feat(cli): add /btw slash command for ephemeral side questions

Allow users to ask quick "by the way" questions that use the current
conversation context but don't pollute the main conversation history.

Closes #2370

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/cli/src/services/BuiltinCommandLoader.ts

@@ -11,6 +11,7 @@ import { aboutCommand } from '../ui/commands/aboutCommand.js';
 import { agentsCommand } from '../ui/commands/agentsCommand.js';
 import { approvalModeCommand } from '../ui/commands/approvalModeCommand.js';
 import { authCommand } from '../ui/commands/authCommand.js';
+import { btwCommand } from '../ui/commands/btwCommand.js';
 import { bugCommand } from '../ui/commands/bugCommand.js';
 import { clearCommand } from '../ui/commands/clearCommand.js';
 import { compressCommand } from '../ui/commands/compressCommand.js';
@@ -63,6 +64,7 @@ export class BuiltinCommandLoader implements ICommandLoader {
       agentsCommand,
       approvalModeCommand,
       authCommand,
+      btwCommand,
       bugCommand,
       clearCommand,
       compressCommand,

packages/cli/src/ui/commands/btwCommand.ts

@@ -0,0 +1,138 @@
+/**
+ * @license
+ * Copyright 2025 Qwen Code
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type {
+  CommandContext,
+  SlashCommand,
+  SlashCommandActionReturn,
+} from './types.js';
+import { CommandKind } from './types.js';
+import { MessageType } from '../types.js';
+import type { HistoryItemBtw } from '../types.js';
+import { t } from '../../i18n/index.js';
+
+export const btwCommand: SlashCommand = {
+  name: 'btw',
+  get description() {
+    return t(
+      'Ask a quick side question without affecting the main conversation',
+    );
+  },
+  kind: CommandKind.BUILT_IN,
+  action: async (
+    context: CommandContext,
+    args: string,
+  ): Promise<void | SlashCommandActionReturn> => {
+    const question = args.trim();
+
+    if (!question) {
+      return {
+        type: 'message',
+        messageType: 'error',
+        content: t('Please provide a question. Usage: /btw <your question>'),
+      };
+    }
+
+    const { config } = context.services;
+    const { ui } = context;
+    const abortSignal = context.abortSignal;
+
+    if (!config) {
+      return {
+        type: 'message',
+        messageType: 'error',
+        content: t('Config not loaded.'),
+      };
+    }
+
+    const geminiClient = config.getGeminiClient();
+    if (!geminiClient) {
+      return {
+        type: 'message',
+        messageType: 'error',
+        content: t('No chat client available.'),
+      };
+    }
+
+    // Show pending state
+    const pendingItem: HistoryItemBtw = {
+      type: MessageType.BTW,
+      btw: {
+        question,
+        answer: '',
+        isPending: true,
+      },
+    };
+    ui.setPendingItem(pendingItem);
+
+    try {
+      // Get current conversation history
+      const history = geminiClient.getHistory();
+
+      // Make an ephemeral generateContent call with the conversation context
+      // but WITHOUT tools — the btw response is purely based on existing context
+      const response = await geminiClient.generateContent(
+        [
+          ...history,
+          {
+            role: 'user',
+            parts: [
+              {
+                text: `[Side question - answer briefly and concisely, this is a "by the way" question that doesn't need to be part of our main conversation]\n\n${question}`,
+              },
+            ],
+          },
+        ],
+        {},
+        abortSignal ?? new AbortController().signal,
+        config.getModel(),
+      );
+
+      if (abortSignal?.aborted) {
+        ui.setPendingItem(null);
+        return;
+      }
+
+      // Extract the response text
+      const parts = response.candidates?.[0]?.content?.parts;
+      const answer =
+        parts
+          ?.map((part) => part.text)
+          .filter((text): text is string => typeof text === 'string')
+          .join('') || t('No response received.');
+
+      // Clear pending and show the completed btw item
+      ui.setPendingItem(null);
+      ui.addItem(
+        {
+          type: MessageType.BTW,
+          btw: {
+            question,
+            answer,
+            isPending: false,
+          },
+        } as HistoryItemBtw,
+        Date.now(),
+      );
+    } catch (error) {
+      if (abortSignal?.aborted) {
+        ui.setPendingItem(null);
+        return;
+      }
+
+      ui.setPendingItem(null);
+      ui.addItem(
+        {
+          type: MessageType.ERROR,
+          text: t('Failed to answer btw question: {{error}}', {
+            error: error instanceof Error ? error.message : String(error),
+          }),
+        },
+        Date.now(),
+      );
+    }
+  },
+};

