claude.ai: a chat inside a Project cannot open a conversation link the user pastes from outside that Project

Concerns the claude.ai web app (merged Chat/Cowork surface), not the CLI. CLI-only template fields: not applicable.

What happens
I paste a link to one of my own conversations (https://claude.ai/chat/<uuid>) into a chat that sits inside a Project. Claude cannot open it. read_conversation returns "Conversation not found or not accessible", and recent_chats / conversation_search only list conversations from the current Project. Claude then has to ask me to describe the other chat by hand.

Why it is a bug

• It is my own conversation, on my own account, and I pasted the link explicitly. That is consent to read it.
• Before the Chat/Cowork merge (7-8 Oct 2026) my sessions did not hit this wall in practice; now most of my work runs inside Projects, so the scope blocks the common case.
• The error text says "not found", which is wrong: the chat exists. It should say it is out of scope.

Expected
A conversation the user links directly is readable from any of that user's chats, whatever Project either one is in. Keep the Project scope for open-ended searching if you want, but not for an explicit link.

Related: #86611 (a session can only read the project it started in), #98702 (merge regressions).