Extract the admin trackerHead <head> injection into a pure injectTrackerHead()
and test it: a snippet containing $&/$$/backtick-dollar survives BYTE-FOR-BYTE
(pins the function-replacer fix), empty/whitespace/undefined and a missing </head>
leave the html unchanged.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>