[tedy69]

Fixes #6112.

Match multipart boundaries with their CRLF prefix so boundary text inside a field or file is preserved. Adds Request and Response tests for text fields, binary files, following parts, and missing delimiters.

Validated with the fetch, unit, Web IDL, and busboy suites (2,233 tests passed), plus TypeScript and lint checks.

[mcollina]

lgtm

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.61%. Comparing base (671acb3) to head (0974956).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6113   +/-   ##
=======================================
  Coverage   91.61%   91.61%           
=======================================
  Files         113      113           
  Lines       44070    44071    +1     
=======================================
+ Hits        40375    40376    +1     
  Misses       3695     3695           

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