Multi-user permission conflict with shared /tmp/claude/ directory

Description

When multiple users on the same machine use Claude Code, permission errors occur because the /tmp/claude/ directory is shared across all users.

Steps to Reproduce

1. User A runs Claude Code - this creates /tmp/claude/ owned by User A
2. Switch to User B on the same machine
3. User B runs Claude Code and attempts any Bash command
4. Error occurs: EACCES: permission denied, mkdir '/tmp/claude/-Users-...'

Error Message

Error: EACCES: permission denied, mkdir '/tmp/claude/-Users-userB-path-to-project/tasks'

Expected Behavior

Each user should have isolated temp directories that don't conflict with other users on the system.

Suggested Fix

Use per-user temp directories instead of a shared path:

• $TMPDIR/claude/ (macOS sets this per-user)
• /tmp/claude-$USER/
• /tmp/claude/$UID/

Environment

• OS: macOS (Darwin 24.6.0)
• Multiple local user accounts on shared machine

Workaround

Run sudo rm -rf /tmp/claude when switching users.