feat: restore voice-call plugin parity

extensions/voice-call/src/providers/base.ts

@@ -0,0 +1,67 @@
+import type {
+  HangupCallInput,
+  InitiateCallInput,
+  InitiateCallResult,
+  PlayTtsInput,
+  ProviderName,
+  ProviderWebhookParseResult,
+  StartListeningInput,
+  StopListeningInput,
+  WebhookContext,
+  WebhookVerificationResult,
+} from "../types.js";
+
+/**
+ * Abstract base interface for voice call providers.
+ *
+ * Each provider (Telnyx, Twilio, etc.) implements this interface to provide
+ * a consistent API for the call manager.
+ *
+ * Responsibilities:
+ * - Webhook verification and event parsing
+ * - Outbound call initiation and hangup
+ * - Media control (TTS playback, STT listening)
+ */
+export interface VoiceCallProvider {
+  /** Provider identifier */
+  readonly name: ProviderName;
+
+  /**
+   * Verify webhook signature/HMAC before processing.
+   * Must be called before parseWebhookEvent.
+   */
+  verifyWebhook(ctx: WebhookContext): WebhookVerificationResult;
+
+  /**
+   * Parse provider-specific webhook payload into normalized events.
+   * Returns events and optional response to send back to provider.
+   */
+  parseWebhookEvent(ctx: WebhookContext): ProviderWebhookParseResult;
+
+  /**
+   * Initiate an outbound call.
+   * @returns Provider call ID and status
+   */
+  initiateCall(input: InitiateCallInput): Promise<InitiateCallResult>;
+
+  /**
+   * Hang up an active call.
+   */
+  hangupCall(input: HangupCallInput): Promise<void>;
+
+  /**
+   * Play TTS audio to the caller.
+   * The provider should handle streaming if supported.
+   */
+  playTts(input: PlayTtsInput): Promise<void>;
+
+  /**
+   * Start listening for user speech (activate STT).
+   */
+  startListening(input: StartListeningInput): Promise<void>;
+
+  /**
+   * Stop listening for user speech (deactivate STT).
+   */
+  stopListening(input: StopListeningInput): Promise<void>;
+}