fix(openai): keep opening prompt collapsible

src/core/openai.ts

@@ -229,12 +229,6 @@ function contentText(content: OpenAIChatMessage['content']): string {
     .join('\n\n');
 }
 
-function contentParts(content: OpenAIChatMessage['content']): OpenAIContentPart[] {
-  if (typeof content === 'string') return [{ type: 'text', text: content }];
-  if (Array.isArray(content)) return content.slice();
-  return [];
-}
-
 function setTextContent(msg: OpenAIChatMessage, text: string): void {
   if (Array.isArray(msg.content)) {
     const kept = msg.content.filter((p) => !isTextPart(p));
@@ -647,11 +641,17 @@ export async function transformOpenAIChatCompletions(
   info.imagePngs = images.map((img) => img.png);
   info.imageDims = images.map((img) => ({ width: img.width, height: img.height }));
 
-  const firstUserMsg = req.messages[firstUserIdx]!;
-  firstUserMsg.content = [
-    ...imageParts,
-    { type: 'text', text: '[End of rendered GPT system/tool context.]' },
-    ...contentParts(firstUserMsg.content),
+  const slabUserMsg: OpenAIChatMessage = {
+    role: 'user',
+    content: [
+      ...imageParts,
+      { type: 'text', text: '[End of rendered GPT system/tool context.]' },
+    ],
+  };
+  req.messages = [
+    ...req.messages.slice(0, firstUserIdx),
+    slabUserMsg,
+    ...req.messages.slice(firstUserIdx),
   ];
 
   for (const msg of req.messages) {
@@ -660,9 +660,9 @@ export async function transformOpenAIChatCompletions(
     setTextContent(msg, CHAT_POINTER);
   }
 
-  // Collapse the OLD conversation prefix into history image(s). The first user
-  // message (firstUserIdx) carries the static slab and is protected; the bulk is
-  // the transcript OpenCode resends every turn.
+  // Collapse the OLD conversation prefix into history image(s). The inserted slab
+  // item carries static images and is protected; the original opening user prompt
+  // remains collapsible history instead of looking like the live request.
   if (o.collapseHistory) {
     const turns = chatMessagesToTurns(req.messages);
     const profitable = (text: string, cols: number) =>
@@ -842,12 +842,18 @@ export async function transformOpenAIResponses(
       ],
     }];
   } else {
-    // Prepend images to the first user item's content.
-    const firstUserItem = inputItems[firstUserIdx] as ResponsesInputItem;
-    const originalContent = typeof firstUserItem.content === 'string'
-      ? [{ type: 'input_text', text: firstUserItem.content } as ResponsesInputTextPart]
-      : (firstUserItem.content as ResponsesContentPart[]).slice();
-    firstUserItem.content = [...imagePartsResp, endMarker, ...originalContent];
+    // Insert a dedicated static-slab item. Do not attach it to the opening real
+    // user prompt: that prompt is old history on long stateless Responses calls,
+    // and protecting it made stale first-turn requests look live.
+    const slabUserItem: ResponsesInputItem = {
+      role: 'user',
+      content: [...imagePartsResp, endMarker],
+    };
+    inputItems = [
+      ...inputItems.slice(0, firstUserIdx),
+      slabUserItem,
+      ...inputItems.slice(firstUserIdx),
+    ];
     req.input = inputItems;
   }
 
@@ -868,9 +874,9 @@ export async function transformOpenAIResponses(
     }
   }
 
-  // Collapse the OLD conversation prefix into history image(s). The static slab
-  // is small; the transcript OpenCode resends every turn is the real cost. Skip
-  // for bare-string input (single message, nothing to collapse).
+  // Collapse the OLD conversation prefix into history image(s). The inserted slab
+  // item is protected; the transcript OpenCode resends every turn is the real cost.
+  // Skip for bare-string input (single message, nothing to collapse).
   if (o.collapseHistory && !inputWasString) {
     const turns = responsesItemsToTurns(inputItems);
     const profitable = (text: string, cols: number) =>

tests/openai-gpt5.test.ts

@@ -333,20 +333,27 @@ describe('transformOpenAIResponses (gpt-5.6)', () => {
 // -- Task 4: GPT history-image collapse (the growing transcript) ---------------
 
 const BIG_SLAB = 'You are a coding agent with detailed instructions. '.repeat(80); // ~4k chars
+const OPENING_PROMPT_MARKER = 'OPENING_PROMPT_SHOULD_BE_HISTORY';
+const LIVE_PROMPT_MARKER = 'LIVE_CURRENT_PROMPT_SHOULD_STAY_TEXT';
 
