restore(lang): full lang tree from ff3ef452 (306 files) — compiler, vm, shared, runner, c-abi, etc.\n\n- Restores lang/ directory (files≈306, dirs≈64) as per historical branch with selfhost sources\n- Keeps our recent parser index changes in compiler/* (merged clean by checkout)\n- Unblocks selfhost development and documentation references

lang/src/compiler/parser/parser_box.hako

@@ -14,11 +14,13 @@ using lang.compiler.parser.stmt.parser_control_box
 box ParserBox {
   gpos
   usings_json
+  externs_json
   stage3
 
   birth() {
     me.gpos = 0
     me.usings_json = "[]"
+    me.externs_json = "[]"
     me.stage3 = 0
     return 0
   }
@@ -152,6 +154,36 @@ box ParserBox {
     return me.usings_json
   }
 
+  // === extern_c annotations ===
+  add_extern_c(symbol, func) {
+    // Entry shape: {"symbol":"hako_add","func":"Name/Arity"}
+    local sym = match symbol { null => "", _ => symbol }
+    local fn  = match func   { null => "", _ => func }
+    local entry = "{\"symbol\":\"" + me.esc_json(sym) + "\",\"func\":\"" + me.esc_json(fn) + "\"}"
+    local cur = me.externs_json
+    if cur == null || cur.size() == 0 { cur = "[]" }
+    if cur == "[]" {
+      me.externs_json = "[" + entry + "]"
+      return 0
+    }
+    local pos = cur.lastIndexOf("]")
+    if pos < 0 {
+      me.externs_json = "[" + entry + "]"
+      return 0
+    }
+    me.externs_json = cur.substring(0, pos) + "," + entry + "]"
+    return 0
+  }
+
+  extract_externs(_src) {
+    // MVP: rely on ParserStmtBox to call add_extern_c during parse; here no-op for now.
+    return 0
+  }
+
+  get_externs_json() {
+    return me.externs_json
+  }
+
   // === Delegation to ParserExprBox ===
   parse_expr2(src, i) {
     local expr = new ParserExprBox()
@@ -236,4 +268,3 @@ static box ParserStub {
     return 0
   }
 }
-