@@ -0,0 +1,15 @@
+---
+'@objectstack/spec': minor
+---
+
+feat(spec/ui): `navItemVisibleDataNeedsDataSource` is exported from `@objectstack/spec/ui`, so a mirror of `NavigationItemSchema` attaches the spec's own rule by identifier
+
+Clause-②: yes (widening)
+
+- **What is added.** One function export, `navItemVisibleDataNeedsDataSource(item, ctx)`: the refinement `NavigationItemSchema` already runs, which refuses a navigation entry with no `dataSource` whose `visible` reads `data`. It is exported the way `objectNavTargetExclusivity`, `checkPageRegionPlacement` and `checkPageMainRegionWidth` are, so a hand-written mirror of the navigation item can chain the same function in its own `superRefine` instead of restating the rule.
+- **What does not change.** No schema accepts or refuses anything new. The issue is the same: one `custom` issue at `visible`, with the same message. `NavigationItemSchema` still attaches the same function, once, by name.
+- **What the function reads.** Both spellings of `visible`, so it answers the same on an entry as authored and as parsed:
+  - the authored bare string (`'data.total == 1'`), normalised by `EvaluatedExpressionInputSchema`, the slot's own schema, exactly as the spec's parse normalises it;
+  - the parsed `{ dialect: 'cel', source }` envelope.
+
+  A boolean or absent `visible` judges nothing. So a mirror whose own `visible` stays the authored string chains the function as it is and refuses what the spec refuses.
@@ -540,6 +540,7 @@
     "isViewContainerShaped (function)",
     "listViewGroupKeyPredicate (function)",
     "misplacedDefaultPageRefusal (function)",
+    "navItemVisibleDataNeedsDataSource (function)",
     "normalizeFilterOperator (function)",
     "normalizeInlineAction (function)",
     "objectNavTargetExclusivity (function)",
 
@@ -525,6 +525,7 @@
     "isViewContainerShaped": "src/ui/assembled-views.zod.ts#isViewContainerShaped (function)",
     "listViewGroupKeyPredicate": "src/ui/view-grouping-query.ts#listViewGroupKeyPredicate (function)",
     "misplacedDefaultPageRefusal": "src/ui/default-record-page.ts#misplacedDefaultPageRefusal (function)",
+    "navItemVisibleDataNeedsDataSource": "src/ui/app.zod.ts#navItemVisibleDataNeedsDataSource (function)",
     "normalizeFilterOperator": "src/ui/view.zod.ts#normalizeFilterOperator (function)",
     "normalizeInlineAction": "src/ui/action.zod.ts#normalizeInlineAction (function)",
     "objectNavTargetExclusivity": "src/ui/app.zod.ts#objectNavTargetExclusivity (function)",
 
@@ -0,0 +1,308 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * [#24534] `navItemVisibleDataNeedsDataSource` is EXPORTED, and the export IS
+ * the check `NavigationItemSchema` runs, so a hand-written mirror of the
+ * navigation item attaches the spec's own rule by identifier instead of
+ * restating it. The rule itself (what is refused, where, and with which
+ * words) is pinned in `app-nav-visible-data-needs-data-source.test.ts`; this
+ * file pins only the export, on the same four legs as
+ * `app-nav-target-exclusivity-export.test.ts`, plus the export's input
+ * contract:
+ *
+ *  1. PARITY over the check's matrix (every refusing branch and every
+ *     accepting path) between the export called directly with a collecting
+ *     ctx and `NavigationItemSchema`'s own parse. The matrix authors `visible`
+ *     as the `{ dialect, source }` envelope, the one spelling whose parsed
+ *     value equals what was written, so the two runners read the same input.
+ *  2. MOUNT: the union `NavigationItemSchema` lazily resolves to carries
+ *     exactly one `custom` check, and that check's issue vector over the
+ *     matrix equals the export's.
+ *  3. ATTACHMENT BY IDENTIFIER: the module declares the export exactly once
+ *     and chains it by name exactly once, read from the source, so the door
+ *     cannot be running an inline copy that merely agrees on this matrix.
+ *  4. BARREL identity: `./index` (what `@objectstack/spec/ui` ships) exports
+ *     the very same function object, with the `(value, ctx)` arity.
+ *  5. BOTH SPELLINGS: the export accepts `visible` as authored (the bare
+ *     string a mirror whose own `visible` stays the authored string hands it)
+ *     and as parsed (the envelope the spec's door hands it), and answers the
+ *     same on both. The card's own entry as written draws the door's identical
+ *     issue from a direct call, and so does its parsed `visible`. Over the leg-1
+ *     matrix rewritten with bare strings, the direct call and the door agree
+ *     issue for issue. The same bare string with a `dataSource` draws nothing,
+ *     and neither does a boolean or absent `visible`. So a mirror attaches the
+ *     export as it is, by identifier.
