@@ -0,0 +1,20 @@
+---
+'@objectstack/metadata': patch
+---
+
+fix(metadata): `FilesystemLoader` remembers which file a metadata name resolves to, so a repeated read stops probing the filesystem (#24537)
+
+Clause-②: no
+
+`FilesystemLoader` used to make one `fs.access` call per resolvable extension (five under `MetadataPlugin`'s format set) on every `load()`, `exists()` and `stat()`, for a name no file holds as well as for one a file holds. Every authenticated request paid this cost: the security catalog asks the metadata service for each held permission set the engine registry does not serve, and in an artifact-mode runtime no such file exists.
+
+Each loader instance now remembers the answer for each `(type, name)`: the path, or no file. Only something that can change the answer retires it:
+
+- a `save()` through the loader;
+- a walk of the type's directory by the loader (`list()`, `loadMany()`, `loadManyKeyed()`), so a name `list()` reports is not answered `null` by `get()`;
+- a read with `useCache: false`, which re-resolves from disk. The file watcher's re-read on an `added` or `changed` event is such a read;
+- a remembered path that the next read finds deleted. That read resolves the name again from disk and logs no stat failure. This covers an `unlink` event, and a deletion that no event reports.
+
+The memo holds at most 10,000 names and then starts over.
+
+One change is not seen at once. Suppose a name has already been answered "no file", and then another process creates that file under the loader's root while no watcher runs (`watch: false`). The loader does not see the file until the next walk of that type, the next `save()` through the loader, or a restart. Content edits to a file that already resolves are still read on the next request. Nothing in the public API changes.
@@ -0,0 +1,378 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * #24537 — `FilesystemLoader.findFile` remembers what it resolved, so a
+ * request stops probing the filesystem.
+ *
+ * ---------------------------------------------------------------------------
+ * The cost (measured on `origin/main` @ 2667e2402, the first case below)
+ * ---------------------------------------------------------------------------
+ * `plugin-security`'s catalog read (`createSecurityCatalogReader().resolve`)
+ * asks the metadata service for every held permission set the engine registry
+ * does not serve, on every authenticated request. That falls through
+ * `MetadataManager.getDiagnosed` to `FilesystemLoader.load`, and `findFile`
+ * probed one `fs.access` per resolvable extension, every time:
+ *
+ *   a name no file holds   5 probes per resolution, every resolution
+ *   a name a file holds    2 probes per resolution (`load` and `stat` each
+ *                          resolved it), every resolution
+ *
+ * The miss is the common case: an artifact-mode runtime has no
+ * `ROOT/permission/*.json` at all.
+ *
+ * ---------------------------------------------------------------------------
+ * What retires a remembered answer, and the case that pins each
+ * ---------------------------------------------------------------------------
+ *   the loader's own write (`save`)            "a save through the loader …"
+ *   the watcher's re-read (`added` event,      "an `added` file event …"
+ *     `useCache: false`)
+ *   a remembered path found gone on read       "an `unlink` event …",
+ *     (`unlink` event, or no event at all)     "a deletion nothing reported …"
+ *   the loader's own walk of the type          "RECORD: a file created with no
+ *                                                watcher …"
+ *   a probe already on disk when it retires    "a probe that was on disk …"
+ *
+ * `RECORD:` pins the one change no event reaches — a file another process
+ * creates under the root while no watcher runs (`watch: false`, every shipped
+ * composition) — so the gap is visible in a diff rather than implicit. It is
+ * closed by the next walk of that type, which is also what keeps a name
+ * `list()` reports from being answered `null` by `get()`.
+ *
+ * Writing a permission set never reaches this memo at all: a definition saved
+ * through the metadata protocol lands in the engine registry, which the catalog
+ * read asks first, and `register()` lands in the manager's registry, which
+ * `getDiagnosed` asks before any loader. The two "writing a permission set"
+ * cases pin that a remembered miss cannot hide either.
+ *
+ * Probes are counted at `node:fs/promises.access`, the call `findFile` makes,
+ * for paths under this test's root only.
+ */
+
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import * as os from 'node:os';
+import * as path from 'node:path';
+
+const { probes, logger } = vi.hoisted(() => ({
+  probes: {
+    paths: [] as string[],
+    /** Holds ONE probe of `path` after it has read the disk, until released. */
+    hold: undefined as undefined | { path: string; reached: () => void; release: Promise<void> },
+  },
+  logger: {
+    info: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn(),
+    debug: vi.fn(),
+  },
+}));
+
+vi.mock('node:fs/promises', async (importOriginal) => {
+  const actual = await importOriginal<typeof import('node:fs/promises')>();
+  return {
+    ...actual,
+    access: async (target: Parameters<typeof actual.access>[0], mode?: number) => {
+      const probed = String(target);
+      probes.paths.push(probed);
+
+      let failure: unknown;
+      let failed = false;
+      try {
+        await actual.access(target, mode);
+      } catch (error) {
+        failed = true;
+        failure = error;
+      }
+
+      const hold = probes.hold;
+      if (hold && probed === hold.path) {
+        probes.hold = undefined;
+        hold.reached();
+        await hold.release;
+      }
+
+      if (failed) throw failure;
+    },
+  };
+});
+
+vi.mock('@objectstack/core', async (orig) => ({
+  // Spread the REAL module: the catalog reader under test comes from it.
