fix(worker): one-shot run exits 1 on success — invert to exit 0

[RealDiligent]

Problem

validator/src/eval_backend/worker.py main() one-shot branch:

if not args.loop:
    raise SystemExit(process_once(session_factory, settings))

process_once returns 1 when it processed a job and 0 when the queue was empty — a "did work" signal for the --loop sleep decision, not a process exit status (the --loop branch uses it as if processed == 0: sleep(...)). Passing it to SystemExit inverts exit semantics: a run that successfully processes a job exits 1 (which supervisors/cron/systemd oneshot/CI read as failure), and an empty queue exits 0.

Impact

Any one-shot invocation (python -m eval_backend.worker per timer tick, instead of --loop) reports every successful evaluation as a failed process — spurious alerts/retries or a unit stuck failed.

Fix

-    if not args.loop:
-        raise SystemExit(process_once(session_factory, settings))
+    if not args.loop:
+        process_once(session_factory, settings)
+        raise SystemExit(0)

A completed one-shot pass exits 0 whether or not the queue had work; genuine failures already raise (the except Exception: ... raise inside process_once) and still exit nonzero.

Tests

New validator/tests/test_worker_exit.py stubs the DB/engine bootstrap and asserts: one-shot exits 0 for both process_once returns (1 = did work, 0 = idle), and a raising process_once still propagates (nonzero). Verified the process_once==1 case exits 1 on the old code and 0 with the fix.

Risk / tradeoffs

Minimal. --loop behavior is unchanged. Only the one-shot exit code changes, from an inverted value to correct success/failure semantics.

Closes #168

[RealDiligent]

Included the same stale-test fix as noted in #160 (the pre-existing red on main's test_wrong_theta_length_fails) so this PR's test-router passes; the substantive change is the validator worker exit code. Happy to drop that commit once #160/#161 lands.