docs(todos): capture plugin-registered cabana field types

.planning/todos/pending/cabana-plugin-registered-field-types.md

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+---
+created: 2026-10-09T16:45:00Z
+title: Let plugins register their own value-bearing cabana field types (Winter registerFormWidgets successor)
+area: framework
+severity: major
+files:
+  - modules/cabana/form_schema.go
+  - modules/cabana/crud.go
+  - modules/cabana/extension.go
+  - modules/pact
+  - admin/src/components/form/registry.ts
+---
+
+## Problem
+
+WinterCMS plugins ship their own form widgets through `registerFormWidgets()` and use them as `type: <widget>` fields that own a column value. cabana has no equivalent:
+
+- The field-type set is closed. `modules/cabana/form_schema.go` (the known-types map, around lines 25-29), `modules/cabana/crud.go` (the scalar type switch, around line 1226) and the SPA renderer registry `admin/src/components/form/registry.ts` list every type, and an unknown type fails boot.
+- The Phase 10.1 `type: widget` extension (`modules/cabana/extension.go`) mounts a plugin custom element, but the field is valueless: it runs a controller action and writes back declared scalar sibling fields through `fill:`. It cannot own a value, define its JSON shape, validate and decode it on save, or render it in lists.
+
+Plugins about to be ported deliver their own fields that cannot become cabana core types (raised during the Phase 18 discussion, 2026-10-09). Without this, each one forces a framework release or a workaround through widget actions.
+
+## Solution
+
+Add a capability interface in `pact` (for example `HasFormFieldTypes`) through which a plugin registers a namespaced field type (`{vendor}-{plugin}-*` or `vendor.plugin::type`):
+
+- Server side: a Go type that validates the field's YAML options at boot (fail-loud, like the built-ins), decodes and validates the submitted value (any JSON shape), maps it to the column, and optionally formats it for list columns.
+- Client side: a custom element served through the existing `pact.AdminClientAssets` mechanism. It binds a value through a documented contract (a `value` property plus a `summer-change` event) instead of the action/fill round-trip, and reads the public `--c-*` CSS variables only.
+- The form schema and the generated TS types carry plugin types as a generic `plugin-field` shape so the SPA build does not need to know them.
+- Update the cabana README and `docs/`, the admin OpenAPI and the generated types, and commit `dist/`, all in the same change.
+
+Decide in a framework phase (or a decimal phase before the first plugin that needs it). Phase 18's `money` field stays a core cabana type (18-CONTEXT); this todo covers the plugins that follow.