@@ -0,0 +1,19 @@
+---
+'@objectstack/metadata-protocol': patch
+---
+
+fix(metadata-protocol)!: `GET /api/v1/meta/:type/:name/diff` refuses a `from` or `to` version that has no history row with 404 `VERSION_NOT_FOUND`, as the rollback door already does, instead of answering 200 "no change" or "everything removed"
+
+Clause-②: no (narrowing) — `diffMetaItem` (and the REST `/diff` door that forwards to it) refuses a named version with no history row of the item, which it answered 200 before. The default range and every version that has a row answer exactly as before.
+Metadata-protocol: none
+
+<!-- adr-0087: not-required (no-migration-prescription) A read door's answer to a version that does not exist: no key of any metadata schema is added, removed, renamed or re-shaped, no export or type changes, and the refusal is the existing VERSION_NOT_FOUND code the rollback door answers. There is nothing for `objectstack migrate meta` to rewrite and no tombstone. -->
+
+**BREAKING** accept-set narrowing at `diffMetaItem` (`@objectstack/metadata-protocol`), served by `GET /api/v1/meta/:type/:name/diff`.
+
+- **Before.** A `from` or `to` version the item has no history row at was compared as an empty document. `?from=998&to=999` answered 200 with nothing added, removed or changed, which reads as "these versions are identical". `?from=1&to=999` answered 200 with every top-level key of version 1 under `removed`, which reads as "the item was deleted". An item that never existed answered 200 "no change". The rollback door refused the same numbers with 404.
+- **Now.** A named `from` or `to` with no history row of the item is refused 404 `VERSION_NOT_FOUND`, with the rollback door's own sentence: `No history row at version N for TYPE/NAME.` An item with no history at all is refused the same way. A version number that exists only in another item's history is this item's miss, refused the same way; it was never read from the other item.
+- **Unchanged.** The default range (no `from` / `to`) answers as before, for every item, including one with no history. A version that has a row answers as before, a delete tombstone included (compared as an empty side). A history read failure is still the 503 `SERVICE_UNAVAILABLE`, and a deployment that never provisioned the history table still gets the empty default diff.
+- **Who sees it.** A caller who names a version that does not exist, for example a mistyped or pruned number, or `from=0` used to mean "before the first version". It now gets 404 instead of a 200 that described a change that did not happen.
+
+**The remedy.** Name versions from `GET /api/v1/meta/:type/:name/history`. To compare a version against nothing, omit `from` on an item's first version: the default from side is absent when no earlier version differs.
@@ -278,8 +278,12 @@ describe('#8868 — diffMetaItem folds its type at the request boundary', () =>
     it('does NOT refuse a spelling that reaches for no declared type — the refusal stays narrow', async () => {
         // A plugin-registered runtime kind must never be refused by a static
         // rule. `fieldz` is not a plural of anything declared, so the boundary
-        // is silent and the request is served (with no rows, truthfully).
-        const { engine } = makeStubEngine();
+        // is silent and the request is served.
+        // [#26462] Served from rows of its own: with none, the two named
+        // versions are a 404 `VERSION_NOT_FOUND` miss, which a weakened
+        // assertion here could not tell from a boundary refusal.
+        const { engine, tables } = makeStubEngine();
+        seedTwoVersions(tables, PLUGIN_SHAPED_SPELLING, 'x');
         const protocol = new ObjectStackProtocolImplementation(engine);
 
         const res: any = await protocol.diffMetaItem({
@@ -290,7 +294,7 @@ describe('#8868 — diffMetaItem folds its type at the request boundary', () =>
         });
 
         expect(res.type).toBe(PLUGIN_SHAPED_SPELLING);
-        expect(res.changed).toEqual([]);
+        expect(res).toMatchObject(REAL_DIFF_BODY);
     });
 });
 
@@ -320,20 +324,28 @@ describe('#8833 — a history-store outage stops masquerading as an empty diff',
         // SELECTIVE rather than a blanket "any failure 503s" — which would
         // break first boot on a minimal deployment that never provisioned
         // `sys_metadata_history`.
+        //
+        // [#26462] What "benign" answers moved, not the discrimination: with no
+        // history rows, a NAMED version is a miss — 404 `VERSION_NOT_FOUND`,
+        // the rollback door's refusal, as for any item with no history — and
+        // the default range is the empty diff. Neither is the 503.
         const { engine } = makeStubEngine({ historyError: MISSING_TABLE_ERROR });
         const protocol = new ObjectStackProtocolImplementation(engine);
 
