fix: harden secret-file readers

src/plugin-sdk/core.ts

@@ -18,6 +18,13 @@ export {
   listDevicePairing,
   rejectDevicePairing,
 } from "../infra/device-pairing.js";
+export {
+  DEFAULT_SECRET_FILE_MAX_BYTES,
+  loadSecretFileSync,
+  readSecretFileSync,
+  tryReadSecretFileSync,
+} from "../infra/secret-file.js";
+export type { SecretFileReadOptions, SecretFileReadResult } from "../infra/secret-file.js";
 
 export {
   runPluginCommandWithTimeout,