evalComptimeType did `interp.call(...) catch return null`, dropping the
interp's last_bail_detail; callers poisoned to .unresolved with no
diagnostic, so the sentinel reached LLVM emission and panicked
("unresolved type reached LLVM emission"), or hid behind a downstream
cascade.
Clear last_bail_detail before the call; on the catch emit a build-gating
.err at the construction expr's span ("comptime type construction
failed: {detail}", mirroring the #run surfacing in emit_llvm.zig), then
return null to keep the .unresolved poison — now gated by a real message
so no unresolved type reaches emission unannounced.
Empty-variant define now prints 'comptime define(): enum has no
variants' and exits 1 (no panic); make_enum-style computed-slice
failures show their root reason at the construction site.
37ec3da8cb