diff --git a/.changeset/13459-refuse-invalid-gantt-block.md b/.changeset/13459-refuse-invalid-gantt-block.md
new file mode 100644
index 0000000000..57910f5830
--- /dev/null
+++ b/.changeset/13459-refuse-invalid-gantt-block.md
@@ -0,0 +1,11 @@
+---
+"@object-ui/plugin-gantt": patch
+"@object-ui/app-shell": patch
+---
+
+Clause-②: no
+Metadata-protocol: narrowed
+
+An invalid `gantt` block is refused instead of drawn (objectui#13459). `ObjectGantt` used to log `Invalid gantt configuration` and render the block anyway, so a block with a misspelt or missing key still drew a chart. It now renders a refusal that names each `GanttConfigSchema` issue by its path in the block (`gantt.endDateField: …`); a valid block and the flat ObjectView / ListView spelling render as before.
+
+The Studio designers' spec derivations (`dashboard`, `package`, `page`, `report` and `view` schemas in `metadata-admin`) no longer catch a failed derivation and return `undefined`, which rendered a designer form silently missing fields. Their only input is the bundled spec, so a failure is a build-time fact that fails their tests; at runtime it reaches the route's error boundary.
diff --git a/packages/app-shell/src/views/metadata-admin/dashboard-schema.ts b/packages/app-shell/src/views/metadata-admin/dashboard-schema.ts
index 7cf9b63a38..22fb2a5153 100644
--- a/packages/app-shell/src/views/metadata-admin/dashboard-schema.ts
+++ b/packages/app-shell/src/views/metadata-admin/dashboard-schema.ts
@@ -39,20 +39,19 @@ const FORM_FIELDS_OWNED_ELSEWHERE = new Set([
   'name', // record identity — not user-editable here
 ]);
 
+/**
+ * No `try`/`catch` around the spec derivations in this file (objectui#13459).
+ * Their only input is the bundled `@objectstack/spec`, so a derivation that
+ * fails is a build-time fact: the tests beside this file go red, and at runtime
+ * the throw reaches the route's error boundary. It used to be caught, warned
+ * about in the console and turned into `undefined`, which rendered a designer
+ * form silently missing fields that the author could then save past.
+ */
 let _dashboardDocSchema: JsonSchema | undefined;
-let _dashboardDocFailed = false;
 
 /** JSONSchema for the whole (flat) Dashboard document. */
-export function getDashboardSchema(): JsonSchema | undefined {
-  if (_dashboardDocSchema || _dashboardDocFailed) return _dashboardDocSchema;
-  try {
-    _dashboardDocSchema = z.toJSONSchema(DashboardSchema, TO_JSON_OPTS) as JsonSchema;
-  } catch (err) {
-    _dashboardDocFailed = true;
-    if (typeof console !== 'undefined') {
-      console.warn('[dashboard-schema] failed to derive Dashboard JSONSchema from spec', err);
-    }
-  }
+export function getDashboardSchema(): JsonSchema {
+  _dashboardDocSchema ??= z.toJSONSchema(DashboardSchema, TO_JSON_OPTS) as JsonSchema;
   return _dashboardDocSchema;
 }
 
