bf: pass aiohttp timeouts to fsspec in RemoteReadableAsset.open()

The dandi-archive CLI integration tests started hanging for 6 hours
on November 24, 2025 (dandi/dandi-archive#1762).

Investigation of tinuous CI logs showed:

- Nov 21 (last success): test_nwb2asset_remote_asset XFAIL'd in 0.4s
- Nov 24 (first hang): same test hung for 6 hours until GitHub killed it
- ALL test runs on Nov 24-25 hung, across unrelated PRs

The code flow that hangs is:

  nwb2asset() → get_metadata() → _get_pynwb_metadata()
    → open_readable() → RemoteReadableAsset.open()
      → fsspec.open(url).open()
        → aiohttp HTTP read from minio in Docker
          → fsspec sync() blocks in threading.Event.wait()

The key environmental change between Nov 21 and Nov 24 was dandi-cli
PR #1744 updating dandischema from <0.12.0 to ~=0.12.0.  With
dandischema 0.11.x, the test hit a quick model validation mismatch
(completing as XFAIL in 0.4s before reaching the fsspec read).  With
dandischema 0.12.0 (vendor-configurable models, schema 0.7.0), that
mismatch no longer occurs, so the test now proceeds to the actual
fsspec HTTP read — which hangs.

The hang itself is a known interaction between h5py, fsspec, and GC:

- h5py holds a global lock while reading from Python file objects
- fsspec's sync() runs async aiohttp coroutines on a background thread
  and blocks the calling thread in threading.Event.wait()
- Without socket-level timeouts, aiohttp blocks forever on stalled
  connections (aio-libs/aiohttp#11740)
- GC running during this window can deadlock with h5py's lock
  (h5py/h5py#2019)

The fix: pass explicit ClientTimeout to aiohttp via fsspec's
client_kwargs so that stalled connections raise TimeoutError instead
of blocking indefinitely.

Additionally, the dandi-archive CI never had a pytest --timeout because
dandi-cli's tox.ini [pytest] addopts (--timeout=300) are not read when
pytest runs from the dandi-archive rootdir via `pytest --pyargs dandi`.

References:
- fsspec/filesystem_spec#1666
- h5py/h5py#2019
- aio-libs/aiohttp#11740
- #1762
- #1450

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: yarikoptic

dandi/misctypes.py

@@ -345,10 +345,27 @@ def open(self) -> IO[bytes]:
         # Optional dependency:
         import fsspec
 
+        from aiohttp import ClientTimeout
+
         # We need to call open() on the return value of fsspec.open() because
         # otherwise the filehandle will only be opened when used to enter a
         # context manager.
-        return cast(IO[bytes], fsspec.open(self.url, mode="rb").open())
+        #
+        # Pass explicit timeouts to aiohttp to prevent indefinite hangs in
+        # fsspec's sync() wrapper.  Without these, a stalled connection to S3
+        # (or minio in tests) causes fsspec's background IO thread to block
+        # forever, which in turn blocks the calling thread in
+        # threading.Event.wait() — see https://github.com/fsspec/filesystem_spec/issues/1666
+        return cast(
+            IO[bytes],
+            fsspec.open(
+                self.url,
+                mode="rb",
+                client_kwargs={
+                    "timeout": ClientTimeout(total=120, sock_read=60, sock_connect=30)
+                },
+            ).open(),
+        )
 
     def get_size(self) -> int:
         return self.size