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/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