diff --git a/workflows/coding.mjs b/workflows/coding.mjs
index f5aa7a5..3f2ee84 100644
--- a/workflows/coding.mjs
+++ b/workflows/coding.mjs
@@ -174,7 +174,9 @@ const ACTION_RESULT_SCHEMA = { type:'object', additionalProperties:false,
     error:{type:'string'},
     detail:{type:'string'} } }
 
-const ROOT = args?.projectRoot || '.'
+// 兼容 harness 把 args 以 JSON 字符串（而非对象）传入的情况。
+const ARGS = typeof args === 'string' ? (() => { try { return JSON.parse(args) } catch { return undefined } })() : args
+const ROOT = ARGS?.projectRoot || '.'
 // ROOT 必须是绝对路径——相对 '.' 会绑定到子代理隐式 cwd，无保证。
 if (ROOT === '.' || !(/^(?:\/|[A-Za-z]:[\\/])/.test(ROOT))) {
   throw new Error(`HALT invalid-projectRoot: must be absolute, got ${JSON.stringify(ROOT)}. coding-start 必须把绝对路径传入 args.projectRoot。`)