feat(runtime): session manager, router, and protocol documentation

[koistya]

Summary

• SessionManager: Connection lifecycle (idle → connecting → negotiating → active → retryWait) with automatic reconnection, configurable backoff, and pluggable negotiators
• Router: Subject-based message dispatch with validation (rpc/, event/, stream/, app/ prefixes), handler registration with priority ordering, and built-in RPC envelope processing
• SbpNegotiator: SBP handshake implementation with configurable timeouts and capability exchange
• RpcCorrelationManager: Pending RPC tracking with timeouts and explicit cid correlation
• Protocol documentation restructured under docs/protocols/ with dedicated sections for SBP, SBRP, SBDP, and RPC

Usage

import { createRouter, createSessionManager, SbpNegotiator } from "@sideband/runtime";
import { asPeerId, isMessageFrame } from "@sideband/protocol";

const router = createRouter();
router.route("rpc/user.get", async (msg) => {
  const userId = (msg.rpc?.params as { id: number }).id;
  await msg.rpc?.reply({ id: userId, name: "Ada" });
});

const manager = createSessionManager({
  endpoint: "wss://relay.example.com",
  transportFactory: (url) => connectWebSocket(url),
  negotiator: new SbpNegotiator({ peerId: asPeerId("browser-ui") }),
  onFrame: async (frame) => {
    if (isMessageFrame(frame)) {
      await router.dispatch(frame, session);
    }
  },
});

const session = await manager.connect();

ADRs

• ADR-009: Runtime Session Lifecycle — Three-layer architecture (Transport → Session → Router), peer vs session distinction, state machine
• ADR-010: RPC Correlation — Explicit cid field for request/response matching
• ADR-011: Runtime Message Routing — Handler registration, dispatch ordering, error propagation

Test plan

• SessionManager unit tests (state transitions, backoff, negotiator integration)
• Router unit tests (subject validation, dispatch ordering, RPC context)
• SbpNegotiator unit tests (handshake flow, timeout handling)
• RpcCorrelationManager tests (pending tracking, timeout expiry)