@@ -79,31 +78,24 @@ export function getDashboardForm(locale?: SupportedLocale | string): FormViewSpe
   const cacheKey = String(locale ?? '');
   if (_dashboardForm.has(cacheKey)) return _dashboardForm.get(cacheKey);
   if (!specDashboardForm || typeof specDashboardForm !== 'object') return undefined;
-  try {
-    const clone = JSON.parse(JSON.stringify(specDashboardForm)) as FormViewSpec;
-    for (const section of clone.sections ?? []) {
-      section.fields = (section.fields ?? []).filter((f: any) => {
-        const name = typeof f === 'string' ? f : f?.field;
-        return !FORM_FIELDS_OWNED_ELSEWHERE.has(name);
-      });
-    }
-    // Drop now-empty sections so we don't render bare headers.
-    clone.sections = (clone.sections ?? []).filter(
-      (s: any) => (s.fields ?? []).length > 0,
-    );
-    // Localize AFTER pruning: the overlay only has to reach what renders, and
-    // pruning cannot drop a section the overlay just renamed.
-    const localized = localizeMetadataForm(
-      clone as unknown as Record<string, unknown>,
-      'dashboard',
-      locale,
-    ) as unknown as FormViewSpec;
-    _dashboardForm.set(cacheKey, localized);
-    return localized;
-  } catch (err) {
-    if (typeof console !== 'undefined') {
-      console.warn('[dashboard-schema] failed to prepare dashboardForm from spec', err);
-    }
-    return undefined;
+  const clone = JSON.parse(JSON.stringify(specDashboardForm)) as FormViewSpec;
+  for (const section of clone.sections ?? []) {
+    section.fields = (section.fields ?? []).filter((f: any) => {
+      const name = typeof f === 'string' ? f : f?.field;
+      return !FORM_FIELDS_OWNED_ELSEWHERE.has(name);
+    });
   }
+  // Drop now-empty sections so we don't render bare headers.
+  clone.sections = (clone.sections ?? []).filter(
+    (s: any) => (s.fields ?? []).length > 0,
+  );
+  // Localize AFTER pruning: the overlay only has to reach what renders, and
+  // pruning cannot drop a section the overlay just renamed.
+  const localized = localizeMetadataForm(
+    clone as unknown as Record<string, unknown>,
+    'dashboard',
+    locale,
+  ) as unknown as FormViewSpec;
+  _dashboardForm.set(cacheKey, localized);
+  return localized;
 }
diff --git a/packages/app-shell/src/views/metadata-admin/package-schema.ts b/packages/app-shell/src/views/metadata-admin/package-schema.ts
index 9b717ed095..d5f538fbf1 100644
--- a/packages/app-shell/src/views/metadata-admin/package-schema.ts
+++ b/packages/app-shell/src/views/metadata-admin/package-schema.ts
@@ -50,20 +50,19 @@ export const PACKAGE_FORM_FIELDS = [
   'dependencies',
 ] as const;
 
+/**
+ * No `try`/`catch` around the spec derivations in this file (objectui#13459).
+ * Their only input is the bundled `@objectstack/spec`, so a derivation that
+ * fails is a build-time fact: the tests beside this file go red, and at runtime
+ * the throw reaches the route's error boundary. It used to be caught, warned
+ * about in the console and turned into `undefined`, which rendered a designer
+ * form silently missing fields that the author could then save past.
+ */
 let _schema: JsonSchema | undefined;
-let _schemaFailed = false;
 
 /** JSONSchema for the whole package manifest (memoised, spec-derived). */
-export function getPackageSchema(): JsonSchema | undefined {
-  if (_schema || _schemaFailed) return _schema;
-  try {
-    _schema = z.toJSONSchema(ManifestSchema, TO_JSON_OPTS) as JsonSchema;
-  } catch (err) {
-    _schemaFailed = true;
-    if (typeof console !== 'undefined') {
-      console.warn('[package-schema] failed to derive manifest JSONSchema from spec', err);
-    }
-  }
+export function getPackageSchema(): JsonSchema {
+  _schema ??= z.toJSONSchema(ManifestSchema, TO_JSON_OPTS) as JsonSchema;
   return _schema;
 }
 
diff --git a/packages/app-shell/src/views/metadata-admin/page-schema.ts b/packages/app-shell/src/views/metadata-admin/page-schema.ts
index 89da29282d..3a45e8582c 100644
--- a/packages/app-shell/src/views/metadata-admin/page-schema.ts
+++ b/packages/app-shell/src/views/metadata-admin/page-schema.ts
@@ -39,20 +39,19 @@ const TO_JSON_OPTS = { io: 'input', unrepresentable: 'any' } as const;
  */
 export const PAGE_FIELDS_OWNED_ELSEWHERE = new Set(['name', 'regions', 'children']);
 
+/**
+ * No `try`/`catch` around the spec derivations in this file (objectui#13459).
+ * Their only input is the bundled `@objectstack/spec`, so a derivation that
+ * fails is a build-time fact: the tests beside this file go red, and at runtime
+ * the throw reaches the route's error boundary. It used to be caught, warned
+ * about in the console and turned into `undefined`, which rendered a designer
+ * form silently missing fields that the author could then save past.
+ */
 let _pageSchema: JsonSchema | undefined;
-let _pageSchemaFailed = false;
 
