diff --git a/.changeset/dashboard-widget-strict-3251.md b/.changeset/dashboard-widget-strict-3251.md
new file mode 100644
index 0000000000..b0f0858f76
--- /dev/null
+++ b/.changeset/dashboard-widget-strict-3251.md
@@ -0,0 +1,36 @@
+---
+"@objectstack/spec": minor
+"@objectstack/lint": patch
+---
+
+feat(spec)!: `DashboardWidgetSchema.strict()` — reject undeclared widget keys (framework#3251)
+
+The ADR-0021 analytics endpoint. `DashboardWidgetSchema` now rejects any
+undeclared top-level key instead of silently stripping it, moving a whole class
+of author error (a hallucinated or legacy key that renders as a silent no-op)
+from fallible human review to deterministic CI. `options: z.unknown()` remains
+the escape hatch for renderer-specific extras.
+
+A custom error map names the offending key(s) and, when a key is a removed
+pre-ADR-0021 inline-analytics key (`object` / `categoryField` / `valueField` /
+`aggregate`, pivot `rowField` / `columnField`) or an objectui-internal prop
+(`component`, inline `data`), points the author at the dataset shape
+(`dataset` + `dimensions` + `values`).
+
+Recorded as protocol-16 migration `step16`
+(`dashboard-widget-strict-unknown-keys`), mirroring protocol-15's `step15`
+strict flip on the form/page schemas (ADR-0089 D3a). The inline-analytics shape
+itself was already removed at protocol 9 (single-form cutover), so there is no
+mechanical rewrite — the residue is the strictness, delegated to the author.
+
+**Breaking:** shipped as `minor` per the launch-window policy (a breaking change
+does not burn a major while the stack is in lockstep), riding the already-pending
+16.0.0 train. The release train's Version-Packages PR must set
+`PROTOCOL_VERSION = '16.0.0'`; until then `step16` is inert
+(`composeMigrationChain` caps at `PROTOCOL_MAJOR`).
+
+`@objectstack/lint` — the `widget-legacy-analytics-shape` /
+`widget-legacy-analytics-unrenderable` rules are retained as the friendly,
+suppressible bridge on the raw-config lint/doctor paths (strict preempts them on
+the schema-parsed compile/validate paths); doc comment updated to explain the
+interplay.
diff --git a/packages/lint/src/validate-widget-bindings.ts b/packages/lint/src/validate-widget-bindings.ts
index 992ea09c36..8f9f1401da 100644
--- a/packages/lint/src/validate-widget-bindings.ts
+++ b/packages/lint/src/validate-widget-bindings.ts
@@ -81,6 +81,14 @@ export const WIDGET_LEGACY_ANALYTICS_UNRENDERABLE = 'widget-legacy-analytics-unr
  * errored) because they still parse and a legacy object-bound widget keeps
  * rendering — the author is just being steered to the governed shape.
  * (liveness audit #1878 / #1894).
+ *
+ * Interplay with `DashboardWidgetSchema.strict()` (framework#3251, protocol 16):
+ * on the schema-parsed CLI paths (`compile`, `validate`) strict rejects these
+ * keys as a hard parse error *before* binding validation runs, so these rules
+ * are effectively preempted there. They remain the friendly, suppressible
+ * bridge on the raw-config paths (`lint`, `doctor`) that hand
+ * `validateWidgetBindings` un-parsed config — keeping the actionable
+ * "steer to the dataset shape" message rather than a bare unknown-key error.
  */
 const LEGACY_ANALYTICS_KEYS = [
   'categoryField', 'valueField', 'xAxisField', 'yAxisFields',
diff --git a/packages/spec/src/migrations/registry.ts b/packages/spec/src/migrations/registry.ts
index f6d4f9c680..7beb2f525d 100644
--- a/packages/spec/src/migrations/registry.ts
+++ b/packages/spec/src/migrations/registry.ts
@@ -277,6 +277,51 @@ const step15: MigrationStep = {
   ],
 };
 
