diff --git a/src/agents/internal-event-contract.ts b/src/agents/internal-event-contract.ts
new file mode 100644
index 00000000000..38c2aa3bf57
--- /dev/null
+++ b/src/agents/internal-event-contract.ts
@@ -0,0 +1,14 @@
+export const AGENT_INTERNAL_EVENT_TYPE_TASK_COMPLETION = "task_completion" as const;
+
+export const AGENT_INTERNAL_EVENT_SOURCES = [
+  "subagent",
+  "cron",
+  "video_generation",
+  "music_generation",
+] as const;
+
+export const AGENT_INTERNAL_EVENT_STATUSES = ["ok", "timeout", "error", "unknown"] as const;
+
+export type AgentInternalEventType = typeof AGENT_INTERNAL_EVENT_TYPE_TASK_COMPLETION;
+export type AgentInternalEventSource = (typeof AGENT_INTERNAL_EVENT_SOURCES)[number];
+export type AgentInternalEventStatus = (typeof AGENT_INTERNAL_EVENT_STATUSES)[number];
diff --git a/src/agents/internal-events.ts b/src/agents/internal-events.ts
index d2106a67b33..7b0025f158a 100644
--- a/src/agents/internal-events.ts
+++ b/src/agents/internal-events.ts
@@ -1,19 +1,22 @@
+import {
+  AGENT_INTERNAL_EVENT_TYPE_TASK_COMPLETION,
+  type AgentInternalEventSource,
+  type AgentInternalEventStatus,
+} from "./internal-event-contract.js";
 import {
   escapeInternalRuntimeContextDelimiters,
   INTERNAL_RUNTIME_CONTEXT_BEGIN,
   INTERNAL_RUNTIME_CONTEXT_END,
 } from "./internal-runtime-context.js";
 
-export type AgentInternalEventType = "task_completion";
-
 export type AgentTaskCompletionInternalEvent = {
-  type: "task_completion";
-  source: "subagent" | "cron" | "video_generation" | "music_generation";
+  type: typeof AGENT_INTERNAL_EVENT_TYPE_TASK_COMPLETION;
+  source: AgentInternalEventSource;
   childSessionKey: string;
   childSessionId?: string;
   announceType: string;
   taskLabel: string;
-  status: "ok" | "timeout" | "error" | "unknown";
+  status: AgentInternalEventStatus;
   statusLabel: string;
   result: string;
   statsLine?: string;
diff --git a/src/gateway/protocol/schema/agent.ts b/src/gateway/protocol/schema/agent.ts
index 57a40c3eca8..2f3b2fd6cc5 100644
--- a/src/gateway/protocol/schema/agent.ts
+++ b/src/gateway/protocol/schema/agent.ts
@@ -1,15 +1,20 @@
 import { Type } from "@sinclair/typebox";
+import {
+  AGENT_INTERNAL_EVENT_SOURCES,
+  AGENT_INTERNAL_EVENT_STATUSES,
+  AGENT_INTERNAL_EVENT_TYPE_TASK_COMPLETION,
+} from "../../../agents/internal-event-contract.js";
 import { InputProvenanceSchema, NonEmptyString, SessionLabelString } from "./primitives.js";
 
 export const AgentInternalEventSchema = Type.Object(
   {
-    type: Type.Literal("task_completion"),
-    source: Type.String({ enum: ["subagent", "cron", "video_generation"] }),
+    type: Type.Literal(AGENT_INTERNAL_EVENT_TYPE_TASK_COMPLETION),
+    source: Type.String({ enum: [...AGENT_INTERNAL_EVENT_SOURCES] }),
     childSessionKey: Type.String(),
     childSessionId: Type.Optional(Type.String()),
     announceType: Type.String(),
     taskLabel: Type.String(),
-    status: Type.String({ enum: ["ok", "timeout", "error", "unknown"] }),
+    status: Type.String({ enum: [...AGENT_INTERNAL_EVENT_STATUSES] }),
     statusLabel: Type.String(),
     result: Type.String(),
     statsLine: Type.Optional(Type.String()),
diff --git a/src/gateway/server-methods/agent.test.ts b/src/gateway/server-methods/agent.test.ts
index 87bc5ff3602..1381fb8bbb8 100644
--- a/src/gateway/server-methods/agent.test.ts
+++ b/src/gateway/server-methods/agent.test.ts
@@ -759,6 +759,44 @@ describe("gateway agent handler", () => {
     );
   });
 
+  it("accepts music generation internal events", async () => {
+    primeMainAgentRun();
+    mocks.agentCommand.mockClear();
+    const respond = vi.fn();
+
+    await invokeAgent(
+      {
+        message: "music generation finished",
+        sessionKey: "agent:main:main",
+        internalEvents: [
+          {
+            type: "task_completion",
+            source: "music_generation",
+            childSessionKey: "music:task-123",
+            childSessionId: "task-123",
+            announceType: "music generation task",
+            taskLabel: "compose a loop",
+            status: "ok",
+            statusLabel: "completed successfully",
+            result: "MEDIA: https://example.test/song.mp3",
+            replyInstruction: "Reply in your normal assistant voice now.",
+          },
+        ],
+        idempotencyKey: "music-generation-event",
+      },
+      { reqId: "music-generation-event-1", respond },
+    );
+
+    await waitForAssertion(() => expect(mocks.agentCommand).toHaveBeenCalled());
+    expect(respond).not.toHaveBeenCalledWith(
+      false,
+      undefined,
+      expect.objectContaining({
+        message: expect.stringContaining("invalid agent params"),
+      }),
+    );
+  });
+
   it("only forwards workspaceDir for spawned sessions with stored workspace inheritance", async () => {
     primeMainAgentRun();
     mockMainSessionEntry({