diff --git a/docs/plugin-platform/registry-client.md b/docs/plugin-platform/registry-client.md
index 0f5b59b66..59cb52447 100644
--- a/docs/plugin-platform/registry-client.md
+++ b/docs/plugin-platform/registry-client.md
@@ -12,14 +12,16 @@ prove the repository or an online artifact is available.
 `id`, `version`, `name`, `description`, `author`, `repository` (`owner/repository`),
 `commit` (full 40-character SHA), `license`, `readme` (relative Markdown path),
 and `manifest`. Optional `artifact` contains `url` and SHA-256 `sha256`.
-The existing manifest schema, browser-only distribution policy, identity/version
+Unknown catalog-entry and artifact fields are rejected. The whole JSON value,
+including manifest defaults, uses the existing 128-level / 100,000-value budget
+and finite-number validation. The existing manifest schema, browser-only distribution policy, identity/version
 and license checks apply. Source-only entries remain build-and-import examples.
 No download counts, ratings, or timestamps are invented. Brand previews remain
 bundled and reviewed; arbitrary author image URLs are never loaded.
 
 Reads are anonymous HTTPS, redirect-free for the registry, bounded to 2 MiB,
-and time out after 30 seconds. All entries must validate before replacing the
-current snapshot. Invalid JSON/schema, network failure, and oversized responses
+and time out after 30 seconds. All entries must validate, safely clone, and generate every selection token before
+atomically replacing the current snapshot. Invalid JSON/schema, network failure, and oversized responses
 leave the previous good snapshot intact. Errors and Retry remain visible. The Community header also has Refresh, including
 when the last refresh succeeded; it is disabled while a request is pending.
 The last good catalog is retained **in memory for this application session**;
diff --git a/electron/plugins/catalogService.cjs b/electron/plugins/catalogService.cjs
index 70e58e9da..dad468923 100644
--- a/electron/plugins/catalogService.cjs
+++ b/electron/plugins/catalogService.cjs
@@ -8,6 +8,9 @@ const { getTempFilePath } = require("../bridges/tempDirBridge.cjs");
 const { createDefinitionValidator, formatValidationErrors } = require("./contractValidator.cjs");
 const validateManifest = createDefinitionValidator("PluginManifest");
 const { assertCatalogManifest } = require("./catalogPolicy.cjs");
+const { assertPluginJsonValue } = require("./jsonBoundary.cjs");
+const MAX_CATALOG_BYTES = 2 * 1024 * 1024;
+const CATALOG_FIELDS = new Set(["id", "version", "name", "description", "author", "repository", "commit", "license", "readme", "manifest", "artifact"]);
 
 const DOWNLOAD_HOSTS = new Set(["github.com", "raw.githubusercontent.com", "release-assets.githubusercontent.com", "objects.githubusercontent.com"]);
 function assertDownloadUrl(value) {
@@ -28,10 +31,11 @@ function pinnedReadmeUrl(entry) {
   return url.href;
 }
 function validateCatalog(entries) {
+  assertPluginJsonValue(entries, { maxBytes: MAX_CATALOG_BYTES });
   if (!Array.isArray(entries) || entries.length > 1000) throw new Error("Invalid plugin catalog");
   const ids = new Set();
   for (const entry of entries) {
-    if (!entry || ["id", "version", "name", "description", "author", "repository", "commit", "license", "readme"].some((key) => typeof entry[key] !== "string" || entry[key].length > 4096) || !/^[a-z0-9][a-z0-9.-]+$/u.test(entry.id) || ids.has(entry.id)
+    if (!entry || Object.keys(entry).some((key) => !CATALOG_FIELDS.has(key)) || ["id", "version", "name", "description", "author", "repository", "commit", "license", "readme"].some((key) => typeof entry[key] !== "string" || entry[key].length > 4096) || !/^[a-z0-9][a-z0-9.-]+$/u.test(entry.id) || ids.has(entry.id)
       || !/^[A-Za-z0-9_.-]+\/[A-Za-z0-9_.-]+$/u.test(entry.repository)
       || !/^[a-f0-9]{40}$/u.test(entry.commit)
       || !entry.license || !entry.author || !entry.name
@@ -43,7 +47,12 @@ function validateCatalog(entries) {
     if (!validateManifest(entry.manifest)) throw new Error(`Catalog manifest is invalid: ${formatValidationErrors(validateManifest.errors)}`);
     assertCatalogManifest(entry.manifest, entry);
     ids.add(entry.id);
-    if (entry.artifact) {
+    if (Object.hasOwn(entry, "artifact")) {
+      if (!entry.artifact || typeof entry.artifact !== "object" || Array.isArray(entry.artifact)
+        || Object.keys(entry.artifact).some((key) => key !== "url" && key !== "sha256")
+        || typeof entry.artifact.url !== "string" || typeof entry.artifact.sha256 !== "string") {
+        throw new Error("Invalid catalog artifact metadata");
+      }
       assertDownloadUrl(entry.artifact.url);
       if (!/^[a-f0-9]{64}$/u.test(entry.artifact.sha256)) throw new Error("Catalog artifact requires SHA-256");
     }
@@ -82,7 +91,7 @@ async function fetchBounded(url, limit, fetchImpl = fetch, maxRedirects = 4) {
 }
 class PluginCatalogService {
   constructor(options) {
-    this.entries = validateCatalog(structuredClone(options.entries ?? catalog));
+    this.entries = structuredClone(validateCatalog(options.entries ?? catalog));
     this.fetch = options.fetch ?? fetch;
     this.getTempFilePath = options.getTempFilePath ?? getTempFilePath;
     this.manager = options.manager;
@@ -118,4 +127,4 @@ class PluginCatalogService {
     }
   }
 }
-module.exports = { PluginCatalogService, assertDownloadUrl, fetchBounded, validateCatalog, pinnedReadmeUrl };
+module.exports = { PluginCatalogService, assertDownloadUrl, fetchBounded, validateCatalog, pinnedReadmeUrl, MAX_CATALOG_BYTES };
diff --git a/electron/plugins/registryCatalogService.cjs b/electron/plugins/registryCatalogService.cjs
index 10ec50b0f..ef086e49b 100644
--- a/electron/plugins/registryCatalogService.cjs
+++ b/electron/plugins/registryCatalogService.cjs
@@ -1,14 +1,20 @@
 "use strict";
 
