fix(gateway): harden agent provider routing

src/utils/message-provider.ts

@@ -8,17 +8,7 @@ export function normalizeMessageProvider(
   return normalized;
 }
 
-export type GatewayMessageProvider =
-  | "whatsapp"
-  | "telegram"
-  | "discord"
-  | "slack"
-  | "signal"
-  | "imessage"
-  | "msteams"
-  | "webchat";
-
-const GATEWAY_MESSAGE_PROVIDERS: GatewayMessageProvider[] = [
+export const DELIVERABLE_MESSAGE_PROVIDERS = [
   "whatsapp",
   "telegram",
   "discord",
@@ -26,13 +16,48 @@ const GATEWAY_MESSAGE_PROVIDERS: GatewayMessageProvider[] = [
   "signal",
   "imessage",
   "msteams",
+] as const;
+
+export type DeliverableMessageProvider =
+  (typeof DELIVERABLE_MESSAGE_PROVIDERS)[number];
+
+export const INTERNAL_MESSAGE_PROVIDER = "webchat" as const;
+export type InternalMessageProvider = typeof INTERNAL_MESSAGE_PROVIDER;
+
+export type GatewayMessageProvider =
+  | DeliverableMessageProvider
+  | InternalMessageProvider;
+
+export const GATEWAY_MESSAGE_PROVIDERS = [
+  ...DELIVERABLE_MESSAGE_PROVIDERS,
   "webchat",
-];
+] as const;
+
+export const GATEWAY_AGENT_PROVIDER_ALIASES = ["imsg", "teams"] as const;
+export type GatewayAgentProviderAlias =
+  (typeof GATEWAY_AGENT_PROVIDER_ALIASES)[number];
+
+export type GatewayAgentProviderHint =
+  | GatewayMessageProvider
+  | "last"
+  | GatewayAgentProviderAlias;
+
+export const GATEWAY_AGENT_PROVIDER_VALUES = [
+  ...GATEWAY_MESSAGE_PROVIDERS,
+  "last",
+  ...GATEWAY_AGENT_PROVIDER_ALIASES,
+] as const;
 
 export function isGatewayMessageProvider(
   value: string,
 ): value is GatewayMessageProvider {
-  return (GATEWAY_MESSAGE_PROVIDERS as string[]).includes(value);
+  return (GATEWAY_MESSAGE_PROVIDERS as readonly string[]).includes(value);
+}
+
+export function isDeliverableMessageProvider(
+  value: string,
+): value is DeliverableMessageProvider {
+  return (DELIVERABLE_MESSAGE_PROVIDERS as readonly string[]).includes(value);
 }
 
 export function resolveGatewayMessageProvider(