The /api/media endpoint only serves files from ~/.hermes, /tmp, and the
active workspace. Power users with media in custom directories (models,
Downloads, Pictures, ComfyUI outputs) have no way to serve those files
inline without copying or symlinking.
Add MEDIA_ALLOWED_ROOTS env var — a colon-separated list of absolute
paths — that extends the allowed roots at runtime. Each entry is resolved
and validated as an existing directory before being appended. Non-existent
or invalid paths are silently skipped.
This is purely additive: the built-in security whitelist is unchanged,
and if MEDIA_ALLOWED_ROOTS is unset, behavior is identical to before.
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