@@ -1518,6 +1518,10 @@ the transport neither truncates history nor creates a Python decision or new
 authority. Missing, changed, non-private or over-64-MiB files fail closed.
 After a handler may have committed, an unverifiable response stays ambiguous
 and requires exact receipt readback, never automatic mutation retry.
+Both inline and private-file responses apply this rule to invalid encoding,
+JSON value limits and excessive nesting. A decoder failure cannot enter the
+pre-send startup retry path or erase possible durable acceptance; it reports
+`runtime_response_ambiguous` through the existing transport adapter.
 
 Source read and read/check reduction now compose inside one TypeScript request.
 Both context reading and commit preflight use one checkpoint request instead of
 
@@ -1066,6 +1066,9 @@ Goal 与重放；源码验证不代表已安装宿主采用或整 Goal 资格通
 使用同 UID 私有文件及字节数、SHA-256 摘要绑定；其他 effect 的默认传输边界不变。
 文件缺失、改变、权限不符或超过 64 MiB 时拒绝。Handler 可能已经提交后，无法验证
 的响应仍按不明确结果处理，要求精确回执回读，不能自动重试写入。
+内联响应和私有文件响应都将此规则用于编码无效、JSON 值超限和嵌套过深的情况。
+解码失败不能进入发送前的启动重试路径，也不能抹掉可能已经持久化的事实；
+既有传输 adapter 将其报告为 `runtime_response_ambiguous`。
 
 来源读取和 read/check 归约现在在一次 TypeScript 请求内完成。上下文读取与提交前
 检查各从两次 checkpoint 请求降为一次，完整权威事实不再先返回 Python 再传回 TS。
 
@@ -786,7 +786,8 @@ def _request_with_info(
                 raise EffectRuntimeResponseAmbiguous(method, timeout=timeout) from exc
         try:
             response = json.loads(b"".join(chunks).split(b"\n", 1)[0])
-        except (json.JSONDecodeError, IndexError):
+        except (ValueError, RecursionError):
+            # Decoder limits can fail after commit; they cannot authorize a retry.
             raise EffectRuntimeResponseAmbiguous(method, timeout=timeout) from None
         if isinstance(response, dict) and "result_ref" in response:
             response = _read_local_snapshot_response(
@@ -832,7 +833,7 @@ def _read_local_snapshot_response(
         if not isinstance(result, dict):
             raise ValueError("invalid local snapshot response")
         return result
-    except (OSError, ValueError, json.JSONDecodeError) as exc:
+    except (OSError, ValueError, RecursionError) as exc:
         raise EffectRuntimeResponseAmbiguous(method, timeout=timeout) from exc
 
 
 
@@ -0,0 +1,91 @@
+from __future__ import annotations
+
+import hashlib
+import json
+import os
+import socket
+from concurrent.futures import ThreadPoolExecutor
+from pathlib import Path
+from threading import Event
+
+import pytest
+
+from loopx.control_plane import effect_runtime
+
+
+@pytest.mark.parametrize("snapshot", [False, True], ids=["inline", "snapshot"])
+@pytest.mark.parametrize(
+    "result_bytes",
+    [b"[" * 100_000 + b"0" + b"]" * 100_000, b'"\xff"'],
+    ids=["excessive-depth", "invalid-utf8"],
+)
+def test_undecodable_response_is_ambiguous_without_redispatch(
+    tmp_path: Path, monkeypatch, snapshot: bool, result_bytes: bytes,
+) -> None:
+    monkeypatch.setattr(effect_runtime, "_runtime_dir", lambda: tmp_path)
+    fingerprint = effect_runtime._runtime_fingerprint_for_request()
+    finished = Event()
+    received_requests = []
+    with socket.socket() as listener:
+        listener.bind(("127.0.0.1", 0))
+        listener.listen()
+        listener.settimeout(0.05)
+        info = {
+            "schema_version": effect_runtime.EFFECT_RUNTIME_INFO_SCHEMA_VERSION,
+            "fingerprint": fingerprint,
+            "pid": os.getpid(),
+            "host": "127.0.0.1",
+            "port": listener.getsockname()[1],
+            "token": "fixture-token",
+        }
+        locator = effect_runtime._runtime_info_path(fingerprint)
+        locator.write_text(json.dumps(info), encoding="utf-8")
+
+        def serve_responses() -> None:
+            while not finished.is_set():
+                try:
+                    connection = listener.accept()[0]
+                except TimeoutError:
+                    continue
+                with connection:
+                    connection.settimeout(2)
+                    request_bytes = b""
+                    while b"\n" not in request_bytes:
+                        chunk = connection.recv(65536)
+                        if not chunk:
+                            raise AssertionError("request ended before its frame")
+                        request_bytes += chunk
+                    request = json.loads(request_bytes)
+                    received_requests.append(request)
+                    envelope = {
+                        "schema_version": effect_runtime.EFFECT_RUNTIME_RESPONSE_SCHEMA_VERSION,
+                        "request_id": request["request_id"],
+                        "ok": True,
+                    }
+                    response = json.dumps(envelope).encode()[:-1] + b',"result":' + result_bytes + b"}\n"
+                    if snapshot:
+                        Path(request["response_sink"]).write_bytes(response)
+                        envelope["result_ref"] = {
+                            "byte_count": len(response),
+                            "sha256": hashlib.sha256(response).hexdigest(),
+                        }
+                        response = json.dumps(envelope).encode() + b"\n"
+                    connection.sendall(response)
+
+        with ThreadPoolExecutor(max_workers=1) as executor:
+            server = executor.submit(serve_responses)
+            try:
+                with pytest.raises(effect_runtime.EffectRuntimeResponseAmbiguous) as error:
+                    effect_runtime.effect_runtime_request(
+                        "goal.checkpoint_read_context.commit" if snapshot else "turn_journal.write",
+                        {"operation_id": "fixture-operation"},
+                        timeout=2,
+                        large_local_snapshot=snapshot,
+                    )
+            finally:
+                finished.set()
+                server.result(timeout=3)
+
+    assert error.value.diagnostic_code == "runtime_response_ambiguous"
+    assert len(received_requests) == 1
+    assert json.loads(locator.read_text(encoding="utf-8")) == info