fix(core): start standalone DevTools once for multi-environment builds

packages/core/src/node/__tests__/integration.test.ts

@@ -169,6 +169,16 @@ describe('devToolsIntegration', () => {
     )
   })
 
+  it('starts standalone DevTools once for multiple build environments', async () => {
+    const plugins = await DevToolsIntegration(createIntegrationOptions('build'))
+    const config = createResolvedConfig('build', { client: {} as never, ssr: {} as never })
+    Object.assign(config, { plugins, devtools: normalizeDevToolsConfig({ apply: 'build' }, 'localhost') })
+
+    await runDevTools({ config })
+
+    expect(startDevTools).toHaveBeenCalledTimes(1)
+  })
+
   it('does not run standalone DevTools for a manual plugin config', async () => {
     const config = createResolvedConfig('build', { client: {} as never })
     Object.assign(config, {

packages/core/src/node/plugins/integration.ts

@@ -54,20 +54,23 @@ export async function runDevTools(
 
   if (!isDevToolsEnabled(devtoolsConfig, config.command))
     return
-  for (const _environment of getDevToolsEnvironments(config, devtoolsConfig)) {
-    try {
-      const { startDevTools } = await import('../start')
-      await startDevTools({
-        ...devtoolsConfig.config,
-        root: devtoolsConfig.config.root ?? config.root,
-      }, devtoolsConfig)
-    }
-    catch (error: any) {
-      config.logger.error(
-        `Failed to run Vite DevTools: ${error?.message || error?.stack || error}`,
-        { error },
-      )
-    }
+
+  // A single standalone server covers every environment, so start it once.
+  if (!getDevToolsEnvironments(config, devtoolsConfig).length)
+    return
+
+  try {
+    const { startDevTools } = await import('../start')
+    await startDevTools({
+      ...devtoolsConfig.config,
+      root: devtoolsConfig.config.root ?? config.root,
+    }, devtoolsConfig)
+  }
+  catch (error: any) {
+    config.logger.error(
+      `Failed to run Vite DevTools: ${error?.message || error?.stack || error}`,
+      { error },
+    )
   }
 }