[BUG] Plugin command with arguments: unprefixed name gives "Unknown command" in the interactive CLI

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet (closest: #36210, closed, same "Args from unknown skill" symptom for a plugin command with arguments)
• [x] This is a single bug report
• [x] I am using the latest version of Claude Code

What's Wrong?

In the interactive CLI, typing a plugin command by its unprefixed name with arguments fails:

⏺ Unknown command: /hello. Did you mean /help?
⏺ Args from unknown skill: world

The prefixed form works: /hellotest:hello world → runs.

What Should Happen?

The command should run. The skills docs say the bare name "also invokes the skill unless another command already uses that name" (https://code.claude.com/docs/en/skills), and nothing else uses hello.

Steps to Reproduce

1. Create a minimal plugin:

• hellotest/.claude-plugin/plugin.json: { "name": "hellotest", "version": "0.0.1" }
• hellotest/commands/hello.md:

``
---
description: "Reply with HELLO-RAN and the arguments."
argument-hint: "<anything>"
---
Reply with exactly one line: HELLO-RAN args=<the arguments>. The arguments were: $ARGUMENTS
``

1. In an empty git repo, run claude --plugin-dir ../hellotest.
2. Type /hello world and press Enter (keep typing; don't pick from the autocomplete menu).
3. Result: "Unknown command: /hello" / "Args from unknown skill: world".
4. Type /hellotest:hello world → HELLO-RAN args=world.

Notes

• Headless works: claude -p "/hello world" runs the command, so this looks specific to interactive input parsing.
• With no arguments, the bare name only appears to work because the autocomplete menu fills in the plugin: prefix on Enter. Once a space and arguments are typed the menu closes and the bare name fails.
• Also reproduced with a real plugin whose commands also ship as skills/<name>/SKILL.md — same failure, so it does not depend on the commands/ vs skills/ layout.
• Plugins installed from a marketplace (user scope) fail the same way as --plugin-dir.

Environment

• Claude Code 2.1.281 on macOS (Darwin 25.5), and 2.1.282 on Debian bookworm arm64 (fresh VM, no prior config)
• Model: Opus 5.5; permission mode: auto