EXAMPLES:

  # Content overwrite
  iwe update -k notes/draft -c "# Draft\n\nNew content."
  cat new-content.md | iwe update -k notes/draft -c -

  # Frontmatter mutation on a single document
  iwe update -k notes/draft --set status=published --set priority=10

  # Frontmatter mutation across many documents
  iwe update --filter 'status: draft' --set 'reviewed=true'
  iwe update --filter 'status: archived' --unset draft_notes

  # Preview without writing
  iwe update --filter 'status: draft' --set status=published --dry-run

VALUE PARSING:

  --set FIELD=VALUE parses VALUE as a YAML scalar:
    --set 'priority=5'       -> integer 5
    --set 'reviewed=true'    -> boolean true
    --set 'status=draft'     -> string "draft"
    --set 'tags=[a, b]'      -> list ["a", "b"]
    --set 'count="5"'        -> string "5"

NOTES:

  - The --content mode does not touch frontmatter; the --set/--unset mode
    does not touch the document content. Use both in two passes if needed.
  - Frontmatter is re-serialized as YAML 1.2 after mutation, so quote
    styles may change on untouched fields.
  - Mutation mode protects reserved frontmatter fields (names starting
    with _, $, ., #, or @) from being set or unset.
