fix(harness): preserve session migration JSON errors

harness/tests/test_session_migrate_cmd.py

@@ -26,3 +26,22 @@ def test_session_migrate_status_is_pristine_and_idempotent():
     assert second.exit_code == 0, second.output
     assert json.loads(first.stdout) == expected
     assert json.loads(second.stdout) == expected
+
+
+def test_session_migrate_status_database_failure_is_pristine_json():
+    result = CliRunner().invoke(
+        app,
+        [
+            "session",
+            "migrate",
+            "--database-url",
+            "postgresql+psycopg2://test:test@127.0.0.1:1/test",
+            "--status",
+            "--json",
+        ],
+    )
+
+    assert result.exit_code == 1
+    assert result.stderr == ""
+    assert "Traceback" not in result.stdout
+    assert json.loads(result.stdout)["error"]

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: