docs: BACKLOG + ARCH-BINDINGS appendix + RFC v1.2 for registry alignment (WS-6)

Two new BACKLOG entries capture the deliberate v1 deferrals:

  - ARTIST-ADV-BINDING-MODEL — design how artist_advance form data
    relates to Artist + AdvanceSection entities (when, if ever, an
    Eloquent Artist class is needed, and whether bindings are even
    the right abstraction for OUTPUT-shaped advance forms).

  - FORM-BINDING-JSON-PATH — extend binding registry to support
    JSON-path attributes (custom_fields.dietary_preferences etc).
    For v1 the recommendation is TAG_PICKER + tag_categories config.

ARCH-BINDINGS.md gets an appendix explaining the v1 scope decisions
explicitly: why 'artist' has no registry entries (model class
absent + advance forms are OUTPUT-shaped, not provisioning-shaped),
why JSON-path attributes are out of scope (v1 is column-level only),
and how BindingTypeRegistryConsistencyTest prevents future drift.

RFC-WS-6.md → v1.2 with a §3 Q9 addendum tracking the registry
alignment + the 3 renames, 5 removals, and 1 new column landed in
this branch.

Refs: WS-6 sessie 3a binding-target drift audit, sessie 3a.5 cleanup

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

dev-docs/ARCH-BINDINGS.md

@@ -4,6 +4,7 @@
 
 - v0.1 (skeleton) — 2026-04-25
 - v0.4 — 2026-04-28 — § 8.2 IDOR class tests (sessie 3a backend hardening)
+- v0.5 — 2026-04-28 — Appendix on v1 registry scope (sessie 3a.5 model alignment)
 - Owner: Bert
 - Authoritative for the binding pipeline architecture, complementing
   ARCH-FORM-BUILDER.md §17 and §31.
@@ -594,6 +595,57 @@ might never persist on rollback — fixed in WS-6.
 - **Daily failure digest mailable** — depends on notification framework
 - **Wall-clock concurrent load testing** — BACKLOG: `LOAD-TEST-FOUNDATION`
 
+## Appendix — v1 binding registry scope
+
+The `App\FormBuilder\Bindings\BindingTypeRegistry` covers the four
+binding-target entities active in WS-6 v1: `person`, `company`,
+`user`, and an intentionally-empty `artist` (omitted from registry).
+
+### Why `artist` has no registry entries in v1
+
+The `artists` table exists (since 2026-04-08) and `subject_type='artist'`
+is a valid `form_submissions` value. But:
+
+1. No Eloquent `Artist` model class exists yet. Polymorphic subject
+   relations work via the morph map (string → table) but cannot be
+   Eloquent-loaded without a class.
+2. The `artist_advance` purpose is OUTPUT-shaped: the advance form
+   **gathers** information FROM the artist (rider, hospitality,
+   technical needs) — it does not provision Artist attributes the way
+   `event_registration` provisions Person attributes.
+3. Bindings as a concept may not be the correct abstraction for advance
+   forms. v2 work tracked via BACKLOG `ARTIST-ADV-BINDING-MODEL`.
+
+In v1: `artist_advance` schemas may exist with `required_bindings: []`.
+PublishGuards enforce only the cross-cutting invariants (no identity
+key conflicts, no append-on-scalar, etc). The applicator runs (per
+RFC §3 Q4 two-transaction pattern) but resolves bindings to an empty
+list, completing in COMPLETED state with zero applications. The
+Person/Company/User-level effects of WS-6 (apply_status, action_failures,
+retry/dismiss workflows) all apply uniformly.
+
+### Why JSON-path attributes are not in v1
+
+`persons.custom_fields` is a JSON column; semantically a Person can
+have `dietary_preferences` (etc.) inside that column. But binding
+targets in v1 are **column-level** scalars, lists, and relations —
+not JSON-path. Adding JSON-path support is tracked via BACKLOG
+`FORM-BINDING-JSON-PATH`.
+
+For v1 the recommendation: model `dietary_preferences` (and similar
+`custom_fields` properties) as a `TAG_PICKER` form_field with a
+`tag_categories` config. The TAG_PICKER → user_organisation_tags sync
+(per ARCH-FORM-BUILDER §31.10) handles this without requiring
+binding-target column mapping.
+
+### Drift prevention
+
+`BindingTypeRegistryConsistencyTest::test_every_registry_entity_maps_to_an_eloquent_model_with_the_attribute`
+asserts that every registry entry corresponds to a real Eloquent model
+class plus a real column on that model's table. Future drift (renamed
+column without registry update, or registry entry without column)
+becomes a test failure, not a runtime surprise.
+
 ## 11. Related docs
 
 - `RFC-WS-6.md` — design decisions