fix: honor zero-valued voice-call STT settings

Landed from contributor PR #39196 by @scoootscooob.

Co-authored-by: scoootscooob <zhentongfan@gmail.com>

extensions/voice-call/src/providers/stt-openai-realtime.test.ts

@@ -0,0 +1,38 @@
+import { describe, expect, it } from "vitest";
+import type { RealtimeSTTConfig } from "./stt-openai-realtime.js";
+import { OpenAIRealtimeSTTProvider } from "./stt-openai-realtime.js";
+
+type ProviderInternals = OpenAIRealtimeSTTProvider & {
+  vadThreshold: number;
+  silenceDurationMs: number;
+};
+
+function createProvider(config: RealtimeSTTConfig): ProviderInternals {
+  return new OpenAIRealtimeSTTProvider(config) as ProviderInternals;
+}
+
+describe("OpenAIRealtimeSTTProvider constructor defaults", () => {
+  it("uses vadThreshold: 0 when explicitly configured (max sensitivity)", () => {
+    const provider = createProvider({
+      apiKey: "sk-test",
+      vadThreshold: 0,
+    });
+    expect(provider.vadThreshold).toBe(0);
+  });
+
+  it("uses silenceDurationMs: 0 when explicitly configured", () => {
+    const provider = createProvider({
+      apiKey: "sk-test",
+      silenceDurationMs: 0,
+    });
+    expect(provider.silenceDurationMs).toBe(0);
+  });
+
+  it("falls back to defaults when values are undefined", () => {
+    const provider = createProvider({
+      apiKey: "sk-test",
+    });
+    expect(provider.vadThreshold).toBe(0.5);
+    expect(provider.silenceDurationMs).toBe(800);
+  });
+});

extensions/voice-call/src/providers/stt-openai-realtime.ts

@@ -62,8 +62,8 @@ export class OpenAIRealtimeSTTProvider {
     }
     this.apiKey = config.apiKey;
     this.model = config.model || "gpt-4o-transcribe";
-    this.silenceDurationMs = config.silenceDurationMs || 800;
-    this.vadThreshold = config.vadThreshold || 0.5;
+    this.silenceDurationMs = config.silenceDurationMs ?? 800;
+    this.vadThreshold = config.vadThreshold ?? 0.5;
   }
 
   /**