fix(#2312): scrub model-authored result field before sentinel scan to stop false auth/prompt-too-long DoS

hive-claude/src/classify.rs

@@ -75,7 +75,26 @@ impl Sentinels {
         if matches!(ty, Some("assistant" | "user")) {
             return;
         }
-        self.scan_failure_markers(raw);
+        // The terminal `result` event carries the model's final answer in its
+        // `result` field — model-authored text, same trust level as an
+        // assistant message. A marker quoted there (e.g. the model explaining
+        // *this* code, or echoing an error string back) would falsely trip a
+        // sentinel and needlessly kill/downgrade the turn. So for a `result`
+        // event, scan the control fields (`subtype` / `error` / `is_error`)
+        // but scrub the model-authored `result` field first; a genuine
+        // prompt-too-long/auth/session signal lives in those control fields
+        // (it's emitted *instead of* a successful model answer), never in the
+        // `result` text. Other control events (`error` / `system`) are
+        // claude-authored end to end, so they scan raw.
+        if ty == Some("result") {
+            let mut scrubbed = event.clone();
+            if let Some(obj) = scrubbed.as_object_mut() {
+                obj.remove("result");
+            }
+            self.scan_failure_markers(&scrubbed.to_string());
+        } else {
+            self.scan_failure_markers(raw);
+        }
         // Rate-limit stays scoped to `error` events (unchanged): the only
         // control event that carries a rate-limit marker.
         if ty == Some("error") && RATE_LIMIT_MARKERS.iter().any(|m| raw.contains(m)) {
@@ -145,6 +164,39 @@ mod tests {
         assert!(matches!(s.soft_error(), Some(Error::PromptTooLong)));
     }
 
+    #[test]
+    fn result_field_model_text_quoting_marker_is_ignored() {
+        // The terminal `result` event's `result` field is the model's final
+        // answer. A marker quoted there (the model discussing this very code,
+        // or echoing an API error string) must NOT trip a sentinel — that was
+        // a turn-kill DoS. Covers prompt-too-long, auth, and session markers.
+        for marker in [
+            "Prompt is too long",
+            "Failed to authenticate. API Error: 401",
+            "does not match any session title",
+        ] {
+            let s = Sentinels::default();
+            let raw = format!(
+                r#"{{"type":"result","subtype":"success","is_error":false,"result":"the harness scans stdout for {marker} — see classify.rs"}}"#
+            );
+            s.scan_stdout_json(&json(&raw), &raw);
+            assert!(
+                s.soft_error().is_none(),
+                "marker {marker:?} in the model-authored result field must be ignored"
+            );
+        }
+    }
+
+    #[test]
+    fn result_control_field_still_trips_even_with_clean_result_text() {
+        // Scrubbing `result` must not blind us to a genuine signal in a
+        // control field of the same event.
+        let s = Sentinels::default();
+        let raw = r#"{"type":"result","subtype":"error","is_error":true,"error":"Failed to authenticate. API Error: 401","result":"ok"}"#;
+        s.scan_stdout_json(&json(raw), raw);
+        assert!(matches!(s.soft_error(), Some(Error::AuthFailed)));
+    }
+
     #[test]
     fn raw_non_json_marker_is_detected() {
         let s = Sentinels::default();