 /** JSONSchema for the whole Page document (memoised, spec-derived). */
-export function getPageSchema(): JsonSchema | undefined {
-  if (_pageSchema || _pageSchemaFailed) return _pageSchema;
-  try {
-    _pageSchema = z.toJSONSchema(PageSchema, TO_JSON_OPTS) as JsonSchema;
-  } catch (err) {
-    _pageSchemaFailed = true;
-    if (typeof console !== 'undefined') {
-      console.warn('[page-schema] failed to derive Page JSONSchema from spec', err);
-    }
-  }
+export function getPageSchema(): JsonSchema {
+  _pageSchema ??= z.toJSONSchema(PageSchema, TO_JSON_OPTS) as JsonSchema;
   return _pageSchema;
 }
 
@@ -67,21 +66,14 @@ let _pageForm: FormViewSpec | undefined;
 export function getPageForm(): FormViewSpec | undefined {
   if (_pageForm) return _pageForm;
   if (!specPageForm || typeof specPageForm !== 'object') return undefined;
-  try {
-    const clone = JSON.parse(JSON.stringify(specPageForm)) as FormViewSpec;
-    for (const section of clone.sections ?? []) {
-      section.fields = (section.fields ?? []).filter((f: any) => {
-        const name = typeof f === 'string' ? f : f?.field;
-        return !PAGE_FIELDS_OWNED_ELSEWHERE.has(name);
-      });
-    }
-    clone.sections = (clone.sections ?? []).filter((s) => (s.fields ?? []).length > 0);
-    _pageForm = clone;
-  } catch (err) {
-    if (typeof console !== 'undefined') {
-      console.warn('[page-schema] failed to prune Page authoring form from spec', err);
-    }
-    _pageForm = specPageForm as FormViewSpec;
+  const clone = JSON.parse(JSON.stringify(specPageForm)) as FormViewSpec;
+  for (const section of clone.sections ?? []) {
+    section.fields = (section.fields ?? []).filter((f: any) => {
+      const name = typeof f === 'string' ? f : f?.field;
+      return !PAGE_FIELDS_OWNED_ELSEWHERE.has(name);
+    });
   }
+  clone.sections = (clone.sections ?? []).filter((s) => (s.fields ?? []).length > 0);
+  _pageForm = clone;
   return _pageForm;
 }
diff --git a/packages/app-shell/src/views/metadata-admin/report-schema.ts b/packages/app-shell/src/views/metadata-admin/report-schema.ts
index 6422915143..e9540bc9c8 100644
--- a/packages/app-shell/src/views/metadata-admin/report-schema.ts
+++ b/packages/app-shell/src/views/metadata-admin/report-schema.ts
@@ -38,20 +38,19 @@ const FORM_FIELDS_OWNED_ELSEWHERE = new Set([
   'name', // record identity — not user-editable here
 ]);
 
+/**
+ * No `try`/`catch` around the spec derivations in this file (objectui#13459).
+ * Their only input is the bundled `@objectstack/spec`, so a derivation that
+ * fails is a build-time fact: the tests beside this file go red, and at runtime
+ * the throw reaches the route's error boundary. It used to be caught, warned
+ * about in the console and turned into `undefined`, which rendered a designer
+ * form silently missing fields that the author could then save past.
+ */
 let _reportDocSchema: JsonSchema | undefined;
-let _reportDocFailed = false;
 
 /** JSONSchema for the whole (flat) Report document. */
-export function getReportSchema(): JsonSchema | undefined {
-  if (_reportDocSchema || _reportDocFailed) return _reportDocSchema;
-  try {
-    _reportDocSchema = z.toJSONSchema(ReportSchema, TO_JSON_OPTS) as JsonSchema;
-  } catch (err) {
-    _reportDocFailed = true;
-    if (typeof console !== 'undefined') {
-      console.warn('[report-schema] failed to derive Report JSONSchema from spec', err);
-    }
-  }
+export function getReportSchema(): JsonSchema {
+  _reportDocSchema ??= z.toJSONSchema(ReportSchema, TO_JSON_OPTS) as JsonSchema;
   return _reportDocSchema;
 }
 
