fix(ai): synthesize trailing orphaned tool results closes #3555

packages/ai/CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Fixed
 
 - Fixed `google-gemini-cli` built-in model discovery to include `gemini-3.1-flash-lite-preview`, so Cloud Code Assist model lists expose it without requiring manual `--model` fallback selection ([#3545](https://github.com/badlogic/pi-mono/issues/3545))
+- Fixed `transformMessages()` to synthesize missing trailing tool results for transcripts that end with unresolved assistant tool calls during direct low-level history replay ([#3555](https://github.com/badlogic/pi-mono/issues/3555))
 
 ## [0.68.1] - 2026-04-22
 

packages/ai/src/providers/transform-messages.ts

@@ -213,5 +213,8 @@ export function transformMessages<TApi extends Api>(
 		}
 	}
 
+	// If the conversation ends with unresolved tool calls, synthesize results now.
+	insertSyntheticToolResults();
+
 	return result;
 }

packages/ai/test/transform-messages-copilot-openai-to-anthropic.test.ts

@@ -26,6 +26,26 @@ function makeCopilotClaudeModel(): Model<"anthropic-messages"> {
 	};
 }
 
+function makeAssistantMessage(content: AssistantMessage["content"]): AssistantMessage {
+	return {
+		role: "assistant",
+		content,
+		api: "openai-responses",
+		provider: "github-copilot",
+		model: "gpt-5",
+		usage: {
+			input: 0,
+			output: 0,
+			cacheRead: 0,
+			cacheWrite: 0,
+			totalTokens: 0,
+			cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+		},
+		stopReason: "toolUse",
+		timestamp: Date.now(),
+	};
+}
+
 describe("OpenAI to Anthropic session migration for Copilot Claude", () => {
 	it("converts thinking blocks to plain text when source model differs", () => {
 		const model = makeCopilotClaudeModel();
@@ -112,4 +132,60 @@ describe("OpenAI to Anthropic session migration for Copilot Claude", () => {
 
 		expect(toolCall.thoughtSignature).toBeUndefined();
 	});
+
+	it("adds synthetic tool results for trailing orphaned tool calls", () => {
+		const model = makeCopilotClaudeModel();
+		const messages: Message[] = [
+			{ role: "user", content: "read the file", timestamp: Date.now() },
+			makeAssistantMessage([
+				{
+					type: "toolCall",
+					id: "call_123|fc_123",
+					name: "read",
+					arguments: { path: "README.md" },
+				},
+			]),
+		];
+
+		const result = transformMessages(messages, model, anthropicNormalizeToolCallId);
+		const lastMessage = result[result.length - 1];
+
+		expect(lastMessage).toMatchObject({
+			role: "toolResult",
+			toolCallId: "call_123_fc_123",
+			toolName: "read",
+			isError: true,
+			content: [{ type: "text", text: "No result provided" }],
+		});
+	});
+
+	it("adds synthetic results only for trailing tool calls that are still missing results", () => {
+		const model = makeCopilotClaudeModel();
+		const messages: Message[] = [
+			{ role: "user", content: "run commands", timestamp: Date.now() },
+			makeAssistantMessage([
+				{ type: "toolCall", id: "call_1|fc_1", name: "read", arguments: { path: "README.md" } },
+				{ type: "toolCall", id: "call_2|fc_2", name: "bash", arguments: { command: "pwd" } },
+			]),
+			{
+				role: "toolResult",
+				toolCallId: "call_1|fc_1",
+				toolName: "read",
+				content: [{ type: "text", text: "done" }],
+				isError: false,
+				timestamp: Date.now(),
+			},
+		];
+
+		const result = transformMessages(messages, model, anthropicNormalizeToolCallId);
+		const syntheticResults = result.filter((message) => message.role === "toolResult" && message.isError);
+
+		expect(syntheticResults).toHaveLength(1);
+		expect(syntheticResults[0]).toMatchObject({
+			role: "toolResult",
+			toolCallId: "call_2_fc_2",
+			toolName: "bash",
+			content: [{ type: "text", text: "No result provided" }],
+		});
+	});
 });