+  ...((await orig()) as object),
+  createLogger: () => logger,
+}));
+
+import * as fs from 'node:fs/promises';
+import type { MetadataFormat } from '@objectstack/spec/system';
+import { createSecurityCatalogReader, type SecurityCatalogReader } from '@objectstack/core';
+import { NodeMetadataManager } from '../node-metadata-manager.js';
+import { FilesystemLoader } from './filesystem-loader.js';
+import { JSONSerializer } from '../serializers/json-serializer.js';
+import type { MetadataSerializer } from '../serializers/serializer-interface.js';
+
+/** The format set `MetadataPlugin` constructs its manager with. */
+const PLUGIN_FORMATS: MetadataFormat[] = ['yaml', 'json', 'typescript', 'javascript'];
+/** …and the extensions `findFile` probes under it, in precedence order. */
+const PLUGIN_EXTENSIONS = ['.json', '.yaml', '.yml', '.ts', '.js'];
+
+let rootDir: string;
+const managers: NodeMetadataManager[] = [];
+
+beforeEach(async () => {
+  vi.clearAllMocks();
+  probes.paths.length = 0;
+  probes.hold = undefined;
+  rootDir = await fs.mkdtemp(path.join(os.tmpdir(), 'os-24537-'));
+});
+
+afterEach(async () => {
+  for (const mgr of managers.splice(0)) await mgr.stopWatching();
+  await fs.rm(rootDir, { recursive: true, force: true });
+});
+
+const permissionSet = (name: string, label = name) => ({ name, label, objects: {} });
+
+async function writeSetFile(name: string, body: object = permissionSet(name), ext = '.json'): Promise<string> {
+  const dir = path.join(rootDir, 'permission');
+  await fs.mkdir(dir, { recursive: true });
+  const filePath = path.join(dir, `${name}${ext}`);
+  await fs.writeFile(filePath, ext === '.json' ? JSON.stringify(body) : `name: ${name}\nlabel: ${(body as { label?: string }).label ?? name}\n`, 'utf-8');
+  return filePath;
+}
+
+/** The plugin's manager over `rootDir`: no loaders given, so the default FilesystemLoader. */
+function makeManager(): NodeMetadataManager {
+  const mgr = new NodeMetadataManager({ rootDir, watch: false, formats: PLUGIN_FORMATS });
+  managers.push(mgr);
+  return mgr;
+}
+
+/** An engine registry that serves `held` only — empty unless a case writes to it. */
+function makeRegistry(held: Map<string, Record<string, unknown>> = new Map()) {
+  return {
+    getItem: (_type: string, name: string) => held.get(name),
+    listItems: () => [...held.values()],
+    isPackageDisabled: () => false,
+  };
+}
+
+function makeCatalog(mgr: NodeMetadataManager, held?: Map<string, Record<string, unknown>>): SecurityCatalogReader {
+  return createSecurityCatalogReader({ registry: makeRegistry(held), metadata: mgr as never });
+}
+
+/** `fs.access` probes made under this test's root since the last call. */
+function probesSince(mark: { at: number }): number {
+  const count = probes.paths.slice(mark.at).filter((p) => p.startsWith(rootDir)).length;
+  mark.at = probes.paths.length;
+  return count;
+}
+
+/** Probes per resolution, over `times` resolutions of `name` by the catalog read. */
+async function probesPerResolution(catalog: SecurityCatalogReader, name: string, times = 5): Promise<number[]> {
+  const mark = { at: probes.paths.length };
+  const counts: number[] = [];
+  for (let i = 0; i < times; i++) {
+    await catalog.resolve('permission', name);
+    counts.push(probesSince(mark));
+  }
+  return counts;
+}
+
+function fireFileEvent(mgr: NodeMetadataManager, eventType: 'added' | 'changed' | 'deleted', filePath: string): Promise<void> {
+  return (
+    mgr as unknown as { handleFileEvent(t: 'added' | 'changed' | 'deleted', p: string): Promise<void> }
+  ).handleFileEvent(eventType, filePath);
+}
+
+const statFailureLogs = () => logger.error.mock.calls.filter((call) => call[0] === 'Failed to stat file');
+
+describe('#24537 — repeated resolutions of one name probe the filesystem once', () => {
+  it('a name no file holds: one probe per extension on the first resolution, none after', async () => {
+    const catalog = makeCatalog(makeManager());
+
+    // On main @ 2667e2402: 5 probes on every resolution (measured over four).
