fix(adapter): route multiline prompts over stdin on Windows .cmd shims

On Windows, an npm-installed `claude` resolves to a .cmd shim, so
_resolve_launch_command wraps it in `cmd.exe /d /s /c ...`. cmd.exe treats a
newline inside an argument as end-of-command, silently truncating a multiline
prompt at the first line break -- the agent received only the "## Task Brief"
heading and replied that no task was included.

Detect this case in _interactive_prompt_transport and deliver the prompt over
the existing stdin channel instead. The guard requires all three of: nt
platform, a newline in the prompt, and a command that resolves to .cmd/.bat.
It reuses _resolve_windows_command_shim so the check matches the same
resolution logic that decides whether cmd.exe wrapping happens.

Also records prompt_transport_reason in the stdin metadata to distinguish this
trigger from the pre-existing oversized-prompt path.

Verified against the real claude CLI: transport flips to stdin and the CLI
confirms all prompt lines arrive intact.

opc/layer3_agent/adapters/claude_code.py

@@ -3,6 +3,8 @@
 from __future__ import annotations
 
 import asyncio
+import os
+import shutil
 from pathlib import Path
 from typing import Any
 
@@ -250,10 +252,16 @@ class ClaudeCodeAdapter(ExternalAgentAdapter):
         }
 
     def _build_stdin_prompt_metadata(self, prompt: str) -> dict[str, object]:
+        prompt_bytes = len(prompt.encode("utf-8"))
         return {
             "prompt_transport": "stdin",
-            "prompt_bytes": len(prompt.encode("utf-8")),
+            "prompt_bytes": prompt_bytes,
             "stdin_prompt_channel": "pipe",
+            "prompt_transport_reason": (
+                "prompt_too_large_for_argv"
+                if prompt_bytes > self._INTERACTIVE_ARGV_PROMPT_MAX_BYTES
+                else "windows_multiline_argv_unsafe"
+            ),
             "interactive_input_limitation": (
                 "large initial prompt is delivered through stdin; live approval replies "
                 "are unavailable after stdin closes"
@@ -261,8 +269,28 @@ class ClaudeCodeAdapter(ExternalAgentAdapter):
         }
 
     def _interactive_prompt_transport(self, prompt: str) -> str:
-        prompt_bytes = len(prompt.encode("utf-8"))
+        if len(prompt.encode("utf-8")) > self._INTERACTIVE_ARGV_PROMPT_MAX_BYTES:
-        return "argv" if prompt_bytes <= self._INTERACTIVE_ARGV_PROMPT_MAX_BYTES else "stdin"
+            return "stdin"
+        return "stdin" if self._windows_multiline_argv_is_unsafe(prompt) else "argv"
+
+    def _windows_multiline_argv_is_unsafe(self, prompt: str) -> bool:
+        # `claude` installed via npm resolves to a `.cmd` shim on Windows, so
+        # the spawn path wraps it in `cmd.exe /d /s /c ...`. cmd.exe treats a
+        # newline inside an argument as end-of-command, which silently
+        # truncates a multiline prompt at the first line break (the agent then
+        # sees just "## Task Brief"). Route such prompts over stdin instead.
+        if os.name != "nt":
+            return False
+        if "\n" not in prompt and "\r" not in prompt:
+            return False
+        command = self.configured_command()
+        resolved = shutil.which(command)
+        if not resolved:
+            # Unresolvable here means _resolve_launch_command will also fail to
+            # resolve it and spawn the bare name, which cmd.exe never wraps.
+            return False
+        resolved = self._resolve_windows_command_shim(command, resolved)
+        return os.path.splitext(str(resolved))[1].lower() in {".cmd", ".bat"}
 
     @staticmethod
     def _redact_prompt_arg(cmd: list[str], prompt: str) -> list[str]:

tests/test_external_agent_monitoring.py

@@ -3137,6 +3137,7 @@ class ExternalAgentMonitoringTests(unittest.IsolatedAsyncioTestCase):
         task = Task(title="demo", description="body")
         prompt = adapter.build_task_prompt(task)
 
+        with patch.object(ClaudeCodeAdapter, "_windows_multiline_argv_is_unsafe", return_value=False):
             cmd, metadata = adapter.build_interactive_invocation(task, workspace_path="/repo")
 
         self.assertEqual(cmd[-2:], ["--", prompt])
@@ -3150,6 +3151,7 @@ class ExternalAgentMonitoringTests(unittest.IsolatedAsyncioTestCase):
             config=ExternalAgentConfig(command="claude", approval_mode="full-auto")
         )
         task = Task(title="demo", description="body")
+        with patch.object(ClaudeCodeAdapter, "_windows_multiline_argv_is_unsafe", return_value=False):
             cmd, metadata = adapter.build_interactive_invocation(task, workspace_path="/repo")
         proc = type("Proc", (), {"pid": 321, "stdin": None, "stdout": object(), "stderr": object()})()
 
