fix(lifecycle): OAuth pw 500, invite lockout, reminder re-arm, partial-unique

Drift-audit Group 8 (lifecycle gaps):

- change_password no longer 500s for OAuth-only users: short-circuit when
  password_hash is None (verify_password would crash on None) so the route
  returns a clean 4xx instead of a 500.
- register_with_invitation no longer locks the invitee out on a username
  collision: create the user FIRST, then mark the token used, so a failed
  creation (409) leaves the single-use invite valid for retry.
- update_event re-arms reminder_sent_at when start_dt/reminder_minutes change,
  so a rescheduled event fires again instead of being permanently suppressed.
- Migration 0061: uq_topic_per_rulebook / uq_rule_per_topic become PARTIAL
  unique indexes (WHERE deleted_at IS NULL). Trashing 'X' then recreating it
  no longer 500s on the dead row's title. Model __table_args__ updated to match.

Deferred: per-occurrence reminders for recurring events (event_scheduler) —
needs a per-occurrence reminder-state design, not a one-line gate tweak.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/fabledassistant/services/auth.py

@@ -106,6 +106,11 @@ async def change_password(user_id: int, current_password: str, new_password: str
         user = await session.get(User, user_id)
         if not user:
             return None
+        # OAuth-only accounts have no local password hash — verify_password
+        # would crash on None. Treat as "no local credential to change" (the
+        # route turns None into a clean 4xx, not a 500).
+        if user.password_hash is None:
+            return None
         if not verify_password(current_password, user.password_hash):
             return None
         user.password_hash = hash_password(new_password)
@@ -325,12 +330,23 @@ async def register_with_invitation(raw_token: str, username: str, password: str)
         if not invitation or invitation.used or invitation.expires_at < datetime.now(timezone.utc):
             return None
 
-        invitation.used = True
-        await session.commit()
+        invitation_id = invitation.id
+        invite_email = invitation.email
 
-    # Create user outside the invitation session
-    user = await create_user(username, password, invitation.email)
-    logger.info("User '%s' registered via invitation for %s", username, invitation.email)
+    # Create the user FIRST, then consume the token. create_user can fail (e.g.
+    # a username collision raises and the route returns 409); marking the token
+    # used before that would burn this single-use invite and lock the invitee
+    # out of retrying. Ordering it after means a failed creation leaves the
+    # token valid.
+    user = await create_user(username, password, invite_email)
+
+    async with async_session() as session:
+        invitation = await session.get(InvitationToken, invitation_id)
+        if invitation is not None:
+            invitation.used = True
+            await session.commit()
+
+    logger.info("User '%s' registered via invitation for %s", username, invite_email)
     return user
 
 

src/fabledassistant/services/events.py

@@ -331,6 +331,11 @@ async def update_event(user_id: int, event_id: int, **fields) -> Event | None:
         for key, value in fields.items():
             if key in allowed and (value is not None or key in nullable):
                 setattr(event, key, value)
+        # Re-arm the reminder when the timing changes, so an event moved to a
+        # new (future) time — or given a new lead time — fires again instead of
+        # being permanently suppressed by a stale reminder_sent_at.
+        if "start_dt" in fields or "reminder_minutes" in fields:
+            event.reminder_sent_at = None
         await session.commit()
         await session.refresh(event)