Add optimistic writeback flow with kanban drag-drop transitions

tests/lib/writeback.test.ts

@@ -0,0 +1,55 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+
+import { applyOptimisticStatus, planStatusTransition } from '../../src/lib/writeback';
+import type { BeadIssue } from '../../src/lib/types';
+
+test('planStatusTransition maps open -> closed to close command', () => {
+  const steps = planStatusTransition({ id: 'bb-1', status: 'open' }, 'closed');
+  assert.deepEqual(steps, [{ operation: 'close', payload: { id: 'bb-1', reason: 'Moved to closed via board drag-and-drop' } }]);
+});
+
+test('planStatusTransition maps closed -> in_progress to reopen + update', () => {
+  const steps = planStatusTransition({ id: 'bb-2', status: 'closed' }, 'in_progress');
+  assert.deepEqual(steps, [
+    { operation: 'reopen', payload: { id: 'bb-2', reason: 'Moved from closed via board drag-and-drop' } },
+    { operation: 'update', payload: { id: 'bb-2', status: 'in_progress' } },
+  ]);
+});
+
+test('planStatusTransition maps non-closed transitions to update', () => {
+  const steps = planStatusTransition({ id: 'bb-3', status: 'blocked' }, 'open');
+  assert.deepEqual(steps, [{ operation: 'update', payload: { id: 'bb-3', status: 'open' } }]);
+});
+
+test('applyOptimisticStatus updates selected issue status and timestamps', () => {
+  const issues: BeadIssue[] = [
+    {
+      id: 'bb-1',
+      title: 'One',
+      description: null,
+      status: 'open',
+      priority: 2,
+      issue_type: 'task',
+      assignee: null,
+      owner: null,
+      labels: [],
+      dependencies: [],
+      created_at: '2026-01-01T00:00:00Z',
+      updated_at: '2026-01-01T00:00:00Z',
+      closed_at: null,
+      close_reason: null,
+      closed_by_session: null,
+      created_by: null,
+      due_at: null,
+      estimated_minutes: null,
+      external_ref: null,
+      metadata: {},
+    },
+  ];
+
+  const updated = applyOptimisticStatus(issues, 'bb-1', 'closed', '2026-02-12T00:00:00Z');
+  assert.equal(updated[0].status, 'closed');
+  assert.equal(updated[0].closed_at, '2026-02-12T00:00:00Z');
+  assert.equal(updated[0].updated_at, '2026-02-12T00:00:00Z');
+});