Edit/Write/Bash tools fail with JSON Parse error: Unterminated string when content contains LaTeX math or special characters

[iwantapear]

Bug Description

Tools edit, write, bash, and task consistently fail with JSON Parse error: Unterminated string when the parameter content contains:

• LaTeX math delimiters ($, $$)
• Backslash sequences (\tanh, \sum, \frac, \text)
• Pipes (|)
• Mixed CJK + ASCII characters
• Content exceeding ~50 lines

The read tool works fine (parameters are simple paths + numbers with no special characters).

Reproduction

1. Open any file containing LaTeX math (e.g., a markdown file with $...$ formulas)
2. Try to use the edit tool to replace a section containing $, $$, \frac, etc.
3. Tool call fails immediately with: JSON Parse error: Unterminated string

Minimal reproduction — even this fails:

edit(file_path="/tmp/test.md", old_string="hello", new_string="world")
→ JSON Parse error: Unterminated string

Root Cause Analysis

Tool parameters are passed via XML invoke tags and internally serialized to JSON. The JSON serializer cannot properly escape special characters ($, ", \, \n) in string-type parameters, causing the string termination boundary to be misdetected.

• Works: read tool (parameters are file paths + integers, no special chars)
• Fails: edit, write, bash, task (parameters contain markdown/LaTeX content with $, \, ")

Environment

• MiMo Code version: 0.1.3
• Platform: linux (ARM64)
• Binary: ~/.mimocode/bin/mimo (ELF 64-bit LSB executable, ARM aarch64)

Workaround

Delegate file edits to subagents — subagents use a different parameter passing path that doesn't trigger this bug.

Impact

This bug makes it impossible to directly edit any file containing LaTeX math, markdown formulas, or mixed-language content. Every edit/write attempt consumes a full turn cycle with no visible output to the user, appearing as a terminal hang.

Related

• Observed across multiple sessions (confirmed in session checkpoints)
• Also affects bash tool with any content
• task tool with long prompts also fails