fix(audit): raise on write-after-close + weakref.finalize + parametrized event coverage

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/markovian_rsa_mlx/audit.py

@@ -7,6 +7,7 @@ from __future__ import annotations
 import dataclasses
 import io
 import json
+import weakref
 from dataclasses import dataclass, field
 from pathlib import Path
 from typing import Any, Literal
@@ -128,22 +129,36 @@ class ErrorEvent(_BaseEvent):
 
 
 class AuditWriter:
-    """Streaming JSONL writer. No-op when path is None."""
-    def __init__(self, path: Path | str | None, mode: str = "w") -> None:
+    """Streaming JSONL writer. No-op when path is None.
+
+    Once `close()` is called, subsequent `write()` calls raise ValueError.
+    Use as a context manager (`with AuditWriter(p) as w:`) for guaranteed close.
+    """
+    def __init__(self, path: Path | str | None, mode: Literal["w", "a"] = "w") -> None:
         self._path = Path(path) if path is not None else None
-        self._fp: io.TextIOBase | None = None
+        self._enabled = self._path is not None
+        self._closed = False
+        self._fp: io.TextIOWrapper | None = None
         if self._path is not None:
             self._path.parent.mkdir(parents=True, exist_ok=True)
             self._fp = self._path.open(mode, encoding="utf-8")
+        if self._fp is not None:
+            weakref.finalize(self, self._fp.close)
 
     def write(self, event: _BaseEvent) -> None:
-        if self._fp is None:
+        if not self._enabled:
             return
+        if self._closed:
+            raise ValueError("AuditWriter is closed")
+        assert self._fp is not None
         self._fp.write(json.dumps(event.to_dict(), ensure_ascii=False))
         self._fp.write("\n")
-        self._fp.flush()
+        self._fp.flush()  # flush per event so a crash mid-run preserves the audit trail
 
     def close(self) -> None:
+        if self._closed:
+            return
+        self._closed = True
         if self._fp is not None:
             self._fp.close()
             self._fp = None
@@ -151,5 +166,5 @@ class AuditWriter:
     def __enter__(self) -> "AuditWriter":
         return self
 
-    def __exit__(self, *args) -> None:
+    def __exit__(self, exc_type, exc_val, exc_tb) -> None:
         self.close()