+ *
+ * What it does NOT prove: reference identity between the export and the
+ * check object the schema holds. zod 4 wraps the function handed to
+ * `superRefine` in a closure and keeps no handle to it; legs 2 + 3 are the
+ * substitute, as in the two sibling export pins.
+ *
+ * The fixtures are SHAPE-VALID on purpose and the parse leg throws otherwise,
+ * so "both refuse" can never be true for the wrong reason.
+ */
+
+import { describe, it, expect } from 'vitest';
+import type { z } from 'zod';
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { NavigationItemSchema, navItemVisibleDataNeedsDataSource } from './app.zod';
+import { EvaluatedExpressionInputSchema } from '../shared/expression.zod';
+import * as ui from './index';
+
+const HERE = path.dirname(fileURLToPath(import.meta.url));
+
+// ---------------------------------------------------------------------------
+// Harness
+// ---------------------------------------------------------------------------
+
+interface IssueSig {
+  code: string;
+  path: string;
+  message: string;
+}
+
+interface RawIssueLike {
+  code?: string;
+  path?: readonly PropertyKey[];
+  message?: string;
+}
+
+const sig = (i: RawIssueLike): IssueSig => ({
+  code: String(i.code),
+  path: (i.path ?? []).map(String).join('.'),
+  message: String(i.message),
+});
+
+const sorted = (issues: IssueSig[]): IssueSig[] =>
+  [...issues].sort((a, b) => JSON.stringify(a).localeCompare(JSON.stringify(b)));
+
+/** Leg (a): call the export directly with a collecting ctx. */
+function runExport(value: unknown): IssueSig[] {
+  const issues: RawIssueLike[] = [];
+  const ctx = {
+    value,
+    issues,
+    addIssue: (issue: string | RawIssueLike) => {
+      issues.push(typeof issue === 'string' ? { code: 'custom', message: issue } : { code: 'custom', ...issue });
+    },
+  };
+  navItemVisibleDataNeedsDataSource(value, ctx as unknown as z.RefinementCtx);
+  return sorted(issues.map(sig));
+}
+
+interface ZodCheckLike {
+  _zod: {
+    def: { check: string };
+    check: (payload: { value: unknown; issues: RawIssueLike[] }) => unknown;
+  };
+}
+
+/** Leg (b): run ONE of the schema's own check objects in isolation. */
+function runCheckObject(check: ZodCheckLike, value: unknown): IssueSig[] {
+  const payload = { value, issues: [] as RawIssueLike[] };
+  check._zod.check(payload);
+  return sorted(payload.issues.map(sig));
+}
+
+/** Leg (c): the door's full parse, restricted to object-level (`custom`) issues.
+ *  Throws when the fixture is not shape-valid — see the header. */
+function runParse(value: unknown): IssueSig[] {
+  const r = NavigationItemSchema.safeParse(value);
+  if (r.success) return [];
+  const foreign = r.error.issues.filter((i) => i.code !== 'custom');
+  if (foreign.length > 0) {
+    throw new Error(`fixture is not shape-valid — the object-level check never ran: ${JSON.stringify(foreign)}`);
+  }
+  return sorted(r.error.issues.map((i) => sig(i as RawIssueLike)));
+}
+
+/**
+ * The checks held by the discriminated union `NavigationItemSchema` lazily
+ * resolves to — the one place this module chains the refinement (its
+ * branches carry their own checks; those are not this export's).
+ */
+function unionChecksOf(schema: unknown): ZodCheckLike[] {
+  const lazyDef = (schema as { _zod: { def: { type: string; getter: () => unknown } } })._zod.def;
+  expect(lazyDef.type).toBe('lazy');
+  const union = lazyDef.getter() as { _zod: { def: { type: string; checks?: ZodCheckLike[] } } };
+  expect(union._zod.def.type).toBe('union');
+  return union._zod.def.checks ?? [];
+}
+
+/** One issue vector per runner over the matrix — the equality's key. */
+const vectorOf = (run: (value: unknown) => IssueSig[], values: unknown[]): string =>
+  JSON.stringify(values.map(run));
+
+// ---------------------------------------------------------------------------
+// Fixture matrix — every refusing branch, plus every accepting path
+// ---------------------------------------------------------------------------
+
+interface Fixture {
+  label: string;
+  value: Record<string, unknown>;
+  /** The paths the check is expected to refuse at; `[]` is an accepting path. */
+  refusesAt: string[];
+}
+
+/** The card's entry, as written there. */
+const CARD_ENTRY = { id: 'nav_envs', type: 'object', objectName: 'sys_environment', visible: 'data.total == 1' } as const;
+const API_BINDING = { provider: 'api', read: { url: '/api/v1/cloud/home' }, path: 'data.environments' } as const;
+const cel = (source: string) => ({ dialect: 'cel', source }) as const;
+
+const fixtures: Fixture[] = [
+  // Refusals — the one rule, on the branches that spread the base.
