Extract directives and rewrite header in one pass
Remove has written body hacks

No longer needed for require self since include is removed
Note include has been removed
Skip dup'in root
Drop asset root
Todo to avoid env digest for later
Append processed header to new buffer
Flip conditional order
Merge format and engine extension lookups
Engine content types can be looked up by extnames
Lazily check file outside of paths error
Drop :root_path from processor input hash
Merge into hash
Pass known content type into process