fix(ai): handle OpenAI Responses reasoning text deltas

packages/ai/CHANGELOG.md

@@ -2,6 +2,11 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed OpenAI Responses reasoning text streaming for LM Studio and other compatible providers that emit `response.reasoning_text.delta` events ([#4191](https://github.com/badlogic/pi-mono/pull/4191) by [@yaanfpv](https://github.com/yaanfpv)).
+- Fixed OpenAI Codex OAuth refresh failures writing directly to stderr while the TUI is active ([#4141](https://github.com/badlogic/pi-mono/issues/4141)).
+
 ## [0.73.0] - 2026-05-04
 
 ### Breaking Changes

packages/ai/src/providers/openai-responses-shared.ts

@@ -354,6 +354,16 @@ export async function processResponsesStream<TApi extends Api>(
 					});
 				}
 			}
+		} else if (event.type === "response.reasoning_text.delta") {
+			if (currentItem?.type === "reasoning" && currentBlock?.type === "thinking") {
+				currentBlock.thinking += event.delta;
+				stream.push({
+					type: "thinking_delta",
+					contentIndex: blockIndex(),
+					delta: event.delta,
+					partial: output,
+				});
+			}
 		} else if (event.type === "response.content_part.added") {
 			if (currentItem?.type === "message") {
 				currentItem.content = currentItem.content || [];
@@ -429,7 +439,9 @@ export async function processResponsesStream<TApi extends Api>(
 			const item = event.item;
 
 			if (item.type === "reasoning" && currentBlock?.type === "thinking") {
-				currentBlock.thinking = item.summary?.map((s) => s.text).join("\n\n") || "";
+				const summaryText = item.summary?.map((s) => s.text).join("\n\n") || "";
+				const contentText = item.content?.map((c) => c.text).join("\n\n") || "";
+				currentBlock.thinking = summaryText || contentText || currentBlock.thinking;
 				currentBlock.thinkingSignature = JSON.stringify(item);
 				stream.push({
 					type: "thinking_end",