@@ -0,0 +1,13 @@
+---
+'@objectstack/metadata-protocol': patch
+'@objectstack/runtime': patch
+---
+
+perf(metadata-protocol,runtime): served metadata lists parse each unchanged document once, and the dispatcher's `/meta/app` reads objects on the execution face
+
+Clause-②: no
+Metadata-protocol: none
+
+- **Diagnostics verdicts are memoized.** `computeMetadataDiagnostics` remembers a verdict per schema object and per document content (a SHA-256 of an encoding that keeps apart everything the parse keeps apart), so a served list of unchanged documents parses each one once instead of on every read. A replaced type schema starts from nothing, each caller gets its own copy, and a document with no faithful key is parsed every time as before. The served bytes are unchanged. Measured on the showcase app (108 objects, local, main-thread CPU per request): `GET /meta/object` 85.75 ms → 37 ms.
+- **The dispatcher's `/meta/app`** (the `${prefix}/*` catch-all) reads each object's `enable` for its nav prune through `getMetaItemsForExecution` where the protocol has it, as `RestServer` does, and `getMetaItems` otherwise.
+- **No public surface moves.** The built `dist/index.d.ts` of both packages is byte-identical at `cb0a2fcf` and at this head.
@@ -0,0 +1,13 @@
+---
+'@objectstack/rest': patch
+---
+
+perf(rest): `GET /meta/app` judges its navigation on the protocol's execution face, so it no longer schema-parses every object on each read
+
+Clause-②: yes (widening): the exported `RestProtocol` type gains one optional member, `getMetaItemsForExecution?`. Measured on the built `dist/index.d.ts` at `cb0a2fcf` (before) and at this head (after): the export list is unchanged (67 names), and outside doc comments the one changed line is that member. Every other member signature is byte-identical. The member is optional, so nothing a protocol must provide changes.
+
+Metadata-protocol: none
+
+- **What.** The nav-servability gate (#24031) reads each object's `enable` to prune the nav entries whose object refuses `list`. It read them through the served `getMetaItems`, which stamps `_diagnostics` on every object, so every `/meta/app` read ran a full schema parse of every object definition. `RestServer.metaListSource` now asks `getMetaItemsForExecution` for `object` when the protocol has it (the same list, without the serving decorations) and `getMetaItems` otherwise. The batch route's exposure gate and the by-name gate's list fallback read the same source. The `book` and `doc` lists stay on the served face.
+- **Measured** on the showcase app (108 objects, local, main-thread CPU per request): `GET /meta/app` 73.25 ms → 16.75 ms.
+- **Unchanged.** Every `/meta` answer: the same nav prune, and `GET /meta/object` still serves `_diagnostics` on every object.
@@ -0,0 +1,216 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * #25783 — the diagnostics verdict memo answers what a fresh parse answers,
+ * and parses a document once per schema however many reads serve it.
+ *
+ * Every served metadata read stamps `_diagnostics` on every item, and that
+ * stamp was a full `safeParse` per item per read: 60 ms of an 86 ms
+ * `GET /meta/object` over 108 unchanged objects. `computeMetadataDiagnostics`
+ * now remembers a verdict by the schema object and the document's content
+ * ("The verdict memo" in `metadata-diagnostics.ts`). These rows pin the two
+ * halves of that promise:
+ *
+ *  - **The served bytes do not move.** A memo hit serves, byte for byte, what
+ *    a fresh parse of the same document under a schema with no memo serves —
+ *    a valid document and an invalid one, on the real `object` schema.
+ *  - **Nothing the parse can tell apart shares a key.** A changed document, a
+ *    replaced schema, `undefined` against a missing key, an array hole against
+ *    `null`, `NaN` against `null` — each is parsed again and gets its own
+ *    verdict. A document with no faithful key (a function, `-0`, a nesting past
+ *    the keyable depth) is parsed every time, as before the memo.
+ *
+ * The instrument: a schema behind a proxy that counts its `safeParse` calls,
+ * registered for a probe type through `registerMetadataTypeSchema`. A fresh
+ * proxy per test is a fresh memo, because the memo is held per schema object.
