Prevent orphaned tool outputs from triggering Codex 400s

lib/request/request-transformer.ts

@@ -443,8 +443,8 @@ export async function transformRequestBody(
 		}
 
 		// Filter orphaned function_call_output items (where function_call was an item_reference that got filtered)
-		// Keep matched pairs for compaction context
-		if (!body.tools && body.input) {
+		// Keep matched pairs for compaction context but drop unmatched outputs to avoid Codex API 400 errors
+		if (body.input) {
 			// Collect all call_ids from function_call items
 			const functionCallIds = new Set(
 				body.input
@@ -454,7 +454,10 @@ export async function transformRequestBody(
 			// Only filter function_call_output items that don't have a matching function_call
 			body.input = body.input.filter((item) => {
 				if (item.type === "function_call_output") {
-					return functionCallIds.has(item.call_id);
+					return (
+						typeof item.call_id === "string" &&
+						functionCallIds.has(item.call_id)
+					);
 				}
 				return true;
 			});

test/request-transformer.test.ts

@@ -881,6 +881,49 @@ describe('Request Transformer Module', () => {
 			expect(result.input![2].type).toBe('function_call_output');
 		});
 
+		it('should drop orphaned function_call_output even when tools are present', async () => {
+			const body: RequestBody = {
+				model: 'gpt-5-codex',
+				input: [
+					{ type: 'message', role: 'user', content: 'hello' },
+					{ type: 'function_call_output', role: 'assistant', call_id: 'call_ghost', output: '{}' } as any,
+				],
+				tools: [{ name: 'task' }],
+			};
+
+			const result = await transformRequestBody(body, codexInstructions);
+
+			expect(result.input).toBeDefined();
+			const outputs = result.input!.filter(
+				(item) => item.type === 'function_call_output',
+			);
+			expect(outputs).toHaveLength(0);
+		});
+
+		it('should keep matched function_call pairs when tools are present', async () => {
+			const body: RequestBody = {
+				model: 'gpt-5-codex',
+				input: [
+					{ type: 'message', role: 'user', content: 'hello' },
+					{ type: 'function_call', call_id: 'call_keep', name: 'task', arguments: '{}' } as any,
+					{ type: 'function_call_output', call_id: 'call_keep', output: 'success' } as any,
+				],
+				tools: [{ name: 'task' }],
+			};
+
+			const result = await transformRequestBody(body, codexInstructions);
+
+			expect(result.input).toBeDefined();
+			const outputs = result.input!.filter(
+				(item) => item.type === 'function_call_output',
+			);
+			expect(outputs).toHaveLength(1);
+			const calls = result.input!.filter(
+				(item) => item.type === 'function_call' && item.call_id === 'call_keep',
+			);
+			expect(calls).toHaveLength(1);
+		});
+
 		describe('CODEX_MODE parameter', () => {
 			it('should use bridge message when codexMode=true and tools present (default)', async () => {
 				const body: RequestBody = {