feat(spec): page form uses filter-mode widget for userFilters + ADR-0047 §3.4a

page.form.ts: the Interface section's interfaceConfig composite now lists
its sub-fields explicitly so userFilters can use the dedicated
'filter-mode' selector widget (None / Tabs / Dropdown / Toggle, objectui).

ADR-0047 §3.4a records the design decision: 'no filter bar' is the
ABSENCE of userFilters, not a literal element: 'none'. Rationale —
declarative-metadata hygiene (off = key absent, like every other optional
capability), no orphaned sub-config, clean overlay diffs, presence and
style are orthogonal axes. The authoring UI provides the explicit
None/Tabs/Dropdown/Toggle affordance; storage stays clean.

Pairs with objectui#1694 (the filter-mode widget). An unknown widget name
degrades gracefully to the prior composite rendering, so this is
independently mergeable.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: os-zhuang

docs/adr/0047-object-ui-run-modes.md

@@ -153,6 +153,35 @@ have; we do not rely on lint to forbid what the type can simply not express.
 | User-created views | Allowed, governed by permissions + view `sharing` | Never |
 | Filter state | Session-scoped (URL-param sync is a later, orthogonal step) | Session-scoped |
 
+### 3.4a "No filter bar" is omission, not a literal `element: 'none'`
+
+Airtable's User-filters control is a single tri-state selector
+(**None / Tabs / Dropdown**). We deliberately do **not** mirror that as a
+literal enum value. The `userFilters.element` enum stays
+`dropdown | tabs | toggle`; **"none" is the ABSENCE of `userFilters`**.
+
+Rationale (declarative-metadata hygiene):
+
+- **Consistency.** Every optional capability in the protocol is "off = key
+  absent" (`kanban`, `grouping`, …). A literal `element: 'none'` would be the
+  one special case authors and tooling must learn.
+- **No dead config.** `element: 'none'` would leave an object whose `fields` /
+  `tabs` are orphaned — undefined semantics for validation, overlay merge, and
+  AI generation. Omission has one unambiguous meaning.
+- **Cleaner diffs / overlays.** Disabling the bar is a key deletion (ADR-0005
+  overlay semantics), not a value mutation dragging stale sub-config along.
+- **Orthogonal axes.** "Is there a filter bar?" (presence) and "what style?"
+  (`element`) are independent; one enum would couple them, and we carry four
+  styles (`+toggle`) to Airtable's three.
+
+**Storage and authoring UI are separate layers.** The Studio editor exposes a
+first-class **None / Tabs / Dropdown / Toggle** segmented selector (the
+`filter-mode` widget) — selecting *None* writes `onChange(undefined)`, removing
+the key. Authors get Airtable's explicit affordance; the protocol stays clean.
+
+If a "disable but remember the configured fields/tabs" need ever arises, the
+right shape is a separate `enabled: false` flag — never `element: 'none'`.
+
 ### 3.5 AI authoring rules (inherits ADR-0033's draft gate)
 
 1. **Default output**: objects + list views + navigation → objects. *No pages.*

packages/spec/src/ui/page.form.ts

@@ -50,7 +50,28 @@ export const pageForm = defineForm({
           field: 'interfaceConfig',
           type: 'composite',
           helpText:
-            'source/sourceView bind the object view (columns, base filter and sort are inherited — the iron rule); userFilters picks the element style (dropdown / tabs / toggle) and exposed fields; appearance.allowedVisualizations whitelists renderers (one entry = locked); userActions toggles the toolbar.',
+            'source/sourceView bind the object view (columns, base filter and sort are inherited — the iron rule); appearance.allowedVisualizations whitelists renderers (one entry = locked); userActions toggles the toolbar.',
+          // Explicit sub-fields so `userFilters` can use the dedicated
+          // filter-mode selector (None / Tabs / Dropdown / Toggle, ADR-0047).
+          // None maps to ABSENCE of userFilters — the protocol stores
+          // "no filter bar" as omission, not a literal element: 'none'.
+          // Keep this list in sync with InterfacePageConfigSchema.
+          fields: [
+            { field: 'source' },
+            { field: 'sourceView' },
+            { field: 'levels' },
+            { field: 'filterBy', type: 'repeater' },
+            { field: 'appearance', type: 'composite' },
+            {
+              field: 'userFilters',
+              widget: 'filter-mode',
+              helpText: 'End-user filter bar: None (no bar) / Tabs (named presets) / Dropdown (per-field) / Toggle. None removes the config.',
+            },
+            { field: 'userActions', type: 'composite' },
+            { field: 'addRecord', type: 'composite' },
+            { field: 'showRecordCount' },
+            { field: 'allowPrinting' },
+          ],
         },
       ],
     },