Fix race create sessione su CPX: ready solo dopo MediaMTX.

I nodi cloud restano in provisioning finché :9997 risponde; retry su create_path e 503 retryable se l’ingest è ancora irraggiungibile.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/services/streams/node_health.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+module Streams
+  # Probe reachability of MediaMTX API on a stream node (:9997).
+  class NodeHealth
+    def self.mediamtx_up?(node, timeout: 2)
+      new(node, timeout: timeout).mediamtx_up?
+    end
+
+    def self.promote_if_healthy!(node, timeout: 2)
+      return false unless node.status == "provisioning"
+      return false unless mediamtx_up?(node, timeout: timeout)
+
+      node.update!(status: "ready", last_health_at: Time.current)
+      true
+    end
+
+    def initialize(node, timeout: 2)
+      @node = node
+      @timeout = timeout
+    end
+
+    def mediamtx_up?
+      Mediamtx::Client.new(base_url: @node.api_base_url).reachable?(timeout: @timeout)
+    end
+  end
+end