[asselstine]

Summary

• Persist stop intent in both run state records and keep it monotonic across stale polls, late launch completion, and finalization retries.
• Retry idempotent cancellation automatically, record request/attempt activity, and retain the launched handle if stop arrives during startup.
• Route cancellation through both exe.dev and Amp backends.
• Cover poll-vs-stop and launch-vs-stop interleavings in PostgreSQL; existing browser coverage verifies one request reaches stopping and terminal states.

Validation

• npm ci
• npm test (full backend, isolated PostgreSQL integration, and Chromium browser suite)

[linear]

GEN-2716