Description

When a Durable Object method throws an Error whose message contains non-ASCII characters (e.g. Chinese UTF-8), wrangler dev displays garbled/corrupted text in the terminal.

Steps to reproduce

1. Create a Durable Object with a method that throws an Error with Chinese characters:

class MyDO extends DurableObject {
  myMethod() {
    throw new Error("RESOURCE_NOT_FOUND|->资源不存在");
  }
}

2. Call this method via RPC (the caller catches the error properly via mightFail / try-catch)
3. Observe the terminal output in wrangler dev

Expected behavior

✘ [ERROR] RESOURCE_NOT_FOUND|->资源不存在 Error
    at myMethod (file:///path/to/file.ts:3:11)

Actual behavior

✘ [ERROR] ﾬ唕饞몐Ѐ Error
    at value (file:///path/to/file.ts:3:11)

The error message is garbled — Chinese UTF-8 bytes are displayed as wrong Unicode codepoints. The ASCII Error suffix at the end displays correctly.

Other examples of garbled output observed:

• ꨠۥ詠齙 (should be a validation error message)
• 귕嚏对琀 (should be a duplicate name error message)

Analysis

The garbled characters are NOT the result of simple latin1 or UTF-16LE misinterpretation of UTF-8 bytes (we verified this). It appears to be a deeper encoding issue in workerd's C++ error logging layer.

Notes

• The RPC error propagation works correctly — the caller receives the full error message with proper encoding
• This is purely a display issue in wrangler dev terminal output
• Only affects the ✘ [ERROR] log lines that workerd prints for exceptions in DO methods
• ASCII-only error messages display correctly

Environment

• wrangler 4.99.0
• macOS (Darwin 25.4.0)
• Terminal: zsh with UTF-8 locale