feat(tests): make the suite runnable under bun test --parallel

[TheGreatAxios]

Summary

• Adds bun run test:parallel, a seeded bun test --parallel wrapper with a stall watchdog that kills livelocked runs and retries them
• Exposes config overrides for the tool-watchdog salvage grace, exec-shutdown teardown deadline, and agents-panel linger so timing-sensitive tests inject deterministic values
• Replaces wall-clock sleeps with condition polling, flush barriers, and a frozen clock in the approval-log, transcript-anchor, and stall-recovery tests

Verification

• bun run check passes, including the serial suite (7313 pass, 0 fail)
• scripts/test-parallel.test.ts covers the watchdog retry and argument handling

Fixes CL-7909

[linear-code]

CL-7909

[TheGreatAxios]

Critic review · Comment (merge-ready with doc nits)

Note: this PR is feat(tests): make the suite runnable under bun test --parallel (16 files), not a PerfTrace doc fix — reviewing what is actually here.

Mechanism verified by reading the diff plus runtime probes on Bun 1.4.0: detached: true does put the child in its own process group (pgid == pid; without it pgid == parent group), so the group SIGTERM/SIGKILL stall kill and the grandchild-reap test are sound. Bun.spawn + detached also passes this repo's tsc flags clean. Approval-log flush() chains synchronously at settle() time, so awaiting it post-decision is deterministic. Linger/salvage/teardown overrides thread correctly (constructor arg order, spread order, and Partial forwarding all check out), and CI (.github/workflows/ci.yml) is indeed still test:paths-only.

Should-fix (doc accuracy, non-blocking)

• scripts/test-parallel.ts header + docs/IMPLEMENTATION.md parallel-runs bullet — the failure signature ("worker spins at 100% CPU holding a zombie git child") contradicts the cited upstream issue: bun test --parallel intermittently deadlocks: one worker wedges with all threads in condvar waits (lost wakeup), parent hangs forever oven-sh/bun#36235 is now Closed, and its diagnostics say the opposite — all worker threads parked in condvar waits, nothing spinning, and "no child processes". Either describe the locally-observed signature without pinning it on #36235, or re-cite. "Still open as of 1.4.2" is stale.
• src/tui/transcript-anchor.test.ts frameWith — returns the last frame on deadline instead of throwing, so a genuine never-paints failure surfaces as a confusing content diff rather than a timeout. Consider an explicit timeout assertion.

Nits

• src/index.ts teardownDeadlineMs — process-global, last-wins, no validation; the documented single-setter assumption makes this fine, noting only.
• src/subagent/nudge-director.test.ts frozenNow — frozen clock means the stall nudge can never fire in those three tests; correct for non-timing tests, just do not copy the pattern into a stall-behavior test.

Verdict

Merge-ready. The watchdog design is signature-agnostic, so the issue-citation drift does not affect correctness; fix the citation wording before or just after merge.