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.
Step 4A final follow-up's lock-in. `type_name(<arg>)` where
<arg> is NOT a statically resolvable type expression (e.g.
`list[i]` indexing into a `$args`-derived `[]Type` slice)
silently folds to "s64" today because `resolveTypeArg`'s
index_expr fall-through returns `.s64` (the catch-all `else =>
.s64` at the bottom of the switch).
This is exactly the kind of silent unimplemented arm the
project's REJECTED PATTERNS section forbids — the user gets
"s64" for every element of an arbitrary pack, not the per-
position concrete type they expect.
`examples/171-pack-dynamic-type-name.sx` exercises a builder-
shaped fn: walks `$args` via runtime indexing, calls
`type_name(list[i])` per position, concatenates the results.
For `walk(42, "hi")` the expected output is "s64string".
Today's output is "s64s64" — the silent fold strikes twice.
Cadence shape 2: expected output is the WORKING shape; today's
diff fails. Next commit teaches `tryLowerReflectionCall` to
detect "arg not statically resolvable" and emit a builtin_call
to `.type_name` so the interp's runtime arm (wired in commit
9600ba5, M5.A.next.4.1) handles the dynamic case.
210/210 + 1 expected-failing = 211 total. zig build test green.
