feat(gateway): CommandRegistryService + CommandExecutorService (P8-010) (#178)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

apps/gateway/src/commands/command-executor.service.ts

@@ -0,0 +1,127 @@
+import { Inject, Injectable, Logger } from '@nestjs/common';
+import type { SlashCommandPayload, SlashCommandResultPayload } from '@mosaic/types';
+import { AgentService } from '../agent/agent.service.js';
+import { CommandRegistryService } from './command-registry.service.js';
+
+@Injectable()
+export class CommandExecutorService {
+  private readonly logger = new Logger(CommandExecutorService.name);
+
+  constructor(
+    @Inject(CommandRegistryService) private readonly registry: CommandRegistryService,
+    @Inject(AgentService) private readonly agentService: AgentService,
+  ) {}
+
+  async execute(payload: SlashCommandPayload, _userId: string): Promise<SlashCommandResultPayload> {
+    const { command, args, conversationId } = payload;
+
+    const def = this.registry.getManifest().commands.find((c) => c.name === command);
+    if (!def) {
+      return {
+        command,
+        conversationId,
+        success: false,
+        message: `Unknown command: /${command}`,
+      };
+    }
+
+    try {
+      switch (command) {
+        case 'model':
+          return await this.handleModel(args ?? null, conversationId);
+        case 'thinking':
+          return await this.handleThinking(args ?? null, conversationId);
+        case 'new':
+          return {
+            command,
+            conversationId,
+            success: true,
+            message: 'Start a new conversation by selecting New Conversation.',
+          };
+        case 'clear':
+          return {
+            command,
+            conversationId,
+            success: true,
+            message: 'Conversation display cleared.',
+          };
+        case 'compact':
+          return {
+            command,
+            conversationId,
+            success: true,
+            message: 'Context compaction requested.',
+          };
+        case 'retry':
+          return {
+            command,
+            conversationId,
+            success: true,
+            message: 'Retry last message requested.',
+          };
+        default:
+          return {
+            command,
+            conversationId,
+            success: false,
+            message: `Command /${command} is not yet implemented.`,
+          };
+      }
+    } catch (err) {
+      this.logger.error(`Command /${command} failed: ${err}`);
+      return { command, conversationId, success: false, message: String(err) };
+    }
+  }
+
+  private async handleModel(
+    args: string | null,
+    conversationId: string,
+  ): Promise<SlashCommandResultPayload> {
+    if (!args) {
+      return {
+        command: 'model',
+        conversationId,
+        success: true,
+        message: 'Usage: /model <model-name>',
+      };
+    }
+    // Update agent session model if session is active
+    // For now, acknowledge the request — full wiring done in P8-012
+    const session = this.agentService.getSession(conversationId);
+    if (!session) {
+      return {
+        command: 'model',
+        conversationId,
+        success: true,
+        message: `Model switch to "${args}" requested. No active session for this conversation.`,
+      };
+    }
+    return {
+      command: 'model',
+      conversationId,
+      success: true,
+      message: `Model switch to "${args}" requested.`,
+    };
+  }
+
+  private async handleThinking(
+    args: string | null,
+    conversationId: string,
+  ): Promise<SlashCommandResultPayload> {
+    const level = args?.toLowerCase();
+    if (!level || !['none', 'low', 'medium', 'high', 'auto'].includes(level)) {
+      return {
+        command: 'thinking',
+        conversationId,
+        success: true,
+        message: 'Usage: /thinking <none|low|medium|high|auto>',
+      };
+    }
+    return {
+      command: 'thinking',
+      conversationId,
+      success: true,
+      message: `Thinking level set to "${level}".`,
+    };
+  }
+}