test(gate): tolerate EPIPE in the no-node test; harness asserts skill.triage

The no-node test runs the hook with an empty PATH, so cat is missing too
and the script exits before reading stdin; on Linux the test's write can
lose that race (CI run 6483). The child exiting unread is the no-node
path working. Harness: assert_skill_triage on chain and microvm — the
event must exist; agreement with what the agent read is reported.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01WZb5A2kfVfjpdwSochkuHz

crates/cm-api/src/vm_tool_gate.rs

@@ -890,14 +890,15 @@ mod shell_tests {
             .stderr(Stdio::piped())
             .spawn()
             .expect("spawn sh");
-        child
-            .stdin
-            .as_mut()
-            .unwrap()
-            .write_all(
-                br#"{"tool_name":"Bash","tool_input":{"command":"git push --force origin main"}}"#,
-            )
-            .unwrap();
+        // With an empty PATH `cat` is missing too, so the script never reads
+        // its stdin and may exit before this write lands. EPIPE here IS the
+        // no-node path succeeding, not a failure: CI run 6483 lost that race
+        // on Linux after every earlier run had won it.
+        if let Err(e) = child.stdin.as_mut().unwrap().write_all(
+            br#"{"tool_name":"Bash","tool_input":{"command":"git push --force origin main"}}"#,
+        ) {
+            assert_eq!(e.kind(), std::io::ErrorKind::BrokenPipe, "{e}");
+        }
         let out = child.wait_with_output().expect("wait");
 
         assert_eq!(