phase: 20.49 COMPLETE; 20.50 Flow+String minimal reps; 20.51 selfhost v0/v1 minimal (Option A/B); hv1-inline binop/unop/copy; docs + run_all + CURRENT_TASK -> 21.0

apps/macros/examples/array_prepend_zero_macro.hako

@@ -0,0 +1,46 @@
+// array_prepend_zero_macro.hako
+// MacroBoxSpec.expand: prepend 0 to every Array elements list in AST JSON v0
+// Contract: expand(json: string) -> string (AST JSON v0)
+
+static box MacroBoxSpec {
+  expand(json) {
+    local s, out, i, pat, plen, ins
+    s = json
+    out = ""
+    i = 0
+    pat = "\"kind\":\"Array\",\"elements\":["
+    plen = pat.length()
+    ins = "{\"kind\":\"Literal\",\"value\":{\"type\":\"int\",\"value\":0}}"
+
+    loop(i < s.length()) {
+      if i + plen <= s.length() && s.substring(i, i + plen) == pat {
+        // Copy the Array header
+        out = out + pat
+        // Look ahead: if next is ']' it's empty array; otherwise add comma after inserted element
+        if i + plen < s.length() && s.substring(i + plen, i + plen + 1) != "]" {
+          out = out + ins + ","
+        } else {
+          out = out + ins
+        }
+        i = i + plen
+        continue
+      }
+      // Also support reversed key order: ..."elements":[ ... ],"kind":"Array"
+      if i + 12 <= s.length() && s.substring(i, i + 12) == "\"elements\":[" {
+        // We will inject blindly here assuming this 'elements' belongs to Array (per schema it does)
+        out = out + "\"elements\":["
+        if i + 12 < s.length() && s.substring(i + 12, i + 13) != "]" {
+          out = out + ins + ","
+        } else {
+          out = out + ins
+        }
+        i = i + 12
+        continue
+      }
+      // Copy-through
+      out = out + s.substring(i, i + 1)
+      i = i + 1
+    }
+    return out
+  }
+}