Plugin-defined preToolUse hooks (hooks.json) do not fire - neither in main session nor subagents

[solvaholic]

Describe the bug

preToolUse hooks defined in a plugin's hooks.json file are never executed. The hooks don't fire in the main agent session or in subagents spawned via the task tool.

This is distinct from #2392, which reports that config.json-defined hooks work in the main session but not subagents. In our case, plugin-sourced hooks don't fire anywhere.

Affected version

1.0.18 (macOS)

Steps to reproduce the behavior

1. Install a local plugin that defines a preToolUse hook in hooks.json:

   {
     "version": 1,
     "hooks": {
       "preToolUse": [
         {
           "type": "command",
           "bash": "./scripts/guardrails.sh",
           "cwd": ".",
           "timeoutSec": 10
         }
       ]
     }
   }

2. The plugin's plugin.json references it with "hooks": "hooks.json"
3. The guardrails script outputs {"permissionDecision": "deny", ...} for matching commands (verified by running the script manually with piped JSON input)
4. Start a session in a project that has this plugin installed
5. Run a bash command that should be blocked (e.g., one containing ghe-config-apply)
6. Result: Command executes without any hook intervention
7. Manually running the same script with the same input correctly returns a deny decision

Expected behavior

Plugin-defined preToolUse hooks should be loaded and executed for all tool calls, the same way config.json-defined hooks are.

Additional context

• macOS, zsh, Copilot CLI 1.0.18
• Plugin installed via local path (source.path in config.json installed_plugins)
• The plugin's skills load and work correctly - only hooks are not firing
• Tested with two separate local plugins, both define preToolUse hooks in hooks.json, neither fires
• Related: preToolUse hooks are not enforced in subagents #2392 (subagent hook enforcement), preToolUse hook returning 'allow' should short-circuit built-in tool dialogs like exit_plan_mode #2349 (hook allow short-circuit), sessionStart hook in .github/hooks/ does not fire in Copilot CLI (v0.0.420) #1730 (sessionStart hooks)