diff --git a/packages/egg/src/lib/application.ts b/packages/egg/src/lib/application.ts
index 54727e0f34..71b83f7825 100644
--- a/packages/egg/src/lib/application.ts
+++ b/packages/egg/src/lib/application.ts
@@ -193,16 +193,17 @@ export class Application extends EggApplicationCore {
   }
 
   /**
-   * save routers to `run/router.json`
+   * save routers to `${rundir}/router.json`
    * @private
    */
   dumpConfig(): void {
     super.dumpConfig();
 
     // dump routers to router.json
-    const rundir = this.config.rundir;
+    const rundir = this.getRuntimeRundir();
     const FULLPATH = this.loader.FileLoader.FULLPATH;
     try {
+      fs.mkdirSync(rundir, { recursive: true });
       const dumpRouterFile = path.join(rundir, 'router.json');
       const routers = [];
       for (const layer of this.router.stack) {
diff --git a/packages/egg/src/lib/egg.ts b/packages/egg/src/lib/egg.ts
index a27e479da7..8ecce9af91 100644
--- a/packages/egg/src/lib/egg.ts
+++ b/packages/egg/src/lib/egg.ts
@@ -38,6 +38,8 @@ import { convertObject, createTransparentProxy } from './core/utils.ts';
 import type { EggApplicationLoader } from './loader/index.ts';
 import type { EggAppConfig } from './types.ts';
 
+const DEFAULT_WORKER_START_TIMEOUT = 10 * 60 * 1000;
+
 export interface EggApplicationCoreOptions extends Omit<EggCoreOptions, 'baseDir'> {
   mode?: 'cluster' | 'single';
   clusterPort?: number;
@@ -561,15 +563,13 @@ export class EggApplicationCore extends EggCore {
   }
 
   /**
-   * save app.config to `run/${type}_config.json`
+   * save app.config to `${rundir}/${type}_config.json`
    * @private
    */
   dumpConfig(): void {
-    const rundir = this.config.rundir;
+    const rundir = this.getRuntimeRundir();
     try {
-      if (!fs.existsSync(rundir)) {
-        fs.mkdirSync(rundir);
-      }
+      fs.mkdirSync(rundir, { recursive: true });
 
       // get dumped object
       const { config, meta } = this.dumpConfigToObject();
@@ -589,7 +589,8 @@ export class EggApplicationCore extends EggCore {
   dumpTiming(): void {
     try {
       const items = this.timing.toJSON();
-      const rundir = this.config.rundir;
+      const rundir = this.getRuntimeRundir();
+      fs.mkdirSync(rundir, { recursive: true });
       const dumpFile = path.join(rundir, `${this.type}_timing_${process.pid}.json`);
       fs.writeFileSync(dumpFile, CircularJSON.stringify(items, null, 2));
       this.coreLogger.info(this.timing.toString());
@@ -641,27 +642,41 @@ export class EggApplicationCore extends EggCore {
   }
 
   #setupTimeoutTimer(): void {
+    const workerStartTimeout = this.getWorkerStartTimeout();
     const startTimeoutTimer = setTimeout(() => {
       this.coreLogger.error(this.timing.toString());
-      this.coreLogger.error(`${this.type} still doesn't ready after ${this.config.workerStartTimeout} ms.`);
+      this.coreLogger.error(`${this.type} still doesn't ready after ${workerStartTimeout} ms.`);
       // log unfinished
       const items = this.timing.toJSON();
       for (const item of items) {
         if (item.end) continue;
         this.coreLogger.error(`unfinished timing item: ${CircularJSON.stringify(item)}`);
       }
-      this.coreLogger.error(
-        '[egg][setupTimeoutTimer] check run/%s_timing_%s.json for more details.',
-        this.type,
-        process.pid,
-      );
+      const dumpTimingFile = path.join(this.getRuntimeRundir(), `${this.type}_timing_${process.pid}.json`);
+      this.coreLogger.error('[egg][setupTimeoutTimer] check %s for more details.', dumpTimingFile);
       this.emit('startTimeout');
       this.dumpConfig();
       this.dumpTiming();
-    }, this.config.workerStartTimeout);
+    }, workerStartTimeout);
     this.ready(() => clearTimeout(startTimeoutTimer));
   }
 
+  protected getRuntimeRundir(): string {
+    const rundir = this.config.rundir;
+    if (typeof rundir === 'string' && rundir.length > 0) {
+      return rundir;
+    }
+    return path.join(this.baseDir, 'run');
+  }
+
+  private getWorkerStartTimeout(): number {
+    const workerStartTimeout = this.config.workerStartTimeout;
+    if (typeof workerStartTimeout === 'number' && Number.isFinite(workerStartTimeout) && workerStartTimeout > 0) {
+      return workerStartTimeout;
+    }
+    return DEFAULT_WORKER_START_TIMEOUT;
+  }
+
   get config() {
     return super.config as EggAppConfig;
   }
diff --git a/packages/egg/test/egg.test.ts b/packages/egg/test/egg.test.ts
index 9d4f7ecda2..e99d4c3876 100644
--- a/packages/egg/test/egg.test.ts
+++ b/packages/egg/test/egg.test.ts
@@ -263,6 +263,53 @@ describe.sequential('test/egg.test.ts', () => {
     });
   });
 
+  describe('runtime diagnostics fallback config', () => {
+    const baseDir = getFilepath('apps/dumpconfig');
+    const runDir = path.join(baseDir, 'run');
+    let app: MockApplication;
+
+    beforeAll(async () => {
+      app = createApp('apps/dumpconfig');
+      await app.ready();
+    });
+
+    afterAll(() => app.close());
+
+    it('should dump config and timing to baseDir/run when rundir is missing', () => {
+      fs.rmSync(runDir, { recursive: true, force: true });
+      const originalRundir = app.config.rundir;
+      Reflect.set(app.config, 'rundir', undefined);
+      try {
+        app.dumpConfig();
+        app.dumpTiming();
+      } finally {
+        Reflect.set(app.config, 'rundir', originalRundir);
+      }
+
+      assertFile(path.join(runDir, 'application_config.json'));
+      assertFile(path.join(runDir, `application_timing_${process.pid}.json`));
+      assertFile(path.join(runDir, 'router.json'));
+    });
+
+    it('should use the default worker start timeout when config is missing or invalid', () => {
+      const originalWorkerStartTimeout = app.config.workerStartTimeout;
+      try {
+        Reflect.set(app.config, 'workerStartTimeout', undefined);
+        assert.equal((app as any).getWorkerStartTimeout(), 10 * 60 * 1000);
+        Reflect.set(app.config, 'workerStartTimeout', 0);
+        assert.equal((app as any).getWorkerStartTimeout(), 10 * 60 * 1000);
+        Reflect.set(app.config, 'workerStartTimeout', -1);
+        assert.equal((app as any).getWorkerStartTimeout(), 10 * 60 * 1000);
+        Reflect.set(app.config, 'workerStartTimeout', Number.POSITIVE_INFINITY);
+        assert.equal((app as any).getWorkerStartTimeout(), 10 * 60 * 1000);
+        Reflect.set(app.config, 'workerStartTimeout', 1);
+        assert.equal((app as any).getWorkerStartTimeout(), 1);
+      } finally {
+        Reflect.set(app.config, 'workerStartTimeout', originalWorkerStartTimeout);
+      }
+    });
+  });
+
   describe('custom config from env', () => {
     let app: MockApplication;
     let baseDir: string;