Convert log to string for fallback server

src/openflexure_microscope_server/server/__init__.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import json
 import logging
 import os
 from argparse import Namespace
@@ -150,7 +151,8 @@ def serve_from_cli(argv: Optional[list[str]] = None) -> None:
             print(f"Error: {e}")  # noqa: T201
             print("Starting fallback server.")  # noqa: T201
             try:
-                log_history = OFM_HANDLER.log_history
+                # The log is a list of dicts, fallback server expects a string
+                log_history = json.dumps(OFM_HANDLER.log_history, indent=2)
             except BaseException:
                 # If log history fails for any reason carry on.
                 log_history = None