phase-20.45: PRIMARY no-fallback reps + MIR v0 shape fixes

- Fix MIR v0 shape in lowers: functions[] + name="main" + blocks.id
  * lower_return_int_box.hako
  * lower_return_binop_box.hako
- runner_min: adopt LowerReturnBinOpBox before ReturnInt
- Add PRIMARY no-fallback canaries (all PASS):
  * return-binop / array-size / load-store / return-logical (OR)
- Fix phase2043 runner_min canary alias (Runner -> BuilderRunnerMinBox)
- Update docs: phase-20.45 README (PRIMARY reps), CURRENT_TASK progress

Ancillary: keep builder/provider/canary files in sync; no unrelated behavior changes.

src/runner/modes/vm_fallback.rs

@@ -57,39 +57,14 @@ impl NyashRunner {
         // Dev sugar pre-expand: @name = expr → local name = expr
         code2 = crate::runner::modes::common_util::resolve::preexpand_at_local(&code2);
         // Hako-friendly normalize: strip leading `local ` at line head for Nyash parser compatibility.
-        fn looks_like_hako_code(s: &str) -> bool {
-            s.contains("using selfhost.") || s.lines().any(|l| l.trim_start().starts_with("local "))
-        }
-        fn strip_local_decl(s: &str) -> String {
-            let mut out = String::with_capacity(s.len());
-            for line in s.lines() {
-                let leading = line.len() - line.trim_start().len();
-                let (indent, rest) = line.split_at(leading);
-                if rest.starts_with("local ") || rest.starts_with("local\t") {
-                    let bytes = rest.as_bytes();
-                    let mut i = 5; // skip 'local'
-                    while i < bytes.len() && (bytes[i] == b' ' || bytes[i] == b'\t') { i += 1; break; }
-                    out.push_str(indent);
-                    out.push_str(&rest[i..]);
-                    out.push('\n');
-                } else {
-                    out.push_str(line);
-                    out.push('\n');
-                }
-            }
-            out
-        }
-        if looks_like_hako_code(&code2) {
-            code2 = strip_local_decl(&code2);
+        if crate::runner::modes::common_util::hako::looks_like_hako_code(&code2) {
+            code2 = crate::runner::modes::common_util::hako::strip_local_decl(&code2);
         }
 
         // Fail‑Fast (opt‑in): Hako 構文を Nyash VM 経路で実行しない
         // 目的: .hako は Hakorune VM、MIR は Core/LLVM に役割分離するためのガード
         {
-            let on = match std::env::var("HAKO_FAIL_FAST_ON_HAKO_IN_NYASH_VM").ok().as_deref() {
-                Some("0")|Some("false")|Some("off") => false,
-                _ => true,
-            };
+            let on = crate::runner::modes::common_util::hako::fail_fast_on_hako();
             if on {
                 let s = code2.as_str();
                 let hako_like = s.contains("static box ") || s.contains("using selfhost.") || s.contains("using hakorune.");