fix: duplicate command check

[planger]

What it does

On startup we can observe warnings like:

logger-protocol.ts:118 2025-12-05T18:17:54.751Z root WARN Command name 'clear' is used by multiple fragments: claude-code-slash-clear and claude-code-slash-clear

This is caused by a check for duplicates AFTER the command was actually already added. Also it does not take the agents for which it was defined into account.

How to test

Build and check that the logs are now gone.

To test whether the warning shows up correctly, you can change the registered commands in examples/api-samples/src/browser/chat/sample-chat-command-contribution.ts so they register for instance the command clear, which is also registered for ClaudeCode. When doing that, a warning should be logged.

Follow-ups

Breaking changes

• This PR introduces breaking changes and requires careful review. If yes, the breaking changes section in the changelog has been updated.

Attribution

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines
• User-facing text is internationalized using the nls service (for details, please see the Internationalization/Localization section in the Coding Guidelines)

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[ndoschek]

Thank you for the fix @planger, works great for me!
The warnings on startup are gone and the expected warning for a duplicate registration is logged as expected 👍