diff --git a/extensions/voice-call/src/providers/mock.test.ts b/extensions/voice-call/src/providers/mock.test.ts
new file mode 100644
index 00000000000..854ccdbf8b8
--- /dev/null
+++ b/extensions/voice-call/src/providers/mock.test.ts
@@ -0,0 +1,78 @@
+import { describe, expect, it } from "vitest";
+import type { WebhookContext } from "../types.js";
+import { MockProvider } from "./mock.js";
+
+function createWebhookContext(rawBody: string): WebhookContext {
+  return {
+    headers: {},
+    rawBody,
+    url: "http://localhost/voice/webhook",
+    method: "POST",
+    query: {},
+  };
+}
+
+describe("MockProvider", () => {
+  it("preserves explicit falsy event values", () => {
+    const provider = new MockProvider();
+    const result = provider.parseWebhookEvent(
+      createWebhookContext(
+        JSON.stringify({
+          events: [
+            {
+              id: "evt-error",
+              type: "call.error",
+              callId: "call-1",
+              timestamp: 0,
+              error: "",
+              retryable: false,
+            },
+            {
+              id: "evt-ended",
+              type: "call.ended",
+              callId: "call-2",
+              reason: "",
+            },
+            {
+              id: "evt-speech",
+              type: "call.speech",
+              callId: "call-3",
+              transcript: "",
+              isFinal: false,
+            },
+          ],
+        }),
+      ),
+    );
+
+    expect(result.events).toEqual([
+      {
+        id: "evt-error",
+        type: "call.error",
+        callId: "call-1",
+        providerCallId: undefined,
+        timestamp: 0,
+        error: "",
+        retryable: false,
+      },
+      {
+        id: "evt-ended",
+        type: "call.ended",
+        callId: "call-2",
+        providerCallId: undefined,
+        timestamp: expect.any(Number),
+        reason: "",
+      },
+      {
+        id: "evt-speech",
+        type: "call.speech",
+        callId: "call-3",
+        providerCallId: undefined,
+        timestamp: expect.any(Number),
+        transcript: "",
+        isFinal: false,
+        confidence: undefined,
+      },
+    ]);
+  });
+});
diff --git a/extensions/voice-call/src/providers/mock.ts b/extensions/voice-call/src/providers/mock.ts
index 36211538ed6..7dcb201ff30 100644
--- a/extensions/voice-call/src/providers/mock.ts
+++ b/extensions/voice-call/src/providers/mock.ts
@@ -65,10 +65,10 @@ export class MockProvider implements VoiceCallProvider {
     }
 
     const base = {
-      id: evt.id || crypto.randomUUID(),
+      id: evt.id ?? crypto.randomUUID(),
       callId: evt.callId,
       providerCallId: evt.providerCallId,
-      timestamp: evt.timestamp || Date.now(),
+      timestamp: evt.timestamp ?? Date.now(),
     };
 
     switch (evt.type) {
@@ -83,7 +83,7 @@ export class MockProvider implements VoiceCallProvider {
         return {
           ...base,
           type: evt.type,
-          text: payload.text || "",
+          text: payload.text ?? "",
         };
       }
 
@@ -98,7 +98,7 @@ export class MockProvider implements VoiceCallProvider {
         return {
           ...base,
           type: evt.type,
-          transcript: payload.transcript || "",
+          transcript: payload.transcript ?? "",
           isFinal: payload.isFinal ?? true,
           confidence: payload.confidence,
         };
@@ -109,7 +109,7 @@ export class MockProvider implements VoiceCallProvider {
         return {
           ...base,
           type: evt.type,
-          durationMs: payload.durationMs || 0,
+          durationMs: payload.durationMs ?? 0,
         };
       }
 
@@ -118,7 +118,7 @@ export class MockProvider implements VoiceCallProvider {
         return {
           ...base,
           type: evt.type,
-          digits: payload.digits || "",
+          digits: payload.digits ?? "",
         };
       }
 
@@ -127,7 +127,7 @@ export class MockProvider implements VoiceCallProvider {
         return {
           ...base,
           type: evt.type,
-          reason: payload.reason || "completed",
+          reason: payload.reason ?? "completed",
         };
       }
 
@@ -136,7 +136,7 @@ export class MockProvider implements VoiceCallProvider {
         return {
           ...base,
           type: evt.type,
-          error: payload.error || "unknown error",
+          error: payload.error ?? "unknown error",
           retryable: payload.retryable,
         };
       }