@@ -80,48 +79,41 @@ let _reportForm: FormViewSpec | undefined;
 export function getReportForm(): FormViewSpec | undefined {
   if (_reportForm) return _reportForm;
   if (!specReportForm || typeof specReportForm !== 'object') return undefined;
-  try {
-    const clone = JSON.parse(JSON.stringify(specReportForm)) as FormViewSpec;
-    const schemaProps = getReportSchema()?.properties as Record<string, unknown> | undefined;
-    for (const section of clone.sections ?? []) {
-      section.fields = (section.fields ?? []).filter((f: any) => {
-        const name = typeof f === 'string' ? f : f?.field;
-        if (FORM_FIELDS_OWNED_ELSEWHERE.has(name)) return false;
-        // Schema-subset pass: drop form fields the schema no longer carries.
-        if (schemaProps && !(name in schemaProps)) return false;
-        return true;
-      });
-    }
-    if (schemaProps && 'runtimeFilter' in schemaProps) {
-      const declared = new Set<string>();
-      for (const s of clone.sections ?? []) {
-        for (const f of s.fields ?? []) {
-          declared.add(typeof f === 'string' ? f : (f as any)?.field);
-        }
-      }
-      if (!declared.has('runtimeFilter')) {
-        clone.sections = [
-          ...(clone.sections ?? []),
-          {
-            label: 'Filter',
-            description: 'Render-time scope filter, ANDed at query time.',
-            collapsible: true,
-            collapsed: true,
-            fields: [{ field: 'runtimeFilter', widget: 'json' }],
-          },
-        ];
+  const clone = JSON.parse(JSON.stringify(specReportForm)) as FormViewSpec;
+  const schemaProps = getReportSchema().properties as Record<string, unknown> | undefined;
+  for (const section of clone.sections ?? []) {
+    section.fields = (section.fields ?? []).filter((f: any) => {
+      const name = typeof f === 'string' ? f : f?.field;
+      if (FORM_FIELDS_OWNED_ELSEWHERE.has(name)) return false;
+      // Schema-subset pass: drop form fields the schema no longer carries.
+      if (schemaProps && !(name in schemaProps)) return false;
+      return true;
+    });
+  }
+  if (schemaProps && 'runtimeFilter' in schemaProps) {
+    const declared = new Set<string>();
+    for (const s of clone.sections ?? []) {
+      for (const f of s.fields ?? []) {
+        declared.add(typeof f === 'string' ? f : (f as any)?.field);
       }
     }
-    // Drop now-empty sections so we don't render bare headers.
-    clone.sections = (clone.sections ?? []).filter(
-      (s: any) => (s.fields ?? []).length > 0,
-    );
-    _reportForm = clone;
-  } catch (err) {
-    if (typeof console !== 'undefined') {
-      console.warn('[report-schema] failed to prepare reportForm from spec', err);
+    if (!declared.has('runtimeFilter')) {
+      clone.sections = [
+        ...(clone.sections ?? []),
+        {
+          label: 'Filter',
+          description: 'Render-time scope filter, ANDed at query time.',
+          collapsible: true,
+          collapsed: true,
+          fields: [{ field: 'runtimeFilter', widget: 'json' }],
+        },
+      ];
     }
-    return undefined;
   }
+  // Drop now-empty sections so we don't render bare headers.
+  clone.sections = (clone.sections ?? []).filter(
+    (s: any) => (s.fields ?? []).length > 0,
+  );
+  _reportForm = clone;
   return _reportForm;
 }
diff --git a/packages/app-shell/src/views/metadata-admin/spec-derivation-13459.test.ts b/packages/app-shell/src/views/metadata-admin/spec-derivation-13459.test.ts
new file mode 100644
index 0000000000..7f579c8c6d
--- /dev/null
+++ b/packages/app-shell/src/views/metadata-admin/spec-derivation-13459.test.ts
@@ -0,0 +1,73 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * objectui#13459 — the designer forms' spec derivations fail LOUDLY.
+ *
+ * The five `*-schema.ts` modules derive their JSONSchema from the bundled
+ * `@objectstack/spec`. That input is fixed at build time, so a derivation that
+ * fails is a build-time fact: this file goes red for it. At runtime the throw
+ * reaches the route's error boundary instead of being caught, warned about and
+ * turned into `undefined` — which used to render a designer form silently
+ * missing fields.
+ *
+ * Two halves: every derivation succeeds against the bundled spec, and a
+ * derivation that throws reaches the caller instead of becoming `undefined`.
+ */
+
+import { describe, it, expect, vi, afterEach } from 'vitest';
+
+const DERIVATIONS = [
+  ['dashboard-schema', 'getDashboardSchema'],
+  ['package-schema', 'getPackageSchema'],
+  ['page-schema', 'getPageSchema'],
+  ['report-schema', 'getReportSchema'],
+  ['view-schema', 'getListVariantSchema'],
+  ['view-schema', 'getFormVariantSchema'],
+  ['view-schema', 'getListColumnSchema'],
+] as const;
+
+const LOADERS: Record<(typeof DERIVATIONS)[number][0], () => Promise<unknown>> = {
+  'dashboard-schema': () => import('./dashboard-schema'),
+  'package-schema': () => import('./package-schema'),
+  'page-schema': () => import('./page-schema'),
+  'report-schema': () => import('./report-schema'),
+  'view-schema': () => import('./view-schema'),
+};
+
+/** A fresh module instance per case, so a memoised result cannot answer. */
+async function derive(file: (typeof DERIVATIONS)[number][0], getter: string): Promise<unknown> {
+  vi.resetModules();
+  const mod = (await LOADERS[file]()) as Record<string, () => unknown>;
+  return mod[getter]();
+}
+
+// `vi.doMock`, not a hoisted `vi.mock`: the failing `toJSONSchema` is scoped to
+// the cases that ask for it, and undone after each, so it cannot reach another
+// test file sharing this worker's module registry.
+afterEach(() => {
+  vi.doUnmock('zod');
+  vi.resetModules();
+});
+
+describe('designer spec derivations (objectui#13459)', () => {
+  it.each(DERIVATIONS)('%s.%s derives an object schema from the bundled spec', async (file, getter) => {
+    const schema = (await derive(file, getter)) as { type?: unknown; properties?: unknown } | undefined;
+    expect(schema).toBeDefined();
+    expect(schema?.type).toBe('object');
+    expect(schema?.properties).toBeTypeOf('object');
+  });
+
+  it.each(DERIVATIONS)('%s.%s throws when the derivation fails, never returns undefined', async (file, getter) => {
+    const warn = vi.spyOn(console, 'warn').mockImplementation(() => {});
+    vi.doMock('zod', async (importOriginal) => {
+      const actual = await importOriginal<typeof import('zod')>();
+      const toJSONSchema = (): never => {
+        throw new Error('derivation failed (test)');
+      };
+      return { ...actual, z: { ...actual.z, toJSONSchema } };
+    });
+    await expect(derive(file, getter)).rejects.toThrow('derivation failed (test)');
+    expect(warn).not.toHaveBeenCalled();
+    warn.mockRestore();
+  });
+});
diff --git a/packages/app-shell/src/views/metadata-admin/view-schema.ts b/packages/app-shell/src/views/metadata-admin/view-schema.ts
index df81623624..2ab90258e8 100644
--- a/packages/app-shell/src/views/metadata-admin/view-schema.ts
+++ b/packages/app-shell/src/views/metadata-admin/view-schema.ts
@@ -44,46 +44,36 @@ const FORM_FIELDS_OWNED_ELSEWHERE = new Set([
   'name', // record identity — not user-editable here
 ]);
 
