## Why
MCP config reloads updated resolved server and authentication values, but did not
carry managed server constraints or plugin requirements into active threads.
## What changed
- Refresh MCP state from the typed thread config, including its managed
requirements, while retaining the thread's user layer and unrelated settings.
- Apply the refreshed config directly through `CodexThread` instead of encoding it
as a protocol operation.
- Re-evaluate effective plugins immediately after account changes so their MCP
requirements reach existing threads.
## Testing
- Cover replacement and enforcement of managed server and plugin requirements.
- Verify refreshed MCP settings are installed without changing the active model.
GitOrigin-RevId: 3cf0d69f51ef4893a4d722ee803fcbfdf1cd959e