fix(mcp): retry stale pipe transport failures

Treat closed-resource, closed-transport, broken-pipe, and EOF MCP failures as stale session equivalents so the existing reconnect/retry-once path can recover. Add regression coverage for the stale-pipe marker variants.\n\nChecks:\n- python -m py_compile tools/mcp_tool.py tests/tools/test_mcp_tool_session_expired.py\n- python -m pytest tests/tools/test_mcp_tool_session_expired.py -q -o addopts=\n- selected secret scan over touched files

tests/tools/test_mcp_tool_session_expired.py

@@ -53,6 +53,17 @@ def test_is_session_expired_detects_session_terminated():
     assert _is_session_expired_error(RuntimeError("Session terminated")) is True
 
 
+def test_is_session_expired_detects_stale_pipe_and_closed_transport_variants():
+    """Stdio/AnyIO stale-pipe failures usually surface as closed-resource
+    or broken-pipe text, not an HTTP session-expired JSON-RPC error."""
+    from tools.mcp_tool import _is_session_expired_error
+    assert _is_session_expired_error(RuntimeError("ClosedResourceError")) is True
+    assert _is_session_expired_error(RuntimeError("closed resource in MCP child")) is True
+    assert _is_session_expired_error(RuntimeError("transport is closed")) is True
+    assert _is_session_expired_error(RuntimeError("Broken pipe while writing request")) is True
+    assert _is_session_expired_error(RuntimeError("End of file from MCP server")) is True
+
+
 def test_is_session_expired_is_case_insensitive():
     """Match uses lower-cased comparison so servers that emit the
     message in different cases (SDK formatter quirks) still trigger."""

tools/mcp_tool.py

@@ -1739,6 +1739,12 @@ _SESSION_EXPIRED_MARKERS: tuple = (
     "session not found",
     "unknown session",
     "session terminated",
+    "closedresourceerror",
+    "closed resource",
+    "transport is closed",
+    "connection closed",
+    "broken pipe",
+    "end of file",
 )