+/**
+ * No `try`/`catch` around the spec derivations in this file (objectui#13459).
+ * Their only input is the bundled `@objectstack/spec`, so a derivation that
+ * fails is a build-time fact: the tests beside this file go red, and at runtime
+ * the throw reaches the route's error boundary. It used to be caught, warned
+ * about in the console and turned into `undefined`, which rendered a designer
+ * form silently missing fields that the author could then save past.
+ */
 let _viewDocSchema: JsonSchema | undefined;
-let _viewDocFailed = false;
 
-function viewDocSchema(): JsonSchema | undefined {
-  if (_viewDocSchema || _viewDocFailed) return _viewDocSchema;
-  try {
-    _viewDocSchema = z.toJSONSchema(ViewSchema, TO_JSON_OPTS) as JsonSchema;
-  } catch (err) {
-    _viewDocFailed = true;
-    if (typeof console !== 'undefined') {
-      console.warn('[view-schema] failed to derive View JSONSchema from spec', err);
-    }
-  }
+function viewDocSchema(): JsonSchema {
+  _viewDocSchema ??= z.toJSONSchema(ViewSchema, TO_JSON_OPTS) as JsonSchema;
   return _viewDocSchema;
 }
 
 /** JSONSchema for a single LIST-family view (grid/kanban/calendar/…). */
 export function getListVariantSchema(): JsonSchema | undefined {
-  return viewDocSchema()?.properties?.list;
+  return viewDocSchema().properties?.list;
 }
 
 /** JSONSchema for a single FORM-family view. */
 export function getFormVariantSchema(): JsonSchema | undefined {
-  return viewDocSchema()?.properties?.form;
+  return viewDocSchema().properties?.form;
 }
 
 let _listColumnSchema: JsonSchema | undefined;
-let _listColumnFailed = false;
 
 /** JSONSchema for a single list column (ListColumn). */
-export function getListColumnSchema(): JsonSchema | undefined {
-  if (_listColumnSchema || _listColumnFailed) return _listColumnSchema;
-  try {
-    _listColumnSchema = z.toJSONSchema(ListColumnSchema, TO_JSON_OPTS) as JsonSchema;
-  } catch (err) {
-    _listColumnFailed = true;
-    if (typeof console !== 'undefined') {
-      console.warn('[view-schema] failed to derive ListColumn JSONSchema from spec', err);
-    }
-  }
+export function getListColumnSchema(): JsonSchema {
+  _listColumnSchema ??= z.toJSONSchema(ListColumnSchema, TO_JSON_OPTS) as JsonSchema;
   return _listColumnSchema;
 }
 
