fix(toolwalk): retain immutable timeout cancellation authority across subsequent run selection

[dennisonbertram]

[dennisonbertram]

Hosted CI follow-up: PR #1146 head 05ee403 exposed a fixture race in B-before-A EOF/terminal tests. A now has a submission-bound 80ms deadline, while waitForTerminal no longer controls it; under load timeout can legitimately win before EOF. Acceptance addition: use the injected frozen monotonic clock for EOF/terminal-before-timeout ordering, never advance it; synchronize causally on A event-stream registration and lifecycle failure/terminal; retain B selection/no-action proof. Narrow waitForTerminal so it no longer accepts an ignored timeout configuration. No duplicate issue: this is deterministic proof hardening within open #1136.