## Why
Regular chats start MCP servers eagerly even when cached tool definitions are available and the servers go unused. Allow those chats to use the cached catalog and defer eligible stdio servers until first use.
## What changed
- Add the disabled-by-default `mcp_lazy_stdio_startup` feature and expose it through experimental feature configuration.
- Defer cached stdio servers in regular chats when enabled, while keeping servers that require a live startup connection eager. Required servers with `startup_readiness = "catalog"` may defer; explicit reconnects remain eager.
- Announce the full eager startup batch before terminal statuses and exclude dormant servers from the initial startup summary. Update TUI tracking so deferred servers can report startup independently in later rounds.
## Testing
Add scenario coverage for a cached server staying dormant during unrelated work, starting on first use, and refreshing tool definitions and visibility. Cover required live startup, eager event ordering, experimental feature configuration, and TUI status handling.
GitOrigin-RevId: 74075fcd4f26c8c79b5901b6a8cb03fdb9e35a7f
Charlie Marsh
af9a98b074