refactor(chat): route browser chat through one runtime (P3 Slice-Zero Task 5) (#1172)

Co-authored-by: shaggy <[email protected]>

apps/gateway/src/harness/harness.module.ts

@@ -1,7 +1,12 @@
 import { Module } from '@nestjs/common';
 import { HarnessRegistry } from './harness.registry.js';
 import { HarnessService } from './harness.service.js';
-import { HARNESS_REGISTRY, HARNESS_SERVICE } from './harness.tokens.js';
+import {
+  HARNESS_CONVERSATION_SERVICE,
+  HARNESS_CONVERSATION_SERVICE_UNAVAILABLE,
+  HARNESS_REGISTRY,
+  HARNESS_SERVICE,
+} from './harness.tokens.js';
 import { HarnessController } from './harness.controller.js';
 import { HarnessSelectionController } from './harness-selection.controller.js';
 import { HarnessSelectionService } from './harness-selection.service.js';
@@ -20,9 +25,13 @@ import { HarnessSelectionRepository } from './harness-selection.repository.js';
   providers: [
     { provide: HARNESS_REGISTRY, useFactory: () => new HarnessRegistry() },
     { provide: HARNESS_SERVICE, useClass: HarnessService },
+    // Task Five: bind the conversation-service token to its explicit "not yet bound"
+    // sentinel. The pi-rpc router treats this as a hard, typed startup failure; Task 14
+    // replaces it with a real service. Exported so ChatModule's router can inject it.
+    { provide: HARNESS_CONVERSATION_SERVICE, useValue: HARNESS_CONVERSATION_SERVICE_UNAVAILABLE },
     HarnessSelectionRepository,
     HarnessSelectionService,
   ],
-  exports: [HARNESS_REGISTRY, HARNESS_SERVICE],
+  exports: [HARNESS_REGISTRY, HARNESS_SERVICE, HARNESS_CONVERSATION_SERVICE],
 })
 export class HarnessModule {}

apps/gateway/src/harness/harness.tokens.ts

@@ -4,8 +4,42 @@
  * String tokens follow the existing Gateway convention (see `memory/memory.tokens.ts`)
  * and remain valid Nest `InjectionToken`s for `@Inject(...)`.
  */
+import type { HarnessConversationService } from '@mosaicstack/types';
+
 export const HARNESS_REGISTRY = 'HARNESS_REGISTRY' as const;
 export const HARNESS_SERVICE = 'HARNESS_SERVICE' as const;
 
 export type HarnessRegistryToken = typeof HARNESS_REGISTRY;
 export type HarnessServiceToken = typeof HARNESS_SERVICE;
+
+/**
+ * Token for the {@link HarnessConversationService} that {@link HarnessChatRuntime}
+ * depends on. Until Task 14 provides a real implementation, `HarnessModule` binds
+ * the {@link HARNESS_CONVERSATION_SERVICE_UNAVAILABLE} sentinel here, and the
+ * `pi-rpc` router treats that sentinel as a hard, typed startup failure.
+ */
+export const HARNESS_CONVERSATION_SERVICE = 'HARNESS_CONVERSATION_SERVICE' as const;
+
+export type HarnessConversationServiceToken = typeof HARNESS_CONVERSATION_SERVICE;
+
+/**
+ * Explicit "not yet bound" value for {@link HARNESS_CONVERSATION_SERVICE}. It is a
+ * distinct sentinel — never `null`/`undefined` — so an unbound service is an
+ * intentional, checkable state rather than an accidental nil that could read as
+ * "present". Replaced by a real service in Task 14.
+ */
+export const HARNESS_CONVERSATION_SERVICE_UNAVAILABLE: unique symbol = Symbol(
+  'HARNESS_CONVERSATION_SERVICE_UNAVAILABLE',
+);
+
+/** A binding for {@link HARNESS_CONVERSATION_SERVICE}: a real service or the sentinel. */
+export type HarnessConversationServiceBinding =
+  | HarnessConversationService
+  | typeof HARNESS_CONVERSATION_SERVICE_UNAVAILABLE;
+
+/** Narrows a binding to a usable service, excluding the unavailable sentinel. */
+export function isHarnessConversationServiceAvailable(
+  binding: HarnessConversationServiceBinding,
+): binding is HarnessConversationService {
+  return binding !== HARNESS_CONVERSATION_SERVICE_UNAVAILABLE;
+}