Two somewhat annoying fixes:
- we are going to index tools for non-MCP toolgroups always (like we
used to do). because there are just random assumptions in our tests,
etc. and I don't want to fix them right now
- we need to handle the funny case of toolgroups like
`builtin::rag/knowledge_search` where we added the tool name to use in
the toolgroup itself.
When registering a MCP endpoint, we cannot list tools (like we used to)
since the MCP endpoint may be behind an auth wall. Registration can
happen much sooner (via run.yaml).
Instead, we do listing only when the _user_ actually calls listing.
Furthermore, we cache the list in-memory in the server. Currently, the
cache is not invalidated -- we may want to periodically re-list for MCP
servers. Note that they must call `list_tools` before calling
`invoke_tool` -- we use this critically.
This will enable us to list MCP servers in run.yaml
## Test Plan
Existing tests, updated tests accordingly.
