[BUG] Desktop app blocks sending message when a custom slash command is combined with a URL

Description

In the Claude desktop app (Code tab), sending a message that combines a custom slash command (from ~/.claude/commands/*.md) with a URL in the same input is blocked entirely — nothing is sent. This previously worked (slash command + link together in one message), and started failing without any action on my part.

Steps to reproduce

1. Have a custom slash command defined, e.g. ~/.claude/commands/리뷰대응.md that takes a URL as $ARGUMENTS.
2. In the input box, type the slash command followed by a URL on the same line, e.g.:

``
/리뷰대응 https://github.com/owner/repo/pull/24
``

1. Press enter / click send.

Expected behavior

The message sends normally, invoking the slash command with the URL as its argument (as it did before).

Actual behavior

Nothing is sent. A warning banner appears over the input box:

명령에는 파일 @멘션만 포함할 수 있으며 다른 @멘션, 슬래시 명령, 링크, 인라인 서식은 포함할 수 없어 아무것도 전송되지 않았습니다. 해당 항목을 제거해주세요. (×6)

(Translation: "Commands can only include file @mentions; other @mentions, slash commands, links, or inline formatting are not allowed, so nothing was sent. Please remove that item.")

The banner counter (×6, then ×8 on repeat attempts) increments each time send is retried, confirming every attempt silently fails client-side with no message reaching the assistant.

Workaround

• Sending the slash command alone (no URL) works, and the URL can be sent as a separate follow-up message.
• Sending the whole thing as a plain natural-language sentence without the leading / (no slash command) also sends successfully.

Only the combination of leading slash command + URL in the same message triggers the block.

Environment

• Claude desktop app, Code tab
• macOS (Darwin)