diff --git a/plugins/provider-codex/src/ai/chatgpt-client.test.ts b/plugins/provider-codex/src/ai/chatgpt-client.test.ts
index b30bc97ef..c21bba3f2 100644
--- a/plugins/provider-codex/src/ai/chatgpt-client.test.ts
+++ b/plugins/provider-codex/src/ai/chatgpt-client.test.ts
@@ -136,7 +136,7 @@ function openSseResponse(events: JsonValue[]): {
 } {
   let canceled = false;
   const bytes = new TextEncoder().encode(
-    `${events.map((event) => `data: ${JSON.stringify(event)}`).join("\n\n")}\n\n`,
+    `${events.map((event) => `data: ${event === "[DONE]" ? event : JSON.stringify(event)}`).join("\n\n")}\n\n`,
   );
   return {
     response: new Response(
@@ -317,6 +317,77 @@ describe("Codex ChatGPT client", () => {
     expect(requestBody.text).toBeUndefined();
   });
 
+  it.each([
+    { terminalType: "response.completed", finalText: "Final result" },
+    { terminalType: "response.done", finalText: "Final result" },
+    { terminalType: "response.completed", finalText: "" },
+    { terminalType: "[DONE]", finalText: "" },
+  ])(
+    "returns text and cancels an open SSE body after $terminalType with final text '$finalText'",
+    async ({ terminalType, finalText }) => {
+      const homeDir = await makeTempHome();
+      await writeCodexApiKeyAuth({ homeDir, apiKey: "sk-codex-api-key" });
+      const fetchMock = setupFetchMock();
+      const completedResponse = openSseResponse([
+        { type: "response.output_text.delta", delta: "Partial result" },
+        terminalType === "[DONE]"
+          ? "[DONE]"
+          : {
+              type: terminalType,
+              response: {
+                output: [
+                  {
+                    type: "message",
+                    content: [{ type: "output_text", text: finalText }],
+                  },
+                ],
+              },
+            },
+        "[DONE]",
+      ]);
+      fetchMock.mockResolvedValueOnce(completedResponse.response);
+
+      await expect(
+        completeCodexInference(
+          {
+            model: "gpt-5.6-luna",
+            prompt: "Return a title",
+            timeoutMs: 100,
+          },
+          new AbortController().signal,
+        ),
+      ).resolves.toBe(finalText || "Partial result");
+      expect(completedResponse.wasCanceled()).toBe(true);
+    },
+  );
+
+  it.each(["response.completed", "[DONE]"])(
+    "rejects an empty open SSE body after %s without waiting for EOF",
+    async (terminalType) => {
+      const homeDir = await makeTempHome();
+      await writeCodexApiKeyAuth({ homeDir, apiKey: "sk-codex-api-key" });
+      const fetchMock = setupFetchMock();
+      const completedResponse = openSseResponse([
+        terminalType === "[DONE]"
+          ? "[DONE]"
+          : { type: terminalType, response: { output: [] } },
+      ]);
+      fetchMock.mockResolvedValueOnce(completedResponse.response);
+
+      await expect(
+        completeCodexInference(
+          {
+            model: "gpt-5.6-luna",
+            prompt: "Return a title",
+            timeoutMs: 100,
+          },
+          new AbortController().signal,
+        ),
+      ).rejects.toMatchObject({ detailCode: "codex_response_invalid" });
+      expect(completedResponse.wasCanceled()).toBe(true);
+    },
+  );
+
   it("classifies streamed overload failures as service unavailable", async () => {
     const homeDir = await makeTempHome();
     await writeCodexApiKeyAuth({
diff --git a/plugins/provider-codex/src/ai/chatgpt-client.ts b/plugins/provider-codex/src/ai/chatgpt-client.ts
index 92a1a57d4..84a421813 100644
--- a/plugins/provider-codex/src/ai/chatgpt-client.ts
+++ b/plugins/provider-codex/src/ai/chatgpt-client.ts
@@ -580,9 +580,10 @@ async function readResponseTextFromSse(
   let deltaText = "";
   let finalText: string | null = null;
   let totalBytes = 0;
+  let completed = false;
 
   try {
-    while (true) {
+    while (!completed) {
       const chunk = await readChunkWithTimeout({
         deadline: args.deadline,
         reader,
@@ -614,7 +615,11 @@ async function readResponseTextFromSse(
           .map((line) => line.slice(5).trim())
           .join("\n")
           .trim();
-        if (eventData && eventData !== "[DONE]") {
+        if (eventData === "[DONE]") {
+          completed = true;
+          break;
+        }
+        if (eventData) {
           const eventValue = parseSseEventValue(eventData);
           const event = toJsonObject(eventValue);
           if (event) {
@@ -625,15 +630,16 @@ async function readResponseTextFromSse(
                 result.failure.message,
               );
             }
+            if (
+              optionalString(event.type) === "response.completed" ||
+              optionalString(event.type) === "response.done"
+            ) {
+              finalText = result.text || null;
+              completed = true;
+              break;
+            }
             if (result.text) {
-              if (
-                optionalString(event.type) === "response.completed" ||
-                optionalString(event.type) === "response.done"
-              ) {
-                finalText = result.text;
-              } else {
-                deltaText += result.text;
-              }
+              deltaText += result.text;
             }
           }
         }
@@ -641,6 +647,9 @@ async function readResponseTextFromSse(
       }
     }
     buffer += decoder.decode();
+    if (completed) {
+      await cancelReaderBestEffort(reader);
+    }
   } catch (error) {
     await cancelReaderBestEffort(reader);
     throw error;