fix(session): skip corrupt lines in load_transcript instead of crashing (#1744)

Wrap json.loads() in load_transcript() with try/except JSONDecodeError
so that partial JSONL lines (from mid-write crashes like OOM/SIGKILL)
are skipped with a warning instead of crashing the entire transcript
load. The rest of the history loads fine.

Adds a logger.warning with the session ID and truncated corrupt line
content for debugging visibility.

Salvaged from PR #1193 by alireza78a.
Closes #1193

gateway/session.py

@@ -944,7 +944,13 @@ class SessionStore:
             for line in f:
                 line = line.strip()
                 if line:
-                    messages.append(json.loads(line))
+                    try:
+                        messages.append(json.loads(line))
+                    except json.JSONDecodeError:
+                        logger.warning(
+                            "Skipping corrupt line in transcript %s: %s",
+                            session_id, line[:120],
+                        )
         
         return messages