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/scripts/setup-mail-delegate.mjs

@@ -0,0 +1,95 @@
+#!/usr/bin/env node
+
+/**
+ * setup-mail-delegate.mjs
+ *
+ * Configures bd's mail.delegate to point at the bb-mail-shim.mjs bundled
+ * alongside this script. Uses import.meta.url to resolve the absolute path
+ * so the caller never needs to know where the skill is installed.
+ *
+ * Usage: node {baseDir}/scripts/setup-mail-delegate.mjs
+ * Output: JSON { ok, configured, delegate } or { ok, error_code, reason }
+ */
+
+import { spawnSync } from 'node:child_process';
+import { fileURLToPath } from 'node:url';
+import { dirname, join } from 'node:path';
+
+import { findCommandInPath } from './lib/driver-lib.mjs';
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const shimPath = join(__dirname, 'bb-mail-shim.mjs');
+const delegateCommand = `node ${shimPath}`;
+
+async function main() {
+  const dryRun = process.argv.includes('--dry-run');
+  const bdPath = await findCommandInPath('bd');
+
+  if (!bdPath) {
+    process.stdout.write(
+      `${JSON.stringify(
+        {
+          ok: false,
+          error_code: 'BD_NOT_FOUND',
+          reason: 'Could not find bd in PATH. Install with: npm install -g beads-cli',
+          delegate: null,
+        },
+        null,
+        2,
+      )}\n`,
+    );
+    return;
+  }
+
+  if (dryRun) {
+    process.stdout.write(
+      `${JSON.stringify(
+        {
+          ok: true,
+          dry_run: true,
+          configured: false,
+          delegate: delegateCommand,
+        },
+        null,
+        2,
+      )}\n`,
+    );
+    return;
+  }
+
+  const result = spawnSync(bdPath, ['config', 'set', 'mail.delegate', delegateCommand], {
+    stdio: 'pipe',
+    shell: false,
+  });
+
+  if (result.status !== 0) {
+    const stderr = result.stderr?.toString().trim() || '';
+    process.stdout.write(
+      `${JSON.stringify(
+        {
+          ok: false,
+          error_code: 'BD_CONFIG_FAILED',
+          reason: stderr || 'bd config set mail.delegate exited non-zero.',
+          delegate: delegateCommand,
+        },
+        null,
+        2,
+      )}\n`,
+    );
+    return;
+  }
+
+  process.stdout.write(
+    `${JSON.stringify(
+      {
+        ok: true,
+        configured: true,
+        delegate: delegateCommand,
+      },
+      null,
+      2,
+    )}\n`,
+  );
+}
+
+void main();