-        const res: any = await protocol.diffMetaItem({
-            type: PRESENT_TYPE,
-            name: 'grid',
-            fromVersion: 1,
-            toVersion: 2,
-        });
+        const res: any = await protocol.diffMetaItem({ type: PRESENT_TYPE, name: 'grid' });
 
         expect(res.added).toEqual([]);
         expect(res.removed).toEqual([]);
         expect(res.changed).toEqual([]);
         expect(res.type).toBe(PRESENT_TYPE);
+
+        const err: any = await protocol
+            .diffMetaItem({ type: PRESENT_TYPE, name: 'grid', fromVersion: 1, toVersion: 2 })
+            .then(() => null, (e: unknown) => e);
+
+        expect(err).toBeInstanceOf(Error);
+        expect(err.code).toBe('VERSION_NOT_FOUND');
+        expect(err.status).toBe(404);
     });
 
     it('the 503 does not depend on the type — gated-shut types propagate identically', async () => {
 
@@ -0,0 +1,281 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * #26462 — `diffMetaItem` answered a version the item has no history row at
+ * as an EMPTY side, with a 200: `?from=998&to=999` read as "no change",
+ * `?from=1&to=999` as "everything removed", and an item that never existed as
+ * "no change". ADR-0110 D3 rules that kind of answer out — a miss must never
+ * read as a fact about the document — and the rollback door on the same item
+ * already refuses the same number 404 `VERSION_NOT_FOUND`.
+ *
+ * The refusal is the rollback door's own ({@link versionNotFoundError}), so
+ * both doors name a missing version in one sentence; the parity arm below
+ * pins that by comparing the two answers, not by pinning the prose.
+ *
+ * What stays served, and is pinned here as the controls:
+ *  - a named version that HAS a row, including a delete tombstone (a body-less
+ *    row is a real version: the item did not exist there);
+ *  - the default range (no `from` / `to`, #20397 / #20451), for any item.
+ */
+import { describe, expect, it } from 'vitest';
+import { assertEngineDeleteDispatch, assertEngineUpdateDispatch, hashSpec, assertEngineFindOnePredicate } from '@objectstack/metadata-core';
+import { ObjectStackProtocolImplementation } from './index.js';
+import { SysMetadataRepository } from './sys-metadata-repository.js';
+
+const TYPE = 'dashboard';
+const NAME = 'qa_diff_probe';
+
+/**
+ * Scalar equality only, and it REFUSES a combinator rather than guessing —
+ * `check:where-matcher` shape (b): treating `$or` as a column name silently
+ * excludes rows and greens the suite against a query nobody wrote.
+ */
+function matches(r: Record<string, unknown>, where: Record<string, unknown>): boolean {
+    for (const [k, v] of Object.entries(where)) {
+        if (k.startsWith('$')) {
+            throw new Error(
+                `stub engine: WHERE combinator '${k}' is not implemented by this double — `
+                + 'it matches scalar equality only. Implement it here rather than letting it '
+                + 'be read as a field name.',
+            );
+        }
+        if (v === undefined) continue;
+        if (r[k] !== v) return false;
+    }
+    return true;
+}
+
+function makeStubEngine() {
+    const tables: Record<string, Array<Record<string, unknown>>> = {
+        sys_metadata: [],
+        sys_metadata_history: [],
+    };
+    const engine: any = {
+        async find(table: string, o: { where: Record<string, unknown>; limit?: number }) {
+            const rows = (tables[table] ?? []).filter((r) => matches(r, o.where));
+            return typeof o?.limit === 'number' ? rows.slice(0, o.limit) : rows;
+        },
+        async findOne(table: string, o: { where: Record<string, unknown> }) {
+            assertEngineFindOnePredicate(table, o);
+            return (tables[table] ?? []).find((r) => matches(r, o.where)) ?? null;
+        },
+        async insert() { return { id: 'stub' }; },
+        async update(_t: string, data: Record<string, unknown>, o: { where: Record<string, unknown> }) {
+            assertEngineUpdateDispatch(data, o);
+            return { id: null };
+        },
+        async delete(_t: string, o?: Record<string, unknown>) {
+            assertEngineDeleteDispatch(o);
+            return { deleted: 0 };
+        },
+        async transaction<T>(cb: (ctx: any, info: { owned: boolean }) => Promise<T>): Promise<T> {
+            return cb(undefined, { owned: true });
+        },
+        async syncObjectSchema() { /* no DDL in this stub */ },
+        registry: {
+            listItems: () => [],