 /** A long Responses `input`: first user, then many closed tool-call turns + a
  *  recent tail. Each turn is ~600 chars so the collapsed prefix clears the 8000
  *  minCollapseChars floor. */
 function buildResponsesInput(turns: number): Array<Record<string, unknown>> {
   const items: Array<Record<string, unknown>> = [
-    { role: 'user', content: 'Start the task. '.repeat(40) },
+    { role: 'user', content: `${OPENING_PROMPT_MARKER} `.repeat(40) },
   ];
   for (let i = 0; i < turns; i++) {
     const id = `call_${i}`;
     items.push({ role: 'assistant', content: `Working on step ${i}. `.repeat(30) });
     items.push({ type: 'function_call', call_id: id, name: 'read', arguments: `{"path":"f${i}"}` });
     items.push({ type: 'function_call_output', call_id: id, output: `result ${i} `.repeat(50) });
-    items.push({ role: 'user', content: `Continue with ${i}. `.repeat(20) });
+    items.push({
+      role: 'user',
+      content: i === turns - 1
+        ? `${LIVE_PROMPT_MARKER} `.repeat(20)
+        : `Continue with ${i}. `.repeat(20),
+    });
   }
   return items;
 }
@@ -354,7 +361,7 @@ function buildResponsesInput(turns: number): Array<Record<string, unknown>> {
 function buildChatMessages(turns: number): Array<Record<string, unknown>> {
   const msgs: Array<Record<string, unknown>> = [
     { role: 'system', content: BIG_SLAB },
-    { role: 'user', content: 'Start the task. '.repeat(40) },
+    { role: 'user', content: `${OPENING_PROMPT_MARKER} `.repeat(40) },
   ];
   for (let i = 0; i < turns; i++) {
     const id = `call_${i}`;
@@ -364,7 +371,12 @@ function buildChatMessages(turns: number): Array<Record<string, unknown>> {
       tool_calls: [{ id, type: 'function', function: { name: 'read', arguments: `{"path":"f${i}"}` } }],
     });
     msgs.push({ role: 'tool', tool_call_id: id, content: `result ${i} `.repeat(50) });
-    msgs.push({ role: 'user', content: `Continue with ${i}. `.repeat(20) });
+    msgs.push({
+      role: 'user',
+      content: i === turns - 1
+        ? `${LIVE_PROMPT_MARKER} `.repeat(20)
+        : `Continue with ${i}. `.repeat(20),
+    });
   }
   return msgs;
 }
@@ -397,11 +409,14 @@ describe('transformOpenAIResponses — history collapse', () => {
       );
     });
     expect(historyItems).toHaveLength(1);
+    const serialized = JSON.stringify(out.input);
+    expect(serialized).not.toContain(OPENING_PROMPT_MARKER);
+    expect(serialized).toContain(LIVE_PROMPT_MARKER);
     // The recent tail is still raw text items (function_call / user), not collapsed.
     const lastUser = [...out.input].reverse().find(
       (item) => (item as { role?: string }).role === 'user',
     ) as { content?: string };
-    expect(typeof lastUser.content === 'string' && lastUser.content.includes('Continue with 19')).toBe(true);
+    expect(typeof lastUser.content === 'string' && lastUser.content.includes(LIVE_PROMPT_MARKER)).toBe(true);
   });
 
   it('produces a byte-stable history image sha across identical requests', async () => {
@@ -454,6 +469,9 @@ describe('transformOpenAIChatCompletions — history collapse', () => {
       );
     });
     expect(historyMsgs).toHaveLength(1);
+    const serialized = JSON.stringify(out.messages);
+    expect(serialized).not.toContain(OPENING_PROMPT_MARKER);
+    expect(serialized).toContain(LIVE_PROMPT_MARKER);
   });
 });