## Why
Configuration loading can finish before a pending startup is visible to the thread manager. Reloads need a cancellation scope that also covers these configuration snapshots.
## What changed
- Capture an enterprise managed authentication (EMA) cancellation token before loading configuration and carry it through config layers, role overrides, runtime refreshes, and `McpConfig`.
- Cancel the previous scope on MCP or user configuration reloads and cloud config loader changes, then create a fresh scope for subsequent loads.
- Cancel the session's token when enterprise MCP authentication is disabled or a refresh leaves it unavailable.
## Testing
Extend the MCP reload test to verify that existing thread and pending startup tokens are cancelled while a fresh startup receives an uncancelled token.
GitOrigin-RevId: 5fc0658b74c360e7dc9ab3488339fcf19bfe9fae
jif
cca40e57a4