[BUG] Windows: ${CLAUDE_PLUGIN_ROOT} left unexpanded in Claude Desktop (Cowork), PreToolUse Bash hook fully blocked #65579

Preflight Checklist

• I have searched existing issues and this hasn't been reported yet
• This is a single bug report (please file separate reports for different bugs)
• I am using the latest version of Claude Code

What's Wrong?

Windows: plugin hook ${CLAUDE_PLUGIN_ROOT} left unsubstituted in
Claude Desktop (Cowork), breaking PreToolUse Bash hooks
Related: #39550 (canonical, closed, macOS), #43380, #18527 — this is the Windows manifestation with blocking (non-cosmetic) severity

Environment:

• Claude Desktop (Cowork), latest, Windows 11
• Python 3.14
• Org-managed (remote) plugins with PreToolUse Bash hooks

Symptom:
Running a Bash tool call fails. The hook command is shell form:
"command": "python3 ${CLAUDE_PLUGIN_ROOT}/hooks/scripts/check-bash.py"
and produces:
python.exe: can't open file
'...\outputs${CLAUDE_PLUGIN_ROOT}\hooks\scripts\check-bash.py':
[Errno 2] No such file or directory

Root cause:
On Windows, ${CLAUDE_PLUGIN_ROOT} is NOT substituted before the hook
subprocess is spawned. The literal string "${CLAUDE_PLUGIN_ROOT}" is
passed through and resolved relative to the session cwd, so the file
is never found. This matches #43380 (CLAUDE_PLUGIN_ROOT not injected
at hook execution time) and #11984 (portability). Related backslash-
handling variants on Windows: #18527, #22449, #23204.

Request:
Substitute ${CLAUDE_PLUGIN_ROOT} as a plain string into command/args
before spawning on Windows (as documented for exec form), and ensure
the path is correct for the target shell.

Note: a .sh-based hook in the same plugin also fails on Windows
(cannot be spawned directly); cf. #21847.

What Should Happen?

Expected Behavior:
${CLAUDE_PLUGIN_ROOT} should be substituted to the plugin's actual
installation directory before the hook subprocess is spawned on
Windows — the same as on macOS/Linux — so the hook script is found
and runs.

Concretely:

• The literal string "${CLAUDE_PLUGIN_ROOT}" must never reach the
  spawned process unexpanded.
• The substituted path must be in a form the target interpreter/shell
  can resolve on Windows (handle backslashes and spaces in the path).
• This should hold for both shell form and exec form, and regardless
  of the interpreter (python3, node, bash, etc.).
• Result: the PreToolUse Bash hook runs without error and the Bash
  tool is usable on Windows.

Error Messages/Logs

PreToolUse:mcp__workspace__bash hook error: 
[python3 ${CLAUDE_PLUGIN_ROOT}/hooks/scripts/check-bash.py]: 
C:\Users\...\AppData\Local\Python\pythoncore-3.14-64\python.exe: 
can't open file 
'C:\Users\...\AppData\Roaming\Claude\local-agent-mode-sessions\
...\outputs\${CLAUDE_PLUGIN_ROOT}\hooks\scripts\check-bash.py': 
[Errno 2] No such file or directory

Steps to Reproduce

Steps to Reproduce:

Environment: Windows 11, Claude Desktop (Cowork), latest.

1. Create a minimal plugin with a PreToolUse Bash hook in SHELL form
   (no "args"), referencing the placeholder. hooks/hooks.json:

   {
   "hooks": {
   "PreToolUse": [
   { "matcher": "Bash",
   "hooks": [
   { "type": "command",
   "command": "python3 ${CLAUDE_PLUGIN_ROOT}/hooks/scripts/check-bash.py" }
   ] }
   ]
   }
   }

2. Add the referenced script so the path is valid when expanded:
   hooks/scripts/check-bash.py -> print("ok")

3. Install/enable the plugin in Claude Desktop (Cowork) on Windows.

4. In a session, trigger any Bash tool call.

Observed:
python.exe: can't open file
'...\outputs${CLAUDE_PLUGIN_ROOT}\hooks\scripts\check-bash.py':
[Errno 2] No such file or directory

-> "${CLAUDE_PLUGIN_ROOT}" is left literal and resolved relative to
the session cwd; the file is never found and the Bash tool is blocked.

Notes:

• Same hooks.json works on macOS/Linux.
• Reproduces regardless of whether the user profile path contains a
  space (a space makes it worse; cf. path tokenization).

Claude Model

None

Is this a regression?

I don't know

Last Working Version

No response

Claude Code Version

Claude 1.11187.1 (370d3b) 2026-06-04T17:30:35.000Z

Platform

Other

Operating System

Windows

Terminal/Shell

PowerShell

Additional Information

No response