feat: agent-to-agent communication, dynamic agent creation, self-modification tools

Agent-to-agent: host routes messages with channel_type='agent' to target
agent's inbound.db, enriches with sender info, wakes target container.
Bidirectional routing works via inherited routing context.

Dynamic agents: create_agent MCP tool + system action handler creates
agent groups, folders, and optional CLAUDE.md on the fly.

Self-modification: install_packages (apt/npm, requires admin approval),
add_mcp_server (no approval), request_rebuild (builds per-agent-group
Docker image with approved packages). Approval flow reuses interactive
card infrastructure with pending_approvals table.

Also includes fixes from prior session: attachment download, reply context
extraction, message editing (platform message ID tracking), delivery retry
limits, and card update on button click.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/db/sessions.ts

@@ -1,4 +1,4 @@
-import type { PendingQuestion, Session } from '../types.js';
+import type { PendingApproval, PendingQuestion, Session } from '../types.js';
 import { getDb } from './connection.js';
 
 // ── Sessions ──
@@ -90,3 +90,24 @@ export function getPendingQuestion(questionId: string): PendingQuestion | undefi
 export function deletePendingQuestion(questionId: string): void {
   getDb().prepare('DELETE FROM pending_questions WHERE question_id = ?').run(questionId);
 }
+
+// ── Pending Approvals ──
+
+export function createPendingApproval(pa: PendingApproval): void {
+  getDb()
+    .prepare(
+      `INSERT INTO pending_approvals (approval_id, session_id, request_id, action, payload, created_at)
+       VALUES (@approval_id, @session_id, @request_id, @action, @payload, @created_at)`,
+    )
+    .run(pa);
+}
+
+export function getPendingApproval(approvalId: string): PendingApproval | undefined {
+  return getDb().prepare('SELECT * FROM pending_approvals WHERE approval_id = ?').get(approvalId) as
+    | PendingApproval
+    | undefined;
+}
+
+export function deletePendingApproval(approvalId: string): void {
+  getDb().prepare('DELETE FROM pending_approvals WHERE approval_id = ?').run(approvalId);
+}