Hotdeploy in a Gradle-based Spring Boot project fails

### Description of the bug

When `vaadin.frontend.hotdeploy=true` is enabled in a Gradle-based Spring Boot application, Vite first applies the frontend updates successfully on the client. Immediately afterward, a Gradle build is triggered, which runs the vaadinPrepareFrontend task. After that, the Vite dev server restart fails.

It occurs both with and without Spring Boot DevTools.

Relevant Log:
```
...
----------------- Frontend compiled successfully. -----------------
2026-04-11T13:08:10.237+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : 
2026-04-11T13:08:10.237+02:00  INFO 27058 --- [onPool-worker-1] c.v.b.devserver.AbstractDevServerRunner  : Started Vite. Time: 806ms
2026-04-11T13:08:10.237+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   ➜  Local:   http://127.0.0.1:52292/VAADIN/
2026-04-11T13:08:10.677+02:00  INFO 27058 --- [in-dev-server-2] c.v.b.d.DevModeHandlerManagerImpl        : Application running at http://localhost:8080/
2026-04-11T13:08:11.069+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : 
2026-04-11T13:08:11.069+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : [TypeScript] Found 0 errors. Watching for file changes.
2026-04-11T13:08:15.478+02:00  WARN 27058 --- [nio-8080-exec-2] c.vaadin.copilot.JavaSourcePathDetector  : Multiple content roots ([.../base-starter-spring-gradle-25-1-1/src/main, .../base-starter-spring-gradle-25-1-1/build/vaadin-generated]) found for module base-starter-spring-gradle-25-1-1.main with Java source paths [.../base-starter-spring-gradle-25-1-1/src/main/java]
2026-04-11T13:08:28.801+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : [vite] build/vaadin-dev-server-settings.json changed, restarting server...
2026-04-11T13:08:28.802+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : [vite] (client) page reload generated/vaadin-featureflags.js
2026-04-11T13:08:28.803+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : [vite] (client) page reload generated/app-shell-imports.js
2026-04-11T13:08:28.803+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : [vite] (client) page reload generated/vite-devmode.ts
2026-04-11T13:08:28.804+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : [vite] (client) hmr update /generated/index.tsx
2026-04-11T13:08:28.804+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : [vite] (client) hmr update /generated/vaadin-react.tsx
2026-04-11T13:08:28.804+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : [vite] (client) hmr update /generated/flow/Flow.tsx
2026-04-11T13:08:28.831+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : vite v7.3.1 building client environment for development...
2026-04-11T13:08:28.849+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : transforming...
2026-04-11T13:08:28.931+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : ✓ 79 modules transformed.
2026-04-11T13:08:28.948+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : rendering chunks...
2026-04-11T13:08:28.954+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : ✓ built in 123ms
2026-04-11T13:08:28.964+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : [vite] server restarted.
2026-04-11T13:08:28.969+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : [vite] (client) Pre-transform error: Failed to load url /generated/vite-devmode.ts (resolved id: /generated/vite-devmode.ts). Does the file exist?
2026-04-11T13:08:28.973+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : [vite] (client) Pre-transform error: Failed to resolve import "./index" from "src/main/frontend/generated/vaadin.ts". Does the file exist?
2026-04-11T13:08:28.974+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   Plugin: vite:import-analysis
2026-04-11T13:08:28.974+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   File: .../base-starter-spring-gradle-25-1-1/src/main/frontend/generated/vaadin.ts:51:7
2026-04-11T13:08:28.974+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   43 |  import "@vaadin/icons/vaadin-iconset.js";
2026-04-11T13:08:28.974+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   44 |  import "@vaadin/icon/vaadin-icon.js";
2026-04-11T13:08:28.974+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   45 |  import "./index";
2026-04-11T13:08:28.974+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :      |          ^
2026-04-11T13:08:28.974+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   46 |  import "./vaadin-react.js";
2026-04-11T13:08:28.974+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   47 |  import "Frontend/generated/jar-resources/vaadin-dev-tools/vaadin-dev-tools.js";
2026-04-11T13:08:29.130+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   : [vite] Internal server error: Failed to resolve import "./index" from "src/main/frontend/generated/vaadin.ts". Does the file exist?
2026-04-11T13:08:29.130+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   Plugin: vite:import-analysis
2026-04-11T13:08:29.130+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   File: .../base-starter-spring-gradle-25-1-1/src/main/frontend/generated/vaadin.ts:51:7
2026-04-11T13:08:29.130+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   43 |  import "@vaadin/icons/vaadin-iconset.js";
2026-04-11T13:08:29.130+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   44 |  import "@vaadin/icon/vaadin-icon.js";
2026-04-11T13:08:29.130+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   45 |  import "./index";
2026-04-11T13:08:29.130+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :      |          ^
2026-04-11T13:08:29.131+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   46 |  import "./vaadin-react.js";
2026-04-11T13:08:29.131+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :   47 |  import "Frontend/generated/jar-resources/vaadin-dev-tools/vaadin-dev-tools.js";
2026-04-11T13:08:29.131+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :       at TransformPluginContext._formatLog (file://.../base-starter-spring-gradle-25-1-1/node_modules/vite/dist/node/chunks/config.js:28999:43)
2026-04-11T13:08:29.131+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :       at TransformPluginContext.error (file://.../base-starter-spring-gradle-25-1-1/node_modules/vite/dist/node/chunks/config.js:28996:14)
2026-04-11T13:08:29.131+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :       at normalizeUrl (file://.../base-starter-spring-gradle-25-1-1/node_modules/vite/dist/node/chunks/config.js:27119:18)
2026-04-11T13:08:29.131+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :       at process.processTicksAndRejections (node:internal/process/task_queues:104:5)
2026-04-11T13:08:29.131+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :       at async file://.../base-starter-spring-gradle-25-1-1/node_modules/vite/dist/node/chunks/config.js:27177:32
2026-04-11T13:08:29.131+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :       at async Promise.all (index 30)
2026-04-11T13:08:29.131+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :       at async TransformPluginContext.transform (file://.../base-starter-spring-gradle-25-1-1/node_modules/vite/dist/node/chunks/config.js:27145:4)
2026-04-11T13:08:29.131+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :       at async EnvironmentPluginContainer.transform (file://.../base-starter-spring-gradle-25-1-1/node_modules/vite/dist/node/chunks/config.js:28797:14)
2026-04-11T13:08:29.131+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :       at async loadAndTransform (file://.../base-starter-spring-gradle-25-1-1/node_modules/vite/dist/node/chunks/config.js:22670:26)
2026-04-11T13:08:29.131+02:00  INFO 27058 --- [v-server-output] c.v.b.devserver.DevServerOutputTracker   :       at async viteTransformMiddleware (file://.../base-starter-spring-gradle-25-1-1/node_modules/vite/dist/node/chunks/config.js:24542:20)
...
````
Additionally, although it may be unrelated, the file vaadin-dev-server-settings.json changes, as shown in the logs, when vaadinPrepareFrontend is invoked after the CSS modification. The path's with `.../build/classes/...` changes to `.../build/resources/main/...`

