fix(vscode-lm): order text parts before tool calls in assistant messages

daniel-lxs · daniel-lxs · commit 3a355839dbe6 · 2026-01-09T09:45:26.000-05:00
The VS Code LM API requires that tool call parts within an assistant message
come at the END, so they are properly followed by the next user message
containing matching LanguageModelToolResultPart objects.

Previously, tool calls were placed BEFORE text parts, causing the error:
"Invalid request: Tool call part must be followed by a User message with
a LanguageModelToolResultPart with a matching callId."

Fixes ROO-427
diff --git a/src/api/transform/__tests__/vscode-lm-format.spec.ts b/src/api/transform/__tests__/vscode-lm-format.spec.ts
@@ -143,9 +143,11 @@ describe("convertToVsCodeLmMessages", () => {
 		expect(result).toHaveLength(1)
 		expect(result[0].role).toBe("assistant")
 		expect(result[0].content).toHaveLength(2)
-		const [toolCall, textContent] = result[0].content as [MockLanguageModelToolCallPart, MockLanguageModelTextPart]
-		expect(toolCall.type).toBe("tool_call")
+		// Text must come before tool calls so that tool calls are at the end,
+		// properly followed by user message with tool results
+		const [textContent, toolCall] = result[0].content as [MockLanguageModelTextPart, MockLanguageModelToolCallPart]
 		expect(textContent.type).toBe("text")
+		expect(toolCall.type).toBe("tool_call")
 	})
 
 	it("should handle image blocks with appropriate placeholders", () => {
diff --git a/src/api/transform/vscode-lm-format.ts b/src/api/transform/vscode-lm-format.ts
@@ -114,9 +114,18 @@ export function convertToVsCodeLmMessages(
 					{ nonToolMessages: [], toolMessages: [] },
 				)
 
-				// Process tool messages first then non-tool messages
+				// Process non-tool messages first, then tool messages
+				// Tool calls must come at the end so they are properly followed by user message with tool results
 				const contentParts = [
-					// Convert tool messages to ToolCallParts first
+					// Convert non-tool messages to TextParts first
+					...nonToolMessages.map((part) => {
+						if (part.type === "image") {
+							return new vscode.LanguageModelTextPart("[Image generation not supported by VSCode LM API]")
+						}
+						return new vscode.LanguageModelTextPart(part.text)
+					}),
+
+					// Convert tool messages to ToolCallParts after text
 					...toolMessages.map(
 						(toolMessage) =>
 							new vscode.LanguageModelToolCallPart(
@@ -125,14 +134,6 @@ export function convertToVsCodeLmMessages(
 								asObjectSafe(toolMessage.input),
 							),
 					),
-
-					// Convert non-tool messages to TextParts after tool messages
-					...nonToolMessages.map((part) => {
-						if (part.type === "image") {
-							return new vscode.LanguageModelTextPart("[Image generation not supported by VSCode LM API]")
-						}
-						return new vscode.LanguageModelTextPart(part.text)
-					}),
 				]
 
 				// Add the assistant message to the list of messages
