docs: add WS-6 Deferred backlog items (WS-6)

Five backlog items tracking explicit out-of-scope decisions from
RFC-WS-6.md §6.

Refs: RFC-WS-6.md §6, §9

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

dev-docs/BACKLOG.md

@@ -1099,5 +1099,50 @@ follows organically as features land or are touched.
 
 ---
 
+### WS-6 Deferred
+
+#### ARTIST-ADV-SECTION-APPLY
+
+Section-level binding apply runtime activation.
+**Removal trigger:** when artist_advance feature work begins (post-S5).
+**Action:** set `FORM_BUILDER_SECTION_APPLY=true`, write section-scoped tests,
+activate `ApplyBindingsOnFormSectionSubmitted` listener registration, remove
+the feature-flag early-return guard from the listener.
+**Refs:** RFC-WS-6.md §3 Q10.
+
+#### FORM-BINDING-COMPOSITE-IDENTITY
+
+Multi-attribute identity-key resolution (e.g. `email OR (first_name+last_name+DOB)`).
+**Trigger:** when a purpose requires composite identity matching that single
+binding cannot satisfy. Currently `MaxOneIdentityKeyPerTargetEntity` guard
+enforces single-key only.
+**Refs:** RFC-WS-6.md §3 Q8, §6.
+
+#### FORM-LIBRARY-RESYNC
+
+Admin action to propagate `FormFieldLibrary` binding updates to existing
+field instances. Currently library-bindings are copy-on-instantiation
+only (see `ARCH-BINDINGS.md §1`).
+**Trigger:** when organisations report friction updating shared field
+templates.
+**Refs:** RFC-WS-6.md §3 Q11.
+
+#### FORM-FAILURE-DAILY-DIGEST
+
+Daily digest mailable for orgs with open `FormSubmissionActionFailure` rows
+above a threshold.
+**Deferred until** notification framework lands (post-accreditation engine).
+Requires NotificationBell + NotificationCenter infrastructure.
+**Refs:** RFC-WS-6.md §3 Q5.
+
+#### LOAD-TEST-FOUNDATION
+
+Wall-clock concurrent load testing infrastructure (k6 or equivalent) against
+staging-API. Separate workstream from WS-6.
+**Trigger:** pre-release hardening phase.
+**Refs:** RFC-WS-6.md §4 V4.
+
+---
+
 _Laatste update: April 2026_
 _Voeg nieuwe items toe met prefix: ARCH-, COMM-, OPS-, VOL-, ART-, FORM-, SUP-, DIFF-, APPS-, TECH-, UX-_