+ */
+import { beforeEach, describe, expect, it } from 'vitest';
+import { z } from 'zod';
+import { getMetadataTypeSchema, registerMetadataTypeSchema } from '@objectstack/spec/kernel';
+import { computeMetadataDiagnostics, decorateMetadataItem } from './metadata-diagnostics.js';
+
+/** A type no build registers, so binding it touches no real type's schema. */
+const PROBE = 'memo_probe_25783';
+
+const PROBE_SCHEMA = z.object({
+    name: z.string(),
+    tags: z.array(z.string().nullable()).optional(),
+    weight: z.number().nullable().optional(),
+    nested: z.unknown().optional(),
+    handler: z.unknown().optional(),
+}).strict();
+
+let parses = 0;
+
+/** Bind `schema` to `type` behind a proxy that counts parses; returns the proxy. */
+function bindCounting(type: string, schema: z.ZodType): z.ZodType {
+    const counting = new Proxy(schema, {
+        get(target, prop, receiver) {
+            if (prop === 'safeParse') {
+                return (...args: unknown[]) => {
+                    parses += 1;
+                    return (target.safeParse as (...a: unknown[]) => unknown).apply(target, args);
+                };
+            }
+            return Reflect.get(target, prop, receiver);
+        },
+    });
+    registerMetadataTypeSchema(type, counting);
+    return counting;
+}
+
+beforeEach(() => {
+    parses = 0;
+    bindCounting(PROBE, PROBE_SCHEMA);
+});
+
+describe('#25783 the verdict memo — one parse per document per schema', () => {
+    it('answers a repeated document from the memo, a structurally equal copy included', () => {
+        const doc = { name: 'a', tags: ['x'] };
+        expect(computeMetadataDiagnostics(PROBE, doc)).toEqual({ valid: true });
+        expect(computeMetadataDiagnostics(PROBE, doc)).toEqual({ valid: true });
+        // A row read again from the store is a new object with the same content.
+        expect(computeMetadataDiagnostics(PROBE, JSON.parse(JSON.stringify(doc)))).toEqual({ valid: true });
+        expect(parses).toBe(1);
+    });
+
+    it('keys the document without its read decorations, as the parse sees it', () => {
+        const doc = { name: 'a' };
+        computeMetadataDiagnostics(PROBE, doc);
+        // The served body of the same document, decorations and all.
+        computeMetadataDiagnostics(PROBE, { ...doc, _diagnostics: { valid: true } });
+        expect(parses).toBe(1);
+    });
+
+    it('parses a changed document again', () => {
+        expect(computeMetadataDiagnostics(PROBE, { name: 'a' })?.valid).toBe(true);
+        expect(computeMetadataDiagnostics(PROBE, { name: 'a', bogus: 1 })?.valid).toBe(false);
+        expect(computeMetadataDiagnostics(PROBE, { name: 'b' })?.valid).toBe(true);
+        expect(parses).toBe(3);
+    });
+
+    it('starts from nothing when the type schema is replaced', () => {
+        const doc = { name: 'a', extra: 1 };
+        expect(computeMetadataDiagnostics(PROBE, doc)?.valid).toBe(false);
+        bindCounting(PROBE, PROBE_SCHEMA.passthrough());
+        expect(computeMetadataDiagnostics(PROBE, doc)?.valid).toBe(true);
+        expect(parses).toBe(2);
+    });
+
+    it('hands each caller its own copy of a verdict', () => {
+        const doc = { name: 'a', bogus: 1 };
+        const first = computeMetadataDiagnostics(PROBE, doc)!;
+        const pristine = JSON.stringify(first);
+        first.valid = true;
+        first.errors![0]!.message = 'edited by a caller';
+        first.errors!.push({ path: 'x', message: 'pushed by a caller', code: 'custom' } as never);
+        expect(JSON.stringify(computeMetadataDiagnostics(PROBE, doc))).toBe(pristine);
+        expect(parses).toBe(1);
+    });
+
+    it('keeps at most 4096 verdicts per schema, the least recently used out first', () => {
+        computeMetadataDiagnostics(PROBE, { name: 'kept' });
+        computeMetadataDiagnostics(PROBE, { name: 'evicted' });
+        for (let i = 0; i < 4094; i++) computeMetadataDiagnostics(PROBE, { name: `n${i}` });
+        // 4096 held. Touch `kept`, so `evicted` is now the least recently used.
