Speculative fix for a sometimes speech crash bug.

tests/unit/test_remote_instance_registry.py

@@ -0,0 +1,35 @@
+import json
+import time
+
+from fenrirscreenreader.core import remoteInstanceRegistry
+
+
+def test_write_instance_prunes_stale_registry_files(tmp_path, monkeypatch):
+    monkeypatch.setattr(
+        remoteInstanceRegistry, "get_registry_dir", lambda: str(tmp_path)
+    )
+    monkeypatch.setattr(
+        remoteInstanceRegistry,
+        "process_exists",
+        lambda pid: pid == 456,
+    )
+
+    stale_instance = tmp_path / "123.json"
+    stale_instance.write_text(
+        json.dumps(
+            {
+                "pid": 123,
+                "updated_at": time.time(),
+            }
+        )
+        + "\n",
+        encoding="utf-8",
+    )
+    invalid_instance = tmp_path / "invalid.json"
+    invalid_instance.write_text("not json\n", encoding="utf-8")
+
+    remoteInstanceRegistry.write_instance({"pid": 456})
+
+    assert not stale_instance.exists()
+    assert not invalid_instance.exists()
+    assert (tmp_path / "456.json").exists()