refactor(rsc): use emitFile and virtual scan placeholder for env imports

Replace direct rollupOptions.input mutation with:
- Virtual scan placeholder for scan builds without configured entries
- emitFile in buildStart for emitting discovered entries in real builds

This follows the fullstack plugin pattern and provides cleaner separation
between scan and real build phases.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: hi-ogawa

packages/plugin-rsc/src/plugin.ts

@@ -29,6 +29,7 @@ import { cjsModuleRunnerPlugin } from './plugins/cjs'
 import { vitePluginFindSourceMapURL } from './plugins/find-source-map-url'
 import {
   ENV_IMPORTS_MANIFEST_NAME,
+  ENV_IMPORTS_SCAN_VIRTUAL,
   vitePluginImportEnvironment,
 } from './plugins/import-environment'
 import {
@@ -459,44 +460,22 @@ export default function vitePluginRsc(
     logStep('[1/5] analyze client references...')
     await builder.build(builder.environments.rsc!)
 
-    // TODO: let's configuere dummy input e.g. __vite_rsc_xxx: "virtual:..."
-    // Inject RSC → other environment imports discovered during RSC scan
-    // This must happen before SSR scan so SSR has input
-    for (const meta of Object.values(manager.environmentImportMetaMap)) {
-      const targetEnv = builder.environments[meta.targetEnv]
-      if (targetEnv) {
-        const input = (targetEnv.config.build.rollupOptions.input ??=
-          {}) as Record<string, string>
-        if (!(meta.entryName in input)) {
-          input[meta.entryName] = meta.resolvedId
-        }
-      }
-    }
-
     // Check if we need SSR scan (has input or discovered imports targeting SSR)
-    // TODO: no need of optimization yet. just leave it as future follow TODO.
-    const ssrInputAfterRsc = builder.environments.ssr!.config.build
-      .rollupOptions.input as Record<string, string> | undefined
-    const hasSsrInputAfterRsc =
-      ssrInputAfterRsc && Object.keys(ssrInputAfterRsc).length > 0
+    const hasRscToSsrImports = Object.values(
+      manager.environmentImportMetaMap,
+    ).some((meta) => meta.targetEnv === 'ssr')
 
-    if (hasSsrInput || hasSsrInputAfterRsc) {
+    if (hasSsrInput || hasRscToSsrImports) {
+      // Use dummy input for scan builds that have no configured input
+      // Real entries are emitted via emitFile in buildStart
+      if (!hasSsrInput) {
+        builder.environments.ssr!.config.build.rollupOptions.input = {
+          __vite_rsc_env_imports_scan: ENV_IMPORTS_SCAN_VIRTUAL,
+        }
+      }
       builder.environments.ssr!.config.build.write = false
       logStep('[2/5] analyze server references...')
       await builder.build(builder.environments.ssr!)
-
-      // Inject SSR → other environment imports discovered during SSR scan
-      // (for bidirectional support)
-      for (const meta of Object.values(manager.environmentImportMetaMap)) {
-        const targetEnv = builder.environments[meta.targetEnv]
-        if (targetEnv) {
-          const input = (targetEnv.config.build.rollupOptions.input ??=
-            {}) as Record<string, string>
-          if (!(meta.entryName in input)) {
-            input[meta.entryName] = meta.resolvedId
-          }
-        }
-      }
     }
 
     manager.isScanBuild = false

packages/plugin-rsc/src/plugins/import-environment.ts

@@ -6,6 +6,7 @@ import type { Plugin, ResolvedConfig, ViteDevServer } from 'vite'
 import { evalValue } from './vite-utils'
 
 export const ENV_IMPORTS_MANIFEST_NAME = '__vite_rsc_env_imports_manifest.js'
+export const ENV_IMPORTS_SCAN_VIRTUAL = 'virtual:vite-rsc/env-imports-scan'
 
 export type EnvironmentImportMeta = {
   resolvedId: string
@@ -18,6 +19,7 @@ export type EnvironmentImportMeta = {
 interface PluginManager {
   server: ViteDevServer
   config: ResolvedConfig
+  isScanBuild: boolean
   environmentImportMetaMap: Record<string, EnvironmentImportMeta>
   environmentImportOutputMap: Record<string, string>
 }
@@ -35,6 +37,30 @@ export function vitePluginImportEnvironment(manager: PluginManager): Plugin[] {
         ) {
           return { id: './' + ENV_IMPORTS_MANIFEST_NAME, external: true }
         }
+        // Virtual scan placeholder for scan builds without entries
+        if (source === ENV_IMPORTS_SCAN_VIRTUAL) {
+          return '\0' + ENV_IMPORTS_SCAN_VIRTUAL
+        }
+      },
+      load(id) {
+        // Empty module for scan placeholder
+        if (id === '\0' + ENV_IMPORTS_SCAN_VIRTUAL) {
+          return 'export {}'
+        }
+      },
+      buildStart() {
+        // Emit discovered entries in real builds (not scan builds)
+        if (this.environment.mode !== 'build' || manager.isScanBuild) return
+
+        for (const meta of Object.values(manager.environmentImportMetaMap)) {
+          if (meta.targetEnv === this.environment.name) {
+            this.emitFile({
+              type: 'chunk',
+              id: meta.resolvedId,
+              name: meta.entryName,
+            })
+          }
+        }
       },
       transform: {
         async handler(code, id) {