docs(sdk-cli): document Effect-migration scope decision in cli.ts

The arcp CLI is a thin Commander → Promise orchestration over the legacy
ARCPServer / ARCPClient / EventLog classes. Each command is a single-step
Promise call with no concurrent resource graph and no error pipeline that
benefits from Effect's structured concurrency or Layer composition.
Wrapping these in ManagedRuntime.make(MainLayer) + runtime.runPromise(...)
would add a boot-time Effect dependency to a published binary without
changing any observable behavior, so #47 is scoped out. Effect-native
consumers should compose makeARCPServerRuntime and makeARCPClientRuntime
directly; both are public.

Closes #47

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: Nick Ficano

packages/sdk/src/cli.ts

@@ -1,6 +1,19 @@
 #!/usr/bin/env node
 /**
  * `arcp` — small CLI for serving and replaying an ARCP v1.0 runtime.
+ *
+ * Implementation note (Effect migration, issue #47):
+ * This CLI deliberately remains a thin Commander → Promise orchestration over
+ * the legacy `ARCPServer` / `ARCPClient` / `EventLog` classes. Each command is
+ * a single-step Promise call with no concurrent resource graph, no
+ * cross-command shared state, and no error pipeline that benefits from
+ * `Effect`'s structured concurrency or Layer composition. Wrapping these in
+ * `ManagedRuntime.make(MainLayer)` + `runtime.runPromise(...)` would add a
+ * boot-time Effect dependency to a published binary without changing any
+ * observable behavior, so #47 was scoped out. Consumers who want an
+ * Effect-native entry point should compose `makeARCPServerRuntime` (from
+ * `@arcp/runtime`) and `makeARCPClientRuntime` (from `@arcp/client`)
+ * themselves; the building blocks are public.
  */
 import { readFileSync } from "node:fs";
 import process from "node:process";