A UTF-8 BOM saved into a SKILL.md (e.g. Notepad or PowerShell `>`) is kept by
read_text(encoding="utf-8"), so the string handed to parse_frontmatter starts
with the BOM and the startswith("---") fence check fails. The whole frontmatter
is then silently dropped: the skill loads with no name/description, `platforms`
gating falls open (a macOS-only skill becomes visible everywhere), and
required_environment_variables / metadata.hermes.config setup never fires.
Strip a single leading BOM at the top of parse_frontmatter, the shared
chokepoint for every local skill-loading path (_parse_skill_file,
discover_all_skill_config_vars, DESCRIPTION.md parsing, _inject_skill_config,
and the tools/skills_tool._parse_frontmatter re-export), so the whole class is
covered, not just the reported site. Only the leading marker is removed; a BOM
mid-content is left as data. Mirrors the existing file-tools BOM handling
(#35278) and CONTRIBUTING.md "File encoding".
Adds tests: BOM'd frontmatter parses identically to plain, the body is
BOM-free, platforms gating and config-var extraction survive a BOM, and an
end-to-end BOM-write / plain-read round trip (mirroring _parse_skill_file).
Que0x
a4ecb3da9a