Plugin auto-update deletes old cache dir, breaking ${CLAUDE_PLUGIN_ROOT} in running sessions

Summary

When a plugin auto-updates on session start, the old cache directory is deleted and replaced with a new hash-versioned directory. Any already-running session that resolved ${CLAUDE_PLUGIN_ROOT} at startup continues pointing to the deleted path, causing every hook invocation to fail.

Steps to reproduce

1. Start a Claude Code session (session A)
2. Start a second session (session B) — this triggers plugin auto-update if upstream changed
3. Return to session A and use any tool
4. Every hookify hook fails: Plugin directory does not exist: .../hookify/<old_hash>

Impact

• Affects any plugin that registers hooks (hookify is the primary one)
• Error fires on every PreToolUse, PostToolUse, and Stop event — dozens of errors per conversation
• Non-blocking but very noisy, and the error message tells users to reinstall when the plugin is already current

Observed behavior

Plugin cache hashes observed changing multiple times in a single day:

• 03804b3b2735 -> a7a83f99ce07 -> 150430d80202

Each transition broke all running sessions referencing the previous hash.

Suggested fixes

1. Keep old cache dirs for a grace period (e.g. 24h) instead of deleting immediately
2. Re-resolve ${CLAUDE_PLUGIN_ROOT} on each hook invocation rather than caching at session start
3. Symlink old -> new during update (this is my current workaround via a SessionStart hook)

Workaround

Created a SessionStart hook that records plugin hashes to a history file and creates symlinks from old hashes to the current version:

ln -s <new_hash> ~/.claude/plugins/cache/claude-plugins-official/hookify/<old_hash>

Environment

• Claude Code 2.1.104
• macOS Darwin 23.4.0
• hookify@claude-plugins-official