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/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(),
+      );
+    }
+  },
+};