fix(py): a panic in the library raises clawhdf5.InternalError, not PanicException

PanicException derives from BaseException, so `except Exception` let a
library bug through. Every call from the bindings into the library now
runs under catch_unwind and a panic becomes InternalError (RuntimeError)
naming the object. Tests: a hidden hook panics inside the guard; and the
v4 chunk indexes are compared with h5py from Python — with the library
fix reverted, ds[0:30] of the implicit-index dataset now raises
InternalError instead of aborting the test run.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

crates/clawhdf5-py/tests/test_read_vs_h5py.py

@@ -467,3 +467,47 @@ def test_threads_read_the_same_file(pair):
     with ThreadPoolExecutor(8) as pool:
         list(pool.map(work, range(8)))
     assert not errors, errors[:3]
+
+
+def _v4_index_fixture(h5py, path):
+    """One 2-D dataset per v4 chunk index (HDF5 1.10+ layout, libver='latest')."""
+    data = (np.arange(37 * 23, dtype="<i4") * 7 - 1000).reshape(37, 23)
+    early = h5py.h5p.create(h5py.h5p.DATASET_CREATE)
+    early.set_alloc_time(h5py.h5d.ALLOC_TIME_EARLY)
+    with h5py.File(path, "w", libver="latest") as f:
+        f.create_dataset("implicit", data=data, chunks=(5, 4), dcpl=early)
+        f.create_dataset("fixed_array", data=data, chunks=(5, 4), compression="gzip")
+        f.create_dataset("extensible_array", data=data, chunks=(5, 4), maxshape=(None, 23), compression="gzip")
+        f.create_dataset("btree2", data=data, chunks=(5, 4), maxshape=(None, None), compression="gzip")
+        f.create_dataset("single_chunk", data=data, chunks=(37, 23), compression="gzip")
+
+
+V4_KEYS = [
+    slice(0, 3), slice(0, 30), (slice(7, 16), slice(3, 9)), (36, 22), (slice(None, None, 3), slice(1, None, 4)),
+    (slice(1, None, 2), Ellipsis), (Ellipsis, slice(2, 22)), [0, 5, 6, 36], (slice(None), [0, 3, 22]), -1, (),
+]
+
+
+def test_every_v4_chunk_index_matches_h5py(h5py, tmp_path):
+    """Partial reads of each v4 chunk index. The implicit index (early
+    allocation, no filters) used to panic in the library for any selection
+    covering more than half the dataset, e.g. ds[0:30]."""
+    path = str(tmp_path / "v4.h5")
+    _v4_index_fixture(h5py, path)
+    with h5py.File(path, "r") as theirs, clawhdf5.File(path, "r") as ours:
+        for name in theirs:
+            for key in V4_KEYS:
+                assert_same(ours[name][key], theirs[name][key], f"{name}[{key!r}]")
+
+
+def test_a_library_panic_is_an_ordinary_exception():
+    """PyO3 turns a Rust panic into PanicException, a BaseException that
+    `except Exception` does not catch. Every call into the library is
+    guarded, so a panic surfaces as clawhdf5.InternalError instead."""
+    assert issubclass(clawhdf5.InternalError, RuntimeError)
+    with pytest.raises(clawhdf5.InternalError, match="deliberate panic"):
+        clawhdf5._panic_for_test()
+    try:
+        clawhdf5._panic_for_test()
+    except Exception:  # noqa: BLE001 - the point of the test
+        pass