Wire Datasette.close into ASGI lifespan shutdown

AsgiLifespan now receives an on_shutdown callback that invokes
Datasette.close(), so resources are released cleanly when the ASGI server
delivers a lifespan.shutdown message (SIGTERM / SIGINT for uvicorn).

Refs #2692

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

datasette/app.py

@@ -2338,10 +2338,13 @@ class Datasette:
                 if not database.is_mutable:
                     await database.table_counts(limit=60 * 60 * 1000)
 
+        async def _close_on_shutdown():
+            self.close()
+
         asgi = CrossOriginProtectionMiddleware(DatasetteRouter(self, routes), self)
         if self.setting("trace_debug"):
             asgi = AsgiTracer(asgi)
-        asgi = AsgiLifespan(asgi)
+        asgi = AsgiLifespan(asgi, on_shutdown=[_close_on_shutdown])
         asgi = AsgiRunOnFirstRequest(asgi, on_startup=[setup_db, self.invoke_startup])
         for wrapper in pm.hook.asgi_wrapper(datasette=self):
             asgi = wrapper(asgi)

tests/test_internals_datasette.py

@@ -256,6 +256,29 @@ async def test_datasette_close_raises_on_use():
         await ds.get_internal_database().execute("select 1")
 
 
+@pytest.mark.asyncio
+async def test_asgi_lifespan_shutdown_closes_datasette():
+    ds = Datasette(memory=True)
+    app = ds.app()
+    # Drive an ASGI lifespan: startup, then shutdown.
+    messages_sent = []
+    inbox = [
+        {"type": "lifespan.startup"},
+        {"type": "lifespan.shutdown"},
+    ]
+
+    async def receive():
+        return inbox.pop(0)
+
+    async def send(message):
+        messages_sent.append(message)
+
+    await app({"type": "lifespan"}, receive, send)
+    assert {"type": "lifespan.startup.complete"} in messages_sent
+    assert {"type": "lifespan.shutdown.complete"} in messages_sent
+    assert ds._closed
+
+
 @pytest.mark.asyncio
 async def test_datasette_close_continues_past_db_error():
     # If one Database raises during close(), the others still get closed.