diff --git a/.gitignore b/.gitignore
index 994aa639..d7d12323 100644
--- a/.gitignore
+++ b/.gitignore
@@ -229,6 +229,12 @@ app/AVAX/
 .DS_Store
 Thumbs.db
 desktop.ini
+app/security_audit.jsonl
+app/credential_audit.jsonl
+
+# Contributor working notes (not project docs)
+CLAUDE.md
+LEARNINGS.md
 
 # Local-only skills (not committed to repo)
 .github/skills/
diff --git a/app/pt_security_logger.py b/app/pt_security_logger.py
index 6d0c9e0b..b418b73f 100644
--- a/app/pt_security_logger.py
+++ b/app/pt_security_logger.py
@@ -47,7 +47,6 @@
 # Security event types
 # ---------------------------------------------------------------------------
 class SecurityEventType(Enum):
-    AUTH_ATTEMPT = "auth_attempt"  # API key authentication attempt
     AUTH_SUCCESS = "auth_success"  # Successful authentication
     AUTH_FAILURE = "auth_failure"  # Failed authentication
     CREDENTIAL_USE = "credential_use"  # Credential accessed/used
@@ -248,16 +247,20 @@ def _create_handler(self) -> _SecureRotatingFileHandler:
 
     def close(self) -> None:
         """Flush and close the underlying handler (call on shutdown).
-        Idempotent: safe to call multiple times."""
-        if self._handler is None:
-            return
-        handler = self._handler
-        self._handler = None
-        try:
-            handler.flush()
-            handler.close()
-        finally:
-            self._audit_logger.removeHandler(handler)
+        Idempotent: safe to call multiple times.
+
+        Acquires the same lock as ``_emit`` so a concurrent emit cannot
+        write to a handler that is mid-teardown."""
+        with self._lock:
+            if self._handler is None:
+                return
+            handler = self._handler
+            self._handler = None
+            try:
+                handler.flush()
+                handler.close()
+            finally:
+                self._audit_logger.removeHandler(handler)
 
     def _emit(self, event: SecurityEvent) -> None:
         """Write security event to audit log (thread-safe)."""
@@ -477,7 +480,11 @@ def log_system_event(
         message: str,
         details: Optional[Dict[str, Any]] = None,
     ) -> None:
-        """Log a system lifecycle event (start, stop, config change, rate limit)."""
+        """Log a system event under the given ``event_type``.
+
+        Accepts any ``SecurityEventType`` (start/stop, config change, rate
+        limit, permission denied, etc.); the listed examples are illustrative,
+        not exhaustive."""
         self._emit(self._make_event(event_type, message, details=details))
 
     def get_recent_events(self, limit: int = 100) -> List[dict]:
@@ -499,13 +506,22 @@ def get_recent_events(self, limit: int = 100) -> List[dict]:
             with open(self._audit_path, "r", encoding="utf-8") as f:
                 tail = collections.deque(f, maxlen=limit)
             events = []
+            corrupt = 0
             for line in tail:
                 line = line.strip()
                 if line:
                     try:
                         events.append(json.loads(line))
                     except json.JSONDecodeError:
-                        pass
+                        # Surface, don't hide: a malformed line in an audit
+                        # trail may indicate truncation or tampering.
+                        corrupt += 1
+            if corrupt:
+                logger.warning(
+                    "Skipped %d unparseable line(s) in audit log %s",
+                    corrupt,
+                    self._audit_path,
+                )
             return events
         except OSError:
             return []
diff --git a/app/test_security_logger.py b/app/test_security_logger.py
index c180edd6..fd892092 100644
--- a/app/test_security_logger.py
+++ b/app/test_security_logger.py
@@ -106,7 +106,7 @@ def test_new_id_uses_utc(self):
     def test_to_dict_has_required_fields(self):
         event = SecurityEvent(
             event_id="SEC_001",
-            event_type=SecurityEventType.AUTH_ATTEMPT.value,
+            event_type=SecurityEventType.AUTH_SUCCESS.value,
             timestamp=time.time(),
             message="test",
             correlation_id=None,