fix(messages): keep UI-only notices out of the model payload

.changeset/fix-display-only-notices.md

@@ -0,0 +1,5 @@
+---
+"@nanocollective/nanocoder": patch
+---
+
+Stopped nanocoder's own UI text from being sent to the model as its past output. Cancellation notices (`_Cancelled by user._`), inline error banners (`**Error:** ...`), the non-interactive "Tool approval required" notice, and the VS Code replies to built-in slash commands (`/help`, `/copy`, `/model`, unrecognized commands) were all pushed into conversation history as `assistant` messages, so on the next turn the provider received harness-authored markdown as if the model had written it — teaching it to imitate the chrome and, on a resumed session, to believe it had errored. These are now marked display-only: they still render in the chat and replay with session history, but they are filtered out before messages are converted to the provider payload. Closes #893.

source/acp/acp-agent.spec.ts

@@ -9,6 +9,7 @@ import {
 	setToolRegistryGetter,
 	setToolManagerGetter,
 } from '@/message-handler';
+import {convertToModelMessages} from '@/ai-sdk-client/converters/message-converter';
 import {sessionManager} from '@/session/session-manager';
 
 console.log('\nacp-agent.spec.ts');
@@ -339,6 +340,10 @@ test('AcpAgent.prompt - propagates API errors cleanly', async t => {
 
 	// Ensure turnActive is reset even on error
 	t.false(session.turnActive);
+
+	const notice = session.messages[session.messages.length - 1];
+	t.is(notice.role, 'assistant');
+	t.true(notice.displayOnly, 'the error notice must never reach the model');
 });
 
 test('AcpAgent.prompt - resolves cleanly on user cancellation instead of throwing', async t => {
@@ -371,6 +376,11 @@ test('AcpAgent.prompt - resolves cleanly on user cancellation instead of throwin
 				u.update?.content?.text?.includes('Cancelled by user'),
 		),
 	);
+
+	const persisted = agent['sessions'].get(session.sessionId)!.messages;
+	const notice = persisted[persisted.length - 1];
+	t.is(notice.role, 'assistant');
+	t.true(notice.displayOnly, 'the cancel notice must never reach the model');
 });
 
 test('AcpAgent.prompt - returns response for valid session', async t => {
@@ -441,6 +451,20 @@ test('AcpAgent.prompt - /copy code is not treated as unrecognized', async t => {
 	t.false(reply.includes('Unrecognized slash command'));
 });
 
+test('AcpAgent.prompt - a built-in command exchange stays out of model context', async t => {
+	const {agent} = createAgent();
+	const session = await agent.newSession({cwd: '/tmp'});
+	await agent.prompt({
+		sessionId: session.sessionId,
+		prompt: [{type: 'text', text: '/help'}],
+	});
+
+	const messages = agent['sessions'].get(session.sessionId)!.messages;
+	t.is(messages.length, 2);
+	t.true(messages.every(m => m.displayOnly));
+	t.deepEqual(convertToModelMessages(messages), []);
+});
+
 test('AcpAgent.prompt - a genuinely unknown command still reports unrecognized', async t => {
 	const reply = await promptForBuiltinReply('/definitelynotacommand');
 	t.true(reply.includes('Unrecognized slash command'));

source/acp/acp-agent.ts

@@ -202,8 +202,12 @@ export class AcpAgent implements Agent {
 					const sendBuiltinReply = (msg: string) => {
 						session.messages = [
 							...session.messages,
-							{role: 'user', content: contextualUserText},
-							{role: 'assistant', content: msg},
+							{
+								role: 'user',
+								content: contextualUserText,
+								displayOnly: true,
+							},
+							{role: 'assistant', content: msg, displayOnly: true},
 						];
 						this.conn.sessionUpdate({
 							sessionId: params.sessionId,
@@ -335,7 +339,11 @@ export class AcpAgent implements Agent {
 						content: {type: 'text', text: cancelNotice},
 					},
 				});
-				session.messages.push({role: 'assistant', content: cancelNotice});
+				session.messages.push({
+					role: 'assistant',
+					content: cancelNotice,
+					displayOnly: true,
+				});
 				return {stopReason: 'cancelled'};
 			}
 
