chore(chat): pass pinned agent in frontend chat service

[planger]

What it does

Support setting a pinnedAgent also in the frontend service.

Reported in #15053 (comment)

How to test

Everything should work as before when creating new chats. However, now commands can also specify a pinned agent via the frontend service, e.g.

@injectable()
export class SampleCommandContribution implements CommandContribution {

    @inject(ChatService)
    protected readonly chatService: ChatService;


    @inject(ChatAgentService)
    protected chatAgentService: ChatAgentService;

    registerCommands(commands: CommandRegistry): void {
        commands.registerCommand(SampleCommand, {
            execute: async () => {
                 const agent = this.chatAgentService.getAgent('Coder');
                // creates a clean session
                const session = this.chatService.createSession(ChatAgentLocation.Panel, { focus: true }, agent);
                // submit a request
                await this.chatService.sendRequest(session.id, { text: 'Hello World!' });
            }
        });
    }
}

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

Reminder for reviewers

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

[eneufeld]

Thank you!