Plugin commands now handle the built-in directory marketplace

What

Claude Code comes with a built-in plugin directory marketplace, which is a catalog of plugins you can install. The plugin commands now recognise it and handle it on its own terms instead of treating it like any other marketplace:

• claude plugin marketplace add now recognises the built-in directory. If your organization's policy blocks it, the command says it "is blocked by your organization". It rejects --sparse and --scope for this marketplace, with the message "is built in and not declared in any settings scope. Omit --sparse and --scope to turn it on." If the marketplace is turned off, add turns it back on.
• remove turns the built-in directory off but keeps the plugins you already installed from it.
• list shows the built-in directory as built in and off when it is turned off, with a "Turn it back on" line.
• /reload-plugins adds a note that the directory "could not be reached, so its plugins were not loaded" when the directory is unreachable.
• claude plugin details now gives specific reasons when a plugin from the built-in directory is unavailable: it is blocked by policy (policy_blocked), or the directory's catalog is missing (directory_catalog_missing). Before, it always reported a generic "not found".

Before this release, add only had an error about the name being reserved, and remove handled the built-in directory the same way as other marketplaces.

Why

When a plugin from the built-in directory is not available, the messages now say why: your organization blocked it, the directory could not be reached, or its catalog is missing. You can also turn the built-in directory off without losing installed plugins, and turn it back on with add.