Traverse `BaseExceptionGroup` peer-close errors

`_peer_closed_errno()` followed cause and context links but did not
descend through grouped exceptions. A reset below a group could
therefore escape as `trio.BrokenResourceError` instead of the
normalized `TransportClosed` boundary.

Walk the exception tree with cycle protection, requiring every
group branch to represent peer closure before normalization. Extend
the `MsgpackTransport.send()` regression to prove all-transport and
mixed-failure behavior.

Review: PR #480 (goodboy)
https://github.com/goodboy/tractor/pull/480

(this patch was generated in some part by `opencode` using
`gpt-5.6-sol` (`openai`))

tests/ipc/test_server.py

@@ -34,31 +34,49 @@ from tractor.msg.types import Aid
 # from ._tcp import TCPAddress
 
 
-def test_send_normalizes_peer_reset():
+def test_send_normalizes_only_grouped_peer_resets():
     '''
-    Normalize Darwin's pre-handshake peer reset as transport closure.
+    Normalize only all-peer-close grouped transport failures.
 
     A UDS peer may disconnect before completing the actor handshake.
     Darwin can report the server's first handshake write as
-    `ECONNRESET`, wrapped by `trio.BrokenResourceError`; allowing
-    that raw error to escape cancels the daemon's shared IPC nursery.
-    This fake stream reproduces the exact exception chain and proves
-    `.send()` raises the expected `TransportClosed` boundary instead.
+    `ECONNRESET`, wrapped by `trio.BrokenResourceError` and potentially
+    nested in an `ExceptionGroup`. This fake stream first groups reset
+    and broken-pipe branches, proving `.send()` normalizes a complete
+    peer-close tree to `TransportClosed`. It then groups a reset with
+    an unrelated `ValueError`, proving the mixed failure remains a
+    `trio.BrokenResourceError` instead of hiding the application error.
 
     '''
-    class ResetStream:
-        async def send_all(self, data: bytes) -> None:
+    def broken_resource(err_no: int) -> trio.BrokenResourceError:
+        try:
+            raise OSError(
+                err_no,
+                'Peer closed',
+            )
+        except OSError as peer_err:
             try:
-                raise OSError(
-                    errno.ECONNRESET,
-                    'Connection reset by peer',
-                )
-            except OSError as reset_err:
-                raise trio.BrokenResourceError from reset_err
+                raise trio.BrokenResourceError from peer_err
+            except trio.BrokenResourceError as broken_err:
+                return broken_err
+
+    class GroupedFailureStream:
+        def __init__(self, exceptions: list[Exception]) -> None:
+            self.exceptions = exceptions
+
+        async def send_all(self, data: bytes) -> None:
+            grouped_err = ExceptionGroup(
+                'concurrent send failures',
+                self.exceptions,
+            )
+            raise trio.BrokenResourceError from grouped_err
 
     async def main():
         transport = object.__new__(MsgpackTransport)
-        transport.stream = ResetStream()
+        transport.stream = GroupedFailureStream([
+            broken_resource(errno.ECONNRESET),
+            broken_resource(errno.EPIPE),
+        ])
         transport._send_lock = trio.StrictFIFOLock()
         transport._laddr = 'local'
         transport._raddr = 'remote'
@@ -70,9 +88,23 @@ def test_send_normalizes_peer_reset():
                 strict_types=False,
             )
 
-        assert exc_info.value.src_exc.__cause__.errno == (
-            errno.ECONNRESET
-        )
+        grouped_err = exc_info.value.src_exc.__cause__
+        assert isinstance(grouped_err, ExceptionGroup)
+        assert len(grouped_err.exceptions) == 2
+
+        transport.stream = GroupedFailureStream([
+            ValueError('unrelated failure'),
+            broken_resource(errno.ECONNRESET),
+        ])
+        with pytest.raises(trio.BrokenResourceError) as exc_info:
+            await transport.send(
+                {'probe': True},
+                strict_types=False,
+            )
+
+        grouped_err = exc_info.value.__cause__
+        assert isinstance(grouped_err, ExceptionGroup)
+        assert isinstance(grouped_err.exceptions[0], ValueError)
 
     trio.run(main)
 

tractor/ipc/_transport.py

@@ -64,29 +64,64 @@ log = get_logger()
 
 def _peer_closed_errno(exc: BaseException) -> int|None:
     '''
-    Find a peer-close errno in a transport exception chain.
+    Classify a complete transport exception tree as peer closure.
+
+    Follow explicit cause/context links. For a `BaseExceptionGroup`,
+    require every child branch to resolve to a peer-close errno so an
+    unrelated concurrent failure is never hidden as `TransportClosed`.
 
     '''
-    seen: set[int] = set()
-    while (
-        exc
-        and
-        id(exc) not in seen
-    ):
-        seen.add(id(exc))
+    def find_peer_errno(
+        current_exc: BaseException,
+        ancestors: set[int],
+    ) -> int|None:
+        exc_id: int = id(current_exc)
+        if exc_id in ancestors:
+            return None
+
+        ancestors = ancestors | {exc_id}
         if (
-            isinstance(exc, OSError)
+            isinstance(current_exc, OSError)
             and
-            exc.errno in {
+            current_exc.errno in {
                 errno.ECONNRESET,
                 errno.EPIPE,
             }
         ):
-            return exc.errno
+            return current_exc.errno
 
-        exc = exc.__cause__ or exc.__context__
+        if isinstance(current_exc, BaseExceptionGroup):
+            child_errnos: list[int|None] = [
+                find_peer_errno(
+                    child_exc,
+                    ancestors,
+                )
+                for child_exc in current_exc.exceptions
+            ]
+            if all(
+                child_errno is not None
+                for child_errno in child_errnos
+            ):
+                return child_errnos[0]
+            return None
 
-    return None
+        chained_exc: BaseException|None = (
+            current_exc.__cause__
+            or
+            current_exc.__context__
+        )
+        if chained_exc is not None:
+            return find_peer_errno(
+                chained_exc,
+                ancestors,
+            )
+
+        return None
+
+    return find_peer_errno(
+        exc,
+        set(),
+    )
 
 
 # (codec, transport)