sessionStart hook in .github/hooks/ does not fire in Copilot CLI (v0.0.420)

[jiaczh]

Describe the bug

sessionStart hooks defined in .github/hooks/*.json do not execute when starting a Copilot CLI session. Other hook types (preToolUse, postToolUse) in the same directory fire correctly.

Environment

• CLI version: v0.0.420
• OS: Windows 11
• Shell: PowerShell 7

Hook configuration

File: .github/hooks/test-hook.json

{
  "version": 1,
  "hooks": {
    "sessionStart": [
      {
        "type": "command",
        "bash": "echo \"Session started: $(date)\" >> logs/session.log",
        "powershell": "Add-Content -Path logs/session.log -Value \"Session started: $(Get-Date)\"",
        "cwd": ".",
        "timeoutSec": 10
      }
    ]
  }
}

Expected behavior

logs/session.log should be created with a timestamp entry when a CLI session starts.

Actual behavior

logs/session.log is never created. The sessionStart hook does not fire.

Additional context

[jiaczh]

Additional context: nested .github/ in a monorepo

Important detail — our Copilot CLI agent workspace lives deep inside a monorepo, not at the git root. The .github/hooks/ directory with the hooks is nested, and we cd into the agent subdirectory before launching copilot:

my-monorepo/                          ← git root
├── .github/
│   ├── copilot-instructions.md
│   ├── hooks/                        ← (empty, no hook files here)
│   ├── agents/
│   ├── skills/
│   └── scripts/
├── src/
│   └── services/
│       └── my-agent/
│           └── agent/                ← cwd when launching `copilot`
│               ├── .github/
│               │   ├── copilot-instructions.md
│               │   ├── hooks/
│               │   │   ├── test-hook.json          ← sessionStart (NOT firing ❌)
│               │   ├── agents/
│               │   │   └── *.agent.md
│               │   ├── skills/
│               │   │   └── */SKILL.md
│               │   └── TSGs/
│               │       └── *.md
│               ├── scripts/
│               │   └── hooks/
│               │       ├── inject_skill_principles.py
│               │       ├── validate_on_edit.py
│               │       └── validation.log          ← proof postToolUse fires
│               ├── logs/
│               │   └── (empty — session.log never created)
│               ├── setup.ps1
│               └── README.md

Why this matters

• The git root .github/hooks/ is empty — no hooks defined there
• The nested .github/hooks/ (relative to cwd) contains both hook files
• preToolUse/postToolUse hooks from the nested .github/hooks/ do fire, proving the CLI finds and loads hooks from the cwd-relative .github/hooks/
• sessionStart fails to trigger from this nested location