Enforce recipient-bound single-use invites and fix issue card layout; clean release tooling

backend/app/db.py

@@ -1573,7 +1573,7 @@ def delete_user_profile(profile_id: int) -> bool:
 
 
 def _row_to_signup_invite(row: Any) -> Dict[str, Any]:
-    max_uses = row[6]
+    max_uses = 1 if row[10] else row[6]
     use_count = int(row[7] or 0)
     expires_at = row[9]
     is_expired = _is_datetime_in_past(expires_at)
@@ -1657,6 +1657,8 @@ def create_signup_invite(
     recipient_email: Optional[str] = None,
     created_by: Optional[str] = None,
 ) -> Dict[str, Any]:
+    if recipient_email:
+        max_uses = 1
     timestamp = datetime.now(timezone.utc).isoformat()
     with _connect() as conn:
         cursor = conn.execute(
@@ -1714,6 +1716,11 @@ def update_signup_invite(
     expires_at: Optional[str],
     recipient_email: Optional[str],
 ) -> Optional[Dict[str, Any]]:
+    existing = get_signup_invite_by_id(invite_id)
+    if recipient_email or (existing and existing.get('recipient_email')):
+        max_uses = 1
+    if existing and existing.get('recipient_email') and int(existing.get('use_count') or 0) > 0 and recipient_email != existing.get('recipient_email'):
+        raise ValueError('A used email invitation cannot be reassigned.')
     timestamp = datetime.now(timezone.utc).isoformat()
     with _connect() as conn:
         cursor = conn.execute(
@@ -1751,6 +1758,24 @@ def delete_signup_invite(invite_id: int) -> bool:
     return cursor.rowcount > 0
 
 
+def reserve_signup_invite_use(invite_id: int) -> bool:
+    """Atomically reserve capacity before any remote account is provisioned."""
+    with _connect() as conn:
+        cursor = conn.execute('''
+            UPDATE signup_invites SET use_count = use_count + 1
+            WHERE id = ? AND enabled = 1
+              AND (expires_at IS NULL OR julianday(expires_at) > julianday('now'))
+              AND ((recipient_email IS NOT NULL AND recipient_email != '' AND use_count < 1)
+                OR ((recipient_email IS NULL OR recipient_email = '') AND (max_uses IS NULL OR use_count < max_uses)))
+        ''', (invite_id,))
+    return cursor.rowcount == 1
+
+
+def release_signup_invite_use(invite_id: int) -> None:
+    with _connect() as conn:
+        conn.execute('UPDATE signup_invites SET use_count = MAX(0, use_count - 1) WHERE id = ?', (invite_id,))
+
+
 def increment_signup_invite_use(invite_id: int) -> None:
     timestamp = datetime.now(timezone.utc).isoformat()
     with _connect() as conn: