Plugin hooks fail: CLAUDE_PLUGIN_ROOT not injected at hook execution time

Description

Plugin hooks that use ${CLAUDE_PLUGIN_ROOT} in their command strings fail because the environment variable is not set when the hook command executes. The variable resolves to empty, causing paths like "${CLAUDE_PLUGIN_ROOT}/hooks/session-start-seen-skills.mjs" to become "/hooks/session-start-seen-skills.mjs" — which doesn't exist.

Affected hooks

All three hook event types show errors:

• SessionStart:startup hook error
• UserPromptSubmit hook error
• PostToolUse:Bash hook error

Affected plugins

Every plugin that defines hooks using ${CLAUDE_PLUGIN_ROOT} is affected:

• vercel@claude-plugins-official (SessionStart, UserPromptSubmit, PostToolUse:Bash)
• superpowers@claude-plugins-official (SessionStart)
• explanatory-output-style@claude-plugins-official (SessionStart)
• vercel-plugin@vercel-vercel-plugin (SessionStart, UserPromptSubmit, PostToolUse:Bash)

Reproduction

1. Enable any of the above plugins
2. Start a new session
3. Observe SessionStart:startup hook error immediately
4. Send a message → UserPromptSubmit hook error
5. Run any Bash command → PostToolUse:Bash hook error

Manual verification

Running a plugin hook manually with CLAUDE_PLUGIN_ROOT set works fine:

CLAUDE_PLUGIN_ROOT="/path/to/plugin/root" node "$CLAUDE_PLUGIN_ROOT/hooks/session-start-seen-skills.mjs"

Without it:

Error: Cannot find module '/hooks/session-start-seen-skills.mjs'

Environment

• Claude Code version: 2.1.92 (latest)
• macOS Darwin 25.4.0
• Node.js v22.22.1
• Plugin cache location: ~/Library/Mobile Documents/com~apple~CloudDocs/claude-config/plugins/cache/

Impact

Cosmetic — plugin skills and tools still work. Only the hook-based features (telemetry, skill injection, session profiling) are broken. The errors appear on every session start, every prompt submit, and every Bash tool use, which is noisy.