fix: cover MCP reconnect edge cases

maintainer edit: handle prompt sessions that report Connection closed outside McpError, and match reconnect registration prefixes with the same sanitization used by MCP wrapper names.

tests/agent/test_mcp_transient_retry.py

@@ -464,3 +464,29 @@ async def test_prompt_reconnects_on_session_terminated():
     assert output == "fresh prompt"
     assert old_session.get_prompt.call_count == 1
     assert new_session.get_prompt.call_count == 1
+
+
+@pytest.mark.asyncio
+async def test_prompt_reconnects_on_connection_closed_exception():
+    """Prompt should reconnect when the SDK reports a closed session as a generic exception."""
+    old_session = AsyncMock()
+    old_session.get_prompt = AsyncMock(side_effect=RuntimeError("Connection closed"))
+    new_session = AsyncMock()
+    new_session.get_prompt = AsyncMock(return_value=_make_prompt_result("fresh prompt"))
+
+    wrapper = MCPPromptWrapper(old_session, "test_server", _make_prompt_def())
+    replacement = MCPPromptWrapper(new_session, "test_server", _make_prompt_def())
+
+    async def reconnect(server_name: str, tool_name: str, stale_tool):
+        assert server_name == "test_server"
+        assert tool_name == "mcp_test_server_prompt_test_prompt"
+        assert stale_tool is wrapper
+        return replacement
+
+    wrapper.set_reconnect_handler(reconnect)
+
+    output = await wrapper.execute()
+
+    assert output == "fresh prompt"
+    assert old_session.get_prompt.call_count == 1
+    assert new_session.get_prompt.call_count == 1