fix(jsc): deliver capped-worker termination after GC

[steipete]

A Worker using resourceLimits.maxOldGenerationSizeMb can keep running full GCs for seconds after its managed live heap exceeds the limit and Bun requests termination. The one-byte allocation allowance leaves very little execution in optimized JavaScript, so JSC's signal sender repeatedly misses the JIT window needed to install trap breakpoints. The correct ERR_WORKER_OUT_OF_MEMORY and exit code 1 arrive late.

Invalidate optimized code from the mutator's GC epilogue when a heap-limit breach has occurred and a trap is pending. This reuses the API-lock entry invalidation helper and respects DeferTraps; existing JavaScript safe points deliver the exception. Full-GC live accounting, ArrayBuffer exclusions, heap budgets and watchdog ownership remain intact. This is independent of the pending cadence changes in #14/#15.

Median time from Worker construction to the error event, five independent runs per arm and cap, using matched Bun source and build settings:

Platform / cap	Unchanged engine median	Candidate median	Node 24 median
macOS arm64 / 32 MiB	544.7 ms	20.3 ms	54.1 ms
macOS arm64 / 256 MiB	6,335.7 ms	97.3 ms	271.4 ms
macOS arm64 / 512 MiB	5,050.1 ms	257.6 ms	526.5 ms
Linux x64 / 32 MiB	1,881.8 ms	56.6 ms	117.0 ms
Linux x64 / 256 MiB	4,623.9 ms	372.2 ms	640.6 ms
Linux x64 / 512 MiB	19,451.1 ms	1,060.1 ms	1,404.2 ms

Node is the contract reference; the macOS Node observations come from the preceding same-host series. The Linux comparison interleaves all three arms. All final Linux trials report the expected error/exit and no guard intervention. These are measurements of a retained-object loop, not a universal runtime benchmark.

The deterministic native regression blocks the signal sender and fails the unchanged engine on a second over-cap full GC. The candidate unwinds after one, in 0.075 ms on macOS and 0.095 ms on Linux. A native survivor retains 30 MiB under a 32 MiB cap while churning temporary arrays; it ends at 31,541,027 managed bytes without OOM. The added Bun Worker survivor retains 22 MiB plus 64 MiB external storage on both platforms. A portable Node/Bun reference uses 20 MiB retained because V8's VM overhead leaves different usable space on x64.

Validation: 15 resource-limit and 310 surrounding Worker cases pass on each platform; nine native controls pass on each. Four unchanged OpenClaw consumers pass before/after, 27 cases per arm, including a warm worker with a 512 MiB cap. Scoped P2 autoreview is clean. Linux artifact compilation caught a test include-path issue hidden by the macOS header map; the corrected packaged-header spelling is re-reviewed and native-tested. The first corrected-head Linux run passed all functional commands, then failed a stale seven-row native-output inventory. The two new cases require nine rows. The downloaded artifact contains all nine passes; replaying the corrected verifier passes 83 selected files / 85 result rows with zero regressions and all engine/compatibility gates. The one-line inventory correction is P2-clean. Fresh exact-head engine CI and Linux ARM64 CI pass at 7335155ebd04d6ba911d1a1b920a787c319fef25.

Upstream's resource-limit proposal oven-sh/bun#32896 remains open; the search found no existing trap-delivery fix. Delivery requires the next qualified OpenClaw WebKit artifact release and a matching Bun rebuild.

Release-line PR; main companion: #19.