Startup:
```json
{
	"frontendFolder": ".../base-starter-spring-gradle-25-1-1/./src/main/frontend",
	"themeFolder": "themes",
	"themeResourceFolder": ".../base-starter-spring-gradle-25-1-1/./src/main/frontend/generated/jar-resources",
	"staticOutput": ".../base-starter-spring-gradle-25-1-1/build/classes/META-INF/VAADIN/webapp/VAADIN/static",
	"generatedFolder": "generated",
	"statsOutput": ".../base-starter-spring-gradle-25-1-1/build/classes/META-INF/VAADIN/config",
	"frontendBundleOutput": ".../base-starter-spring-gradle-25-1-1/build/classes/META-INF/VAADIN/webapp",
	"devBundleOutput": ".../base-starter-spring-gradle-25-1-1/build/dev-bundle/webapp",
	"devBundleStatsOutput": ".../base-starter-spring-gradle-25-1-1/build/dev-bundle/config",
	"i18nOutput": "build/classes/vaadin-i18n",
	"jarResourcesFolder": ".../base-starter-spring-gradle-25-1-1/./src/main/frontend/generated/jar-resources",
	"javaResourceFolder": ".../base-starter-spring-gradle-25-1-1/src/main/resources",
	"themeName": "",
	"clientServiceWorkerSource": ".../base-starter-spring-gradle-25-1-1/build/sw.ts",
	"pwaEnabled": true,
	"offlineEnabled": true,
	"offlinePath": "'.'"
}
```

After change:
```json
{
	"frontendFolder": ".../base-starter-spring-gradle-25-1-1/./src/main/frontend",
	"themeFolder": "themes",
	"themeResourceFolder": ".../base-starter-spring-gradle-25-1-1/./src/main/frontend/generated/jar-resources",
	"staticOutput": ".../base-starter-spring-gradle-25-1-1/build/resources/main/META-INF/VAADIN/webapp/VAADIN/static",
	"generatedFolder": "generated",
	"statsOutput": ".../base-starter-spring-gradle-25-1-1/build/resources/main/META-INF/VAADIN/config",
	"frontendBundleOutput": ".../base-starter-spring-gradle-25-1-1/build/resources/main/META-INF/VAADIN/webapp",
	"devBundleOutput": ".../base-starter-spring-gradle-25-1-1/build/dev-bundle/webapp",
	"devBundleStatsOutput": ".../base-starter-spring-gradle-25-1-1/build/dev-bundle/config",
	"i18nOutput": "build/classes/vaadin-i18n",
	"jarResourcesFolder": ".../base-starter-spring-gradle-25-1-1/./src/main/frontend/generated/jar-resources",
	"javaResourceFolder": ".../base-starter-spring-gradle-25-1-1/src/main/resources",
	"themeName": "",
	"clientServiceWorkerSource": ".../base-starter-spring-gradle-25-1-1/build/sw.ts",
	"pwaEnabled": true,
	"offlineEnabled": true,
	"offlinePath": "'.'"
}
```

### Expected behavior

Hot deployment of frontend files should work without causing the Vite dev server to fail.

### Minimal reproducible example

1. Clone base-starter-spring-gradle
2. Add `vaadin.frontend.hotdeploy=true` to `applications.properties`
3. Start application with bootRun
4. Open page in browser
5. Change something in `styles.css` under `src/main/resources/META-INF/resources`
6. Select browser

### Versions

- Vaadin / Flow version: 25.1.1
- Java version: 21 (Temurin)
- OS version: macOS 26.3.1
- IDE (if applicable): IntelliJ 2026.1


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Hotdeploy in a Gradle-based Spring Boot project fails #24108

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Uh oh!

Hotdeploy in a Gradle-based Spring Boot project fails #24108

Description

Description of the bug

Expected behavior

Minimal reproducible example

Versions

Activity

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

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