 const { createHash } = require("node:crypto");
-const { PluginCatalogService, fetchBounded, validateCatalog } = require("./catalogService.cjs");
+const { PluginCatalogService, fetchBounded, validateCatalog, MAX_CATALOG_BYTES } = require("./catalogService.cjs");
 const REGISTRY_URL = "https://raw.githubusercontent.com/binaricat/netcatty-plugins/main/catalog.json";
-const MAX_CATALOG_BYTES = 2 * 1024 * 1024;
 const tokenFor = (entry) => createHash("sha256").update(JSON.stringify(entry)).digest("hex");
 
+function prepareSnapshot(value) {
+  const entries = structuredClone(validateCatalog(value));
+  const publicEntries = structuredClone(entries).map((entry) => ({ ...entry, selectionToken: tokenFor(entry) }));
+  return { entries, publicEntries };
+}
+
 class RegistryCatalogService extends PluginCatalogService {
   constructor(options) {
     super(options);
+    this.publicEntries = prepareSnapshot(this.entries).publicEntries;
     this.source = "builtin";
     this.error = null;
     this.refreshing = null;
@@ -19,8 +25,10 @@ class RegistryCatalogService extends PluginCatalogService {
       try {
         // No redirects: only this exact registry endpoint can replace the catalog.
         const bytes = await fetchBounded(REGISTRY_URL, MAX_CATALOG_BYTES, this.fetch, 0);
-        const next = validateCatalog(JSON.parse(bytes.toString("utf8")));
-        this.entries = next;
+        const next = prepareSnapshot(JSON.parse(bytes.toString("utf8")));
+        // Publish only after full validation, clones and every token succeeded.
+        this.entries = next.entries;
+        this.publicEntries = next.publicEntries;
         this.source = "registry";
         this.error = null;
         return true;
@@ -35,7 +43,7 @@ class RegistryCatalogService extends PluginCatalogService {
   async list() {
     await this.refresh();
     return {
-      entries: this.entries.map((entry) => ({ ...structuredClone(entry), selectionToken: tokenFor(entry) })),
+      entries: structuredClone(this.publicEntries),
       source: this.source,
       error: this.error,
     };
diff --git a/electron/plugins/registryCatalogService.test.cjs b/electron/plugins/registryCatalogService.test.cjs
index e86183091..ec6e008c6 100644
--- a/electron/plugins/registryCatalogService.test.cjs
+++ b/electron/plugins/registryCatalogService.test.cjs
@@ -111,3 +111,43 @@ test("URL-stripped README controls cannot escape a selected commit or replace th
   assert.match((await service.list()).error, /escapes the pinned commit/);
   assert.ok(requested.every((url) => url === REGISTRY_URL));
 });
+
+test("whole-catalog JSON budgets and unknown fields cannot poison a good offline snapshot", async () => {
+  let response = JSON.stringify(builtin);
+  const service = new RegistryCatalogService({ fetch: async () => {
+    if (response === null) throw new Error("offline");
+    return new Response(response);
+  } });
+  const good = await service.list();
+  let nested = null;
+  for (let depth = 0; depth < 130; depth++) nested = { child: nested };
+  const nonfinite = structuredClone(builtin[0]);
+  nonfinite.manifest.contributes.settings[0].default = "finite-marker";
+  for (const invalid of [
+    JSON.stringify([{ ...builtin[0], unknownNestedField: nested }]),
+    JSON.stringify([{ ...builtin[0], unknownField: true }]),
+    JSON.stringify([nonfinite]).replace('"finite-marker"', '1e999'),
+    JSON.stringify([{ ...builtin[0], artifact: { url: "https://github.com/a/b", sha256: "a".repeat(64), unexpected: true } }]),
+  ]) {
+    response = invalid;
+    const rejected = await service.list();
+    assert.equal(rejected.source, "cached"); assert.ok(rejected.error);
+    assert.deepEqual(rejected.entries, good.entries);
+    response = null;
+    const offline = await service.list();
+    assert.deepEqual(offline.entries, good.entries); assert.match(offline.error, /offline/);
+  }
+});
+
+test("snapshot preparation failure leaves both private entries and public tokens unchanged", async () => {
+  const service = new RegistryCatalogService({ fetch: async () => new Response(JSON.stringify(builtin)) });
+  const good = await service.list();
+  const originalClone = global.structuredClone;
+  try {
+    global.structuredClone = () => { throw new Error("synthetic clone failure"); };
+    assert.equal(await service.refresh(), false);
+  } finally { global.structuredClone = originalClone; }
+  service.fetch = async () => { throw new Error("offline"); };
+  assert.deepEqual((await service.list()).entries, good.entries);
+  assert.equal(service.selected(good.entries[0].id, good.entries[0].selectionToken).id, good.entries[0].id);
+});