@@ -98,24 +88,17 @@ let _viewForm: FormViewSpec | undefined;
 export function getViewForm(): FormViewSpec | undefined {
   if (_viewForm) return _viewForm;
   if (!specViewForm || typeof specViewForm !== 'object') return undefined;
-  try {
-    const clone = JSON.parse(JSON.stringify(specViewForm)) as FormViewSpec;
-    for (const section of clone.sections ?? []) {
-      section.fields = (section.fields ?? []).filter((f: any) => {
-        const name = typeof f === 'string' ? f : f?.field;
-        return !FORM_FIELDS_OWNED_ELSEWHERE.has(name);
-      });
-    }
-    // Drop now-empty sections so we don't render bare headers.
-    clone.sections = (clone.sections ?? []).filter(
-      (s: any) => (s.fields ?? []).length > 0,
-    );
-    _viewForm = clone;
-  } catch (err) {
-    if (typeof console !== 'undefined') {
-      console.warn('[view-schema] failed to prepare viewForm from spec', err);
-    }
-    return undefined;
+  const clone = JSON.parse(JSON.stringify(specViewForm)) as FormViewSpec;
+  for (const section of clone.sections ?? []) {
+    section.fields = (section.fields ?? []).filter((f: any) => {
+      const name = typeof f === 'string' ? f : f?.field;
+      return !FORM_FIELDS_OWNED_ELSEWHERE.has(name);
+    });
   }
+  // Drop now-empty sections so we don't render bare headers.
+  clone.sections = (clone.sections ?? []).filter(
+    (s: any) => (s.fields ?? []).length > 0,
+  );
+  _viewForm = clone;
   return _viewForm;
 }
diff --git a/packages/plugin-gantt/src/ObjectGantt.invalidBlockRefusal-13459.test.tsx b/packages/plugin-gantt/src/ObjectGantt.invalidBlockRefusal-13459.test.tsx
new file mode 100644
index 0000000000..562f83a58a
--- /dev/null
+++ b/packages/plugin-gantt/src/ObjectGantt.invalidBlockRefusal-13459.test.tsx
@@ -0,0 +1,102 @@
+/**
+ * ObjectUI
+ * Copyright (c) 2024-present ObjectStack Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+/**
+ * objectui#13459 — a `gantt` block that fails `GanttConfigSchema` is REFUSED,
+ * never drawn.
+ *
+ * Before this card the block's `safeParse` failure was a `console.warn`, and the
+ * unvalidated block was returned and rendered anyway: a misspelt key or a
+ * missing date field still drew a plausible chart, so the author never learnt
+ * the block was wrong. The refusal names each parse issue by its path inside
+ * the block.
+ *
+ * The CONTROL case pins the other direction: a valid block still renders, so a
+ * fix that refused every block would not pass this file.
+ */
+
+import React from 'react';
+import { describe, it, expect, vi, afterEach, beforeEach } from 'vitest';
+import { render, screen, waitFor, cleanup } from '@testing-library/react';
+import { ObjectGantt } from './ObjectGantt';
+
+vi.mock('./GanttView', () => ({
+  GanttView: ({ tasks }: any) => (
+    <div data-testid="gantt-view">
+      {tasks.map((t: any) => (
+        <div key={t.id} data-testid="gantt-task">{t.title}</div>
+      ))}
+    </div>
+  ),
+}));
+
+const ROWS = [
+  { id: 'r1', name: 'Ada onboarding', start_date: '2024-01-01', end_date: '2024-01-05' },
+];
+
+const inline = (gantt: Record<string, unknown>) =>
+  ({
+    type: 'object-gantt',
+    objectName: 'crm_leave_request',
+    gantt,
+    data: { provider: 'value', items: ROWS },
+  }) as any;
+
+let warn: ReturnType<typeof vi.spyOn>;
+beforeEach(() => {
+  warn = vi.spyOn(console, 'warn').mockImplementation(() => {});
+});
+afterEach(() => {
+  warn.mockRestore();
+  cleanup();
+});
+
+describe('ObjectGantt — an invalid `gantt` block is refused (objectui#13459)', () => {
+  it('REFUSES a block carrying a key the spec does not declare, and names it', async () => {
+    render(
+      <ObjectGantt
+        schema={inline({
+          startDateField: 'start_date',
+          endDateField: 'end_date',
+          titleField: 'name',
+          startField: 'start_date',
+        })}
+      />,
+    );
+    const refusal = await screen.findByTestId('gantt-invalid-config');