+  { label: 'the card\'s entry, `visible` as the envelope', value: { ...CARD_ENTRY, visible: cel('data.total == 1') }, refusesAt: ['visible'] },
+  { label: 'a `dashboard` entry', value: { id: 'nav_ops', type: 'dashboard', dashboardName: 'ops', visible: cel('!data.has_more') }, refusesAt: ['visible'] },
+  { label: 'a `url` entry reading the bare root', value: { id: 'nav_cloud', type: 'url', url: '/apps/cloud', visible: cel('data') }, refusesAt: ['visible'] },
+  { label: 'a `group` entry', value: { id: 'nav_group', type: 'group', children: [], visible: cel('has(data.total)') }, refusesAt: ['visible'] },
+  // Accepting paths — the control the card names, and the reader's edges.
+  { label: 'the card\'s entry WITH a `dataSource` (the control)', value: { ...CARD_ENTRY, visible: cel('data.total == 1'), dataSource: API_BINDING }, refusesAt: [] },
+  { label: 'an ambient root only (`current_user`)', value: { ...CARD_ENTRY, visible: cel('\'org_admin\' in current_user.positions') }, refusesAt: [] },
+  { label: 'a member named `data`, not the root', value: { ...CARD_ENTRY, visible: cel('features.data == true') }, refusesAt: [] },
+  { label: 'no `visible` at all', value: { id: 'nav_envs', type: 'object', objectName: 'sys_environment' }, refusesAt: [] },
+];
+
+const matrix = fixtures.map((f) => f.value);
+const refusing = fixtures.filter((f) => f.refusesAt.length > 0);
+const accepting = fixtures.filter((f) => f.refusesAt.length === 0);
+
+// ---------------------------------------------------------------------------
+// Leg 1 — parity on every fixture between the export and the door
+// ---------------------------------------------------------------------------
+
+describe('navItemVisibleDataNeedsDataSource — parity between the export and NavigationItemSchema', () => {
+  it.each(fixtures)('$label — the direct call refuses at exactly the declared paths', ({ value, refusesAt }) => {
+    const direct = runExport(value);
+    expect(direct.map((i) => i.path).sort()).toEqual([...refusesAt].sort());
+    for (const issue of direct) expect(issue.code).toBe('custom');
+  });
+
+  it.each(fixtures)('$label — the NavigationItemSchema parse and the direct call agree issue for issue', ({ value }) => {
+    expect(runParse(value)).toEqual(runExport(value));
+  });
+
+  it('the matrix has both kinds of path, so agreement is not vacuous', () => {
+    expect(refusing.length).toBeGreaterThanOrEqual(4);
+    expect(accepting.length).toBeGreaterThanOrEqual(4);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Leg 2 — the mount: the union carries the check
+// ---------------------------------------------------------------------------
+
+describe('the mount — the union NavigationItemSchema resolves to carries the check', () => {
+  it('carries exactly one `custom` check', () => {
+    expect(unionChecksOf(NavigationItemSchema).map((c) => c._zod.def.check)).toEqual(['custom']);
+  });
+
+  it('that check is behaviourally identical to the export over the whole matrix', () => {
+    const [check] = unionChecksOf(NavigationItemSchema);
+    expect(vectorOf((v) => runCheckObject(check, v), matrix)).toBe(vectorOf(runExport, matrix));
+    // …and the export is not a no-op on its own matrix (an all-empty vector
+    // would match any dead check).
+    expect(vectorOf(runExport, matrix)).not.toBe(vectorOf(() => [], matrix));
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Leg 3 — attached by identifier, in the module that declares the schema
+// ---------------------------------------------------------------------------
+
+describe('app.zod.ts attaches the export BY IDENTIFIER — no inline copy', () => {
+  const src = fs.readFileSync(path.join(HERE, 'app.zod.ts'), 'utf8');
+  // An attachment is a CODE line carrying `.superRefine(name)`; docblock
+  // (` * `) and `//` lines are excluded, so prose naming the same spelling is
+  // not counted.
+  const attachments = (name: string): number =>
+    src.split(/\r?\n/).filter((line) => !/^[ \t]*(\*|\/\/)/.test(line) && line.includes(`.superRefine(${name})`)).length;
+  // A NAME is only a sound key for that count if the module declares it exactly
+  // once — a second, shadowing binding would satisfy the count while the door
+  // chains a different function object.
