Harden runtime cleanup, cancellation, and event isolation

[vamgan]

Summary

• clean up provisioned runtime resources when startup/streaming fails after provisioning
• prevent cancellation from mutating terminal tasks and avoid racing in-progress cancellation to succeeded
• reject adapter events emitted for the wrong task ID before persistence
• add regression coverage for cleanup failure paths, cancellation races, terminal cancellation, and event isolation

Closes #8
Closes #9
Closes #10

Tests

• npm run typecheck
• npm test -- --run
• npm run build