diff --git a/src/gateway/server-methods/agent.deleted-agent.test.ts b/src/gateway/server-methods/agent.deleted-agent.test.ts
index 6f9da0b569c5..fef9acd09a02 100644
--- a/src/gateway/server-methods/agent.deleted-agent.test.ts
+++ b/src/gateway/server-methods/agent.deleted-agent.test.ts
@@ -12,6 +12,7 @@ import type { RespondFn } from "./types.js";
 
 const agentCommandFromIngressMock = vi.hoisted(() => vi.fn());
 const performGatewaySessionResetMock = vi.hoisted(() => vi.fn());
+const parseMessageWithAttachmentsMock = vi.hoisted(() => vi.fn());
 
 vi.mock("../../commands/agent.js", () => ({
   agentCommandFromIngress: agentCommandFromIngressMock,
@@ -23,11 +24,21 @@ vi.mock("../session-reset-service.js", () => ({
   emitGatewaySessionStartPluginHook: vi.fn(),
 }));
 
+vi.mock("../chat-attachments.js", async () => {
+  const actual =
+    await vi.importActual<typeof import("../chat-attachments.js")>("../chat-attachments.js");
+  return {
+    ...actual,
+    parseMessageWithAttachments: parseMessageWithAttachmentsMock,
+  };
+});
+
 describe("agent RPC deleted-agent guard", () => {
   beforeEach(() => {
     resetDeletedAgentSessionMocks();
     agentCommandFromIngressMock.mockReset();
     performGatewaySessionResetMock.mockReset();
+    parseMessageWithAttachmentsMock.mockReset();
   });
 
   it("rejects keys belonging to a deleted agent", async () => {
@@ -59,6 +70,43 @@ describe("agent RPC deleted-agent guard", () => {
     expect(agentCommandFromIngressMock).not.toHaveBeenCalled();
   });
 
+  it("rejects deleted-agent sessions before media offload or dedupe reservation", async () => {
+    const orphanKey = mockDeletedAgentSession();
+
+    const respond = vi.fn() as unknown as RespondFn;
+    const dedupe = new Map();
+
+    await agentHandlers.agent({
+      req: { id: "req-attach" } as never,
+      params: {
+        sessionKey: orphanKey,
+        message: "see attachment",
+        idempotencyKey: "run-attach",
+        attachments: [
+          { type: "file", mimeType: "application/pdf", fileName: "doc.pdf", content: "aGVsbG8=" },
+        ],
+      },
+      respond,
+      context: {
+        dedupe,
+        chatAbortControllers: new Map(),
+        getRuntimeConfig: () => ({}),
+      } as never,
+      client: null,
+      isWebchatConnect: () => false,
+    });
+
+    expect(respond).toHaveBeenCalledWith(false, undefined, {
+      code: ErrorCodes.INVALID_REQUEST,
+      message: 'Agent "deleted-agent" no longer exists in configuration',
+    });
+    // Guard runs before attachment parsing (inbound media offload), the
+    // pre-accept dedupe reservation, and run dispatch.
+    expect(parseMessageWithAttachmentsMock).not.toHaveBeenCalled();
+    expect(dedupe.size).toBe(0);
+    expect(agentCommandFromIngressMock).not.toHaveBeenCalled();
+  });
+
   it.each(["/reset", "/reset follow up"])(
     "rejects deleted-agent session keys before %s handling",
     async (message) => {
diff --git a/src/gateway/server-methods/agent.ts b/src/gateway/server-methods/agent.ts
index e60fd50c2ec2..1dc5904cec4b 100644
--- a/src/gateway/server-methods/agent.ts
+++ b/src/gateway/server-methods/agent.ts
@@ -1505,6 +1505,17 @@ export const agentHandlers: GatewayRequestHandlers = {
         return;
       }
     }
+    // Reject orphaned deleted-agent session keys before any side effect (dedupe
+    // reservation, attachment media offload, reset, dispatch), matching the
+    // chat.send / sessions.send invariant. Voice-wake auto-routing below only
+    // retargets to knownAgents, so a post-routing key is never deleted; guarding
+    // the original requestedSessionKey here covers every dispatch path.
+    if (
+      requestedSessionKey &&
+      respondDeletedAgentSessionForKey({ sessionKey: requestedSessionKey, agentId, respond })
+    ) {
+      return;
+    }
     // Reserve the run before awaited attachment/session/delivery work so duplicate calls dedupe and
     // pre-registration chat.abort can be made durable by idempotency key.
     const preAcceptedReservedSessionKey =
@@ -1691,13 +1702,6 @@ export const agentHandlers: GatewayRequestHandlers = {
       let skipAgentInitialSessionTouch = false;
       let pendingChatRun: { sessionKey: string; agentId?: string } | undefined;
 
-      if (
-        requestedSessionKey &&
-        respondDeletedAgentSessionForKey({ sessionKey: requestedSessionKey, agentId, respond })
-      ) {
-        return;
-      }
-
       const resetCommandMatch = message.match(RESET_COMMAND_RE);
       if (resetCommandMatch && requestedSessionKey) {
         if (abortForLifecycleRotation({ sessionKey: requestedSessionKey, agentId })) {