refactor(core): unify InjectionService API to single onInjection interface

Remove legacy onUserHint/offUserHint/addUserHint methods. All callers
now use addInjection(text, source) and onInjection/offInjection with
source-based filtering where needed.

packages/core/src/config/injectionService.ts

@@ -20,9 +20,8 @@ export type InjectionListener = (text: string, source: InjectionSource) => void;
  * Service for managing injections into the model conversation.
  *
  * Multiple sources (user steering, background execution completions, etc.)
- * can feed into this service. Consumers register typed listeners via
- * {@link onInjection} to receive injections with source information, or use the
- * legacy {@link onUserHint} API for backward compatibility.
+ * can feed into this service. Consumers register listeners via
+ * {@link onInjection} to receive injections with source information.
  */
 export class InjectionService {
   private readonly injections: Array<{
@@ -31,7 +30,6 @@ export class InjectionService {
     timestamp: number;
   }> = [];
   private readonly injectionListeners: Set<InjectionListener> = new Set();
-  private readonly userHintListeners: Set<(hint: string) => void> = new Set();
 
   constructor(private readonly isEnabled: () => boolean) {}
 
@@ -51,55 +49,25 @@ export class InjectionService {
     }
     this.injections.push({ text: trimmed, source, timestamp: Date.now() });
 
-    // Fire typed listeners (new API)
     for (const listener of this.injectionListeners) {
       listener(trimmed, source);
     }
-
-    // Fire legacy listeners (user_steering only)
-    if (source === 'user_steering') {
-      for (const listener of this.userHintListeners) {
-        listener(trimmed);
-      }
-    }
   }
 
   /**
-   * Adds a new steering hint from the user.
-   * Convenience wrapper around {@link addInjection} with `user_steering` source.
-   */
-  addUserHint(hint: string): void {
-    this.addInjection(hint, 'user_steering');
-  }
-
-  /**
-   * Registers a typed listener for injections from any source.
+   * Registers a listener for injections from any source.
    */
   onInjection(listener: InjectionListener): void {
     this.injectionListeners.add(listener);
   }
 
   /**
-   * Unregisters a typed injection listener.
+   * Unregisters an injection listener.
    */
   offInjection(listener: InjectionListener): void {
     this.injectionListeners.delete(listener);
   }
 
-  /**
-   * Registers a listener for user steering hints only.
-   */
-  onUserHint(listener: (hint: string) => void): void {
-    this.userHintListeners.add(listener);
-  }
-
-  /**
-   * Unregisters a user steering hint listener.
-   */
-  offUserHint(listener: (hint: string) => void): void {
-    this.userHintListeners.delete(listener);
-  }
-
   /**
    * Returns all collected injection texts (all sources).
    */