[DanielNetzer]

Implements issue #294.

Molecule: mol-294-640ebed9458ff7d1093a81f4
Formula: forgecell-github-issue
Base: d26c94b9c86b343d8e71451d03de66aae04bbe05
Delivery: 13809d053b8af01165ee274bef346cfc0314abd3

Awaiting exact-commit CI and human review. Harness-reported checks are not independent CI evidence. No merge, deployment or issue closure is authorized.

[DanielNetzer]

Adversarial review (plugin runtime hardening): one correctness MEDIUM, fixed in this PR with one verify pass. On macOS, waitid(WEXITED|WNOWAIT) can return for a leader that is only stopped, so the group kill could hit a live plugin. waitTerminated now sends the group kill only when si_code is CLD_EXITED, CLD_KILLED or CLD_DUMPED (1–3), and a seam-driven test covers the exited, killed and stopped cases. In the same round, Initialize now compares the server's raw contract (InitializeContract). A contract padded with Cf or bidi characters is refused, and only a sanitized copy is kept for reporting.

There is one by-design base-test change. TestClientIgnoresABoundedNumberOfNotifications scripted protocolVersion: "x", which is now refused. It is declared as an expected protected delta.

LOWs, for later:

1. launch.go waitTerminated: with WNOWAIT, a stopped leader keeps reporting as stopped, so the loop busy-spins until the leader resumes or Shutdown kills it after the grace period. A short backoff on non-terminal codes would fix it.
2. removeRunDir and unlockTree: the run dir is checked with Lstat and then opened with os.OpenRoot by path. Fix: require os.SameFile after OpenRoot. Exploiting this needs write access to the Lab temp root.
3. The configure comment overstates when the group is signalled. os/exec's watchCtx can still Cancel in a tiny window after Process.Wait; Shutdown's own ordering is safe.
4. The interpreter re-verify is a hash-by-path followed by exec-by-path. The remaining window can't be closed without fexecve, and the comment says so.
5. Start's error path ignores the removeRunDir error, so a cleanup failure before any plugin has run is silent.

Integration: I applied this branch to current main (with #297). go vet ./... passes, and so does go test -timeout 20m ./internal/{plugin,safetext,forgesync,ui,tracker}/.... One earlier local run showed a conformance failure while the machine was heavily loaded. It didn't reproduce in 8 more runs, alone or combined. Watch CI.