fix(harness): preserve session migration JSON errors

harness/tht/cli/session_cmd.py

@@ -2,6 +2,7 @@ import json
 from pathlib import Path
 
 import typer
+from sqlalchemy.exc import SQLAlchemyError
 
 from tht.cli.config_cmd import CONFIG_OPT
 from tht.cli.schema_cmd import _load_config_or_exit
@@ -22,7 +23,7 @@ def migrate_cmd(
 
     try:
         status = migration_status(database_url) if status_only else migrate(database_url)
-    except (MigrationError, ValueError) as exc:
+    except (MigrationError, SQLAlchemyError, ValueError) as exc:
         if json_output:
             typer.echo(json.dumps({"error": str(exc)}, sort_keys=True))
         else: