feat: add agent activity events

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

tests/renderer/sessionActivity.test.ts

@@ -0,0 +1,134 @@
+import { describe, expect, test } from 'bun:test';
+
+import {
+  applySessionEventActivity,
+  formatSessionActivityLabel,
+  pruneSessionActivities,
+  shouldAnimateSessionActivity,
+  type SessionActivityMap,
+} from '@renderer/lib/sessionActivity';
+import type { SessionEventRecord } from '@shared/domain/event';
+
+describe('session activity helpers', () => {
+  test('stores the latest agent activity by session', () => {
+    const event: SessionEventRecord = {
+      sessionId: 'session-1',
+      kind: 'agent-activity',
+      occurredAt: '2026-03-23T00:00:00.000Z',
+      activityType: 'tool-calling',
+      agentName: 'Code Reviewer',
+      toolName: 'read_file',
+    };
+
+    expect(applySessionEventActivity({}, event)).toEqual({
+      'session-1': {
+        sessionId: 'session-1',
+        activityType: 'tool-calling',
+        agentName: 'Code Reviewer',
+        toolName: 'read_file',
+      },
+    });
+  });
+
+  test('clears stale activity when a session restarts or finishes', () => {
+    const current: SessionActivityMap = {
+      'session-1': {
+        sessionId: 'session-1',
+        activityType: 'thinking',
+        agentName: 'Primary',
+      },
+      'session-2': {
+        sessionId: 'session-2',
+        activityType: 'handoff',
+        agentName: 'Reviewer',
+      },
+    };
+
+    expect(
+      applySessionEventActivity(current, {
+        sessionId: 'session-1',
+        kind: 'status',
+        occurredAt: '2026-03-23T00:00:00.000Z',
+        status: 'running',
+      }),
+    ).toEqual({
+      'session-2': current['session-2'],
+    });
+
+    expect(
+      applySessionEventActivity(current, {
+        sessionId: 'session-2',
+        kind: 'error',
+        occurredAt: '2026-03-23T00:00:00.000Z',
+        error: 'Boom',
+      }),
+    ).toEqual({
+      'session-1': current['session-1'],
+    });
+  });
+
+  test('formats contextual activity labels and animation state', () => {
+    expect(formatSessionActivityLabel(undefined, 'Primary')).toBe('Primary is thinking…');
+    expect(
+      formatSessionActivityLabel(
+        {
+          sessionId: 'session-1',
+          activityType: 'tool-calling',
+          agentName: 'Reviewer',
+          toolName: 'read_file',
+        },
+        'Primary',
+      ),
+    ).toBe('Reviewer is using read_file…');
+    expect(
+      formatSessionActivityLabel(
+        {
+          sessionId: 'session-1',
+          activityType: 'handoff',
+          agentName: 'Summarizer',
+        },
+        'Primary',
+      ),
+    ).toBe('Handing off to Summarizer…');
+    expect(
+      formatSessionActivityLabel(
+        {
+          sessionId: 'session-1',
+          activityType: 'completed',
+          agentName: 'Reviewer',
+        },
+        'Primary',
+      ),
+    ).toBe('Reviewer completed their turn.');
+    expect(
+      shouldAnimateSessionActivity({
+        sessionId: 'session-1',
+        activityType: 'thinking',
+      }),
+    ).toBe(true);
+    expect(
+      shouldAnimateSessionActivity({
+        sessionId: 'session-1',
+        activityType: 'completed',
+      }),
+    ).toBe(false);
+  });
+
+  test('prunes activity state for sessions that no longer exist', () => {
+    const current: SessionActivityMap = {
+      'session-1': {
+        sessionId: 'session-1',
+        activityType: 'thinking',
+      },
+      'session-2': {
+        sessionId: 'session-2',
+        activityType: 'tool-calling',
+        toolName: 'read_file',
+      },
+    };
+
+    expect(pruneSessionActivities(current, ['session-2'])).toEqual({
+      'session-2': current['session-2'],
+    });
+  });
+});