Claude Fixed a Bold Rendering Bug in markdown-it and Submitted the Pull Request

What Happened

While writing a blog post, I noticed broken rendering:

ホルムズ海峡は世界の海上石油輸送の**20〜25%**が通過する。

The ** markers were displayed as plain text instead of rendering bold.

Adding spaces around the markers fixed it — but inserting spaces in Japanese text is unnatural. This was a bug.

Root Cause

The scanDelims function in markdown-it-py.

In the CommonMark spec, ** must be a right-flanking delimiter to close bold. The check:

right_flanking = not (isLastPunctChar and not (isNextWhiteSpace or isNextPunctChar))

For the closing ** in **46%**を:

lastChar='%' → punctuation → isLastPunctChar=True
nextChar='を' → CJK character → neither whitespace nor punctuation

Result: right_flanking = False. The closing ** is rejected.

CJK characters after ASCII punctuation break bold rendering. This affects Japanese, Chinese, and Korean text.

The Fix

6 lines added to scanDelims in state_inline.py. Treat CJK characters (U+2E80+) as punctuation so they are recognized as word boundaries:

# Treat CJK ideographs as punctuation for flanking delimiter checks
                if not isNextPunctChar and ord(nextChar) > 0x2E7F:
                    isNextPunctChar = True
                if not isLastPunctChar and ord(lastChar) > 0x2E7F:
                    isLastPunctChar = True

Test results:

Input	Before	After
`湾岸の46%を供給`	** remains as text	46% renders bold
`の20〜25%が通過する`	** remains as text	20〜25% renders bold
`日本語の太字テスト`	works	works
`English bold test`	works	works

No impact on English-only text.

What Claude Code Did

From bug discovery to PR submission — I never looked at or read the code myself.

Found the bug — noticed broken rendering in blog build output, instructed Claude
Identified the cause — read markdown-it-py source, analyzed scanDelims flanking delimiter logic
Directed the fix — Claude initially suggested creating a patch script, but I instructed it to fix the package directly. Claude created the 6-line fix treating CJK characters as punctuation
Tested — 8 test patterns in both Japanese and English
Created a fork — aiseed-dev/markdown-it-py with fix/cjk-emphasis branch
Submitted a PR — executablebooks/markdown-it-py#387
Updated the project — switched requirements.txt to the fork, rebuilt all pages

No Need to Outsource

Traditionally, this kind of work would require:

Filing a bug report and commissioning investigation
External library research and fix strategy review
Fork management and PR creation
Test creation and execution

Outsourcing this would cost days to weeks, plus the expense.

I found a bug while writing a blog post, instructed Claude Code, and it did exactly what outsourcing to a contractor would have done.

There is no longer any need to outsource to contractors.

All you need is the ability to describe the problem accurately and judge the results. The ability to read and write code is no longer required on the human side.