packages/cli/src/ui/components/HistoryItemDisplay.tsx

@@ -39,6 +39,7 @@ import { SkillsList } from './views/SkillsList.js';
 import { ToolsList } from './views/ToolsList.js';
 import { McpStatus } from './views/McpStatus.js';
 import { InsightProgressMessage } from './messages/InsightProgressMessage.js';
+import { BtwMessage } from './messages/BtwMessage.js';
 
 interface HistoryItemDisplayProps {
   item: HistoryItem;
@@ -194,6 +195,7 @@ const HistoryItemDisplayComponent: React.FC<HistoryItemDisplayProps> = ({
       {itemForDisplay.type === 'insight_progress' && (
         <InsightProgressMessage progress={itemForDisplay.progress} />
       )}
+      {itemForDisplay.type === 'btw' && <BtwMessage btw={itemForDisplay.btw} />}
     </Box>
   );
 };

packages/cli/src/ui/components/messages/BtwMessage.tsx

@@ -0,0 +1,44 @@
+/**
+ * @license
+ * Copyright 2025 Qwen Code
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type React from 'react';
+import { Box, Text } from 'ink';
+import type { BtwProps } from '../../types.js';
+import Spinner from 'ink-spinner';
+import { Colors } from '../../colors.js';
+
+export interface BtwDisplayProps {
+  btw: BtwProps;
+}
+
+/**
+ * BtwMessage renders the /btw (by the way) sidebar response.
+ * Shows an ephemeral question and answer that doesn't affect the main conversation.
+ */
+export const BtwMessage: React.FC<BtwDisplayProps> = ({ btw }) => (
+    <Box flexDirection="column">
+      <Box flexDirection="row">
+        <Text color={Colors.Gray} dimColor>
+          {'btw> '}
+        </Text>
+        <Text color={Colors.Gray}>{btw.question}</Text>
+      </Box>
+      <Box flexDirection="row" marginTop={0}>
+        {btw.isPending ? (
+          <Box>
+            <Box marginRight={1}>
+              <Spinner type="dots" />
+            </Box>
+            <Text color={Colors.AccentPurple}>Thinking...</Text>
+          </Box>
+        ) : (
+          <Box flexDirection="column">
+            <Text color={Colors.AccentCyan}>{btw.answer}</Text>
+          </Box>
+        )}
+      </Box>
+    </Box>
+  );

packages/cli/src/ui/hooks/slashCommandProcessor.ts

@@ -62,6 +62,7 @@ const SLASH_COMMANDS_SKIP_RECORDING = new Set([
   'reset',
   'new',
   'resume',
+  'btw',
 ]);
 
 interface SlashCommandProcessorActions {

packages/cli/src/ui/types.ts

@@ -262,6 +262,17 @@ export type HistoryItemInsightProgress = HistoryItemBase & {
   progress: InsightProgressProps;
 };
 
+export interface BtwProps {
+  question: string;
+  answer: string;
+  isPending: boolean;
+}
+
+export type HistoryItemBtw = HistoryItemBase & {
+  type: 'btw';
+  btw: BtwProps;
+};
+
 // Using Omit<HistoryItem, 'id'> seems to have some issues with typescript's
 // type inference e.g. historyItem.type === 'tool_group' isn't auto-inferring that
 // 'tools' in historyItem.
@@ -291,7 +302,8 @@ export type HistoryItemWithoutId =
   | HistoryItemToolsList
   | HistoryItemSkillsList
   | HistoryItemMcpStatus
-  | HistoryItemInsightProgress;
+  | HistoryItemInsightProgress
+  | HistoryItemBtw;
 
 export type HistoryItem = HistoryItemWithoutId & { id: number };
 
@@ -315,6 +327,7 @@ export enum MessageType {
   SKILLS_LIST = 'skills_list',
   MCP_STATUS = 'mcp_status',
   INSIGHT_PROGRESS = 'insight_progress',
+  BTW = 'btw',
 }
 
 export interface InsightProgressProps {