## Why
App-server clients can report whether Amazon Bedrock is using
AWS-managed credentials or a Codex-managed API key, but they do not have
a matching API for creating the managed login. This PR defines that
experimental wire contract independently from its implementation.
Managed Bedrock API keys are already a primary `CodexAuth` mode. The API
therefore describes a normal Codex login that replaces the current
stored auth rather than introducing provider-scoped credential storage.
## What changed
- Add the experimental `amazonBedrock` variant to `account/login/start`.
- Accept an API key and AWS region and return a matching discriminated
response.
- Gate the request behind the app-server `experimentalApi` capability.
- Regenerate the JSON and TypeScript protocol schemas.
- Document the login contract, notifications, primary-auth replacement
semantics, restart boundary, and non-transactional durable writes.
## Impact
This PR defines the API shape but does not implement login behavior. The
next PR adds validation, persistence through the existing Codex auth
lifecycle, provider selection, and notifications.
## Validation
- `just test -p codex-app-server-protocol`
## Stack
1. **#31327 Managed Bedrock experimental API** — base: `main`
2. #31326 Managed Bedrock login — base: `codex/managed-bedrock-api`
3. #31325 Managed Bedrock logout — base:
`codex/managed-bedrock-login-v2`
b45fef0774