This PR removes the now-dead direct-routing code:
- Deletes the direct routing implementation.
- Collapses the resolvedModelRoute discriminated union into aiGatewayModelRoute.
- Removes the dead providerKeys cascade.
- Deletes the preferredShortTextCandidates quickgen function.
- Simplifies the advisor override error handling.
- Deprecates the AIGatewayRoutingEnabled deployment option. It is now a no-op so as to not break existing deployments on upgrade.
Once direct routing was gone, the AI Gateway became mandatory for chat, which surfaced gaps in how the product behaves with the gateway disabled:
- Exposes ai-gateway-enabled to the frontend via embedded page metadata.
- Disables the chat composer via the existing AgentSetupNotice when the gateway is disabled, for both new and existing chats.
- Fixes nil/typed-nil chatDaemon panics on startup and shutdown when gateway is disabled.
- Fixes chat WebSocket from retrying the still-gated stream endpoint forever when the gateway is disabled.
Cian Johnston