feat: add agent activity events

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/renderer/lib/sessionActivity.ts

@@ -0,0 +1,95 @@
+import type { SessionEventRecord } from '@shared/domain/event';
+
+export interface SessionActivityState {
+  sessionId: string;
+  activityType?: SessionEventRecord['activityType'];
+  agentName?: string;
+  toolName?: string;
+}
+
+export type SessionActivityMap = Record<string, SessionActivityState | undefined>;
+
+export function applySessionEventActivity(
+  current: SessionActivityMap,
+  event: SessionEventRecord,
+): SessionActivityMap {
+  if (event.kind === 'agent-activity') {
+    return {
+      ...current,
+      [event.sessionId]: {
+        sessionId: event.sessionId,
+        activityType: event.activityType,
+        agentName: event.agentName,
+        toolName: event.toolName,
+      },
+    };
+  }
+
+  if (event.kind === 'status') {
+    if (event.status === 'running' || event.status === 'idle' || event.status === 'error') {
+      return removeSessionActivity(current, event.sessionId);
+    }
+  }
+
+  if (event.kind === 'error') {
+    return removeSessionActivity(current, event.sessionId);
+  }
+
+  return current;
+}
+
+export function pruneSessionActivities(
+  current: SessionActivityMap,
+  sessionIds: Iterable<string>,
+): SessionActivityMap {
+  const allowed = new Set(sessionIds);
+  const next: SessionActivityMap = {};
+  let changed = false;
+
+  for (const [sessionId, activity] of Object.entries(current)) {
+    if (!allowed.has(sessionId)) {
+      changed = true;
+      continue;
+    }
+
+    next[sessionId] = activity;
+  }
+
+  return changed || Object.keys(next).length !== Object.keys(current).length ? next : current;
+}
+
+export function formatSessionActivityLabel(
+  activity: SessionActivityState | undefined,
+  fallbackAgentName = 'Agent',
+): string {
+  const agentName = activity?.agentName?.trim() || fallbackAgentName;
+
+  switch (activity?.activityType) {
+    case 'tool-calling':
+      return `${agentName} is using ${activity.toolName?.trim() || 'a tool'}…`;
+    case 'handoff':
+      return `Handing off to ${agentName}…`;
+    case 'completed':
+      return `${agentName} completed their turn.`;
+    case 'thinking':
+    default:
+      return `${agentName} is thinking…`;
+  }
+}
+
+export function shouldAnimateSessionActivity(activity: SessionActivityState | undefined): boolean {
+  return activity?.activityType !== 'completed';
+}
+
+function removeSessionActivity(
+  current: SessionActivityMap,
+  sessionId: string,
+): SessionActivityMap {
+  if (!(sessionId in current)) {
+    return current;
+  }
+
+  const next = { ...current };
+  delete next[sessionId];
+  return next;
+}