diff --git a/apps/gateway/src/chat/chat.gateway-redaction.spec.ts b/apps/gateway/src/chat/chat.gateway-redaction.spec.ts
new file mode 100644
index 0000000..0ac831a
--- /dev/null
+++ b/apps/gateway/src/chat/chat.gateway-redaction.spec.ts
@@ -0,0 +1,93 @@
+import { describe, expect, it, vi } from 'vitest';
+import { ChatGateway } from './chat.gateway.js';
+
+const CONVERSATION_ID = 'conversation-1';
+const CANARY = 'token=sk_canary12345678';
+
+type GatewayInternals = {
+  clientSessions: Map<string, unknown>;
+  relayEvent(client: unknown, conversationId: string, event: unknown): void;
+};
+
+function buildGateway() {
+  const brain = {
+    conversations: {
+      addMessage: vi.fn().mockResolvedValue(undefined),
+    },
+  };
+  const agentService = {
+    getSession: vi.fn().mockReturnValue(undefined),
+  };
+  const gateway = new ChatGateway(
+    agentService as never,
+    {} as never,
+    brain as never,
+    {} as never,
+    {} as never,
+    {} as never,
+  );
+
+  return { gateway: gateway as unknown as GatewayInternals, brain };
+}
+
+describe('ChatGateway redaction boundary', (): void => {
+  it('redacts an assistant delta before egress and before its persistence buffer', (): void => {
+    const { gateway } = buildGateway();
+    const client = {
+      connected: true,
+      id: 'client-1',
+      data: { user: { id: 'user-1' } },
+      emit: vi.fn(),
+    };
+    const session = {
+      conversationId: CONVERSATION_ID,
+      cleanup: vi.fn(),
+      assistantText: '',
+      toolCalls: [],
+      pendingToolCalls: new Map(),
+      scope: { userId: 'user-1', tenantId: 'tenant-1' },
+    };
+    gateway.clientSessions.set(client.id, session);
+
+    gateway.relayEvent(client, CONVERSATION_ID, {
+      type: 'message_update',
+      assistantMessageEvent: { type: 'text_delta', delta: CANARY },
+    });
+
+    expect(client.emit).toHaveBeenCalledWith('agent:text', {
+      conversationId: CONVERSATION_ID,
+      text: '[REDACTED_SECRET]',
+    });
+    expect(session.assistantText).toBe('[REDACTED_SECRET]');
+    expect(JSON.stringify(client.emit.mock.calls)).not.toContain(CANARY);
+  });
+
+  it('persists only redacted assistant content with classifications', (): void => {
+    const { gateway, brain } = buildGateway();
+    const client = {
+      connected: true,
+      id: 'client-1',
+      data: { user: { id: 'user-1' } },
+      emit: vi.fn(),
+    };
+    gateway.clientSessions.set(client.id, {
+      conversationId: CONVERSATION_ID,
+      cleanup: vi.fn(),
+      assistantText: CANARY,
+      toolCalls: [],
+      pendingToolCalls: new Map(),
+      scope: { userId: 'user-1', tenantId: 'tenant-1' },
+    });
+
+    gateway.relayEvent(client, CONVERSATION_ID, { type: 'agent_end' });
+
+    expect(brain.conversations.addMessage).toHaveBeenCalledWith(
+      expect.objectContaining({
+        content: '[REDACTED_SECRET]',
+        metadata: expect.objectContaining({ classifications: ['secret'] }),
+      }),
+      'user-1',
+    );
+    expect(JSON.stringify(brain.conversations.addMessage.mock.calls)).not.toContain(CANARY);
+  });
+});