The JS contains? used `k in c` which throws TypeError on strings.
The Python version silently returned False for strings. Both now
use indexOf/`in` for substring matching on strings.
Fixes: sx.js MOUNT PARSE ERROR on blog index where
(contains? current-local-href "?") was evaluated client-side.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>