@@ -355,6 +363,7 @@ export class AcpAgent implements Agent {
 			session.messages.push({
 				role: 'assistant',
 				content: formattedError,
+				displayOnly: true,
 			});
 
 			throw error;

source/ai-sdk-client/converters/message-converter.spec.ts

@@ -398,3 +398,154 @@ test('dropOrphanedToolResults drops a tool result lacking a tool_call_id', t =>
 	t.is(result.length, 1);
 	t.is(result[0].role, 'user');
 });
+
+test('convertToModelMessages drops display-only assistant notices', t => {
+	const messages: Message[] = [
+		{role: 'user', content: 'do it'},
+		{
+			role: 'assistant',
+			content: '\n\n_Cancelled by user._\n',
+			displayOnly: true,
+		},
+		{role: 'assistant', content: 'Real reply'},
+	];
+
+	const result = convertToModelMessages(messages);
+	t.is(result.length, 2);
+	t.is(result[0].role, 'user');
+	const content = result[1].content as Array<{type: string; text?: string}>;
+	t.is(content[0].text, 'Real reply');
+});
+
+test('convertToModelMessages keeps messages with displayOnly false or absent', t => {
+	const messages: Message[] = [
+		{role: 'user', content: 'hi', displayOnly: false},
+		{role: 'assistant', content: 'hello'},
+	];
+
+	t.is(convertToModelMessages(messages).length, 2);
+});
+
+test('convertToModelMessages drops display-only messages of every role', t => {
+	const messages: Message[] = [
+		{role: 'system', content: 'sys', displayOnly: true},
+		{role: 'user', content: 'usr', displayOnly: true},
+		{
+			role: 'tool',
+			content: 'res',
+			tool_call_id: 'call_1',
+			name: 'edit',
+			displayOnly: true,
+		},
+	];
+
+	t.deepEqual(convertToModelMessages(messages), []);
+});
+
+test('convertToModelMessages keeps tool results paired across a display-only notice', t => {
+	const messages: Message[] = [
+		{
+			role: 'assistant',
+			content: '',
+			tool_calls: [{id: 'call_1', function: {name: 'edit', arguments: {}}}],
+		},
+		{
+			role: 'assistant',
+			content: '\n\n**Error:** boom\n',
+			displayOnly: true,
+		},
+		{role: 'tool', content: 'edited', tool_call_id: 'call_1', name: 'edit'},
+	];
+
+	const result = convertToModelMessages(messages);
+	t.is(result.length, 2);
+	t.is(result[0].role, 'assistant');
+	t.is(result[1].role, 'tool');
+});
+
+test('convertToModelMessages orphans results whose tool call is display-only', t => {
+	const messages: Message[] = [
+		{
+			role: 'assistant',
+			content: '',
+			tool_calls: [{id: 'call_1', function: {name: 'edit', arguments: {}}}],
+			displayOnly: true,
+		},
+		{role: 'tool', content: 'edited', tool_call_id: 'call_1', name: 'edit'},
+	];
+
+	t.deepEqual(convertToModelMessages(messages), []);
+});
+
+test('convertToModelMessages emits a tool-call round trip with no synthetic assistant text', t => {
+	const history: Message[] = [
+		{role: 'user', content: 'Read config.json'},
+		{
+			role: 'assistant',
+			content: 'Reading it now.',
+			tool_calls: [
+				{
+					id: 'call_1',
+					function: {name: 'read_file', arguments: {path: 'config.json'}},
+				},
+			],
+		},
+		{
+			role: 'tool',
+			content: '{"port":3000}',
+			tool_call_id: 'call_1',
+			name: 'read_file',
+		},
+		{role: 'assistant', content: '\n\n**Error:** boom\n', displayOnly: true},
+		{role: 'user', content: 'and the port?'},
+	];
+
+	const payload = convertToModelMessages(history);
+
+	t.deepEqual(
+		payload.map(m => m.role),
+		['user', 'assistant', 'tool', 'user'],
+	);
+
+	const assistantText = payload
+		.filter(m => m.role === 'assistant')
+		.flatMap(m => m.content as Array<{type: string; text?: string}>)
+		.filter(part => part.type === 'text')
+		.map(part => part.text);
+	t.deepEqual(assistantText, ['Reading it now.']);
+
+	t.deepEqual(payload[2].content, [
+		{
+			type: 'tool-result',
+			toolCallId: 'call_1',
+			toolName: 'read_file',
+			output: {type: 'text', value: '{"port":3000}'},
+		},
+	]);
+});
+
+test('convertToModelMessages never leaks a harness notice into the payload', t => {
+	const notices = [
+		'_Cancelled by user._',
+		'**Error:** stream closed',
+		'Tool approval required for: execute_bash. Exiting non-interactive mode',
+		'Unrecognized slash command: `/nope`. Type `/help` to see available commands.',
+		'Use the model selector in the chat header to switch models.',
+	];
+
+	const history: Message[] = [
+		{role: 'user', content: 'go'},
+		...notices.map(content => ({
+			role: 'assistant' as const,
+			content,
+			displayOnly: true,
+		})),
+		{role: 'assistant', content: 'Done.'},
+	];
+
+	const serialized = JSON.stringify(convertToModelMessages(history));
+	for (const notice of notices) {
+		t.false(serialized.includes(notice), `leaked into payload: ${notice}`);
+	}
+	t.true(serialized.includes('Done.'));
+});

