vm/router: minimal special-method extension (equals/1); toString mapping kept

mir: add TypeCertainty to Callee::Method (diagnostic only); plumb through builder/JSON/printer; backends ignore behaviorally

using: confirm unified prelude resolver entry for all runner modes

docs: update Callee architecture with certainty; update call-instructions; CURRENT_TASK note

tests: quick 40/40 PASS; integration (LLVM) 17/17 PASS

apps/lib/json_native/lexer/scanner.nyash

@@ -303,6 +303,10 @@ box JsonScanner {
             if ch == "\"" {
                 // 終了クォート
                 me.advance()
+                // Safety: literal must include both quotes → length >= 2
+                if me.position - start_pos < 2 {
+                    return null
+                }
                 return me.text.substring(start_pos, me.position)
             } else {
                 if ch == "\\" {