+  const declarations = (name: string): number =>
+    src.match(new RegExp(`^\\s*(export )?function ${name}\\b`, 'gm'))?.length ?? 0;
+
+  it('declares `export function navItemVisibleDataNeedsDataSource(` exactly once', () => {
+    expect(src).toContain('export function navItemVisibleDataNeedsDataSource(');
+    expect(declarations('navItemVisibleDataNeedsDataSource')).toBe(1);
+  });
+
+  it('chains it exactly once — on the union, by name', () => {
+    expect(attachments('navItemVisibleDataNeedsDataSource')).toBe(1);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Leg 4 — the barrel ships the same function object
+// ---------------------------------------------------------------------------
+
+describe('`./index` (the `@objectstack/spec/ui` surface) exports the same function object', () => {
+  it('navItemVisibleDataNeedsDataSource — reference identity, and the `(value, ctx)` arity', () => {
+    expect((ui as Record<string, unknown>).navItemVisibleDataNeedsDataSource).toBe(navItemVisibleDataNeedsDataSource);
+    expect(typeof navItemVisibleDataNeedsDataSource).toBe('function');
+    expect(navItemVisibleDataNeedsDataSource.length).toBe(2);
+  });
+});
+
+// ---------------------------------------------------------------------------
+// Leg 5 — both spellings: the export reads `visible` as authored and as parsed
+// ---------------------------------------------------------------------------
+
+/** The leg-1 matrix with each envelope `visible` written back as the bare string an author writes. */
+const authoredFixtures: Fixture[] = fixtures
+  .filter((f) => f.value.visible !== undefined)
+  .map((f) => ({
+    ...f,
+    label: `${f.label}, \`visible\` written as the bare string`,
+    value: { ...f.value, visible: (f.value.visible as { source: string }).source },
+  }));
+
+describe('both spellings — the export reads `visible` as authored and as parsed, and answers the same', () => {
+  const parsedVisible = EvaluatedExpressionInputSchema.parse(CARD_ENTRY.visible);
+
+  it('the spec normalises the bare string to the envelope the check reads', () => {
+    expect(parsedVisible).toEqual(cel('data.total == 1'));
+  });
+
+  it('the door refuses the card\'s entry as written, with one `custom` issue at `visible`', () => {
+    const door = runParse(CARD_ENTRY);
+    expect(door).toHaveLength(1);
+    expect(door[0]).toMatchObject({ code: 'custom', path: 'visible' });
+  });
+
+  it('the export raises the identical issue on that entry\'s parsed `visible`', () => {
+    expect(runExport({ ...CARD_ENTRY, visible: parsedVisible })).toEqual(runParse(CARD_ENTRY));
+  });
+
+  it('the export raises the door\'s identical issue (code, path and message) on the card\'s entry AS WRITTEN', () => {
+    const direct = runExport(CARD_ENTRY);
+    expect(direct).toHaveLength(1);
+    expect(direct).toEqual(runParse(CARD_ENTRY));
+  });
+
+  it.each(authoredFixtures)('$label — the direct call refuses at exactly the declared paths, issue for issue with the door', ({ value, refusesAt }) => {
+    const direct = runExport(value);
+    expect(direct.map((i) => i.path).sort()).toEqual([...refusesAt].sort());
+    expect(runParse(value)).toEqual(direct);
+  });
+
+  it('the authored matrix has both kinds of path, so agreement is not vacuous', () => {
+    expect(authoredFixtures.filter((f) => f.refusesAt.length > 0).length).toBeGreaterThanOrEqual(4);
+    expect(authoredFixtures.filter((f) => f.refusesAt.length === 0).length).toBeGreaterThanOrEqual(3);
+  });
+
+  it('the control — the same bare string with a `dataSource` — draws nothing, from the door or the export', () => {
+    const withSource = { ...CARD_ENTRY, dataSource: API_BINDING };
+    expect(NavigationItemSchema.safeParse(withSource).success).toBe(true);
+    expect(runExport(withSource)).toEqual([]);
+    expect(runExport({ ...withSource, visible: parsedVisible })).toEqual([]);
+  });
+
+  it('a boolean or absent `visible` judges nothing', () => {
+    expect(runExport({ ...CARD_ENTRY, visible: true })).toEqual([]);
+    expect(runExport({ ...CARD_ENTRY, visible: false })).toEqual([]);
+    expect(runExport({ id: CARD_ENTRY.id, type: CARD_ENTRY.type, objectName: CARD_ENTRY.objectName })).toEqual([]);
+  });
+});