refactor: extract iroh wire helpers

docs/production-readiness-roadmap.md

@@ -53,6 +53,8 @@ behavior.
 
 - `[ ]` Extract protected peer-control routing.
   Acceptance criteria:
+  - `[x]` Shared bounded Iroh line-read and send-finish helpers live outside
+    the main feature handler module.
   - `[ ]` Iroh control ALPN handling, nonce checks, peer-card validation, and
     endpoint-binding validation are centralized.
   - `[ ]` Feature handlers receive authenticated caller context rather than