fix(agent): prevent safety guard false positives and streamed message drop

Three independent fixes for issues exposed by PR #3493:

1. shell.py: allow /dev/* paths in workspace guard
   Commands like `rm file.txt 2>/dev/null` were blocked because
   _extract_absolute_paths captured /dev/null as a path outside
   the workspace. Allow /dev like media_path is already allowed.

2. shell.py: remove | from home_paths regex prefix
   Loki query operator `|~` was misinterpreted as pipe + home
   directory, causing false workspace violation errors.

3. loop.py: change _streamed from blacklist to whitelist
   stop_reason "tool_error" was not in the exclusion set
   {"ask_user", "error"}, so _streamed=True was set on fatal
   errors. channel manager then skipped channel.send() because
   it assumed the content was already streamed — but it never
   was. Whitelist to only {"stop", "end_turn", "max_tokens"}.

Also fixes a pre-existing Windows bug in _spawn where
create_subprocess_exec + list2cmdline breaks commands with
paths containing spaces (e.g. D:\Program Files\python.exe).

Closes: #3599, #3605

nanobot/agent/loop.py

@@ -1135,7 +1135,7 @@ class AgentLoop:
             ask_user_options_from_messages(all_msgs) if stop_reason == "ask_user" else [],
             msg.channel,
         )
-        if on_stream is not None and stop_reason not in {"ask_user", "error"}:
+        if on_stream is not None and stop_reason not in {"ask_user", "error", "tool_error"}:
             meta["_streamed"] = True
         return OutboundMessage(
             channel=msg.channel,

nanobot/agent/tools/shell.py

@@ -220,9 +220,12 @@ class ExecTool(Tool):
     ) -> asyncio.subprocess.Process:
         """Launch *command* in a platform-appropriate shell."""
         if _IS_WINDOWS:
-            comspec = env.get("COMSPEC", os.environ.get("COMSPEC", "cmd.exe"))
-            return await asyncio.create_subprocess_exec(
-                comspec, "/c", command,
+            # create_subprocess_exec re-quotes args via list2cmdline, which
+            # breaks commands containing paths with spaces (e.g. "D:\Program
+            # Files\python.exe" "script.py"). create_subprocess_shell passes
+            # the raw command string to COMSPEC without re-quoting.
+            return await asyncio.create_subprocess_shell(
+                command,
                 stdout=asyncio.subprocess.PIPE,
                 stderr=asyncio.subprocess.PIPE,
                 cwd=cwd,
@@ -346,11 +349,14 @@ class ExecTool(Tool):
                     continue
 
                 media_path = get_media_dir().resolve()
+                dev_path = Path("/dev").resolve()
                 if (p.is_absolute()
                     and cwd_path not in p.parents
                     and p != cwd_path
                     and media_path not in p.parents
                     and p != media_path
+                    and dev_path not in p.parents
+                    and p != dev_path
                 ):
                     return (
                         "Error: Command blocked by safety guard (path outside working dir)"
@@ -372,5 +378,5 @@ class ExecTool(Tool):
         # NOTE: `*` is required so `C:\` (nothing after the slash) is still extracted.
         win_paths = re.findall(r"[A-Za-z]:\\[^\s\"'|><;]*", command)
         posix_paths = re.findall(r"(?:^|[\s|>'\"])(/[^\s\"'>;|<]+)", command) # POSIX: /absolute only
-        home_paths = re.findall(r"(?:^|[\s|>'\"])(~[^\s\"'>;|<]*)", command) # POSIX/Windows home shortcut: ~
+        home_paths = re.findall(r"(?:^|[\s>'\"])(~[^\s\"'>;|<]*)", command) # POSIX/Windows home shortcut: ~
         return win_paths + posix_paths + home_paths

tests/tools/test_exec_platform.py

@@ -112,33 +112,31 @@ class TestSpawnUnix:
 class TestSpawnWindows:
 
     @pytest.mark.asyncio
-    async def test_uses_comspec_from_env(self):
+    async def test_uses_create_subprocess_shell(self):
         env = {"COMSPEC": r"C:\Windows\system32\cmd.exe", "PATH": ""}
         with (
             patch("nanobot.agent.tools.shell._IS_WINDOWS", True),
-            patch("asyncio.create_subprocess_exec", new_callable=AsyncMock) as mock_exec,
+            patch("asyncio.create_subprocess_shell", new_callable=AsyncMock) as mock_shell,
         ):
-            mock_exec.return_value = AsyncMock()
-            await ExecTool._spawn("dir", r"C:\Users", env)
+            mock_shell.return_value = AsyncMock()
+            await ExecTool._spawn("dir", r"C:\work", env)
 
-        args = mock_exec.call_args[0]
-        assert "cmd.exe" in args[0]
-        assert "/c" in args
+        args = mock_shell.call_args[0]
         assert "dir" in args
 
     @pytest.mark.asyncio
-    async def test_falls_back_to_default_comspec(self):
-        env = {"PATH": ""}
+    async def test_passes_cwd_and_env(self):
+        env = {"PATH": "/usr/bin"}
         with (
             patch("nanobot.agent.tools.shell._IS_WINDOWS", True),
-            patch.dict("os.environ", {}, clear=True),
-            patch("asyncio.create_subprocess_exec", new_callable=AsyncMock) as mock_exec,
+            patch("asyncio.create_subprocess_shell", new_callable=AsyncMock) as mock_shell,
         ):
-            mock_exec.return_value = AsyncMock()
-            await ExecTool._spawn("dir", r"C:\Users", env)
+            mock_shell.return_value = AsyncMock()
+            await ExecTool._spawn("echo hi", r"C:\work", env)
 
-        args = mock_exec.call_args[0]
-        assert args[0] == "cmd.exe"
+        kwargs = mock_shell.call_args[1]
+        assert kwargs["cwd"] == r"C:\work"
+        assert kwargs["env"] == env
 
 
 # ---------------------------------------------------------------------------

tests/tools/test_tool_validation.py

@@ -315,6 +315,27 @@ def test_exec_guard_blocks_windows_drive_root_outside_workspace(monkeypatch) ->
     assert "hard policy boundary" in error
 
 
+def test_exec_guard_allows_dev_null_redirect(tmp_path) -> None:
+    tool = ExecTool(restrict_to_workspace=True)
+    ws = tmp_path / "workspace"
+    ws.mkdir()
+    (ws / "file.txt").write_text("ok", encoding="utf-8")
+    error = tool._guard_command(f'rm "{ws / "file.txt"}" 2>/dev/null', str(ws))
+    assert error is None
+
+
+def test_exec_guard_allows_dev_urandom(tmp_path) -> None:
+    tool = ExecTool(restrict_to_workspace=True)
+    error = tool._guard_command("cat /dev/urandom | head -c 16 > random.bin", str(tmp_path))
+    assert error is None
+
+
+def test_exec_extract_absolute_paths_ignores_pipe_tilde() -> None:
+    cmd = "python query.py --query '{job=\"app\"} |~ \"error\"'"
+    paths = ExecTool._extract_absolute_paths(cmd)
+    assert not any(p.startswith("~") for p in paths)
+
+
 # --- cast_params tests ---