- Create child scope in Sema_CheckBlock for every block, matching
bootstrap sema.nim behavior (newScope for ekBlock).
- Fixes "var scoping bug in selfhost sema" where variables declared
with var inside if/while blocks shared parent function scope, causing
duplicate-definition errors between sibling if/else blocks, and C
scoping mismatch between user variables and compiled output.
- Remove stale workaround comments from lib/Json.bux (let instead of
var inside if blocks — no longer needed).
- Update sema.bux TODO comment for type table.