Get Shared Project Chats

Get chat history for a shared project (read-only).

Structured tool data IS stripped: tool-call and tool-return parts (e.g. query_sql parcel rows persisted as ToolReturnParts) are removed before the payload reaches the anonymous share wire. Only prose is not stripped — assistant natural-language messages are preserved, because scanning free-form conversation for incidental parcel mentions would mean parsing LLM text, unreliable and out of this restriction's scope.

Args: share: Validated ProjectShare from token share_service: ProjectShareService for fetching chat data

Returns: Chat history with system instructions stripped, or None if no chat exists