Tab-completion does not expand plugin namespace prefixes

Summary

Tab-completion does not expand plugin namespace prefixes. When a plugin named standard-tooling is installed and working, typing /standard-tooling:<tab> does not expand to show available skills under that namespace. Users must know and type the full skill name (e.g. /standard-tooling:publish) manually.

Reproduction

1. Install a plugin with multiple skills (e.g. a plugin named standard-tooling with 8 skills)
2. Verify skills work by typing their full names (e.g. /standard-tooling:publish invokes correctly)
3. Type /standard-tooling: and press Tab
4. Result: No completion suggestions appear

Expected Behavior

Tab-completion after /standard-tooling: should list all available skills under that namespace, e.g.:

• standard-tooling:publish
• standard-tooling:pr-workflow
• standard-tooling:summarize
• etc.

Ideally, typing /standard-<tab> should also expand to /standard-tooling: as an intermediate completion step.

Impact

Without tab-completion, users must memorize exact skill names for every plugin. This significantly reduces the discoverability of plugin skills. The /help command does list them, but interactive tab-completion is the standard discovery mechanism for slash commands.

Environment

• Claude Code CLI (latest)
• macOS