Why Some Attribute Queries Did Work

@MainActor, Sendable conformance, protocol type, Hashable conformance — these all happen to align with token-presence:

• MainActor is also a Swift type name, indexed in docs_fts.symbols at weight 5.0
• Sendable is a Swift protocol name, same
• Hashable same
• protocol is a Swift keyword that appears in titles and content
• actor (in actor type) appears in titles for the 3 actor-defining pages but those pages don't dominate

So the win isn't the symbol-attribute mechanism working; it's a coincidence that the attribute name is also a token-rich symbol name. When the attribute name is a generic English word that doesn't surface as a symbol (initializer, subscript, typealias, generic constraint), the query fails completely.