feat(gateway): MosaicPlugin lifecycle + ReloadService + hot reload (P8-013) (#182)

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

apps/gateway/src/reload/reload.service.ts

@@ -0,0 +1,92 @@
+import {
+  Inject,
+  Injectable,
+  Logger,
+  type OnApplicationBootstrap,
+  type OnApplicationShutdown,
+} from '@nestjs/common';
+import type { SystemReloadPayload } from '@mosaic/types';
+import { CommandRegistryService } from '../commands/command-registry.service.js';
+import { isMosaicPlugin } from './mosaic-plugin.interface.js';
+
+@Injectable()
+export class ReloadService implements OnApplicationBootstrap, OnApplicationShutdown {
+  private readonly logger = new Logger(ReloadService.name);
+  private readonly plugins: Map<string, unknown> = new Map();
+  private shutdownHandlerAttached = false;
+
+  constructor(
+    @Inject(CommandRegistryService) private readonly commandRegistry: CommandRegistryService,
+  ) {}
+
+  onApplicationBootstrap(): void {
+    if (!this.shutdownHandlerAttached) {
+      process.on('SIGHUP', () => {
+        this.logger.log('SIGHUP received — triggering soft reload');
+        this.reload('sighup').catch((err: unknown) => {
+          this.logger.error(`SIGHUP reload failed: ${err}`);
+        });
+      });
+      this.shutdownHandlerAttached = true;
+    }
+  }
+
+  onApplicationShutdown(): void {
+    process.removeAllListeners('SIGHUP');
+  }
+
+  registerPlugin(name: string, plugin: unknown): void {
+    this.plugins.set(name, plugin);
+    this.logger.log(`Plugin registered: ${name}`);
+  }
+
+  /**
+   * Soft reload — unload plugins, reload plugins, broadcast.
+   * Does NOT restart the HTTP server or drop connections.
+   */
+  async reload(
+    trigger: 'command' | 'rest' | 'sighup' | 'file-watch',
+  ): Promise<SystemReloadPayload> {
+    this.logger.log(`Soft reload triggered by: ${trigger}`);
+    const reloaded: string[] = [];
+    const errors: string[] = [];
+
+    // 1. Unload all registered MosaicPlugin instances
+    for (const [name, plugin] of this.plugins) {
+      if (isMosaicPlugin(plugin)) {
+        try {
+          await plugin.onUnload();
+          reloaded.push(name);
+        } catch (err) {
+          errors.push(`${name}: unload failed — ${err}`);
+        }
+      }
+    }
+
+    // 2. Reload all MosaicPlugin instances
+    for (const [name, plugin] of this.plugins) {
+      if (isMosaicPlugin(plugin)) {
+        try {
+          await plugin.onLoad();
+        } catch (err) {
+          errors.push(`${name}: load failed — ${err}`);
+        }
+      }
+    }
+
+    const manifest = this.commandRegistry.getManifest();
+
+    const errorSuffix = errors.length > 0 ? ` Errors: ${errors.join(', ')}` : '';
+    const payload: SystemReloadPayload = {
+      commands: manifest.commands,
+      skills: manifest.skills,
+      providers: [],
+      message: `Reload complete (trigger=${trigger}). Plugins reloaded: [${reloaded.join(', ')}].${errorSuffix}`,
+    };
+
+    this.logger.log(
+      `Reload complete. Reloaded: [${reloaded.join(', ')}]. Errors: ${errors.length}`,
+    );
+    return payload;
+  }
+}