fix(ai): process unterminated Codex SSE terminal events

Flush the SSE decoder at EOF and treat the residual buffer as a complete frame.

fixes #9047

packages/ai/CHANGELOG.md

@@ -10,6 +10,7 @@
 
 - Removed the unnecessary Chord dependency from pi-ai by defining its exported `JsonValue` type directly.
 - Fixed GitHub Copilot Claude Fable 5 requests to use the Anthropic Messages adapter so selected reasoning levels are sent ([#8961](https://github.com/earendil-works/pi/issues/8961)).
+- Fixed OpenAI Codex SSE parsing to process terminal events that are not followed by a blank line ([#9047](https://github.com/earendil-works/pi/issues/9047)).
 
 ## [0.84.4] - 2026-08-28
 

packages/ai/src/api/openai-codex-responses.ts

@@ -779,8 +779,9 @@ async function* parseSSE(response: Response, signal?: AbortSignal): AsyncGenerat
 			if (signal?.aborted) {
 				throw new Error("Request was aborted");
 			}
-			if (done) break;
-			buffer += decoder.decode(value, { stream: true });
+			buffer += done ? decoder.decode() : decoder.decode(value, { stream: true });
+			// Treat EOF as terminating the residual SSE frame.
+			if (done && buffer.trim()) buffer += "\n\n";
 
 			let idx = buffer.indexOf("\n\n");
 			while (idx !== -1) {
@@ -806,6 +807,8 @@ async function* parseSSE(response: Response, signal?: AbortSignal): AsyncGenerat
 				}
 				idx = buffer.indexOf("\n\n");
 			}
+
+			if (done) break;
 		}
 	} finally {
 		signal?.removeEventListener("abort", onAbort);

packages/ai/test/openai-codex-stream.test.ts

@@ -209,6 +209,37 @@ describe("openai-codex streaming", () => {
 		expect(sawDone).toBe(true);
 	});
 
+	// Regression test for https://github.com/earendil-works/pi/issues/9047
+	it("processes a terminal SSE event without a trailing blank line", async () => {
+		const token = mockToken();
+		const sse = buildSSEPayload({ status: "completed" }).trimEnd();
+		const model: Model<"openai-codex-responses"> = {
+			id: "gpt-5.1-codex",
+			name: "GPT-5.1 Codex",
+			api: "openai-codex-responses",
+			provider: "openai-codex",
+			baseUrl: "https://chatgpt.com/backend-api",
+			reasoning: true,
+			input: ["text"],
+			cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+			contextWindow: 400000,
+			maxTokens: 128000,
+		};
+		const context: Context = {
+			systemPrompt: "You are a helpful assistant.",
+			messages: [{ role: "user", content: "Say hello", timestamp: Date.now() }],
+		};
+		const resultStream = streamOpenAICodexResponses(model, context, {
+			apiKey: token,
+			transport: "sse",
+			fetch: async () => new Response(sse, { status: 200, headers: { "content-type": "text/event-stream" } }),
+		});
+		const result = await resultStream.result();
+
+		expect(result.stopReason).toBe("stop");
+		expect(result.content.find((content) => content.type === "text")?.text).toBe("Hello");
+	});
+
 	it("completes after response.completed even when the SSE body stays open", async () => {
 		const tempDir = mkdtempSync(join(tmpdir(), "pi-codex-stream-"));
 		process.env.PI_CODING_AGENT_DIR = tempDir;