fix: return empty blob promise when ByteBlobLoader store is already consumed

src/bun.js/webcore/ByteBlobLoader.zig

@@ -180,7 +180,8 @@ pub fn toBufferedValue(this: *ByteBlobLoader, globalThis: *JSGlobalObject, actio
         return blob.toPromise(globalThis, action);
     }
 
-    return .zero;
+    var empty: Blob.Any = .{ .Blob = Blob.initEmpty(globalThis) };
+    return empty.toPromise(globalThis, action);
 }
 
 pub fn memoryCost(this: *const ByteBlobLoader) usize {

test/js/web/streams/blob-stream-bytes-consumed.test.ts

@@ -0,0 +1,23 @@
+import { expect, test } from "bun:test";
+
+test("bytes() on consumed blob ReadableStream returns valid result", async () => {
+  // Create a blob-backed stream and fully consume it via reader
+  const blob = new Blob(["test data"]);
+  const stream = blob.stream();
+  const reader = stream.getReader();
+  const chunks: Uint8Array[] = [];
+  while (true) {
+    const { value, done } = await reader.read();
+    if (done) break;
+    chunks.push(value);
+  }
+  reader.releaseLock();
+
+  // Stream is closed, source store is consumed.
+  // Calling bytes() should return a valid empty Uint8Array, not crash.
+  // Without the fix, the native toBufferedValue returns .zero without
+  // setting an exception, causing an assertion failure in debug builds.
+  const result = await stream.bytes();
+  expect(result).toBeInstanceOf(Uint8Array);
+  expect(result.length).toBe(0);
+});