refactor: dedupe speech provider coercion helpers

src/plugin-sdk/speech-core.ts

@@ -35,3 +35,9 @@ export {
   normalizeSpeechProviderId,
 } from "../tts/provider-registry.js";
 export { normalizeTtsAutoMode, TTS_AUTO_MODES } from "../tts/tts-auto-mode.js";
+export {
+  asObject,
+  readResponseTextLimited,
+  trimToUndefined,
+  truncateErrorDetail,
+} from "../tts/provider-error-utils.js";