fix: use type-only imports for Node.js stream module

- Changed 'import { Readable } from "stream"' to 'import type { Readable } from "stream"' in:
  - src/packages/AbstractRestClient.ts
  - src/lib/types/DeepgramSource.ts
  - src/lib/helpers.ts
- Updated isReadStreamSource to use duck typing instead of instanceof check
- This prevents bundler errors in browser environments (React, Vite, etc)
- Maintains full type safety while removing runtime dependency on Node.js stream module

Author: lukeocodes

src/lib/helpers.ts

@@ -9,8 +9,9 @@ import {
   TranscriptionSchema,
 } from "./types";
 import { Headers as CrossFetchHeaders } from "cross-fetch";
-import { Readable } from "stream";
+import type { Readable } from "stream";
 import merge from "deepmerge";
+import { isBrowser } from "./runtime";
 
 export function stripTrailingSlash(url: string): string {
   return url.replace(/\/$/, "");
@@ -71,7 +72,18 @@ const isBufferSource = (providedSource: PrerecordedSource): providedSource is Bu
 };
 
 const isReadStreamSource = (providedSource: PrerecordedSource): providedSource is Readable => {
-  return providedSource != null && providedSource instanceof Readable;
+  if (providedSource == null) return false;
+
+  // In browser environments, there's no Readable stream from Node.js
+  if (isBrowser()) return false;
+
+  // Check for stream-like properties without importing Readable
+  return (
+    typeof providedSource === "object" &&
+    typeof (providedSource as any).pipe === "function" &&
+    typeof (providedSource as any).read === "function" &&
+    typeof (providedSource as any)._readableState === "object"
+  );
 };
 
 export class CallbackUrl extends URL {

src/lib/types/DeepgramSource.ts

@@ -1,4 +1,4 @@
-import { Readable } from "stream";
+import type { Readable } from "stream";
 
 export type PrerecordedSource = UrlSource | Buffer | Readable;
 

src/packages/AbstractRestClient.ts

@@ -1,5 +1,5 @@
 import { DeepgramApiError, DeepgramError, DeepgramUnknownError } from "../lib/errors";
-import { Readable } from "stream";
+import type { Readable } from "stream";
 import { fetchWithAuth, resolveResponse } from "../lib/fetch";
 import type { Fetch, FetchOptions, RequestMethodType } from "../lib/types/Fetch";
 import { AbstractClient } from "./AbstractClient";