Torture harness: dump all stacks on the first hang; SQLite 3.53 test fix

test_new_memory_database_is_not_scanned_at_registration filled the memory
database with VACUUM INTO, which SQLite 3.53 (the free-threaded 3.14 build)
refuses for an existing in-memory database; it now uses a plain connection.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EwkLo2rJWidpkDVT3HkvNv

tests/connection_torture.py

@@ -362,6 +362,15 @@ class Torture:
         with self.lock:
             self.problems.append({"kind": kind, "message": message[:2000]})
 
+    def dump_stacks_once(self, why):
+        """Every thread's stack on stderr, the first time something hangs."""
+        with self.lock:
+            if getattr(self, "_dumped", False):
+                return
+            self._dumped = True
+        sys.stderr.write(f"\n=== {why}: stacks of all threads ===\n")
+        faulthandler.dump_traceback(all_threads=True)
+
     def count(self, key):
         with self.lock:
             self.counts[key] += 1
@@ -414,6 +423,7 @@ class Torture:
             value = await asyncio.wait_for(awaitable, timeout)
         except asyncio.TimeoutError:
             self.problem("hang", f"{op} on {group} did not finish in {timeout}s")
+            self.dump_stacks_once(f"{op} on {group} hung")
             return False, None
         except asyncio.CancelledError:
             raise

tests/test_connection_review_fixes.py

@@ -619,10 +619,12 @@ async def test_new_memory_database_is_not_scanned_at_registration():
     state = memory._watch_state
     assert state.scan_future is None
     assert state in watcher._pending
-    # Fill it the way the plugin does
+    # Fill it from a connection of its own, as the plugin does (it uses
-    conn = sqlite3.connect(":memory:")
+    # VACUUM INTO, which newer SQLite versions refuse for an existing
+    # in-memory database, so a plain connection here)
+    conn = sqlite3.connect("file:review_fixes_copy?mode=memory&cache=shared", uri=True)
     conn.execute("create table copied (id integer)")
-    conn.execute("VACUUM INTO 'file:review_fixes_copy?mode=memory&cache=shared'")
+    conn.commit()
     conn.close()
     # The next request scans it
     response = await ds.client.get("/copy.json")