Async scripts still fetching at parser EOF previously entered a queue
behind DOMContentLoaded, allowing a slow defer script to block a ready
async script or its error event. Transfer remaining async work to the
exact Document runtime producer and publish each task when its source
completes, retaining its load-delay lease.
Preserve observed async completion order across parser handoff. Add gated
success, failure, and out-of-order completion tests, and update the WPT
ledger for execution-timing/085.html.
Validation:
- cargo fmt --all
- cargo clippy --workspace --all-targets --all-features -- -D warnings
- cargo nextest run --no-fail-fast: 17,879 passed, 13 skipped
- 270 WPT cases: 257 to 258 passes, no case or subtest regressions