+        computeMetadataDiagnostics(PROBE, { name: 'kept' });
+        computeMetadataDiagnostics(PROBE, { name: 'one more' });
+        const before = parses;
+        computeMetadataDiagnostics(PROBE, { name: 'kept' });
+        expect(parses - before).toBe(0);
+        computeMetadataDiagnostics(PROBE, { name: 'evicted' });
+        expect(parses - before).toBe(1);
+    });
+});
+
+describe('#25783 the verdict memo — no two documents the parse tells apart share a verdict', () => {
+    // Each pair is run in both orders: whichever is diagnosed first, the
+    // second must get its own parse and its own verdict.
+    const pairs: Array<[label: string, accepted: () => unknown, refused: () => unknown]> = [
+        ['a missing key against the same key holding `undefined` (strict schema)',
+            () => ({ name: 'a' }),
+            () => ({ name: 'a', undeclared: undefined })],
+        ['`null` against an array hole',
+            () => ({ name: 'a', tags: [null, 'x'] }),
+            () => {
+                const tags: unknown[] = [];
+                tags[1] = 'x'; // index 0 is a hole: JSON.stringify spells it `null`
+                return { name: 'a', tags };
+            }],
+        ['`null` against `NaN`',
+            () => ({ name: 'a', weight: null }),
+            () => ({ name: 'a', weight: Number.NaN })],
+    ];
+
+    for (const [label, accepted, refused] of pairs) {
+        for (const order of ['accepted first', 'refused first'] as const) {
+            it(`${label} — ${order}`, () => {
+                if (order === 'accepted first') {
+                    expect(computeMetadataDiagnostics(PROBE, accepted())?.valid).toBe(true);
+                    expect(computeMetadataDiagnostics(PROBE, refused())?.valid).toBe(false);
+                } else {
+                    expect(computeMetadataDiagnostics(PROBE, refused())?.valid).toBe(false);
+                    expect(computeMetadataDiagnostics(PROBE, accepted())?.valid).toBe(true);
+                }
+                expect(parses).toBe(2);
+            });
+        }
+    }
+
+    it('parses a document with no faithful key every time: a function, `-0`, a nesting past the keyable depth', () => {
+        let deep: Record<string, unknown> = {};
+        const root = deep;
+        for (let i = 0; i < 300; i++) deep = (deep.next = {}) as Record<string, unknown>;
+        const unkeyable = [
+            { name: 'a', handler: () => 1 },
+            { name: 'a', weight: -0 },
+            { name: 'a', nested: root },
+            { name: 'a', nested: new Date(0) },
+        ];
+        for (const doc of unkeyable) {
+            const before = parses;
+            const first = computeMetadataDiagnostics(PROBE, doc);
+            const second = computeMetadataDiagnostics(PROBE, doc);
+            expect(second).toEqual(first);
+            expect(parses - before).toBe(2);
+        }
+    });
+});
+
+describe('#25783 the verdict memo — a hit serves the bytes a fresh parse serves (real `object` schema)', () => {
+    const OBJECT_SCHEMA = getMetadataTypeSchema('object')!;
+    const documents: Array<[label: string, valid: boolean, doc: Record<string, unknown>]> = [
+        ['a valid object', true, {
+            name: 'memo_widget', label: 'Memo Widget',
+            fields: { title: { name: 'title', type: 'text' } },
+            enable: { apiMethods: ['get', 'list'] },
+        }],
+        ['an invalid object', false, {
+            name: 'memo_widget', label: 'Memo Widget',
+            fields: { title: { name: 'title', type: 'no_such_field_type' } },
+            bogusTopLevelKey: true,
+        }],
+    ];
+
+    for (const [label, valid, doc] of documents) {
+        it(label, () => {
+            try {
+                // A schema with no memo: the reference answer.
+                bindCounting('object', OBJECT_SCHEMA);
+                parses = 0;
+                const fresh = JSON.stringify(decorateMetadataItem('object', structuredClone(doc)));
+                // The same schema object again: the second read is a memo hit.
+                const hit = JSON.stringify(decorateMetadataItem('object', structuredClone(doc)));
+                expect(JSON.parse(fresh)._diagnostics.valid).toBe(valid);
+                expect(parses).toBe(1);
+                expect(hit).toBe(fresh);
+                // And a further fresh schema answers it the same way.
+                bindCounting('object', OBJECT_SCHEMA);
+                expect(JSON.stringify(decorateMetadataItem('object', structuredClone(doc)))).toBe(fresh);
+                expect(parses).toBe(2);
+            } finally {
+                registerMetadataTypeSchema('object', OBJECT_SCHEMA);
+            }
+        });
+    }
+});