Check in the shell guard walks the final segments and appends the unknown-sites block signal twice: the block that caches each segment's walk and refuses a capped one is duplicated verbatim (guard.go, from f38daa9a), so a capped walk adds the same signal two times and the second walk is dead work. Found while fixing review4-guard.

Check in the shell guard walks the final segments and appends the unknown-sites block signal twice: the block that caches each segment's walk and refuses a capped one is duplicated verbatim (guard.go, from f38daa9a), so a capped walk adds the same signal two times and the second walk is dead work. Found while fixing review4-guard.

Grounds

• pursued: Check walks its final segments once and adds the unknown-sites signal at most once; a second copy of the block would show it wrong