docs(20.39): add Next Steps and mark hv1 unify + string scanner fix DONE; loop count_param: accept swapped < / <= (cmp Gt/Ge); add canaries for swapped_lt/lte

lang/src/mir/builder/internal/lower_loop_count_param_box.hako

@@ -79,8 +79,10 @@ static box LowerLoopCountParamBox {
         cmp = (op == ">") ? "Gt" : "Ge"
       } else { return null }
     } else {
-      // swapped (Int on lhs, Var i on rhs): L > i / L >= i (ascending)
-      if op != ">" && op != ">=" { return null }
+      // swapped (Int on lhs, Var i on rhs):
+      //   L > i   / L >= i   → ascending（i < L / i < L+1）→ cmp="Lt"（limit +1 for >=）
+      //   L < i   / L <= i   → descending（i > L / i >= L）→ cmp="Gt" / "Ge"
+      if op != ">" && op != ">=" && op != "<" && op != "<=" { return null }
       local k_lhs = s.indexOf("\"lhs\":{", k_cmp); if k_lhs < 0 { return null }
       local k_lim_t2 = s.indexOf("\"type\":\"Int\"", k_lhs)
       if k_lim_t2 >= 0 {
@@ -91,8 +93,17 @@ static box LowerLoopCountParamBox {
         limit = PatternUtilBox.find_local_int_before(s, lname3, k_cmp)
       }
       if limit == null { return null }
-      if op == ">=" { limit = StringHelpers.int_to_str(JsonFragBox._str_to_int(limit) + 1) }
-      cmp = "Lt"
+      if op == ">" {
+        cmp = "Lt"
+      } else if op == ">=" {
+        limit = StringHelpers.int_to_str(JsonFragBox._str_to_int(limit) + 1)
+        cmp = "Lt"
+      } else if op == "<" {
+        cmp = "Gt"
+      } else {
+        // op == "<="
+        cmp = "Ge"
+      }
     }
     // Body increment: Local i = Binary('+', Var i, Int step)
     local k_body_i = s.indexOf("\"name\":\"" + varname + "\"", k_loop)

lang/src/mir/builder/internal/lower_loop_simple_box.hako

@@ -58,12 +58,19 @@ static box LowerLoopSimpleBox {
         return null
       }
     } else {
-      // swapped: we expect op to be '>' or '>='
+      // swapped: L ? i
       if op == ">" {
         // L > i  ≡  i < L
       } else if op == ">=" {
         // L >= i ≡  i <= L ≡ i < (L+1)
         limit = StringHelpers.int_to_str(JsonFragBox._str_to_int(limit) + 1)
+      } else if op == "<" {
+        // L < i  ≡  i > L → for simple ascending loop (init=0, step=1) this pattern is not canonical;
+        // we treat as descending form not supported by simple box
+        return null
+      } else if op == "<=" {
+        // L <= i ≡ i >= L — same reason as above
+        return null
       } else {
         return null
       }