refactor: extract agent bounded context + fix SSE comments + cleanup unused

- Extract src/lib/agent/ bounded context with types, registry, messaging
- Add comments_count to BeadIssue for SSE comment detection
- Create batch endpoints for mail/reservations APIs
- Add memory validation to session-preflight
- Remove unused empty dirs (mockup, sessions, timeline)
- Move stashes to docs/references, gitignore them

skills/beadboard-driver/tests/setup-mail-delegate.contract.test.mjs

@@ -0,0 +1,67 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import fs from 'node:fs/promises';
+import os from 'node:os';
+import path from 'node:path';
+import { execFile } from 'node:child_process';
+import { promisify } from 'node:util';
+import { fileURLToPath } from 'node:url';
+import { dirname } from 'node:path';
+
+const execFileAsync = promisify(execFile);
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const scriptPath = path.resolve('skills/beadboard-driver/scripts/setup-mail-delegate.mjs');
+const expectedShimPath = path.join(__dirname, '..', 'scripts', 'bb-mail-shim.mjs');
+
+async function withTempDir(run) {
+  const root = await fs.mkdtemp(path.join(os.tmpdir(), 'bb-skill-setupdelegate-'));
+  try {
+    await run(root);
+  } finally {
+    await fs.rm(root, { recursive: true, force: true });
+  }
+}
+
+test('setup-mail-delegate contract: dry-run resolves absolute shim path', async () => {
+  await withTempDir(async (root) => {
+    const { stdout } = await execFileAsync(process.execPath, [scriptPath, '--dry-run'], {
+      cwd: root,
+      env: { ...process.env },
+    });
+
+    const result = JSON.parse(stdout);
+    assert.equal(result.ok, true);
+    assert.equal(result.dry_run, true);
+    assert.ok(
+      result.delegate.includes('bb-mail-shim.mjs'),
+      `delegate should reference bb-mail-shim.mjs, got: ${result.delegate}`,
+    );
+
+    const resolvedPath = result.delegate.replace(/^node\s+/, '');
+    assert.ok(
+      path.isAbsolute(resolvedPath),
+      `delegate path should be absolute, got: ${resolvedPath}`,
+    );
+    assert.equal(
+      resolvedPath,
+      expectedShimPath,
+      `delegate should point to the bundled shim`,
+    );
+  });
+});
+
+test('setup-mail-delegate contract: BD_NOT_FOUND when bd missing', async () => {
+  await withTempDir(async (root) => {
+    const { stdout } = await execFileAsync(process.execPath, [scriptPath], {
+      cwd: root,
+      env: {
+        ...process.env,
+        PATH: '/nonexistent',
+      },
+    });
+
+    const result = JSON.parse(stdout);
+    assert.equal(result.ok, false);
+    assert.equal(result.error_code, 'BD_NOT_FOUND');
+  });
+});