[BUG] export` Command Crashes on Emoji Characters (UTF-8 Boundary Error)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

---
title: Claude Code Bug Report Export Crash
type: guide
component_type: guide
version: 1.0.0
audience: contributor
status: draft
summary: Auto-classified guide document
keywords:

• guide

tokens: ~1000
created: '2026-01-11'
updated: '2026-01-11'
tags:

• guide

---

Bug Report: /export Command Crashes on Emoji Characters (UTF-8 Boundary Error)

Summary

The /export command in Claude Code panics with a fatal runtime error when the conversation contains certain emoji characters. The crash occurs due to incorrect UTF-8 string slicing at a non-character boundary.

Environment

| Component | Value |
|-----------|-------|
| Claude Code Version | 2.1.4 |
| Platform | macOS (Darwin 25.2.0) |
| Architecture | arm64 (Apple Silicon) |
| Kernel | xnu-12377.61.12~1/RELEASE_ARM64_T8132 |

Error Message

thread '<unnamed>' panicked at /rustc/ed61e7d7e242494fb7057f2657300d9e77bb4fcb/library/core/src/str/mod.rs:833:21:
byte index 2 is not a char boundary; it is inside '✅' (bytes 0..3) of `✅`
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
fatal runtime error: failed to initiate panic, error 5, aborting
[1]    14209 abort      claude

Steps to Reproduce

1. Start a Claude Code session in a project containing CLAUDE.md files with emoji characters (specifically ✅, ❌, or similar multi-byte emojis)
2. Have a conversation that includes or references content with these emojis
3. Run the /export command
4. Result: Claude Code crashes with the above panic message

Minimal Reproduction

The crash appears to be triggered when /export processes text containing the ✅ emoji (U+2705, 3 bytes in UTF-8: 0xE2 0x9C 0x85).

The error indicates the code attempts to slice the string at byte index 2, which falls in the middle of the 3-byte emoji sequence.

Frequency

• Highly reproducible - 12 crashes observed in a single session
• Crash occurs consistently when emoji content is present
• Sometimes /export succeeds on retry (possibly different code path or content ordering)

Root Cause Analysis

The panic occurs in Rust's standard library string slicing code (str/mod.rs:833). This indicates:

1. Code is attempting to slice a &str at a byte index that is not a valid UTF-8 character boundary
2. The ✅ emoji occupies bytes 0-2 (3 bytes total)
3. The code tries to slice at index 2, which is inside the emoji
4. Rust panics because this would create an invalid UTF-8 string

Likely Code Pattern Causing the Bug

// INCORRECT - causes panic on multi-byte characters
let truncated = &text[0..2];  // Panics if byte 2 is mid-character

// CORRECT - respects character boundaries
let truncated: String = text.chars().take(2).collect();
// OR
let truncated = &text[..text.char_indices().nth(2).map_or(text.len(), |(i, _)| i)];

Confirmed Crash-Causing Emoji

The specific emoji causing the crash is ✅ (White Heavy Check Mark, U+2705).

The error message explicitly identifies this:

byte index 2 is not a char boundary; it is inside '✅' (bytes 0..3) of `✅`

UTF-8 Byte Analysis

Character: ✅ (U+2705)
UTF-8 bytes: E2 9C 85 (3 bytes)
             ↑  ↑  ↑
             0  1  2  ← byte indices

Attempted slice at index 2 → INVALID (mid-character)

The code attempts to slice the string at byte index 2, which lands on 0x85 - the third byte of the 3-byte emoji sequence. This creates an invalid UTF-8 string, triggering the panic.

Other Potentially Affected Emojis

Any multi-byte emoji could trigger this bug if the slicing logic encounters it:

| Emoji | Unicode | UTF-8 Bytes | Risk |
|-------|---------|-------------|------|
| ✅ | U+2705 | 3 bytes | CONFIRMED |
| ❌ | U+274C | 3 bytes | High (similar encoding) |
| ✓ | U+2713 | 3 bytes | Present |
| ⚠️ | U+26A0 + FE0F | 3+ bytes | Present |
| 🎯 | U+1F3AF | 4 bytes | Present |
| 📁 | U+1F4C1 | 4 bytes | Present |
| 🤖 | U+1F916 | 4 bytes | Present |
| ⚙ | U+2699 | 3 bytes | Present |
| 💻 | U+1F4BB | 4 bytes | Present |

Workarounds

1. Use /export <name> - Providing a name sometimes avoids the crash (different code path?)
2. Retry - The command occasionally succeeds on subsequent attempts
3. Remove emojis - Temporarily remove emoji characters from CLAUDE.md files before exporting

Impact

• Severity: Medium-High
• User Impact: Cannot reliably export conversation history
• Data Loss Risk: Session context may be lost if user cannot export before session ends

Session Data

• Session ID: bf209d5d-c70f-4f42-85a7-bfb0eb16c8f8
• Crash Count: 12 occurrences in single session
• Session Size: 257KB at time of crashes
• Project: Contains 3 CLAUDE.md files with emoji content

Suggested Fix

The fix should ensure all string slicing operations in the export functionality use character-aware methods rather than byte indexing. Specifically:

1. Audit all &str[start..end] operations in export code path
2. Replace with character-boundary-safe alternatives:

• Use .chars() iterator for character-based operations
• Use .char_indices() for finding valid slice points
• Use crates like unicode-segmentation for grapheme-aware slicing

1. Add tests with multi-byte Unicode characters (emojis, CJK, etc.)

Additional Context

The crash message shows the panic handler itself failed (failed to initiate panic, error 5), suggesting this might be happening in a thread or context where normal panic handling is compromised.

Related

• Rust book: Slicing Strings
• Similar issues in other Rust projects with UTF-8 string handling

---

Reported: 2026-01-11
Reporter: Hal Casteel

What Should Happen?

claude code should not crash

Error Messages/Logs

hread '<unnamed>' (6264027) panicked at                         
  /rustc/ed61e7d7e242494fb7057f2657300d9e77bb4fcb/library/core     
  /src/str/mod.rs:833:21:                                          
  byte index 2 is not a char boundary; it is inside '✅'           
  (bytes 0..3) of `✅`                                             
  note: run with `RUST_BACKTRACE=1` environment variable to        
  display a backtrace                                              
  fatal runtime error: failed to initiate panic, error 5,          
  aborting                                                         
  [1]    14209 abort      claude

Steps to Reproduce

hread '<unnamed>' (6264027) panicked at
/rustc/ed61e7d7e242494fb7057f2657300d9e77bb4fcb/library/core
/src/str/mod.rs:833:21:
byte index 2 is not a char boundary; it is inside '✅'
(bytes 0..3) of ✅
note: run with RUST_BACKTRACE=1 environment variable to
display a backtrace
fatal runtime error: failed to initiate panic, error 5,
aborting
[1] 14209 abort claude

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude Code v2.1.4 Opus 4.5 Claude Max

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

VS Code integrated terminal

Additional Information

CLAUDE-CODE-BUG-REPORT-EXPORT-CRASH.md