+    expect(refusal.getAttribute('role')).toBe('alert');
+    expect(refusal.textContent).toContain('Invalid gantt configuration');
+    expect(refusal.textContent).toContain('startField');
+    expect(screen.queryByTestId('gantt-view')).toBeNull();
+    expect(screen.queryByTestId('gantt-task')).toBeNull();
+  });
+
+  it('REFUSES a block missing a required field, naming its path in the block', async () => {
+    render(<ObjectGantt schema={inline({ startDateField: 'start_date', titleField: 'name' })} />);
+    const refusal = await screen.findByTestId('gantt-invalid-config');
+    expect(refusal.textContent).toContain('gantt.endDateField');
+    expect(screen.queryByTestId('gantt-view')).toBeNull();
+  });
+
+  it('keeps the console diagnostic beside the refusal', async () => {
+    render(<ObjectGantt schema={inline({ startDateField: 'start_date', titleField: 'name' })} />);
+    await screen.findByTestId('gantt-invalid-config');
+    expect(warn.mock.calls.some((c: unknown[]) => String(c[0]).includes('Invalid gantt configuration'))).toBe(true);
+  });
+
+  it('CONTROL: a valid block still renders its tasks, with no refusal', async () => {
+    render(
+      <ObjectGantt
+        schema={inline({ startDateField: 'start_date', endDateField: 'end_date', titleField: 'name' })}
+      />,
+    );
+    await waitFor(() => expect(screen.getByTestId('gantt-view')).toBeTruthy());
+    expect(screen.getByText('Ada onboarding')).toBeTruthy();
+    expect(screen.queryByTestId('gantt-invalid-config')).toBeNull();
+  });
+});
diff --git a/packages/plugin-gantt/src/ObjectGantt.tsx b/packages/plugin-gantt/src/ObjectGantt.tsx
index 51ab2a7840..c92aca31a9 100644
--- a/packages/plugin-gantt/src/ObjectGantt.tsx
+++ b/packages/plugin-gantt/src/ObjectGantt.tsx
@@ -604,21 +604,32 @@ function warnOnShadowedFlatGanttKeys(schema: ObjectGanttSchema): void {
  * and worth stating, because the map case cannot produce it: the spec's
  * `GanttConfigSchema` REQUIRES `startDateField` / `endDateField` / `titleField`
  * (`ObjectMapConfigSchema` requires nothing), so an INCOMPLETE block now
- * outranks a complete flat spelling and yields an incomplete config. Both
+ * outranks a complete flat spelling, and that block is REFUSED (below). Both
  * diagnostics fire on that node — `Invalid gantt configuration` from the
  * `safeParse` below, and the shadow warning naming the flat keys that lost.
+ *
+ * A block that fails `GanttConfigSchema` is refused, never drawn (objectui#13459).
+ * It used to be warned about in the console and then returned as-is, so a block
+ * with a misspelt or missing key still rendered something plausible and the
+ * author never learnt it was wrong. `invalidBlock` carries the parse issues to
+ * the refusal screen instead; `config` is `null` on that branch, so nothing
+ * downstream can read the unvalidated block. Same posture as `ObjectTimeline`'s
+ * refusal: the renderer says what is wrong rather than guessing what was meant.
  */
-function getGanttConfig(schema: ObjectGanttSchema): GanttConfigEx | null {
+function getGanttConfig(schema: ObjectGanttSchema): {
+  config: GanttConfigEx | null;
+  invalidBlock: readonly string[] | null;
+} {
   // 1. The `gantt` block (the ObjectGridSchema-style shape) — the authoring
   // face, and the winner whenever it is present.
   if (schema.gantt) {
-    const config = schema.gantt as GanttConfigEx;
-    const result = GanttConfigSchema.safeParse(config);
+    const result = GanttConfigSchema.safeParse(schema.gantt);
+    warnOnShadowedFlatGanttKeys(schema);
     if (!result.success) {
       console.warn(`[ObjectGantt] Invalid gantt configuration:`, result.error.format());
+      return { config: null, invalidBlock: describeGanttBlockIssues(result.error.issues) };
     }
-    warnOnShadowedFlatGanttKeys(schema);
-    return config;
+    return { config: schema.gantt as GanttConfigEx, invalidBlock: null };
   }
 
