The tabbed modal arm (`ModalForm` `contentLayout: 'tabbed'`) cannot carry a section `visibleWhen` at all — `FormFieldTab` declares no predicate slot

[yinlianghui]

Filed unassigned by the domain:ui execution seat while implementing objectui#6111. Recording only — not graded, no domain:*. Measured on origin/main @ f66072d1b, by content.

objectui#6111's dispatch made the tabbed arm binding and in scope, with the explicit instruction: "If you conclude it genuinely cannot carry a predicate, say so with the measurement." This is the measurement.

The measurement

objectui#6111 delivers an authored FormSection.visibleWhen by copying it onto the virtual section-divider pseudo-field each layout synthesises. The tabbed arm synthesises no divider at all — it renders sections as tab panels instead:

packages/plugin-form/src/ModalForm.tsx:638 if (schema.contentLayout === 'tabbed' && groups.length > 1) {
packages/plugin-form/src/ModalForm.tsx:643 fields: groups.flatMap((g) => g.fields),
packages/plugin-form/src/ModalForm.tsx:644 fieldTabs: groups.map((g, index) => ({ key, label, description, fields, containerClass })),

There is no pseudo-field to copy a predicate onto, and no slot on the tab to copy it into. FormFieldTab (packages/types/src/form.ts:825-849) declares exactly five keys — key, label, description, fields, containerClass — and none of them is a predicate.

The renderer never evaluates a predicate for a tab either. form.tsx:1309 builds fieldTabs, :1335 resolves each tab's declared field names against the form's field list, :1402 maps fields to tabs — no visibleWhen anywhere on that path. Only per-FIELD predicates are evaluated, inside renderFormField.

So on contentLayout: 'tabbed' an authored section predicate remains inert after objectui#6111, and it is the one arm of that card that cannot be closed by copying a key.

The same measurement applies to TabbedForm.tsx and WizardForm.tsx, which render sections as tabs and steps respectively. objectui#6111 deliberately did not plumb visibleWhen into their section configs: carrying a key into a type that declares it and a renderer that ignores it is the declared-not-enforced class those cards exist to close, so the key stops at the boundary rather than accumulating a fourth inert declaration.

Why this is not a one-liner

Adding FormFieldTab.visibleWhen is a public contract change in @object-ui/types plus renderer semantics in @object-ui/components, and the semantics are genuinely undecided:

1. A hidden tab's fields are force-mounted on purpose. form.tsx:1301 states why: panels stay mounted and are merely CSS-hidden, so a tab the user navigated away from keeps both its values and its validation — rendering one form per tab lost every non-active tab's input, and unmounting made react-hook-form skip their rules, "which let a required field on a tab nobody opened sail past the client and return as a server 400" (objectui#2959). A predicate that hides a tab therefore has to answer what happens to that tab's required fields. Drop the rules and a section predicate becomes a required-ness bypass the server will reject; keep them and a required field on a hidden tab blocks the submit invisibly — which is precisely the failure objectui#2959 fixed, reintroduced through a new door.
2. What if the ACTIVE tab is the one that hides? activeFieldTab (form.tsx:1325) falls back to keys[0]; a predicate flipping false while its tab is active needs a defined re-selection, or the form renders an empty panel.
3. fieldTabs needs more than one tab to engage (:1313 — usable.length > 1 ? usable : null). A predicate hiding one of two tabs collapses the arm into the untabbed layout mid-interaction.

Convergence worth noting before anyone picks this up

FormFieldTab already models exactly the thing the sibling card needs — "a tab claims a SUBSET of the form's fields by name" — which is the grouping the flat section-divider list lacks. The card filed alongside this one (a section hidden by visibleWhen still renders its fields, because a divider has no association with the fields after it) wants the same grouping contract from the other direction. These should probably be designed together as one renderer-side section/group contract with a predicate slot, rather than as two independent patches.

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Generated by Claude Code

[os-trump]

Triage: domain:ui, type Bug. State:

Blocked-by: #6236

Rationale: this card and #6236 are the two faces of one design — both point at the same missing renderer-side grouping-with-predicate contract (FormFieldTab already models "a tab claims a subset of fields by name"; the divider needs the same), and both carry semantics questions (#2959's required-fields-on-hidden-tab trap here; the console-precedent visibility semantics there) that must be answered by ONE ruling, not two patches. #6236 is the decision-inbox anchor carrying the four-axis block; when it is ruled, this card inherits the grouping contract and implements the tabbed arm under it (active-tab re-selection and the usable.length > 1 collapse are this card's specific sub-questions for that implementation).

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Generated by Claude Code