+    expect(await probesPerResolution(catalog, 'miss_set')).toEqual([PLUGIN_EXTENSIONS.length, 0, 0, 0, 0]);
+    expect(await catalog.resolve('permission', 'miss_set')).toBeUndefined();
+  });
+
+  it('a name a file holds: one probe on the first resolution, none after — and the body is still served', async () => {
+    await writeSetFile('hit_set');
+    const catalog = makeCatalog(makeManager());
+
+    // On main @ 2667e2402: 2 probes on every resolution (measured over four).
+    expect(await probesPerResolution(catalog, 'hit_set')).toEqual([1, 0, 0, 0, 0]);
+    expect(await catalog.resolve('permission', 'hit_set')).toMatchObject({
+      name: 'hit_set',
+      source: 'metadata',
+    });
+  });
+
+  it('CONTROL: a remembered path is not remembered CONTENT — an edit to the file is read on the next resolution', async () => {
+    const filePath = await writeSetFile('edited_set', permissionSet('edited_set', 'before'));
+    const catalog = makeCatalog(makeManager());
+    expect((await catalog.resolve('permission', 'edited_set'))?.definition).toMatchObject({ label: 'before' });
+
+    await fs.writeFile(filePath, JSON.stringify(permissionSet('edited_set', 'after')), 'utf-8');
+
+    expect((await catalog.resolve('permission', 'edited_set'))?.definition).toMatchObject({ label: 'after' });
+  });
+
+  it('two managers do not share what they remember', async () => {
+    const first = makeCatalog(makeManager());
+    const second = makeCatalog(makeManager());
+
+    await first.resolve('permission', 'per_kernel_set');
+    expect(await probesPerResolution(second, 'per_kernel_set', 1)).toEqual([PLUGIN_EXTENSIONS.length]);
+  });
+});
+
+describe('#24537 — writing a permission set is seen on the next resolution', () => {
+  it('a set written to the engine registry: the registry answers before any loader', async () => {
+    const held = new Map<string, Record<string, unknown>>();
+    const catalog = makeCatalog(makeManager(), held);
+    expect(await catalog.resolve('permission', 'authored_set')).toBeUndefined();
+
+    held.set('authored_set', permissionSet('authored_set'));
+
+    expect(await catalog.resolve('permission', 'authored_set')).toMatchObject({ name: 'authored_set', source: 'registry' });
+  });
+
+  it('a set registered with the metadata service: its registry answers before any loader', async () => {
+    const mgr = makeManager();
+    const catalog = makeCatalog(mgr);
+    expect(await catalog.resolve('permission', 'registered_set')).toBeUndefined();
+
+    await mgr.register('permission', 'registered_set', permissionSet('registered_set'));
+
+    expect(await catalog.resolve('permission', 'registered_set')).toMatchObject({
+      name: 'registered_set',
+      source: 'metadata',
+    });
+  });
+
+  it('a save through the loader retires a remembered miss', async () => {
+    const mgr = makeManager();
+    const catalog = makeCatalog(mgr);
+    expect(await catalog.resolve('permission', 'saved_set')).toBeUndefined();
+
+    await mgr.save('permission', 'saved_set', permissionSet('saved_set'), { format: 'json' });
+
+    expect(await catalog.resolve('permission', 'saved_set')).toMatchObject({ name: 'saved_set', source: 'metadata' });
+  });
+});
+
+describe('#24537 — the file watcher retires what it reports', () => {
+  it('an `added` file event: its re-read resolves from disk, announces the body, and the next resolution sees it', async () => {
+    const mgr = makeManager();
+    const catalog = makeCatalog(mgr);
+    const announced: unknown[] = [];
+    mgr.subscribe('permission', (evt) => { announced.push(evt.data); });
+    expect(await catalog.resolve('permission', 'watched_set')).toBeUndefined();
+
+    const filePath = await writeSetFile('watched_set');
+    await fireFileEvent(mgr, 'added', filePath);
+
+    // Without the fresh re-read the event would announce `null` for a file
+    // that was just added, and the remembered miss would stand.
