Here's exactly what each skill says about replying to comments:

  crit:crit skill (SKILL.md, Step 4):

  ▎ 5. Reply to the comment with what you did: crit comment --reply-to <id> --author 'Claude Code' '<what you did>'
  ▎
  ▎ When addressing multiple comments, use --json to reply to them all in one call:
  ▎
  ▎ echo '[
  ▎   {"reply_to": "c_a1b2c3", "body": "Fixed"},
  ▎   {"reply_to": "c_d4e5f6", "body": "Refactored as suggested"}
  ▎ ]' | crit comment --json --author 'Claude Code'

  crit:crit-cli skill (SKILL.md, "Replying to comments" section):

  ▎ After addressing a comment, reply to it using the CLI:
  ▎
  ▎ crit comment --reply-to c_a1b2c3 --author 'Claude Code' 'Fixed by extracting to helper'
  ▎ crit comment --reply-to r_f1e2d3 --author 'Claude Code' 'All issues addressed'
  ▎
  ▎ This adds a reply to the comment thread. Works for both file comment IDs (e.g. c_a1b2c3) and review comment IDs (e.g. r_f1e2d3). Only use --resolve when the user explicitly asks you to resolve a comment — never resolve proactively.

  Neither skill mentions anything about markdown formatting in reply bodies — they only show plain-text examples like 'Fixed', 'Refactored as suggested', 'Added null check on line 42', 'All issues addressed'. So my earlier statement that "the crit skill instructions don't mention markdown is supported in replies" is
  accurate — there's no documentation either way.