Fix migration: parse ISO timestamp strings to datetime objects for asyncpg

asyncpg requires datetime instances for TIMESTAMPTZ columns, not strings.
Added _parse_dt() helper that converts ISO strings (with or without tz) to
timezone-aware datetime, falling back to NOW() if the value is missing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/server/db/migrate_json.py

@@ -13,11 +13,25 @@ import json
 import logging
 import os
 import sys
+from datetime import datetime, timezone
 
 logging.basicConfig(level=logging.INFO)
 logger = logging.getLogger(__name__)
 
 
+def _parse_dt(value) -> datetime | None:
+    """Parse an ISO timestamp string (or None) into a timezone-aware datetime."""
+    if not value:
+        return None
+    try:
+        dt = datetime.fromisoformat(value)
+        if dt.tzinfo is None:
+            dt = dt.replace(tzinfo=timezone.utc)
+        return dt
+    except (ValueError, TypeError):
+        return None
+
+
 async def migrate():
     # Import here to avoid circular issues at module level
     from ..config_runtime import server_config
@@ -38,16 +52,16 @@ async def migrate():
             with open(users_file) as f:
                 users = json.load(f)
             count = 0
+            now = datetime.now(timezone.utc)
             for uid, u in users.items():
                 await conn.execute('''
                     INSERT INTO users (id, email, name, role, active, created_at, last_seen_at)
-                    VALUES ($1, $2, $3, $4, $5,
-                            COALESCE($6::timestamptz, NOW()),
-                            COALESCE($7::timestamptz, NOW()))
+                    VALUES ($1, $2, $3, $4, $5, $6, $7)
                     ON CONFLICT (id) DO NOTHING
                 ''', uid, u.get('email', ''), u.get('name', ''),
                     u.get('role', 'user'), u.get('active', True),
-                    u.get('created'), u.get('last_seen'))
+                    _parse_dt(u.get('created')) or now,
+                    _parse_dt(u.get('last_seen')) or now)
                 count += 1
             logger.info(f"Migrated {count} users")
 
@@ -56,12 +70,14 @@ async def migrate():
         if os.path.exists(clients_file):
             with open(clients_file) as f:
                 clients = json.load(f)
+            now = datetime.now(timezone.utc)
             for c in clients:
                 await conn.execute('''
                     INSERT INTO clients (id, name, has_custom_dropdowns, created_at)
-                    VALUES ($1, $2, $3, COALESCE($4::timestamptz, NOW()))
+                    VALUES ($1, $2, $3, $4)
                     ON CONFLICT (id) DO NOTHING
-                ''', c['id'], c['name'], c.get('hasCustomDropdowns', False), c.get('created'))
+                ''', c['id'], c['name'], c.get('hasCustomDropdowns', False),
+                    _parse_dt(c.get('created')) or now)
             logger.info(f"Migrated {len(clients)} clients")
 
         # ── Global dropdowns ───────────────────────────────────────────────────
@@ -157,16 +173,16 @@ async def migrate():
                             data = json.load(f)
 
                     client_id = sheet_meta.get('client_id') or None
+                    now = datetime.now(timezone.utc)
                     await conn.execute('''
                         INSERT INTO sheets
                             (id, user_id, name, client_id, data, item_count, created_at, modified_at)
-                        VALUES ($1, $2, $3, $4, $5, $6,
-                                COALESCE($7::timestamptz, NOW()),
-                                COALESCE($8::timestamptz, NOW()))
+                        VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
                         ON CONFLICT (id) DO NOTHING
                     ''', sid, user_id, sheet_meta.get('name', 'Untitled'),
                         client_id, data, len(data),
-                        sheet_meta.get('created'), sheet_meta.get('modified'))
+                        _parse_dt(sheet_meta.get('created')) or now,
+                        _parse_dt(sheet_meta.get('modified')) or now)
                     total += 1
             logger.info(f"Migrated {total} sheets")