docs: record the structured-dtype and querying-chart decisions

Also the one the session settled by hand: database nodes stay transport
and credentials, and the Python nodes either side do the query building
and the answer shaping. That is what a series read mode inside the node
would have prevented, so the read-mode item goes with it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ROADMAP.md

@@ -216,6 +216,20 @@ Shares components with the admin view. See `docs/architecture/structure.canvas`
 - [x] Draft and publish, as flows have it: the editor autosaves
       `dashboard.draft.json` and a panel reads only the published document, so a
       half-arranged page never reaches the wall until someone publishes it
+- [x] Declared structured payloads — `series`, `record` and `list` (with its item
+      type) join the scalars in `DType` and are checked the same way, so a widget
+      binds a shape rather than "some JSON" and a wrong binding is refused before
+      anything runs. An agenda over a `list` and a notification over a `record`
+      are the first two to read them, the latter fed either by a flow or by the
+      `dashboard` alert channel
+- [x] Charts that query: a chart publishes a request — the window and the
+      resolution — exactly as a slider publishes a value, and draws the `series`
+      a flow answers with. The answer says what it was computed for and one
+      computed for another window is ignored, so two charts on a node cost a
+      duplicate query rather than the wrong picture. Database nodes stay
+      transport and credentials only: the InfluxDB node runs Flux handed to it
+      and echoes the rest, and Python nodes either side build the query and shape
+      the answer — which is what keeps the widget ignorant of the database
 - [ ] Per-device view
 
 ## Phase 5 — Website and docs