fix(misc): three small defensive fixes from PR #1974

Salvages the three substantive low-severity fixes from Gutslabs' #1974
"misc bug fixes" bundle.  The other 8 claims in that PR were either
already fixed on main with superior implementations (state lock,
firecrawl lazy import, fcntl/msvcrt guard, path normalization, schema
migrations) or did not survive review.

- run_agent: `_materialize_data_url_for_vision` uses
  `NamedTemporaryFile(delete=False)`; if `base64.b64decode` raises on a
  corrupt data URL the temp file would persist forever.  Wrap the
  write in try/except and `os.unlink` the temp on failure.

- gateway/session: `append_to_transcript` JSONL write had no error
  handling, so disk-full / read-only-fs / permission errors crashed the
  message handler.  The SQLite write above is the primary store, so
  swallow OSError on the JSONL fallback with a debug log.

- gateway/status: `_read_pid_record` reads `pid_path.read_text()` after
  an `exists()` check; if the PID file is deleted between the two
  calls (concurrent gateway restart) we hit an unhandled OSError.
  Catch it and return None.

Adds a regression test for the tempfile cleanup; the other two paths
are defensive try/excepts on infrequent OSError that don't warrant
dedicated tests.

Co-authored-by: Teknium <127238744+teknium1@users.noreply.github.com>

tests/run_agent/test_materialize_data_url_cleanup.py

@@ -0,0 +1,54 @@
+"""Regression test: temp file cleanup when materializing data URLs for vision.
+
+`_materialize_data_url_for_vision` creates a `NamedTemporaryFile(delete=False)`
+so the path can be handed to vision backends.  If `base64.b64decode` raises on
+a corrupt/unsupported data URL the temp file would otherwise persist forever
+on disk, leaking once per failed call.
+"""
+
+from __future__ import annotations
+
+import base64
+import os
+import tempfile
+from pathlib import Path
+
+import pytest
+
+from run_agent import AIAgent
+
+
+def _list_anthropic_tmpfiles(tmpdir: str) -> list[str]:
+    return [
+        name for name in os.listdir(tmpdir)
+        if name.startswith("anthropic_image_")
+    ]
+
+
+def test_b64decode_failure_does_not_leak_tempfile(monkeypatch, tmp_path):
+    monkeypatch.setattr(tempfile, "tempdir", str(tmp_path))
+
+    bad_url = "data:image/png;base64,!!!not-valid-base64!!!"
+    with pytest.raises(Exception):
+        AIAgent._materialize_data_url_for_vision(bad_url)
+
+    leftovers = _list_anthropic_tmpfiles(str(tmp_path))
+    assert leftovers == [], f"leaked temp files after decode failure: {leftovers}"
+
+
+def test_successful_decode_returns_path_to_existing_file(monkeypatch, tmp_path):
+    monkeypatch.setattr(tempfile, "tempdir", str(tmp_path))
+
+    payload = b"\x89PNG\r\n\x1a\n" + b"\x00" * 16  # a few bytes is enough
+    encoded = base64.b64encode(payload).decode("ascii")
+    good_url = f"data:image/png;base64,{encoded}"
+
+    path_str, path_obj = AIAgent._materialize_data_url_for_vision(good_url)
+
+    assert isinstance(path_obj, Path)
+    assert path_obj.exists()
+    assert path_obj.read_bytes() == payload
+    assert path_str == str(path_obj)
+    # Caller is responsible for cleanup; mimic that here so the test leaves
+    # no artifacts behind.
+    path_obj.unlink()