feat(backend): expose sanitized tool activity

backend/src/bridge/session-bridge.ts

@@ -1,9 +1,17 @@
 import type { RpcClient } from "../rpc/rpc-client.js";
 
+export type ToolActivity = {
+  kind: "tool";
+  toolCallId: string;
+  toolName: string;
+  status: "running" | "completed" | "failed";
+};
+
 export type ClientEvent =
   | { type: "ui_request"; ui_request: any }
   | { type: "text_delta"; text: string }
   | { type: "activity_delta"; text: string }
+  | { type: "activity_event"; activity: ToolActivity }
   | { type: "info"; [k: string]: any }
   | { type: "system_event"; [k: string]: any };
 
@@ -47,8 +55,11 @@ export class SessionBridge {
         this.fan({ type: "activity_delta", text: m.assistantMessageEvent.delta ?? "" });
       } else if (m.type === "text_delta") {
         this.fan({ type: "text_delta", text: m.text ?? "" });
-      // tool_execution_* events are intentionally NOT forwarded: they clutter
-      // the UI with raw bash/read output the user did not ask for.
+      } else if (m.type === "tool_execution_start") {
+        this.emitToolActivity(m, "start");
+      } else if (m.type === "tool_execution_end") {
+        this.emitToolActivity(m, "end");
+      // Tool updates and raw payloads remain intentionally dropped.
       } else if (m.type === "system_event") {
         this.fan(m as ClientEvent);
       } else if (m.type === "agent_end") {
@@ -63,6 +74,23 @@ export class SessionBridge {
     });
   }
 
+  private emitToolActivity(message: any, lifecycle: "start" | "end"): void {
+    const toolCallId = message.toolCallId;
+    if (typeof toolCallId !== "string" || toolCallId.trim() === "") return;
+
+    const toolName =
+      typeof message.toolName === "string" && message.toolName.trim() !== ""
+        ? message.toolName
+        : "Tool";
+    const status =
+      lifecycle === "start" ? "running" : message.isError === true ? "failed" : "completed";
+
+    this.fan({
+      type: "activity_event",
+      activity: { kind: "tool", toolCallId, toolName, status },
+    });
+  }
+
   private fan(e: ClientEvent) { for (const cb of this.cbs) cb(e); }
 
   turnState(): TurnState { return this.state; }