Harden flow advancement exit assertions

tests/test_routers_core.py

@@ -370,3 +370,25 @@ class TestFlowEndpoints:
 
         r = await client.get(f"/workstreams/{ws['id']}")
         assert r.json()["status"] == "finished"
+
+    async def test_advance_workstream_respects_current_exit_assertions(self, client):
+        await _create_domain(client)
+        topic = await _create_topic(client)
+        ws = await _create_workstream(client, topic["id"], slug="exit-blocked-ws")
+        dependency_ws = await _create_workstream(client, topic["id"], slug="unfinished-dep")
+        task = await _create_task(client, ws["id"])
+        await client.patch(f"/tasks/{task['id']}", json={"status": "done"})
+        await client.post(
+            f"/workstreams/{ws['id']}/dependencies/",
+            json={
+                "to_workstream_id": dependency_ws["id"],
+                "description": "Dependency must finish first",
+            },
+        )
+
+        r = await client.post(f"/flows/workstream/{ws['id']}/advance/finished")
+        assert r.status_code == 409
+        assert r.json()["detail"]["blocking_assertions"][0]["id"] == "dependencies.all_complete"
+
+        r = await client.get(f"/workstreams/{ws['id']}")
+        assert r.json()["status"] == "active"