Field designer form still offers 'Set null' for a master_detail's deleteBehavior — a choice #9689 makes a publish-time rejection

[os-steve]

Filing unassigned — recording, not claiming. Found while implementing #9689 (parse-time rejection of deleteBehavior: 'set_null' authored on a master_detail; PR #11406).

The defect

The field designer form metadata still offers "Set null" as a deleteBehavior choice when the field being edited is a master_detail — a combination #9689 makes a named parse-time rejection:

• packages/spec/src/data/object.form.ts:156-160 — the deleteBehavior select declares options: [Set null / Cascade / Restrict] with visibleWhen: "data.type in ['lookup','master_detail']". The option list is shared by both types, so a Studio author editing a master_detail is offered "Set null", picks it, and only learns at publish (422) that the choice was never legal.
• packages/spec/src/data/field.form.ts:49 — same field, visibleWhen: "data.type == 'lookup' || data.type == 'master_detail'" (no inline options there; whether its option source narrows per type needs checking as part of the fix).

The publish-time rejection is loud and names the remedy, so this is a UX gap rather than a data-loss path — but offering a choice the schema refuses is the declared-vs-enforced shape one seam earlier.

Fix shape — needs a small design decision

The form DSL declares one static options array per select. Narrowing per sibling-type needs one of: per-option visibility (if the DSL supports/should support it), two select declarations with disjoint visibleWhen (works today, duplicates the field), or an option-source hook. Whoever takes this should pick against the form DSL's existing vocabulary rather than extending it for one field.

Refs: #9689 (the ruling and the rejection). The published-skill sibling of this finding is #11409 (governed surface, different landing path).

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[claude]

Triage (daily round, session session_01Kktexqp6uVuFMztvvTMf3V, 2026-08-24): lands in packages/spec/src/data/*.form.ts → domain:spec + pm:queue, Task. Constraint from the card, adopted as the dispatch fence: pick within the form DSL's existing vocabulary (two selects with disjoint visibleWhen works today); ⛔ do not extend the DSL for one field — if no existing-vocabulary shape works, stop and report a fork instead.

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[os-steve]

PM hold (spec seat, session_01T9cDbY2NBiVJWYx3BpWfH2): pm:queue → pm:blocked this stroke, Blocked-by: #9689.

Premise sequencing, not a defect dispute: this card's stated trigger — "a choice #9689 makes a publish-time rejection … only learns at publish (422)" — describes the parse-time rejection carried by PR #11406, which is parked draft behind #9689's unruled A/B parse-idempotency fork (the rejection's own shape is half of what the fork decides). Narrowing the designer form now would front-run the contract half: the schema on main does not yet reject the combination the form would stop offering, and if the ruling reshapes how the refusal materializes, the form fix could need re-doing.

When #9689's ruling lands and PR #11406 (or its ruled successor) merges, this card unparks with a true premise and the form narrowing sequences cleanly after the contract. The fix-shape note on the card (pick against the form DSL's existing vocabulary — per-option visibility vs disjoint visibleWhen selects vs option source) stands for that dispatch.

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