utf-8-sig exists to tolerate BOMs that Windows tooling adds to files
users edit. /proc and /sys files are generated by the Linux kernel, never
BOM'd and absent on Windows, so -sig there only muddies the read/write
policy. Switch every literal /proc/ and /sys/ read to utf-8 and teach
the footgun read rule that string literals starting with /proc/ or
/sys/ are exempt (user-edited files keep utf-8-sig).
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