chore(_task_compat): harden callback suppress + close coro on unsupported backend

Author: qing-ant

src/claude_agent_sdk/_internal/_task_compat.py

@@ -99,7 +99,11 @@ def _mark_done(self, exc: BaseException | None) -> None:
         self._exception = exc
         self._done_event.set()
         for cb in self._callbacks:
-            with suppress(Exception):
+            # Suppress BaseException so a misbehaving callback can never
+            # propagate out of the system-task _runner (which would crash
+            # trio with TrioInternalError). The actual callbacks used here
+            # are set.discard / dict.pop, so this is purely defensive.
+            with suppress(BaseException):
                 cb(self)
         self._callbacks.clear()
 
@@ -146,6 +150,9 @@ async def _runner() -> None:
 
         trio.lowlevel.spawn_system_task(_runner)
         return handle
+    # Unsupported backend: close the coroutine so we don't leak a "coroutine
+    # was never awaited" RuntimeWarning on top of the RuntimeError.
+    coro.close()
     raise RuntimeError(
         f"Unsupported async backend: {backend!r}. "
         "claude_agent_sdk requires asyncio or trio."