[Bug] JSON Parse Error (13310) in Claude Code Action when commit messages contain Markdown links

[haeyongyoon-29cm]

Title: [Bug] JSON Parse Error (13310) in Claude Code Action when commit messages contain Markdown links

Description

anthropics/claude-code-action@v1 throws a SyntaxError: JSON Parse error when processing Pull Requests where commit messages contain Markdown link syntax (e.g., [text](url)).

Error Logs

SDK execution error: 13310
SyntaxError: JSON Parse error: Unable to parse JSON string
      at readMessages (/home/runner/_work/_actions/anthropics/claude-code-action/v1/base-action/node_modules/@anthropic-ai/claude-agent-sdk/sdk.mjs:13315:32)

Root Cause Analysis

The SDK fails to properly escape characters used in Markdown link syntax ([], ()) when serializing CLI configuration or environment data (mcp-config) into the JSONL stream.

Specifically, when Claude Code automatically generates or reads a commit message containing:
🤖 Generated with [Claude Code](https://claude.ai/claude-code)
The internal JSON stringification seems to produce an invalid JSON line, causing the readline interface in the SDK to fail during parsing.

Steps to Reproduce (Verification)

1. Scenario A (Success): PR with a simple commit message (e.g., "fix: update logic"). ✅ Works
2. Scenario B (Failure): PR with a Markdown link in the commit message (e.g., "refactor: use [Claude Code](https://www.google.com/search?q=url)"). ❌ Fails with Error 13310
3. Recovery: After amending the commit message to remove the []() characters, the action runs successfully. ✅ Works

Suggested Fix

The SDK's message-passing layer should ensure that all CLI-derived strings (like commit messages, PR titles, etc.) are strictly escaped using a robust JSON serializer before being piped to stdout.

Environment

• Action Version: anthropics/claude-code-action@v1
• Runner: ubuntu-latest
• Node.js: v18