+    expect(announced).toEqual([permissionSet('watched_set')]);
+    expect(await catalog.resolve('permission', 'watched_set')).toMatchObject({ name: 'watched_set' });
+  });
+
+  it('an `unlink` event: the next read finds the remembered path gone and answers the miss — no stat failure logged', async () => {
+    const mgr = makeManager();
+    const catalog = makeCatalog(mgr);
+    const paths: string[] = [];
+    for (const name of ['unlinked_set', 'unlinked_too']) {
+      paths.push(await writeSetFile(name));
+      expect(await catalog.resolve('permission', name)).toMatchObject({ name });
+    }
+
+    for (const filePath of paths) {
+      await fs.rm(filePath);
+      await fireFileEvent(mgr, 'deleted', filePath);
+    }
+
+    // Each door asked FIRST, while the memo still holds its path: `load()`
+    // (through the catalog read) for one name, `exists()` for the other.
+    expect(await catalog.resolve('permission', 'unlinked_set')).toBeUndefined();
+    expect(await mgr.exists('permission', 'unlinked_too')).toBe(false);
+    expect(await catalog.resolve('permission', 'unlinked_set')).toBeUndefined();
+    expect(statFailureLogs()).toEqual([]);
+  });
+});
+
+describe('#24537 — changes no event reports', () => {
+  it('a deletion nothing reported: the remembered path is re-resolved from disk, whatever it holds now', async () => {
+    const jsonPath = await writeSetFile('moved_set', permissionSet('moved_set', 'from json'));
+    const mgr = makeManager();
+    const catalog = makeCatalog(mgr);
+    expect((await catalog.resolve('permission', 'moved_set'))?.definition).toMatchObject({ label: 'from json' });
+
+    await fs.rm(jsonPath);
+    await writeSetFile('moved_set', permissionSet('moved_set', 'from yaml'), '.yaml');
+
+    expect((await catalog.resolve('permission', 'moved_set'))?.definition).toMatchObject({ label: 'from yaml' });
+    expect(await mgr.exists('permission', 'moved_set')).toBe(true);
+    expect(statFailureLogs()).toEqual([]);
+  });
+
+  it('RECORD: a file created with no watcher is unseen by a remembered miss until the next walk of its type', async () => {
+    const mgr = makeManager();
+    const catalog = makeCatalog(mgr);
+    expect(await catalog.resolve('permission', 'dropped_set')).toBeUndefined();
+
+    await writeSetFile('dropped_set');
+
+    // The named gap: nothing reported the file, so the remembered miss stands.
+    expect(await catalog.resolve('permission', 'dropped_set')).toBeUndefined();
+
+    // The walk behind `list()` sees the file — and retires the type, so the
+    // name it lists is not answered `null` by the door.
+    expect((await mgr.list('permission')).map((item) => (item as { name: string }).name)).toEqual(['dropped_set']);
+    expect(await catalog.resolve('permission', 'dropped_set')).toMatchObject({ name: 'dropped_set' });
+  });
+});
+
+describe('#24537 — what the memo holds', () => {
+  const jsonOnly = () =>
+    new FilesystemLoader(rootDir, new Map<MetadataFormat, MetadataSerializer>([['json', new JSONSerializer()]]), logger as never);
+
+  it('a probe that was on disk when a save retired the memo does not write its older miss back', async () => {
+    const loader = jsonOnly();
+    const target = path.join(rootDir, 'permission', 'late_set.json');
+    let reached!: () => void;
+    let release!: () => void;
+    const onDisk = new Promise<void>((resolve) => { reached = resolve; });
+    probes.hold = { path: target, reached, release: new Promise<void>((resolve) => { release = resolve; }) };
+
+    // This load's probe has already read "absent" when the save lands.
+    const pending = loader.load('permission', 'late_set');
+    await onDisk;
+    await loader.save('permission', 'late_set', permissionSet('late_set'), { format: 'json' });
+    release();
+    expect((await pending).data).toBeNull();
+
+    expect((await loader.load('permission', 'late_set')).data).toEqual(permissionSet('late_set'));
+  });
+
+  it('is bounded: past the cap it starts over rather than growing with every name a caller asks for', async () => {
+    const loader = jsonOnly();
+    const cap = 'RESOLUTION_MEMO_CAP';
+    const original = Reflect.get(FilesystemLoader, cap);
+    Reflect.set(FilesystemLoader, cap, 3);
+    try {
+      const mark = { at: probes.paths.length };
+      for (const name of ['a', 'b', 'c']) await loader.exists('permission', name);
+      probesSince(mark);
+
+      await loader.exists('permission', 'a');
+      expect(probesSince(mark)).toBe(0);           // three remembered, `a` among them
+
+      await loader.exists('permission', 'd');      // the fourth: starts over
+      probesSince(mark);
+      await loader.exists('permission', 'a');
+      expect(probesSince(mark)).toBe(1);           // `a` was dropped with the rest
+    } finally {
+      Reflect.set(FilesystemLoader, cap, original);
+    }
+  });
+});