   // 2. The internal flat form — the ObjectView / ListView flatten product.
@@ -627,7 +638,7 @@ function getGanttConfig(schema: ObjectGanttSchema): GanttConfigEx | null {
   // `safeParse`d, also unchanged: this branch never validated, and adding
   // validation to it is a separate question from precedence.
   if (schema.startDateField && schema.endDateField) {
-      return {
+      const flat: GanttConfigEx = {
           startDateField: schema.startDateField,
           endDateField: schema.endDateField,
           titleField: schema.titleField || 'name',
@@ -658,9 +669,21 @@ function getGanttConfig(schema: ObjectGanttSchema): GanttConfigEx | null {
           timeZone: schema.timeZone,
           dependencyTypes: schema.dependencyTypes,
       };
+      return { config: flat, invalidBlock: null };
   }
 
-  return null;
+  return { config: null, invalidBlock: null };
+}
+
+/**
+ * One line per `GanttConfigSchema` issue, `path: message`, for the refusal
+ * screen. The path is spelled from the block (`gantt.quickFilters.0.field`) so
+ * the author can find the key; an issue on the block itself names `gantt`.
+ */
+function describeGanttBlockIssues(
+  issues: readonly { path: readonly PropertyKey[]; message: string }[],
+): string[] {
+  return issues.map((issue) => `${['gantt', ...issue.path.map(String)].join('.')}: ${issue.message}`);
 }
 
 export const ObjectGantt: React.FC<ObjectGanttProps> = ({
@@ -734,7 +757,7 @@ export const ObjectGantt: React.FC<ObjectGanttProps> = ({
     return rawDataConfig;
   }, [dataConfigKey]);
 
-  const ganttConfig = getGanttConfig(schema);
+  const { config: ganttConfig, invalidBlock: invalidGanttBlock } = getGanttConfig(schema);
   const dataProvider = dataConfig?.provider;
   const hasInlineData = dataProvider === 'value';
   /*
@@ -2317,6 +2340,21 @@ export const ObjectGantt: React.FC<ObjectGanttProps> = ({
     );
   }
 
+  if (invalidGanttBlock) {
+    return (
+      <div className={className}>
+        <div className="flex items-center justify-center h-96">
+          {/* English, like the "configuration required" refusal below: both
+              address the view's author, not the end user. */}
+          <div className="text-destructive" role="alert" data-testid="gantt-invalid-config">
+            Invalid gantt configuration — the `gantt` block does not match the spec, so the
+            chart is not drawn. Fix: {invalidGanttBlock.join('; ')}
+          </div>
+        </div>
+      </div>
+    );
+  }
+
   if (!ganttConfig) {
     return (
       <div className={className}>