Pull the connector node contract forward in the management phase

ROADMAP.md

@@ -40,6 +40,11 @@ external interfaces. See `docs/architecture/structure.canvas` → *Backend – M
       state backends
 - [ ] Secrets/credentials store for node integrations managed via the API/UI;
       `.env` bootstrap-only
+- [ ] Connector node contract: declared I/O schemas, UI-driven credential and
+      setup flow, polling/discretization behaviour, health reporting, packaging
+      metadata — plus an authoring guide and skeleton repo. Device-specific
+      nodes are written against it as external plugins; the registry follows
+      later
 - [ ] Persistence models for flows, nodes, edges and node source, replacing the
       filesystem-and-hot-reload prototype
 - [ ] REST + WebSocket API over the engine: create/read/update flows, run, stream results
@@ -53,7 +58,6 @@ external interfaces. See `docs/architecture/structure.canvas` → *Backend – M
 - [ ] Test nodes: a small node dragged onto an existing one, smoke or unit, blocking
       deployment on failure
 - [ ] User management scoped per flow and per data set
-- [ ] Plugin system for third-party node types
 - [ ] LLM interface for natural-language flow authoring
 
 ## Phase 2 — Backend: processing