diff --git a/apps/desktop/src/preview/BrowserSession.test.ts b/apps/desktop/src/preview/BrowserSession.test.ts
index e258bb2dfc5..743fd6a1fce 100644
--- a/apps/desktop/src/preview/BrowserSession.test.ts
+++ b/apps/desktop/src/preview/BrowserSession.test.ts
@@ -15,6 +15,7 @@ const { fromPartition, sessions } = vi.hoisted(() => ({
       readonly clearStorageData: ReturnType<typeof vi.fn>;
       readonly getUserAgent: ReturnType<typeof vi.fn>;
       readonly setPermissionRequestHandler: ReturnType<typeof vi.fn>;
+      readonly setPermissionCheckHandler: ReturnType<typeof vi.fn>;
       readonly setUserAgent: ReturnType<typeof vi.fn>;
     }
   >(),
@@ -40,6 +41,7 @@ describe("BrowserSession", () => {
         clearStorageData: vi.fn(() => Promise.resolve()),
         getUserAgent: vi.fn(() => "Mozilla/5.0 Electron/41.5.0 t3code/0.0.27"),
         setPermissionRequestHandler: vi.fn(),
+        setPermissionCheckHandler: vi.fn(),
         setUserAgent: vi.fn(),
       };
       sessions.set(partition, browserSession);
@@ -61,6 +63,55 @@ describe("BrowserSession", () => {
     }).pipe(Effect.provide(layer)),
   );
 
+  it.effect("grants clipboard-sanitized-write through both the request and check handlers", () =>
+    Effect.gen(function* () {
+      const browserSessions = yield* BrowserSession.BrowserSession;
+      const partition = yield* browserSessions.getPartition("scope-a");
+      yield* browserSessions.getSession("scope-a");
+
+      const browserSession = sessions.get(partition);
+      assert.isDefined(browserSession);
+
+      const requestHandler = browserSession.setPermissionRequestHandler.mock.calls[0]?.[0];
+      const checkHandler = browserSession.setPermissionCheckHandler.mock.calls[0]?.[0];
+      assert.isFunction(requestHandler);
+      assert.isFunction(checkHandler);
+
+      const requestAllows = (permission: string): boolean => {
+        let granted: boolean | undefined;
+        requestHandler(null, permission, (value: boolean) => {
+          granted = value;
+        });
+        assert.isDefined(granted);
+        return granted;
+      };
+
+      for (const permission of [
+        "clipboard-read",
+        "clipboard-sanitized-write",
+        "notifications",
+        "geolocation",
+      ]) {
+        assert.isTrue(requestAllows(permission), `request handler should allow ${permission}`);
+        assert.isTrue(
+          checkHandler(null, permission) as boolean,
+          `check handler should allow ${permission}`,
+        );
+      }
+
+      // `clipboard-write` is not a real Electron permission — the async write API
+      // uses `clipboard-sanitized-write` — so the stale name must not be granted,
+      // and unrelated permissions stay denied.
+      for (const permission of ["clipboard-write", "midi"]) {
+        assert.isFalse(requestAllows(permission), `request handler should deny ${permission}`);
+        assert.isFalse(
+          checkHandler(null, permission) as boolean,
+          `check handler should deny ${permission}`,
+        );
+      }
+    }).pipe(Effect.provide(layer)),
+  );
+
   it.effect("preserves partition scope and the platform failure chain", () => {
     const nativeCause = new Error("native digest failed");
     const platformCause = PlatformError.systemError({
diff --git a/apps/desktop/src/preview/BrowserSession.ts b/apps/desktop/src/preview/BrowserSession.ts
index afa8dafe976..aa0b0743e93 100644
--- a/apps/desktop/src/preview/BrowserSession.ts
+++ b/apps/desktop/src/preview/BrowserSession.ts
@@ -11,6 +11,20 @@ import * as SynchronizedRef from "effect/SynchronizedRef";
 
 const PREVIEW_PARTITION_PREFIX = "persist:t3code-preview-";
 
+// Permissions granted to preview web content. `clipboard-sanitized-write` is the
+// Electron permission behind `navigator.clipboard.writeText()` — note it is NOT
+// `clipboard-write`, which is not a valid Electron permission name. Async
+// clipboard writes are gated by the permission *check* handler (not only the
+// request handler), so both handlers must allow it; otherwise built-in "Copy"
+// buttons — e.g. the Next.js / Vercel error overlay — fail with
+// `Failed to execute 'writeText' on 'Clipboard': Write permission denied`.
+const ALLOWED_PREVIEW_PERMISSIONS: ReadonlySet<string> = new Set([
+  "clipboard-read",
+  "clipboard-sanitized-write",
+  "notifications",
+  "geolocation",
+]);
+
 export class BrowserSessionPartitionDerivationError extends Schema.TaggedErrorClass<BrowserSessionPartitionDerivationError>()(
   "BrowserSessionPartitionDerivationError",
   {
@@ -120,9 +134,11 @@ export const make = Effect.gen(function* BrowserSessionMake() {
             .replace(/\s*t3code\/[\d.]+/, "");
           browserSession.setUserAgent(userAgent);
           browserSession.setPermissionRequestHandler((_webContents, permission, callback) => {
-            const allowed = ["clipboard-read", "clipboard-write", "notifications", "geolocation"];
-            callback(allowed.includes(permission));
+            callback(ALLOWED_PREVIEW_PERMISSIONS.has(permission));
           });
+          browserSession.setPermissionCheckHandler((_webContents, permission) =>
+            ALLOWED_PREVIEW_PERMISSIONS.has(permission),
+          );
           const next = new Map(sessions);
           next.set(partition, browserSession);
           return [browserSession, next] as const;