@@ -3179,6 +3181,7 @@ class ExternalAgentMonitoringTests(unittest.IsolatedAsyncioTestCase):
             config=ExternalAgentConfig(command="claude", approval_mode="auto")
         )
         task = Task(title="demo", description="body")
+        with patch.object(ClaudeCodeAdapter, "_windows_multiline_argv_is_unsafe", return_value=False):
             cmd, metadata = adapter.build_interactive_invocation(task, workspace_path="/repo")
         proc = type("Proc", (), {"pid": 321, "stdin": None, "stdout": object(), "stderr": object()})()
 
@@ -3203,6 +3206,90 @@ class ExternalAgentMonitoringTests(unittest.IsolatedAsyncioTestCase):
         self.assertEqual(spawn_mock.await_args.kwargs["stdin"], asyncio.subprocess.PIPE)
         self.assertEqual(metadata["stdin_policy"], "pipe_open")
 
+    def test_claude_adapter_windows_multiline_prompt_uses_stdin_transport(self) -> None:
+        adapter = ClaudeCodeAdapter()
+        task = Task(
+            title="demo",
+            description="## Task Brief\n在工作区里创建一个 hello.py\n\n## OpenOPC Context\nctx",
+            metadata={"external_prompt_contract": "description_is_full_prompt"},
+        )
+        prompt = adapter.build_task_prompt(task)
+
+        with patch("opc.layer3_agent.adapters.claude_code.os.name", "nt"), \
+            patch(
+                "opc.layer3_agent.adapters.claude_code.shutil.which",
+                return_value=r"C:\Users\me\AppData\Roaming\npm\claude.CMD",
+            ):
+            cmd, metadata = adapter.build_interactive_invocation(task, workspace_path="/repo")
+
+        self.assertNotIn("--", cmd)
+        self.assertNotIn(prompt, cmd)
+        self.assertIn("--input-format", cmd)
+        self.assertEqual(cmd[cmd.index("--input-format") + 1], "text")
+        self.assertEqual(metadata["prompt_transport"], "stdin")
+        self.assertEqual(metadata["stdin_prompt_channel"], "pipe")
+        self.assertEqual(metadata["prompt_transport_reason"], "windows_multiline_argv_unsafe")
+        self.assertEqual(
+            adapter.stdin_policy_for_process(cmd, metadata),
+            "pipe_prompt_then_close",
+        )
+
+    def test_claude_adapter_windows_single_line_prompt_stays_on_argv(self) -> None:
+        adapter = ClaudeCodeAdapter()
+        task = Task(
+            title="demo",
+            description="创建一个 hello.py",
+            metadata={"external_prompt_contract": "description_is_full_prompt"},
+        )
+        prompt = adapter.build_task_prompt(task)
+
+        with patch("opc.layer3_agent.adapters.claude_code.os.name", "nt"), \
+            patch(
+                "opc.layer3_agent.adapters.claude_code.shutil.which",
+                return_value=r"C:\Users\me\AppData\Roaming\npm\claude.CMD",
+            ):
+            cmd, metadata = adapter.build_interactive_invocation(task, workspace_path="/repo")
+
+        self.assertEqual(cmd[-2:], ["--", prompt])
+        self.assertEqual(metadata["prompt_transport"], "argv")
+
+    def test_claude_adapter_windows_multiline_batch_prompt_uses_stdin_transport(self) -> None:
+        adapter = ClaudeCodeAdapter()
+        task = Task(
+            title="demo",
+            description="## Task Brief\n在工作区里创建一个 hello.py",
+            metadata={"external_prompt_contract": "description_is_full_prompt"},
+        )
+        prompt = adapter.build_task_prompt(task)
+
+        with patch("opc.layer3_agent.adapters.claude_code.os.name", "nt"), \
+            patch(
+                "opc.layer3_agent.adapters.claude_code.shutil.which",
+                return_value=r"C:\Users\me\AppData\Roaming\npm\claude.CMD",
+            ):
+            cmd, metadata = adapter.build_invocation(task, workspace_path="/repo")
+
+        self.assertNotIn("--", cmd)
+        self.assertNotIn(prompt, cmd)
+        self.assertIn("--input-format", cmd)
+        self.assertEqual(metadata["prompt_transport"], "stdin")
+        self.assertEqual(metadata["prompt_transport_reason"], "windows_multiline_argv_unsafe")
+
+    def test_claude_adapter_posix_multiline_prompt_stays_on_argv(self) -> None:
+        adapter = ClaudeCodeAdapter()
+        task = Task(
+            title="demo",
+            description="## Task Brief\nline two",
+            metadata={"external_prompt_contract": "description_is_full_prompt"},
+        )
+        prompt = adapter.build_task_prompt(task)
+
+        with patch("opc.layer3_agent.adapters.claude_code.os.name", "posix"):
+            cmd, metadata = adapter.build_interactive_invocation(task, workspace_path="/repo")
+
+        self.assertEqual(cmd[-2:], ["--", prompt])
+        self.assertEqual(metadata["prompt_transport"], "argv")
+
     def test_claude_adapter_large_interactive_prompt_uses_stdin(self) -> None:
         adapter = ClaudeCodeAdapter()
         prompt = "x" * (ClaudeCodeAdapter._INTERACTIVE_ARGV_PROMPT_MAX_BYTES + 1)