Plugin install & marketplace management need interactive selection / autocomplete (currently full names must be memorized and typed manually)

[dfrysinger]

Summary

Plugin and marketplace management is currently fully manual: the user must memorize and type the full owner/repo (and for marketplaces, the marketplace name + plugin name) with no autocomplete, no interactive picker, and no list-based selection — even when the CLI clearly already has the relevant list available.

Affected surfaces

• copilot plugin install <owner/repo> — no tab-complete, no fuzzy picker
• copilot plugin marketplace install <name> — same
• copilot plugin marketplace browse <marketplace> — lists plugins but doesn't let you select one to install from the list
• copilot plugin enable/disable (see Feature Request: Allow toggling plugins enabled/disabled #2714, Feature Request: --disable-plugin flag for per-session plugin control #3452) would have the same UX problem

Expected

When invoked without arguments, these commands should drop into an interactive picker (similar to existing model/session pickers) backed by:

• For install: the marketplace catalog the CLI already has cached
• For enable/disable: the list of currently installed plugins
• For browse <marketplace> → install: the plugin list already on screen — let the user arrow + Enter

Related

• Have simpler plugin marketplace browse feature and install. #1545 — "Have simpler plugin marketplace browse feature and install" (similar spirit)
• Feature Request: Allow toggling plugins enabled/disabled #2714, Feature Request: --disable-plugin flag for per-session plugin control #3452 — plugin enable/disable (same UX class)
• copilot plugin marketplace browse awesome-copilot - warning: templates not found #3360, Plugin Marketplace clone does not pull submodules #2077, Add git-subdir source type support to plugin marketplace schema #3376 — specific marketplace bugs (not UX)

Why this matters

The current flow assumes the user has the full plugin coordinate memorized, which is fine for power users but defeats the discoverability point of having a marketplace at all.