Markdown Linter

This is a script-strategy skill. The script in scripts/main.py reads the Markdown file path from SKILLFORGE_INPUT, runs a built-in linter against it (no third-party dependencies — only the Python standard library), and prints findings to stdout, one per line.

Output format (one finding per line):

<line_number>:<column>:<severity>:<rule>:<message>

Severities: error, warning, info. Rules:

• heading-order — H2 follows H1, H3 follows H2, no skipped levels.
• trailing-whitespace — lines ending in space or tab.
• tab-indent — tabs used for indent (Markdown prefers spaces).
• missing-alt — ![](url) with empty alt text.
• bare-url — http(s) URL not wrapped in <...> or [text](url).
• mixed-list-marker — list switches between -, *, + inside the same block.

When the file does not exist or SKILLFORGE_INPUT is empty, the script prints 0:0:error:io:no input file and exits 0.

Prerequisites:

• config.security.allowScripts: true.
• python3 on the host's resolved PATH.
• SKILLFORGE_INPUT set to the absolute path of the .md file to lint.