test(obs): exercise the worker's obs path, don't just read its source

The two existing worker tests assert on `inspect.getsource(AgentexWorker.run)` — they
pin that init_sgp_obs() and both drains are CALLED, which is worth pinning, but they
cannot catch a call that is written correctly and then raises. So the claim "a Temporal
worker starts fine without the broker token" rested on source inspection, not on the
path having been run.

That matters because a build with no broker token produces an image with no sgp-obs in
it, and for a Temporal agent the model calls happen in the worker process — the one
this PR newly touches.

Now exercised for real with the import blocked: the module imports, an AgentexWorker
constructs, init_sgp_obs() returns not_installed, and both drains complete with nothing
ever wired. Verified by hand first, at which point it passed — so this is a guard
rather than a fix.

Keeps the source-inspection tests alongside it: one proves the wiring exists, the other
proves it is harmless. Neither alone is enough.

137 tests, ruff clean, pyright 0 errors, all with sgp-obs absent.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: stephen-wang24

src/agentex/lib/sdk/fastacp/base/tests/test_shutdown_hooks.py

@@ -16,6 +16,22 @@
 )
 
 
+def _block_sgp_obs_import(monkeypatch):
+    """Make `import sgp_obs` fail, i.e. the image a tokenless build produces."""
+    import sys
+    import builtins
+
+    monkeypatch.delitem(sys.modules, "sgp_obs", raising=False)
+    real_import = builtins.__import__
+
+    def blocked(name, *args, **kwargs):
+        if name == "sgp_obs" or name.startswith("sgp_obs."):
+            raise ImportError("No module named 'sgp_obs'")
+        return real_import(name, *args, **kwargs)
+
+    monkeypatch.setattr(builtins, "__import__", blocked)
+
+
 class _Processor:
     def __init__(self, explode: bool = False) -> None:
         self.calls = 0
@@ -247,3 +263,40 @@ def shutdown(self):
             f"process took {elapsed:.1f}s to exit with a 30s stalled flush and a "
             "0.25s budget; the flush thread is blocking interpreter shutdown"
         )
+
+
+class TestTheWorkerObsPathRunsWithoutSgpObs:
+    """The image a build with NO broker token produces has no sgp-obs in it, and a
+    Temporal agent's model calls happen in this process.
+
+    The two tests above pin that ``run()`` *calls* these, by reading its source. That
+    cannot catch a call that is written correctly and then raises, so this exercises the
+    sequence for real. Together: one proves the wiring exists, the other proves it is
+    harmless.
+    """
+
+    def test_the_worker_module_imports_and_constructs(self):
+        from agentex.lib.core.temporal.workers.worker import AgentexWorker
+
+        # port 0 so nothing binds a real health port during the test
+        assert AgentexWorker(task_queue="probe", health_check_port=0) is not None
+
+    async def test_init_and_both_drains_are_inert(self, monkeypatch):
+        """Exactly what ``run()`` does: init at entry, both drains in its finally —
+        with nothing wired, which is every agent that has not adopted."""
+        from agentex.lib.core.observability import sgp_obs_setup
+        from agentex.lib.core.observability.sgp_obs_setup import (
+            init_sgp_obs,
+            shutdown_sgp_obs,
+        )
+
+        monkeypatch.delenv("SGP_OBS_ENABLED", raising=False)
+        sgp_obs_setup._reset_for_tests()
+        try:
+            _block_sgp_obs_import(monkeypatch)
+            assert init_sgp_obs() == "not_installed"
+            # Neither drain may raise just because nothing was ever wired.
+            await shutdown_sync_tracing_processors()
+            await shutdown_sgp_obs()
+        finally:
+            sgp_obs_setup._reset_for_tests()