diff --git a/packages/shared/src/types/chat.ts b/packages/shared/src/types/chat.ts
index 36ff15e3..1ddeb689 100644
--- a/packages/shared/src/types/chat.ts
+++ b/packages/shared/src/types/chat.ts
@@ -67,6 +67,7 @@ export interface ChatMessage {
   content: string;
   agentId: string | null;
   messageType: string | null;
+  voiceMode?: "text" | "voice_input" | "full_voice" | null;
   createdAt: string;
   updatedAt: string | null;
   files?: ChatFile[];
diff --git a/packages/shared/src/validators/chat.ts b/packages/shared/src/validators/chat.ts
index 98b15a43..d6b4b957 100644
--- a/packages/shared/src/validators/chat.ts
+++ b/packages/shared/src/validators/chat.ts
@@ -12,11 +12,15 @@ export const updateConversationSchema = z.object({
   archivedAt: z.string().datetime().nullable().optional(),
 });
 
+export const VOICE_MODES = ["text", "voice_input", "full_voice"] as const;
+export type VoiceMode = (typeof VOICE_MODES)[number];
+
 export const createMessageSchema = z.object({
   role: z.enum(["user", "assistant", "system"]),
   content: z.string().min(1).max(100_000),
   agentId: z.string().uuid().optional(),
   messageType: z.string().optional(),
+  voiceMode: z.enum(VOICE_MODES).optional(),
 });
 
 export const handoffSchema = z.object({
diff --git a/server/src/__tests__/36-voice-schema.test.ts b/server/src/__tests__/36-voice-schema.test.ts
new file mode 100644
index 00000000..090eef06
--- /dev/null
+++ b/server/src/__tests__/36-voice-schema.test.ts
@@ -0,0 +1,63 @@
+// [nexus] Schema validation tests for voiceMode field (Plan 36-02)
+import { describe, it, expect } from "vitest";
+import { createMessageSchema } from "@paperclipai/shared/validators/chat";
+
+describe("createMessageSchema — voiceMode field", () => {
+  it("parses voiceMode 'full_voice' and returns the value", () => {
+    const result = createMessageSchema.parse({
+      role: "user",
+      content: "hi",
+      voiceMode: "full_voice",
+    });
+    expect(result.voiceMode).toBe("full_voice");
+  });
+
+  it("parses voiceMode 'voice_input' and returns the value", () => {
+    const result = createMessageSchema.parse({
+      role: "user",
+      content: "hi",
+      voiceMode: "voice_input",
+    });
+    expect(result.voiceMode).toBe("voice_input");
+  });
+
+  it("parses voiceMode 'text' and returns the value", () => {
+    const result = createMessageSchema.parse({
+      role: "user",
+      content: "hi",
+      voiceMode: "text",
+    });
+    expect(result.voiceMode).toBe("text");
+  });
+
+  it("parses without voiceMode and returns undefined for voiceMode", () => {
+    const result = createMessageSchema.parse({
+      role: "user",
+      content: "hi",
+    });
+    expect(result.voiceMode).toBeUndefined();
+  });
+
+  it("throws ZodError when voiceMode is invalid", () => {
+    expect(() =>
+      createMessageSchema.parse({
+        role: "user",
+        content: "hi",
+        voiceMode: "invalid",
+      })
+    ).toThrow();
+  });
+
+  it("preserves existing fields — role, content, agentId, messageType", () => {
+    const result = createMessageSchema.parse({
+      role: "assistant",
+      content: "hello world",
+      agentId: "00000000-0000-0000-0000-000000000001",
+      messageType: "markdown",
+    });
+    expect(result.role).toBe("assistant");
+    expect(result.content).toBe("hello world");
+    expect(result.agentId).toBe("00000000-0000-0000-0000-000000000001");
+    expect(result.messageType).toBe("markdown");
+  });
+});