Byte-id-neutral mechanical prep in the ww driver:
- delete dead helper cstrstartswith (zero call sites)
- isidentbyte: 3 nested if(x){if(y){ -> if(x && y) collapses
- char-lit subs in comparison context: isidentbyte bounds,
locateimport ':', basenameoff '/'
Regenerated main.combined.ww.