing tests still pass once re-enabled.
2. Adds runtime_semantics.rs (15 tests) pinning behaviour that a deno_core / V8 bump can silently change. Written while validating chore: bump deno stack to deno_core 0.412 / deno_ast 0.53 #167; they pass identically on main and on chore: bump deno stack to deno_core 0.412 / deno_ast 0.53 #167's branch.

What the new tests cover

• op_invoke scheduling: tool calls resolve after microtasks; Promise.all calls overlap (and start before any finishes); sequential calls don't overlap
• Tool errors: catchable rejections, allSettled / race, uncaught tool error fails the execution
• op_sleep timers: ordering vs microtasks and by delay, setInterval + clearInterval
• Event loop drains timers and tool calls scheduled after module evaluation (stdout still captured)
• Unhandled rejections fail; runtime errors include a stack; stack overflow is a catchable RangeError
• ICU-backed Intl (time zones, plural rules, collation, locale casing, Japanese era) and Temporal (incl. a DST gap)
• Sync and async WebAssembly (async compile depends on V8 platform tasks being pumped)
• Multi-threaded execution (one current-thread runtime per OS thread, as in the session server) with tool calls, timers and async wasm

Type of Change

• Test coverage improvement

Testing

cargo test -p pctx_executor --lib   # 66 passed, on main and on #167's branch (x4)
cargo fmt --all --check

No new clippy warnings from the added file (clippy isn't enforced in CI; the re-enabled older test files carry a few pre-existing pedantic warnings).

Notes

Not covered here, found while probing — both pre-existing on main, to be filed separately:

• A throw inside a setTimeout callback, or Atomics.waitAsync, hangs execute() indefinitely while holding V8_MUTEX.
• Sandboxed code can dynamically import arbitrary .json / .js files from the host filesystem via FsModuleLoader.

Documentation

• CHANGELOG.md updated under "Unreleased"

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