Show tool and web search activity in the chat UI

Tool calls were invisible until the answer arrived: the only trace was the
sources list, and only for web searches. Surface them as they happen instead.

Add llm.stream_tool_calls(), an incremental version of resolve_tool_calls()
that yields a start and a completion event per tool call and ends with a
"resolved" event carrying the previous return value. resolve_tool_calls() is
kept as a thin wrapper that drops the progress events.

api/chat.py relays those events as a new SSE "tool" event, and wraps the
search-summary/knowledge-save step in one of the same shape, since it is a
noticeable pause of its own.

On the front end, ToolActivityList.vue renders one row per tool above the
assistant bubble (label, target, spinner while running, short result when
done). The store merges events by id and marks anything still running as
interrupted when the stream ends early. Display only - not persisted, so the
rows disappear when the session is reloaded, same as sources.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

frontend/src/stores/chat.ts

@@ -1,7 +1,7 @@
 import { defineStore } from 'pinia'
 import { useNotesStore } from './notes'
 import { ref, computed } from 'vue'
-import { fetchSessions, fetchMessages, deleteSession, exportSession, importSession, streamChat, type SessionInfo, type Source, type ImportPayload } from '../api/client'
+import { fetchSessions, fetchMessages, deleteSession, exportSession, importSession, streamChat, type SessionInfo, type Source, type ToolActivity, type ImportPayload } from '../api/client'
 
 export interface Message {
   role: 'user' | 'assistant'
@@ -11,6 +11,8 @@ export interface Message {
   archived?: boolean
   tags?: string[]
   sources?: Source[]
+  /** この応答を作る際に実行したツール（Web検索・ノート読み書きなど）。表示専用で永続化はしない。 */
+  tools?: ToolActivity[]
 }
 
 export interface Toast {
@@ -102,6 +104,26 @@ export const useChatStore = defineStore('chat', () => {
     }
   }
 
+  /** tool イベントを同じ id の行にマージする（開始時に追加し、完了時に上書きする）。 */
+  function mergeTool(msgIdx: number, activity: ToolActivity) {
+    const msg = messages.value[msgIdx]
+    if (!msg) return
+    const tools = msg.tools ?? (msg.tools = [])
+    const existing = tools.find((t) => t.id === activity.id)
+    if (existing) Object.assign(existing, activity)
+    else tools.push({ ...activity })
+  }
+
+  /** ストリームが終わった時点で running のまま残っているツールを中断扱いにする。 */
+  function settleTools(msgIdx: number) {
+    for (const tool of messages.value[msgIdx]?.tools ?? []) {
+      if (tool.status === 'running') {
+        tool.status = 'error'
+        tool.result = '中断されました'
+      }
+    }
+  }
+
   function sendMessage(text: string): void {
     if (isStreaming.value || !text.trim()) return
 
@@ -122,14 +144,18 @@ export const useChatStore = defineStore('chat', () => {
           messages.value[msgIdx].content += chunk.value as string
         } else if (chunk.type === 'sources' && chunk.value) {
           messages.value[msgIdx].sources = chunk.value as Source[]
+        } else if (chunk.type === 'tool' && chunk.value) {
+          mergeTool(msgIdx, chunk.value as ToolActivity)
         } else if (chunk.type === 'notes_updated') {
           // AIが共有ノートを書き換えたので、開いているノートパネルに反映する
           useNotesStore().load().catch((e) => pushToast(`ノート更新失敗: ${e.message}`))
         } else if (chunk.type === 'done') {
+          settleTools(msgIdx)
           messages.value[msgIdx].pending = false
           isStreaming.value = false
           loadSessions().catch((e) => pushToast(`セッション更新失敗: ${e.message}`))
         } else if (chunk.type === 'error') {
+          settleTools(msgIdx)
           messages.value[msgIdx].content = (chunk.value as string) ?? 'バックエンドでエラーが発生しました。'
           messages.value[msgIdx].pending = false
           messages.value[msgIdx].error = true
@@ -137,6 +163,7 @@ export const useChatStore = defineStore('chat', () => {
         }
       },
       (err) => {
+        settleTools(msgIdx)
         // 途中まで届いていた内容は残しつつ、エラーメッセージを付記する
         const partial = messages.value[msgIdx].content
         messages.value[msgIdx].content = partial ? `${partial}\n\n⚠️ ${err.message}` : err.message