+/**
+ * Protocol 16 step.
+ *
+ * Mechanical: none — the pre-ADR-0021 inline analytics shape
+ * (`object`+`categoryField`+`valueField`+`aggregate`, pivot
+ * `rowField`/`columnField`) was already removed at protocol 9 (the single-form
+ * cutover), below the chain floor, so there is no key to rewrite. Semantic: the
+ * `.strict()` flip on `DashboardWidgetSchema` (framework#3251) turns a
+ * previously silently-stripped undeclared widget key into a parse error — a
+ * class of error that must move from fallible human review to deterministic CI,
+ * with no lossless auto-target for an arbitrary unknown key.
+ */
+const step16: MigrationStep = {
+  toMajor: 16,
+  rationale:
+    'Protocol 16 flipped `DashboardWidgetSchema` to `.strict()` (framework#3251, ' +
+    'ADR-0021 endpoint): an undeclared top-level widget key is now a loud parse ' +
+    'error instead of a silent strip (ADR-0049 enforce-or-remove, ADR-0078 ' +
+    'no-silently-inert). The inline analytics shape it most often catches ' +
+    '(`object`+`categoryField`+`valueField`+`aggregate`, pivot ' +
+    '`rowField`/`columnField`) was already removed at protocol 9, so no mechanical ' +
+    'rewrite applies; the residue is the strictness itself, delegated to the author ' +
+    'because an arbitrary unknown key has no lossless canonical target.',
+  conversionIds: [],
+  semantic: [
+    {
+      id: 'dashboard-widget-strict-unknown-keys',
+      surface: 'dashboard widgets (undeclared top-level keys — legacy inline ' +
+        'analytics, objectui-internal `component`/`data`, or typos)',
+      replacement: 'declared keys only (`dataset` + `dimensions` + `values` for ' +
+        'analytics; `options` for renderer-specific extras)',
+      reason:
+        'The `.strict()` flip turns a previously silently-stripped unknown key into a ' +
+        'parse error. There is no mapping target for an arbitrary unknown key — ' +
+        'auto-deleting it would be exactly the silent data loss ADR-0078 bans — so ' +
+        'each occurrence needs the author to decide: bind a `dataset` and select ' +
+        '`dimensions`/`values`, move a renderer setting under `options`, or delete ' +
+        'the dead key.',
+      acceptanceCriteria:
+        '`objectstack validate` passes with no unknown-key parse errors on dashboard ' +
+        'widgets.',
+    },
+  ],
+};
+
 /** All migration steps, keyed by the major they migrate into. */
 export const MIGRATIONS_BY_MAJOR: Readonly<Record<number, MigrationStep>> = {
   11: step11,
@@ -284,6 +329,7 @@ export const MIGRATIONS_BY_MAJOR: Readonly<Record<number, MigrationStep>> = {
   13: step13,
   14: step14,
   15: step15,
+  16: step16,
 };
 
 /** The majors that have a step, ascending. */
diff --git a/packages/spec/src/ui/dashboard.test.ts b/packages/spec/src/ui/dashboard.test.ts
index b9d497432b..ac2233f3ad 100644
--- a/packages/spec/src/ui/dashboard.test.ts
+++ b/packages/spec/src/ui/dashboard.test.ts
@@ -67,10 +67,50 @@ describe('DashboardWidgetSchema (dataset-bound)', () => {
     expect(() => DashboardWidgetSchema.parse({ id: 'x', type: 'metric', dataset: 'sales', values: [], layout: { x: 0, y: 0, w: 3, h: 2 } })).toThrow();
   });
 
-  it('a widget supplying only the removed inline fields is invalid (no dataset)', () => {
+  it('a widget supplying only the removed inline fields is invalid (missing dataset AND unknown keys)', () => {
+    // Fails twice over now: no `dataset`/`values`, and under `.strict()` the
+    // legacy `object`/`aggregate` keys are unrecognized.
     expect(() => DashboardWidgetSchema.parse({ id: 'x', type: 'metric', object: 'opportunity', aggregate: 'count', layout: { x: 0, y: 0, w: 3, h: 2 } } as any)).toThrow();
   });
 
+  // ── .strict() endpoint (framework#3251, protocol 16 step16) ──────────────
+  it('rejects an otherwise-valid widget carrying a legacy analytics key, and points at the dataset shape', () => {
+    const legacy = { id: 'w_legacy', type: 'bar', dataset: 'sales', values: ['revenue'], categoryField: 'stage' } as any;
+    const res = DashboardWidgetSchema.safeParse(legacy);
+    expect(res.success).toBe(false);
+    if (!res.success) {
+      const unknown = res.error.issues.find((i) => i.code === 'unrecognized_keys');
+      expect(unknown).toBeDefined();
+      const msg = unknown!.message;
+      expect(msg).toContain('categoryField');
+      expect(msg).toContain('dataset');
+    }
+  });
+
+  it('rejects the objectui-internal `component` / inline `data` keys', () => {
+    expect(() => DashboardWidgetSchema.parse({ id: 'w_comp', type: 'metric', dataset: 'sales', values: ['revenue'], component: {} } as any)).toThrow();
+    const res = DashboardWidgetSchema.safeParse({ id: 'w_data', type: 'metric', dataset: 'sales', values: ['revenue'], data: [] } as any);
+    expect(res.success).toBe(false);
+    if (!res.success) {
+      const unknown = res.error.issues.find((i) => i.code === 'unrecognized_keys');
+      expect(unknown!.message).toContain('objectui-internal');
+    }
+  });
+
+  it('rejects an unknown/typo top-level key and names it in the error', () => {
+    const res = DashboardWidgetSchema.safeParse({ id: 'w_typo', type: 'metric', dataset: 'sales', values: ['revenue'], colourVariant: 'blue' } as any);
+    expect(res.success).toBe(false);
+    if (!res.success) expect(JSON.stringify(res.error.issues)).toContain('colourVariant');
+  });
+
+  it('keeps `options` as the free-form renderer-extras escape hatch', () => {
+    const w = DashboardWidgetSchema.parse({
+      id: 'w_opts', type: 'bar', dataset: 'sales', values: ['revenue'],
+      options: { stacked: true, palette: ['#111', '#222'], drillDown: { enabled: true } },
+    });
+    expect((w.options as any).stacked).toBe(true);
+  });
+
   it('keeps the runtime capability gates', () => {
     const w = DashboardWidgetSchema.parse({
       id: 'gated', type: 'metric', dataset: 'sys', values: ['cnt'],
diff --git a/packages/spec/src/ui/dashboard.zod.ts b/packages/spec/src/ui/dashboard.zod.ts
index 8dfaa60629..3cae90aab5 100644
--- a/packages/spec/src/ui/dashboard.zod.ts
+++ b/packages/spec/src/ui/dashboard.zod.ts
@@ -68,6 +68,60 @@ export const DashboardHeaderSchema = lazySchema(() => z.object({
   actions: z.array(DashboardHeaderActionSchema).optional().describe('Header action buttons'),
 }).describe('Dashboard header configuration'));
 
