fix(windows): hide console flashes from LSP server spawn and installer subprocesses

Salvaged from PR #47971 (LSP subset). On Windows, .cmd-wrapped language
servers (e.g. pyright-langserver.CMD launched via cmd.exe /c) and the
npm/go/pip LSP auto-installers spawn without CREATE_NO_WINDOW, so a
console window flashes whenever the spawn happens under a console-less
parent — e.g. a VS Code/Zed extension host running the ACP adapter.

- agent/lsp/client.py::_spawn: pass creationflags=windows_hide_flags()
  to the language-server asyncio subprocess (inert 0 on POSIX;
  start_new_session is kept — it is POSIX-only and ignored on Windows).
- agent/lsp/install.py: same flags on the npm and go installer
  subprocess.run calls. The pip path goes through
  hermes_cli.tools_config._pip_install, which already hides its windows.

Adapted from the PR's hand-rolled _NO_WINDOW constant to the repo's
hermes_cli._subprocess_compat.windows_hide_flags() convention.

agent/lsp/client.py

@@ -56,6 +56,8 @@ from pathlib import Path
 from typing import Any, Awaitable, Callable, Dict, List, Optional, Set
 from urllib.parse import quote, unquote
 
+from hermes_cli._subprocess_compat import windows_hide_flags
+
 from agent.lsp.protocol import (
     ERROR_CONTENT_MODIFIED,
     ERROR_METHOD_NOT_FOUND,
@@ -294,6 +296,12 @@ class LSPClient:
         cmd = self._command
         if sys.platform == "win32":
             cmd = self._win_wrap_cmd(cmd)
+        # Suppress the cmd.exe console window that would otherwise flash
+        # every time we launch a ``.cmd``-wrapped language server
+        # (e.g. pyright-langserver.CMD) from a console-less host such as
+        # a VS Code/Zed extension running the ACP adapter.
+        # windows_hide_flags() is CREATE_NO_WINDOW on Windows, 0 on POSIX.
+        creationflags = windows_hide_flags()
 
         try:
             # start_new_session=True detaches the LSP server into its own
@@ -312,6 +320,7 @@ class LSPClient:
                 env=env,
                 cwd=self._cwd,
                 start_new_session=True,
+                creationflags=creationflags,
             )
         except FileNotFoundError as e:
             raise LSPProtocolError(

agent/lsp/install.py

@@ -35,6 +35,8 @@ import threading
 from pathlib import Path
 from typing import Any, Dict, Optional
 
+from hermes_cli._subprocess_compat import windows_hide_flags
+
 logger = logging.getLogger("agent.lsp.install")
 
 # Package-name → install-strategy hint registry.  Each entry is a
@@ -268,6 +270,7 @@ def _install_npm(
             text=True,
             timeout=300,
             stdin=subprocess.DEVNULL,
+            creationflags=windows_hide_flags(),
         )
         if proc.returncode != 0:
             logger.warning(
@@ -317,6 +320,7 @@ def _install_go(pkg: str, bin_name: str) -> Optional[str]:
             timeout=600,
             env=env,
             stdin=subprocess.DEVNULL,
+            creationflags=windows_hide_flags(),
         )
         if proc.returncode != 0:
             logger.warning(

contributors/emails/hellofrommorgan@users.noreply.github.com

@@ -0,0 +1 @@
+hellofrommorgan