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/common_util/hako.rs

@@ -0,0 +1,48 @@
+/*!
+ * Hako-like source detection and minimal normalization helpers.
+ *
+ * - looks_like_hako_code: heuristics to detect Hako surface in Nyash path
+ * - strip_local_decl: drop leading `local ` at line head for Nyash parser compatibility
+ * - fail_fast_on_hako: env-gated policy (default ON) to fail fast on Hako-like source in Nyash VM path
+ */
+
+/// Heuristic detection of Hako-like source (development-only convenience)
+pub fn looks_like_hako_code(s: &str) -> bool {
+    s.contains("using selfhost.")
+        || s.contains("using hakorune.")
+        || s.lines().any(|l| l.trim_start().starts_with("local "))
+}
+
+/// Remove leading `local ` declarations at line head to keep Nyash parser stable
+pub 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; // after '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
+}
+
+/// Policy toggle: fail fast when Hako-like code enters Nyash VM path
+/// Default: ON (true)
+pub fn fail_fast_on_hako() -> bool {
+    match std::env::var("HAKO_FAIL_FAST_ON_HAKO_IN_NYASH_VM").ok().as_deref() {
+        Some("0") | Some("false") | Some("off") => false,
+        _ => true,
+    }
+}
+