+/**
+ * Legacy / quarantined widget keys that `.strict()` now rejects. Naming them
+ * lets the error map hand the author a fixable message instead of a bare
+ * "unrecognized key". Two families:
+ *
+ * - **Pre-ADR-0021 inline analytics** (`object`/`categoryField`/`valueField`/
+ *   `aggregate`/`rowField`/`columnField`/…): removed from the authorable spec at
+ *   `@objectstack/spec` 9.0.0 (the single-form cutover). Bind a `dataset` and
+ *   select `dimensions`/`values` instead.
+ * - **objectui-internal props** (`component`, inline `data`): renderer-only
+ *   capabilities that are intentionally not modeled server-side (framework#3251
+ *   decision tree) — they must not appear on AI-authored dashboard metadata.
+ */
+const LEGACY_WIDGET_ANALYTICS_KEYS = new Set([
+  'object', 'categoryField', 'categoryGranularity', 'valueField', 'aggregate',
+  'aggregation', 'rowField', 'columnField', 'xAxisField', 'yAxisFields', 'measures',
+]);
+const QUARANTINED_WIDGET_KEYS = new Set(['component', 'data']);
+
+/**
+ * Error map for the strict `DashboardWidgetSchema`. Turns an
+ * `unrecognized_keys` rejection into a *fixable* message: it always names the
+ * offending key(s), and when a key is a removed inline-analytics key or an
+ * objectui-internal prop it points the author at the ADR-0021 dataset shape
+ * (and `options` for renderer-specific extras). Mirrors `strictVisibilityError`
+ * (ADR-0089 D3a); every other issue code defers to zod's default.
+ */
+const strictWidgetAnalyticsError: z.core.$ZodErrorMap = (issue) => {
+  if (issue.code !== 'unrecognized_keys') return undefined;
+  const keys = (issue as { keys?: readonly string[] }).keys ?? [];
+  const list = keys.map((k) => `\`${k}\``).join(', ');
+  const base =
+    `Unrecognized key(s) on this dashboard widget: ${list}. ` +
+    `Undeclared top-level keys were dropped silently before strict validation, ` +
+    `shipping inert metadata; a stale or mis-layered key is now a loud parse error.`;
+  if (keys.some((k) => LEGACY_WIDGET_ANALYTICS_KEYS.has(k))) {
+    return (
+      base +
+      ' The pre-ADR-0021 inline analytics shape (`object` + `categoryField` + ' +
+      '`valueField` + `aggregate`, pivot `rowField`/`columnField`) was removed — ' +
+      'bind a `dataset` and select `dimensions` + `values` by name. Renderer-only ' +
+      'settings belong under `options`.'
+    );
+  }
+  if (keys.some((k) => QUARANTINED_WIDGET_KEYS.has(k))) {
+    return (
+      base +
+      ' `component` and inline `data` are objectui-internal renderer capabilities, ' +
+      'not part of the author-facing dashboard spec (framework#3251).'
+    );
+  }
+  return base;
+};
+
 /**
  * Dashboard Widget Schema
  * A single component on the dashboard grid.
@@ -210,7 +264,13 @@ export const DashboardWidgetSchema = lazySchema(() => z.object({
   aria: AriaPropsSchema.optional().describe('ARIA accessibility attributes'),
   // ADR-0021 single-form: every widget binds a `dataset` and selects `values`
   // (both required above) — there is no inline-query shape to disambiguate.
-}));
+}, { error: strictWidgetAnalyticsError })
+  // ADR-0021 endpoint (framework#3251, protocol 16 `step16`): reject undeclared
+  // top-level keys instead of silently stripping them. A hallucinated or legacy
+  // key is now a deterministic author-time error (CI) rather than a silent
+  // no-op a human reviewer would miss. `options` stays the free-form escape
+  // hatch for renderer-specific extras.
+  .strict());
 
 /**
  * Dynamic options binding for global filters.