## Why
Executor-owned MCP servers must not receive hosted ChatGPT actor credentials or credentials from the host's OAuth store.
## What changed
- Provide the ChatGPT auth provider and consult stored OAuth credentials only for MCP servers in the local environment.
- Require non-local servers configured with `auth = "chatgpt"` to supply a non-empty, valid static `Authorization` header. Reject environment-backed authorization so host secrets are not resolved for an executor-owned server.
- Report unsupported authentication and fail startup before connecting when an executor-owned server has no acceptable explicit authorization.
## Testing
Add coverage for local credential forwarding, non-local credential isolation, static header validation, auth status, OAuth lookup avoidance, and startup rejection.
GitOrigin-RevId: e18f1878f260c93d9babd390a5a7eac86172299b
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