fix: disabling an agent also disables its UIContribution

- agent service had a loop so that a single instance was not created
- code completion agents now check whether they are active
- terminal agent now check whether it is active
- chat-service correctly handles no available agents now

fixes eclipse-theia#14167

packages/ai-chat/src/common/chat-model.ts

@@ -767,3 +767,10 @@ class ChatResponseModelImpl implements ChatResponseModel {
         return this._isError;
     }
 }
+
+export class ErrorChatResponseModelImpl extends ChatResponseModelImpl {
+    constructor(requestId: string, error: Error, agentId?: string) {
+        super(requestId, agentId);
+        this.error(error);
+    }
+}

packages/ai-chat/src/common/chat-service.ts

@@ -26,9 +26,10 @@ import {
     ChatRequest,
     ChatRequestModel,
     ChatResponseModel,
+    ErrorChatResponseModelImpl,
 } from './chat-model';
 import { ChatAgentService } from './chat-agent-service';
-import { Emitter, ILogger } from '@theia/core';
+import { Emitter, ILogger, generateUuid } from '@theia/core';
 import { ChatRequestParser } from './chat-request-parser';
 import { ChatAgent, ChatAgentLocation } from './chat-agents';
 import { ParsedChatRequestAgentPart, ParsedChatRequestVariablePart, ParsedChatRequest } from './parsed-chat-request';
@@ -161,6 +162,16 @@ export class ChatServiceImpl implements ChatService {
         const parsedRequest = this.chatRequestParser.parseChatRequest(request, session.model.location);
 
         const agent = this.getAgent(parsedRequest);
+        if (agent === undefined) {
+            const error = 'No ChatAgents available to handle request!';
+            this.logger.error(error);
+            const chatResponseModel = new ErrorChatResponseModelImpl(generateUuid(), new Error(error));
+            return {
+                requestCompleted: Promise.reject(error),
+                responseCreated: Promise.reject(error),
+                responseCompleted: Promise.resolve(chatResponseModel),
+            };
+        }
         const requestModel = session.model.addRequest(parsedRequest, agent?.id);
 
         for (const part of parsedRequest.parts) {

packages/ai-code-completion/src/browser/ai-code-completion-provider.ts

@@ -21,6 +21,7 @@ import { injectable, inject } from '@theia/core/shared/inversify';
 import { PreferenceService } from '@theia/core/lib/browser';
 import { CancellationTokenSource } from '@theia/core';
 import { PREF_AI_CODE_COMPLETION_PRECOMPUTE } from './ai-code-completion-preference';
+import { AgentService } from '@theia/ai-core';
 
 interface WithArgs<T = unknown[]> {
     args: T;
@@ -33,11 +34,17 @@ export class AICodeCompletionProvider implements monaco.languages.CompletionItem
     @inject(CodeCompletionAgent)
     protected readonly agent: CodeCompletionAgent;
 
+    @inject(AgentService)
+    private readonly agentService: AgentService;
+
     @inject(PreferenceService)
     protected readonly preferenceService: PreferenceService;
 
     async provideCompletionItems(model: monaco.editor.ITextModel, position: monaco.Position,
         context: monaco.languages.CompletionContext, token: monaco.CancellationToken): Promise<monaco.languages.CompletionList | undefined> {
+        if (!this.agentService.isEnabled(this.agent.id)) {
+            return;
+        }
         if (!this.preferenceService.get(PREF_AI_CODE_COMPLETION_PRECOMPUTE, false)) {
             const result = {
                 suggestions: [{

packages/ai-code-completion/src/browser/ai-code-inline-completion-provider.ts

@@ -19,14 +19,20 @@ import * as monaco from '@theia/monaco-editor-core';
 import { inject, injectable } from '@theia/core/shared/inversify';
 import { CodeCompletionAgent } from '../common/code-completion-agent';
 import { CompletionTriggerKind } from '@theia/core/shared/vscode-languageserver-protocol';
+import { AgentService } from '@theia/ai-core';
 
 @injectable()
 export class AICodeInlineCompletionsProvider implements monaco.languages.InlineCompletionsProvider {
     @inject(CodeCompletionAgent)
     protected readonly agent: CodeCompletionAgent;
+    @inject(AgentService)
+    private readonly agentService: AgentService;
 
     async provideInlineCompletions(model: monaco.editor.ITextModel, position: monaco.Position,
         context: monaco.languages.InlineCompletionContext, token: monaco.CancellationToken): Promise<monaco.languages.InlineCompletions | undefined> {
+        if (!this.agentService.isEnabled(this.agent.id)) {
+            return;
+        }
         if (this.agent.provideInlineCompletions) {
             return this.agent.provideInlineCompletions(model, position, context, token);
         }

packages/ai-core/src/common/agent-service.ts

@@ -13,7 +13,7 @@
 //
 // SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-only WITH Classpath-exception-2.0
 // *****************************************************************************
-import { inject, injectable, named, postConstruct } from '@theia/core/shared/inversify';
+import { inject, injectable, named } from '@theia/core/shared/inversify';
 import { ContributionProvider } from '@theia/core';
 import { Agent } from './agent';
 
@@ -57,17 +57,16 @@ export class AgentServiceImpl implements AgentService {
 
     protected disabledAgents = new Set<string>();
 
-    protected agents: Agent[] = [];
+    protected _agents: Agent[] = [];
 
-    @postConstruct()
-    init(): void {
-        for (const agent of this.agentsProvider.getContributions()) {
-            this.registerAgent(agent);
-        }
+    private get agents(): Agent[] {
+        // We can't collect the contributions at @postConstruct because this will lead to a circular dependency
+        // with agents reusing the chat agent service (e.g. orchestrator) which in turn injects the agent service
+        return [...this.agentsProvider.getContributions(), ...this._agents];
     }
 
     registerAgent(agent: Agent): void {
-        this.agents.push(agent);
+        this._agents.push(agent);
     }
 
     getAgents(): Agent[] {

packages/ai-terminal/src/browser/ai-terminal-contribution.ts

@@ -23,6 +23,7 @@ import { TerminalMenus } from '@theia/terminal/lib/browser/terminal-frontend-con
 import { TerminalWidgetImpl } from '@theia/terminal/lib/browser/terminal-widget-impl';
 import { AiTerminalAgent } from './ai-terminal-agent';
 import { AICommandHandlerFactory } from '@theia/ai-core/lib/browser/ai-command-handler-factory';
+import { AgentService } from '@theia/ai-core';
 
 const AI_TERMINAL_COMMAND = {
     id: 'ai-terminal:open',
@@ -41,6 +42,9 @@ export class AiTerminalCommandContribution implements CommandContribution, MenuC
     @inject(AICommandHandlerFactory)
     protected commandHandlerFactory: AICommandHandlerFactory;
 
+    @inject(AgentService)
+    private readonly agentService: AgentService;
+
     registerKeybindings(keybindings: KeybindingRegistry): void {
         keybindings.registerKeybinding({
             command: AI_TERMINAL_COMMAND.id,
@@ -57,7 +61,7 @@ export class AiTerminalCommandContribution implements CommandContribution, MenuC
     registerCommands(commands: CommandRegistry): void {
         commands.registerCommand(AI_TERMINAL_COMMAND, this.commandHandlerFactory({
             execute: () => {
-                if (this.terminalService.currentTerminal instanceof TerminalWidgetImpl) {
+                if (this.terminalService.currentTerminal instanceof TerminalWidgetImpl && this.agentService.isEnabled(this.terminalAgent.id)) {
                     new AiTerminalChatWidget(
                         this.terminalService.currentTerminal,
                         this.terminalAgent