diff --git a/src/CodexEventHandler.ts b/src/CodexEventHandler.ts
index 5ed8ad79..efae65f0 100644
--- a/src/CodexEventHandler.ts
+++ b/src/CodexEventHandler.ts
@@ -72,6 +72,7 @@ export class CodexEventHandler {
     private readonly activeImageGenerationItems = new Set<string>();
     private readonly emittedImageViewItems = new Set<string>();
     private readonly seenReasoningDeltaItemIds = new Set<string>();
+    private readonly seenAgentMessageDeltaItemIds = new Set<string>();
     private readonly terminalCommandIds = new Set<string>();
     private readonly terminalCommandOutputIds = new Set<string>();
 
@@ -230,6 +231,7 @@ export class CodexEventHandler {
     }
 
     private async createTextEvent(event: AgentMessageDeltaNotification): Promise<UpdateSessionEvent> {
+        this.seenAgentMessageDeltaItemIds.add(event.itemId);
         return createAgentTextMessageChunk(event.delta, event.itemId);
     }
 
@@ -387,12 +389,21 @@ export class CodexEventHandler {
                 return this.createExitedReviewModeEvent(event.item);
             case "contextCompaction":
                 return this.createContextCompactedEvent();
+            case "agentMessage": {
+                if (this.seenAgentMessageDeltaItemIds.delete(event.item.id)) {
+                    return null;
+                }
+                const text = event.item.text;
+                if (text.length > 0) {
+                    return createAgentTextMessageChunk(text, event.item.id);
+                }
+                return null;
+            }
             //ignored types
             case "subAgentActivity":
             case "sleep":
             case "userMessage":
             case "hookPrompt":
-            case "agentMessage":
             case "enteredReviewMode":
             case "plan":
                 return null;
diff --git a/src/__tests__/CodexACPAgent/agent-message-fallback.test.ts b/src/__tests__/CodexACPAgent/agent-message-fallback.test.ts
new file mode 100644
index 00000000..b9452d8e
--- /dev/null
+++ b/src/__tests__/CodexACPAgent/agent-message-fallback.test.ts
@@ -0,0 +1,96 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import type { ServerNotification } from "../../app-server";
+import type { SessionState } from "../../CodexAcpServer";
+import { AgentMode } from "../../AgentMode";
+import {
+    createCodexMockTestFixture,
+    createTestSessionState,
+    setupPromptAndSendNotifications,
+    type CodexMockTestFixture
+} from "../acp-test-utils";
+
+describe("CodexEventHandler - agent message fallback", () => {
+    let mockFixture: CodexMockTestFixture;
+    const sessionId = "test-session-id";
+
+    beforeEach(() => {
+        mockFixture = createCodexMockTestFixture();
+        vi.clearAllMocks();
+    });
+
+    const sessionState: SessionState = createTestSessionState({
+        sessionId,
+        currentModelId: "model-id[effort]",
+        agentMode: AgentMode.DEFAULT_AGENT_MODE
+    });
+
+    it("emits agent message text from item/completed when no deltas streamed", async () => {
+        const notifications: ServerNotification[] = [
+            {
+                method: "item/completed",
+                params: {
+                    threadId: sessionId,
+                    turnId: "turn-1",
+                    completedAtMs: 0,
+                    item: {
+                        type: "agentMessage",
+                        id: "msg-1",
+                        text: "Hello!",
+                        phase: null,
+                        memoryCitation: null,
+                    },
+                },
+            },
+        ];
+
+        await setupPromptAndSendNotifications(mockFixture, sessionId, sessionState, notifications);
+
+        await expect(mockFixture.getAcpConnectionDump([])).toMatchFileSnapshot(
+            "data/agent-message-completed-fallback.json"
+        );
+    });
+
+    it("does not duplicate agent message when deltas were streamed", async () => {
+        const notifications: ServerNotification[] = [
+            {
+                method: "item/agentMessage/delta",
+                params: {
+                    threadId: sessionId,
+                    turnId: "turn-1",
+                    itemId: "msg-2",
+                    delta: "Hel",
+                },
+            },
+            {
+                method: "item/agentMessage/delta",
+                params: {
+                    threadId: sessionId,
+                    turnId: "turn-1",
+                    itemId: "msg-2",
+                    delta: "lo!",
+                },
+            },
+            {
+                method: "item/completed",
+                params: {
+                    threadId: sessionId,
+                    turnId: "turn-1",
+                    completedAtMs: 0,
+                    item: {
+                        type: "agentMessage",
+                        id: "msg-2",
+                        text: "Hello!",
+                        phase: null,
+                        memoryCitation: null,
+                    },
+                },
+            },
+        ];
+
+        await setupPromptAndSendNotifications(mockFixture, sessionId, sessionState, notifications);
+
+        await expect(mockFixture.getAcpConnectionDump([])).toMatchFileSnapshot(
+            "data/agent-message-deltas-no-duplicate.json"
+        );
+    });
+});
diff --git a/src/__tests__/CodexACPAgent/data/agent-message-completed-fallback.json b/src/__tests__/CodexACPAgent/data/agent-message-completed-fallback.json
new file mode 100644
index 00000000..d33f9359
--- /dev/null
+++ b/src/__tests__/CodexACPAgent/data/agent-message-completed-fallback.json
@@ -0,0 +1,16 @@
+{
+  "method": "sessionUpdate",
+  "args": [
+    {
+      "sessionId": "test-session-id",
+      "update": {
+        "sessionUpdate": "agent_message_chunk",
+        "messageId": "msg-1",
+        "content": {
+          "type": "text",
+          "text": "Hello!"
+        }
+      }
+    }
+  ]
+}
\ No newline at end of file
diff --git a/src/__tests__/CodexACPAgent/data/agent-message-deltas-no-duplicate.json b/src/__tests__/CodexACPAgent/data/agent-message-deltas-no-duplicate.json
new file mode 100644
index 00000000..15f8da98
--- /dev/null
+++ b/src/__tests__/CodexACPAgent/data/agent-message-deltas-no-duplicate.json
@@ -0,0 +1,32 @@
+{
+  "method": "sessionUpdate",
+  "args": [
+    {
+      "sessionId": "test-session-id",
+      "update": {
+        "sessionUpdate": "agent_message_chunk",
+        "messageId": "msg-2",
+        "content": {
+          "type": "text",
+          "text": "Hel"
+        }
+      }
+    }
+  ]
+}
+{
+  "method": "sessionUpdate",
+  "args": [
+    {
+      "sessionId": "test-session-id",
+      "update": {
+        "sessionUpdate": "agent_message_chunk",
+        "messageId": "msg-2",
+        "content": {
+          "type": "text",
+          "text": "lo!"
+        }
+      }
+    }
+  ]
+}
\ No newline at end of file