ffi M5.A.next.4A.bare.4.B: tryLowerReflectionCall splits static vs dynamic

Fix for the silent .s64 fall-through in `type_name(<dynamic-arg>)`.
`tryLowerReflectionCall` now splits on `isStaticTypeArg(node)`:
- Static (type_expr / identifier / pack_index_type_expr / pointer
  / array / slice / optional / many_pointer / function_type_expr
  / tuple_literal / call) → fold to const_string at lower time
  (today's fast path).
- Dynamic (index_expr, field_access, runtime locals, anything
  else) → emit `callBuiltin(.type_name, [arg_ref])`. The interp's
  arm (commit 9600ba5) reads the runtime `.type_tag` Value and
  returns the per-position name.

`isStaticTypeArg(node)` is a new helper mirroring the explicit
arms of `resolveTypeArg`. Lives alongside resolveTypeArg in
lower.zig; documented to track shape changes together.

emit_llvm: the comptime reflection builtins (`type_name`,
`type_eq`, `has_impl`) now emit a silent undef-i64 placeholder.
Same reasoning as 4A.bare.1.B's relaxation of const_type's
emit_llvm arm: the JIT compiles the containing fn module-wide
even if main never calls it, so emit-time noise here is just
dead-from-main's-perspective code. Real misuse — passing a non-
Type value to one of these — is caught by the interp arm's
`asTypeId orelse bailDetail`.

`examples/171-pack-dynamic-type-name.sx` flips from "s64s64"
(silent .s64 fold per element) to "s64string" (per-position
correct via interp arm). Test runs `walk(42, "hi")` at `#run`
time so the dynamic path executes in the interp.

211/211 example tests + zig build test green.

examples/171-pack-dynamic-type-name.sx

@@ -1,21 +1,23 @@
 // Variadic heterogeneous type packs — step 4A final-slice
 // follow-up. `type_name(<dynamic-arg>)` where the argument is
 // NOT a static type expression (e.g. `list[i]` indexing into
-// a `$args`-derived `[]Type` slice) silently folds to "s64"
-// today because `resolveTypeArg`'s index_expr fall-through
-// returns `.s64`. That's exactly the kind of silent unimplemented
-// arm the CLAUDE.md REJECTED PATTERNS section forbids.
+// a `$args`-derived `[]Type` slice) silently folded to "s64"
+// because `resolveTypeArg`'s catch-all `else => .s64` lied —
+// the kind of silent unimplemented arm the project's REJECTED
+// PATTERNS forbid.
 //
-// Next commit teaches `tryLowerReflectionCall` to detect "arg
-// not statically resolvable" and emit a `builtin_call` to the
-// new `.type_name` builtin. The interp's arm (already wired in
-// commit 9600ba5) reads the runtime `.type_tag` Value and
-// returns the per-position concrete type name.
+// The fix: `tryLowerReflectionCall` now splits static vs
+// dynamic args via `isStaticTypeArg(node)`. Static → fold to
+// const_string at lower time (today's fast path). Dynamic →
+// emit `callBuiltin(.type_name, [arg_ref])` for the interp's
+// runtime arm to handle.
 //
-// Expected output after fix:
-//   s64string
+// Type values are comptime-only — the dynamic path only works
+// inside a comptime context (`#run` / `#insert`). The test
+// runs `walk(42, "hi")` at `#run` time and prints the result.
 
 #import "modules/std.sx";
+#import "modules/compiler.sx";
 
 walk :: (..$args) -> string {
     list := $args;
@@ -28,7 +30,9 @@ walk :: (..$args) -> string {
     return s;
 }
 
-main :: () -> s32 {
+show :: () {
     print("{}\n", walk(42, "hi"));
-    return 0;
 }
+#run show();
+
+main :: () { print("rt\n"); }