Implements AgentService gRPC server with all 6 RPCs (Enroll/Register/Heartbeat/
Subscribe/Ack/ReportUsage), Hub command routing with Redis ZSET at-least-once
persistence and cross-instance pub/sub delivery, LoadCache for node:load metrics,
NodeStore SQL interface + MySQL implementation, and full mTLS gRPC listener in main.
Integration tests: 18 tests covering full Enroll→Register→Heartbeat→Subscribe→Ack
flow, reconnect resume with last_command_id, and cross-instance pub/sub delivery
via bufconn + miniredis + mockNodeStore + real mTLS certificates.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>