source/ai-sdk-client/converters/message-converter.ts

@@ -71,7 +71,8 @@ export function dropOrphanedToolResults(messages: Message[]): Message[] {
  * Orphaned tool results are dropped first (see dropOrphanedToolResults).
  */
 export function convertToModelMessages(messages: Message[]): ModelMessage[] {
-	return dropOrphanedToolResults(messages).map((msg): ModelMessage => {
+	const modelFacing = messages.filter(msg => !msg.displayOnly);
+	return dropOrphanedToolResults(modelFacing).map((msg): ModelMessage => {
 		if (msg.role === 'tool') {
 			// Convert to AI SDK tool-result format
 			// AI SDK expects: { role: 'tool', content: [{ type: 'tool-result', toolCallId, toolName, output }] }

source/hooks/chat-handler/conversation/conversation-loop.spec.ts

@@ -237,6 +237,30 @@ test.serial('processAssistantResponse - exits in non-interactive mode when appro
 	t.pass('Non-interactive exit requires proper mock setup');
 });
 
+test.serial('processAssistantResponse - marks the non-interactive approval notice display-only', async t => {
+	const captured: Message[][] = [];
+
+	const params = createDefaultParams({
+		client: createMockClient({
+			toolCalls: [{id: 'call_1', function: {name: 'some_tool', arguments: {}}}],
+		}),
+		toolManager: createMockToolManager({
+			tools: ['some_tool'],
+			needsApproval: true,
+		}),
+		nonInteractiveMode: true,
+		setMessages: (msgs: Message[]) => captured.push(msgs),
+	});
+
+	await processAssistantResponse(params);
+
+	const latest = captured[captured.length - 1];
+	const notice = latest[latest.length - 1];
+	t.is(notice.role, 'assistant');
+	t.regex(notice.content, /Tool approval required for: some_tool/);
+	t.true(notice.displayOnly, 'the approval notice must never reach the model');
+});
+
 // ============================================================================
 // Auto-Nudge Tests (lines 469-506)
 // ============================================================================

source/hooks/chat-handler/conversation/conversation-loop.tsx

@@ -804,7 +804,11 @@ export const processAssistantResponse = async (
 			);
 			const builder = new MessageBuilder(updatedMessages);
 			builder.addToolResults(turnResults);
-			builder.addMessage({role: 'assistant', content: errorMsg});
+			builder.addMessage({
+				role: 'assistant',
+				content: errorMsg,
+				displayOnly: true,
+			});
 			setMessages(builder.build());
 			setIsGenerating(false);
 			onConversationComplete?.();

source/types/core.ts

@@ -36,6 +36,7 @@ export interface Message {
 	reasoning?: string;
 	structuredContent?: JSONValue;
 	images?: ImageAttachment[];
+	displayOnly?: boolean;
 }
 
 export interface ToolCall {