## What changed
- Add `features.network_proxy.credential_broker` and preserve structured network proxy settings when toggling the feature through config APIs.
- Protect broker enablement and provider context variables from project config, while carrying trusted context into filtered shell environments.
- Propagate brokered credentials through shell snapshots and restore real credentials for unsandboxed escalated commands.
- Normalize broker context environment keys case-insensitively on Windows and avoid conflicting remote managed-network enforcement when no proxy launch configuration is available.
## Testing
- Cover config layering, editing, project sanitization, Windows environment handling, shell snapshots, escalated execution, and end-to-end GitHub credential brokering in the zsh-fork runtime.
GitOrigin-RevId: 500e51e804e1988022052ccfe00b8fac5e495f4f
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