+            isPackageDisabled: () => false,
+            getItem: () => undefined,
+            registerItem: () => {},
+            registerObject: () => {},
+            getPackage: () => undefined,
+        },
+    };
+    return { engine, tables };
+}
+
+/**
+ * The card's reproduction, steps 1–2: v1 and v2 of one item, differing only in
+ * `label`, and v2 live. `bodies` overrides the default pair; a `null` body is
+ * a delete tombstone.
+ */
+function seedHistory(
+    tables: Record<string, Array<Record<string, unknown>>>,
+    name: string,
+    bodies: Array<Record<string, unknown> | null> = [
+        { name, label: 'QA Diff', widgets: [] },
+        { name, label: 'QA Diff v2', widgets: [] },
+    ],
+) {
+    const base = { organization_id: null, type: TYPE, name };
+    bodies.forEach((body, i) => {
+        tables.sys_metadata_history!.push({
+            ...base,
+            id: `h_${name}_${i + 1}`,
+            version: i + 1,
+            event_seq: i + 1,
+            operation_type: body === null ? 'delete' : i === 0 ? 'create' : 'update',
+            metadata: body === null ? null : JSON.stringify(body),
+            checksum: body === null ? null : hashSpec(body),
+            recorded_at: new Date(i + 1).toISOString(),
+        });
+    });
+    const live = bodies[bodies.length - 1];
+    if (live) {
+        tables.sys_metadata!.push({
+            ...base,
+            id: `m_${name}`,
+            state: 'active',
+            version: bodies.length,
+            metadata: JSON.stringify(live),
+        });
+    }
+}
+
+/** The refusal, or `null` when the call answered. */
+async function refusalOf(p: Promise<unknown>): Promise<any> {
+    return p.then(() => null, (e: unknown) => e);
+}
+
+function expectVersionNotFound(err: any, version: number) {
+    // ADR-0112 envelope — code AND status; `.toThrow()` alone stays green on
+    // a bare `Error`.
+    expect(err).toBeInstanceOf(Error);
+    expect(err.code).toBe('VERSION_NOT_FOUND');
+    expect(err.status).toBe(404);
+    // Names the missing version, as the card's expected answer asks.
+    expect(err.message).toContain(`version ${version} `);
+}
+
+describe('#26462 — an explicitly named version with no history row is refused 404 VERSION_NOT_FOUND', () => {
+    it('step 3, the control: two versions that exist answer their diff', async () => {
+        const { engine, tables } = makeStubEngine();
+        seedHistory(tables, NAME);
+        const protocol = new ObjectStackProtocolImplementation(engine);
+
+        const res: any = await protocol.diffMetaItem({ type: TYPE, name: NAME, fromVersion: 1, toVersion: 2 });
+
+        expect(res.fromVersion).toBe(1);
+        expect(res.toVersion).toBe(2);
+        expect(res.changed).toEqual([{ path: 'label', from: 'QA Diff', to: 'QA Diff v2' }]);
+        expect(res.added).toEqual([]);
+        expect(res.removed).toEqual([]);
+    });
+
+    it('step 4: both versions missing — refused, not "no change"', async () => {
+        const { engine, tables } = makeStubEngine();
+        seedHistory(tables, NAME);
+        const protocol = new ObjectStackProtocolImplementation(engine);
+
+        const err = await refusalOf(protocol.diffMetaItem({ type: TYPE, name: NAME, fromVersion: 998, toVersion: 999 }));
+
+        expect(err).not.toBeNull();
+        expect(err.code).toBe('VERSION_NOT_FOUND');
+        expect(err.status).toBe(404);
+    });
+
+    it('step 5: the to side missing — refused, not "everything removed"', async () => {
+        const { engine, tables } = makeStubEngine();
+        seedHistory(tables, NAME);
+        const protocol = new ObjectStackProtocolImplementation(engine);
+
+        const err = await refusalOf(protocol.diffMetaItem({ type: TYPE, name: NAME, fromVersion: 1, toVersion: 999 }));
+
+        expectVersionNotFound(err, 999);
+    });
+
+    it('the from side missing — refused, not "everything added"', async () => {
+        const { engine, tables } = makeStubEngine();
+        seedHistory(tables, NAME);
+        const protocol = new ObjectStackProtocolImplementation(engine);
+
+        const err = await refusalOf(protocol.diffMetaItem({ type: TYPE, name: NAME, fromVersion: 999, toVersion: 2 }));
+
+        expectVersionNotFound(err, 999);
+    });
+
+    it('one side named and missing, the other defaulted — refused on either side', async () => {
+        const { engine, tables } = makeStubEngine();
+        seedHistory(tables, NAME);
+        const protocol = new ObjectStackProtocolImplementation(engine);
