## Why
An MCP connection or tool catalog can change after a model step captures its
available tools. Calls from that step must not be rerouted to a replacement
client or run against a catalog revision the model did not see.
## What changed
- Add `McpBinding` to capture the ready clients, visible tools, resources, and
server metadata for one sampling request.
- Prepare calls against the captured client and reject them if the tool catalog
changes before call preparation and execution finish.
- Keep resource access and cache identity tied to the binding's exact connection
set, and omit servers that do not have a ready client.
- Preserve each client's unfiltered tool catalog so bindings can apply the
current filter consistently.
## Testing
Add coverage for connection replacement, stale catalog rejection, serialized
call preparation and refresh, ready-client capture, and binding-scoped resource
identity.
GitOrigin-RevId: a25da4d2c7f5ed06c41caa0c6d15c464c1698314
## What changed
- Move required-server startup validation into `connection_manager/required.rs`.
- Move tool listing, lookup, metadata attachment, and Codex Apps cache refresh into `connection_manager/tool_catalog.rs`.
- Keep the existing connection-manager API and behavior unchanged.
GitOrigin-RevId: 7249896699f756bdbb6e00bc2bbc4a98098741a9
jif