fix(gateway): tolerate non-UTF-8 status/pid files in gateway status reads

`_read_json_file` caught OSError but not UnicodeDecodeError, so a status
file holding binary/non-UTF-8 bytes (truncated or clobbered write) would
crash the gateway status path instead of being treated as unreadable.
UnicodeDecodeError is a ValueError subclass, not an OSError, so it
escaped the existing guard.

Widen the catch to (OSError, UnicodeDecodeError) at both read sites in
gateway/status.py — `_read_json_file` and the sibling `_read_pid_record`,
which had the identical gap. Adds tests covering binary input (returns
None) and valid input (still parses) for both.

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

gateway/status.py

@@ -227,7 +227,10 @@ def _read_json_file(path: Path) -> Optional[dict[str, Any]]:
         return None
     try:
         raw = path.read_text(encoding="utf-8").strip()
-    except OSError:
+    except (OSError, UnicodeDecodeError):
+        # OSError: file vanished or permission flipped between exists() and
+        # read. UnicodeDecodeError: file holds non-UTF-8 / binary garbage
+        # (a truncated or clobbered status file). Either way it's unusable.
         return None
     if not raw:
         return None
@@ -249,8 +252,9 @@ def _read_pid_record(pid_path: Optional[Path] = None) -> Optional[dict]:
 
     try:
         raw = pid_path.read_text().strip()
-    except OSError:
-        # File was deleted between exists() and read_text(), or permission flipped.
+    except (OSError, UnicodeDecodeError):
+        # File was deleted between exists() and read_text(), permission
+        # flipped, or it holds non-UTF-8 / binary garbage.
         return None
     if not raw:
         return None

tests/gateway/test_status.py

@@ -1036,3 +1036,28 @@ class TestReadProcessCmdlinePsFallback:
         )
         result = status._read_process_cmdline(12345)
         assert "hermes_cli/main.py" in result
+
+
+class TestCorruptStatusFiles:
+    """A status / pid file holding non-UTF-8 (binary) bytes must read as
+    None, not crash the gateway status path with UnicodeDecodeError."""
+
+    def test_read_json_file_returns_none_on_binary_garbage(self, tmp_path):
+        p = tmp_path / "runtime.json"
+        p.write_bytes(b"\xff\xfe\x00\x80not utf-8\x81")
+        assert status._read_json_file(p) is None
+
+    def test_read_json_file_still_parses_valid_json(self, tmp_path):
+        p = tmp_path / "runtime.json"
+        p.write_text(json.dumps({"pid": 7}), encoding="utf-8")
+        assert status._read_json_file(p) == {"pid": 7}
+
+    def test_read_pid_record_returns_none_on_binary_garbage(self, tmp_path):
+        p = tmp_path / "gateway.pid"
+        p.write_bytes(b"\xff\xfe\x00\x80\x81")
+        assert status._read_pid_record(p) is None
+
+    def test_read_pid_record_still_parses_bare_pid(self, tmp_path):
+        p = tmp_path / "gateway.pid"
+        p.write_text("4242", encoding="utf-8")
+        assert status._read_pid_record(p) == {"pid": 4242}