herdr contract: string ids + one-shot-per-connection (CB-101 findings)

2-Message-Server.md

@@ -231,6 +231,13 @@ primary out of herdr — see [Deployment model](#deployment-model).)*
 > launch line" workaround below. Spike this in **Stage 1 (CB-102)** and prefer it if it carries
 > env/model cleanly; the pane-based path stays the documented fallback. (Also available:
 > `worktree.*` for git-isolated workers.)
+>
+> **Two wire facts the Stage-1 client (CB-101) pinned by contract test — both bit the first
+> build:** (1) the request `id` **must be a JSON string** — an integer id is rejected with
+> `invalid_request`. (2) herdr serves **one request/response per connection, then closes it** —
+> a second write on the same socket gets a broken pipe. So the client is **connection-per-call**
+> (open → one frame → one line → close), which as a bonus needs no locking. A long-lived socket is
+> only for the streaming `events.subscribe` path, not request/response.
 
 The pane-based control path (the fallback, and what the examples below use):