fix(server): harden job eviction and worker against missing job id

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_jobs.py

@@ -41,3 +41,15 @@ def test_run_job_failure_sets_failed():
 
 def test_get_unknown_job_returns_none():
     assert jobs.get_job("nope") is None
+
+
+def test_eviction_keeps_within_cap():
+    jobs.JOBS.clear()
+    for i in range(jobs._MAX_JOBS + 25):
+        jobs.create_job(hit={"i": i}, message="m")
+    assert len(jobs.JOBS) <= jobs._MAX_JOBS
+    jobs.JOBS.clear()
+
+
+def teardown_module():
+    jobs.JOBS.clear()