+
+        expectVersionNotFound(await refusalOf(protocol.diffMetaItem({ type: TYPE, name: NAME, toVersion: 999 })), 999);
+        expectVersionNotFound(await refusalOf(protocol.diffMetaItem({ type: TYPE, name: NAME, fromVersion: 999 })), 999);
+    });
+
+    it('step 6: an item that never existed — refused, not "no change"', async () => {
+        const { engine, tables } = makeStubEngine();
+        seedHistory(tables, NAME);
+        const protocol = new ObjectStackProtocolImplementation(engine);
+
+        const err = await refusalOf(protocol.diffMetaItem({ type: TYPE, name: 'qa_no_such_xyz', fromVersion: 1, toVersion: 2 }));
+
+        expect(err).not.toBeNull();
+        expect(err.code).toBe('VERSION_NOT_FOUND');
+        expect(err.status).toBe(404);
+        expect(err.message).toContain(`${TYPE}/qa_no_such_xyz`);
+    });
+
+    it('a version number from ANOTHER item\'s history is this item\'s miss — refused, never that item\'s body', async () => {
+        // The card's open question. `other` has a v3; `NAME` stops at v2. The
+        // history read is keyed by (type, name), so `other`'s v3 is never a
+        // candidate: before the fix this answered `NAME`'s v1 against an
+        // EMPTY side (everything removed), not against `other`'s body.
+        const { engine, tables } = makeStubEngine();
+        seedHistory(tables, NAME);
+        seedHistory(tables, 'other', [
+            { name: 'other', label: 'O1', secret_marker: 'x' },
+            { name: 'other', label: 'O2', secret_marker: 'x' },
+            { name: 'other', label: 'O3', secret_marker: 'x' },
+        ]);
+        const protocol = new ObjectStackProtocolImplementation(engine);
+
+        const err = await refusalOf(protocol.diffMetaItem({ type: TYPE, name: NAME, fromVersion: 1, toVersion: 3 }));
+
+        expectVersionNotFound(err, 3);
+        expect(err.message).toContain(`${TYPE}/${NAME}`);
+        expect(err.message).not.toContain('other');
+    });
+
+    it('the refusal is the rollback door\'s, sentence for sentence', async () => {
+        const { engine, tables } = makeStubEngine();
+        seedHistory(tables, NAME);
+        const protocol = new ObjectStackProtocolImplementation(engine);
+        const repo = new SysMetadataRepository({ engine });
+
+        const diffErr = await refusalOf(protocol.diffMetaItem({ type: TYPE, name: NAME, fromVersion: 1, toVersion: 999 }));
+        const rollbackErr = await refusalOf(repo.restoreVersion({ org: 'system', type: TYPE, name: NAME }, 999, { actor: null }));
+
+        expect(rollbackErr).not.toBeNull();
+        expect(diffErr).not.toBeNull();
+        expect({ code: diffErr.code, status: diffErr.status, message: diffErr.message })
+            .toEqual({ code: rollbackErr.code, status: rollbackErr.status, message: rollbackErr.message });
+    });
+});
+
+describe('#26462 — what stays served', () => {
+    it('a delete tombstone is a real version: diffed as an empty side, not refused', async () => {
+        const { engine, tables } = makeStubEngine();
+        seedHistory(tables, NAME, [
+            { name: NAME, label: 'QA Diff', widgets: [] },
+            null,
+        ]);
+        const protocol = new ObjectStackProtocolImplementation(engine);
+
+        const res: any = await protocol.diffMetaItem({ type: TYPE, name: NAME, fromVersion: 1, toVersion: 2 });
+
+        expect(res.toVersion).toBe(2);
+        expect(res.removed.map((e: any) => e.path).sort()).toEqual(['label', 'name', 'widgets']);
+    });
+
+    it('the default range of an item with history is unchanged', async () => {
+        const { engine, tables } = makeStubEngine();
+        seedHistory(tables, NAME);
+        const protocol = new ObjectStackProtocolImplementation(engine);
+
+        const res: any = await protocol.diffMetaItem({ type: TYPE, name: NAME });
+
+        expect(res.fromVersion).toBe(1);
+        expect(res.toVersion).toBe(2);
+        expect(res.changed).toEqual([{ path: 'label', from: 'QA Diff', to: 'QA Diff v2' }]);
+    });
+
+    it('the default range of an item with no history is unchanged: both sides absent, nothing refused', async () => {
+        const { engine } = makeStubEngine();
+        const protocol = new ObjectStackProtocolImplementation(engine);
+
+        const res: any = await protocol.diffMetaItem({ type: TYPE, name: 'qa_no_such_xyz' });
+
+        expect(res).toMatchObject({ fromVersion: null, toVersion: null, added: [], removed: [], changed: [] });
+    });
+});