Phase 7g: the compiler builds its IR with interpolation, not +

Answering your readability point directly: the compiler's own string-building —
left uglier by the 7c `+` migration, e.g. `emit_bind(("load i32, ptr " + ip))` —
now reads as interpolation:

  emit_bind(("load i32, ptr " + ip))            -> emit_bind(`load i32, ptr {ip}`)
  emit_bind(("icmp eq i32 " + (kv + (", " + itoa(ak)))))
                                                -> emit_bind(`icmp eq i32 {kv}, {itoa(ak)}`)
  perr(("assign to unknown " + t.s))            -> perr(`assign to unknown {t.s}`)

164 concat chains across selfhost converted by a tool that flattens the `+` tree,
keeps call/index parens (only grouping parens are rewritten), and converts only
**brace-free** literals — LLVM IR structure strings full of `{`/`}` stay as `+`
rather than becoming awkward `{{`/`}}`. No new language surface; interpolation
already desugars to the same concat.

Reseeded (22565 lines); C-free fixpoint holds byte-for-byte (the strongest proof
the reconstruction is exact); goldens identical; 18/18.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

selfhost/emit_decl.ludic

@@ -33,7 +33,7 @@ fn emit_fn(d: Node) -> void {
   if not g_term { emit("  br label %ret\n") }
   emit("ret:\n")
   if (rl == "void") { emit("  ret void\n") }
-  else { let r = emit_bind(("load " + (rl + (", ptr %retval"))));  emit("  ret ");  emit(rl);  emit(" ");  emit(r);  emit("\n") }
+  else { let r = emit_bind(`load {rl}, ptr %retval`);  emit("  ret ");  emit(rl);  emit(" ");  emit(r);  emit("\n") }
   code = saved
   emit("define ");  emit(rl);  emit(" @fn_");  emit(d.s);  emit("(");  emit_params_sig(d);  emit(") {\nentry:\n")
   emit(buf_str(falloc))