primitive? in make_server_env was checking env bindings only (NativeFn),
missing all 132 primitives in the Sx_primitives hashtable. Now checks
both primitives table and env. get-primitive similarly fixed.
replace primitive now coerces SxExpr/Thunk/RawHTML/etc to strings instead
of crashing with "replace: 3 string args" — fixes aser JIT DISABLED.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>