fix: SPA fallback via HttpExceptionFilter for non-API 404s

Move SPA fallback from main.ts catch-all (didn't work - NestJS 404
handler runs first) to HttpExceptionFilter. Now non-API GET 404s
serve index.html so client-side routing works for /dashboard/* etc.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/src/common/filters/http-exception.filter.ts

@@ -1,13 +1,16 @@
 import { ExceptionFilter, Catch, ArgumentsHost, HttpException, HttpStatus, Logger } from "@nestjs/common";
-import { Response } from "express";
+import { Request, Response } from "express";
+import { join } from "path";
 import { trace, SpanStatusCode } from "@opentelemetry/api";
 
 @Catch()
 export class HttpExceptionFilter implements ExceptionFilter {
   private readonly logger = new Logger("ExceptionFilter");
+  private readonly indexPath = join(__dirname, "..", "..", "..", "..", "web", "dist", "index.html");
 
   catch(exception: unknown, host: ArgumentsHost) {
     const ctx = host.switchToHttp();
+    const request = ctx.getRequest<Request>();
     const response = ctx.getResponse<Response>();
 
     let status = HttpStatus.INTERNAL_SERVER_ERROR;
@@ -30,6 +33,11 @@ export class HttpExceptionFilter implements ExceptionFilter {
       this.logger.error(`Unhandled error: ${exception.message}`, exception.stack);
     }
 
+    // SPA fallback: serve index.html for non-API GET 404s
+    if (status === HttpStatus.NOT_FOUND && request.method === "GET" && !request.path.startsWith("/api")) {
+      return response.sendFile(this.indexPath);
+    }
+
     // Record error on active OTel span
     const span = trace.getActiveSpan();
     if (span) {

apps/api/src/main.ts

@@ -3,14 +3,12 @@ import "./telemetry/tracing"; // MUST be first — instruments modules before th
 import { NestFactory } from "@nestjs/core";
 import { ConfigService } from "@nestjs/config";
 import helmet from "helmet";
-import { join } from "path";
 import type { Request, Response, NextFunction } from "express";
-import type { NestExpressApplication } from "@nestjs/platform-express";
 import { AppModule } from "./app.module";
 import { fileUploadValidation } from "./common/middleware/file-upload-validation.middleware";
 
 async function bootstrap() {
-  const app = await NestFactory.create<NestExpressApplication>(AppModule);
+  const app = await NestFactory.create(AppModule);
 
   const configService = app.get(ConfigService);
   const port = configService.get<number>("port", 4000);
@@ -54,18 +52,6 @@ async function bootstrap() {
     next();
   });
 
-  await app.init();
-
-  // SPA fallback: serve index.html for non-API GET requests
-  const webDistPath = join(__dirname, "..", "..", "web", "dist");
-  const expressApp = app.getHttpAdapter().getInstance();
-  expressApp.get("*", (req: Request, res: Response, next: NextFunction) => {
-    if (req.path.startsWith("/api")) {
-      return next();
-    }
-    res.sendFile(join(webDistPath, "index.html"));
-  });
-
   await app.listen(port);
   console.log(`API running on http://localhost:${port}`);
 }