diff --git a/packages/core/scripts/check-client-dist.ts b/packages/core/scripts/check-client-dist.ts
new file mode 100644
index 00000000..772b6848
--- /dev/null
+++ b/packages/core/scripts/check-client-dist.ts
@@ -0,0 +1,108 @@
+import { readFile } from 'node:fs/promises'
+import { dirname, relative, resolve } from 'node:path'
+import { findDynamicImports, findExports, findStaticImports } from 'mlly'
+
+interface ForbiddenRule {
+  name: string
+  match: (specifier: string) => boolean
+}
+
+const FORBIDDEN: ForbiddenRule[] = [
+  { name: 'ws', match: id => id === 'ws' || id.startsWith('ws/') },
+  { name: 'h3', match: id => id === 'h3' || id.startsWith('h3/') },
+  { name: 'node:* builtin', match: id => id.startsWith('node:') },
+  { name: 'devframe/rpc/transports/*', match: id => id.startsWith('devframe/rpc/transports/') },
+  { name: 'devframe/node*', match: id => id === 'devframe/node' || id.startsWith('devframe/node/') },
+]
+
+interface ScannedSpecifiers {
+  static: string[]
+  dynamic: string[]
+}
+
+interface Violation {
+  file: string
+  specifier: string
+  rule: string
+}
+
+async function scanSpecifiers(file: string): Promise<ScannedSpecifiers> {
+  const code = await readFile(file, 'utf8')
+  const staticIds = new Set<string>()
+  for (const i of findStaticImports(code))
+    staticIds.add(i.specifier)
+  for (const e of findExports(code)) {
+    if (e.specifier)
+      staticIds.add(e.specifier)
+  }
+  const dynamicIds = new Set<string>()
+  for (const d of findDynamicImports(code)) {
+    // Only consider plain string expressions; ignore variable/template imports.
+    const match = d.expression.match(/^\s*['"]([^'"]+)['"]\s*$/)
+    if (match?.[1])
+      dynamicIds.add(match[1])
+  }
+  return { static: [...staticIds], dynamic: [...dynamicIds] }
+}
+
+export interface CheckClientDistOptions {
+  /** Absolute paths to the client entry chunks to walk from. */
+  entries: string[]
+  /** Used to build relative paths in error messages. */
+  cwd: string
+}
+
+export async function checkClientDist(options: CheckClientDistOptions): Promise<void> {
+  const { entries, cwd } = options
+  const visited = new Set<string>()
+  const violations: Violation[] = []
+
+  async function visit(file: string): Promise<void> {
+    if (visited.has(file))
+      return
+    visited.add(file)
+
+    let scanned: ScannedSpecifiers
+    try {
+      scanned = await scanSpecifiers(file)
+    }
+    catch (err) {
+      throw new Error(`[check-client-dist] Failed to read ${relative(cwd, file)}: ${(err as Error).message}`)
+    }
+
+    // Static imports load eagerly when the file is evaluated — they're the leak
+    // vector this guard exists to catch. Flag any forbidden specifier.
+    for (const id of scanned.static) {
+      const hit = FORBIDDEN.find(r => r.match(id))
+      if (hit)
+        violations.push({ file, specifier: id, rule: hit.name })
+    }
+
+    // Follow both static and dynamic relative imports to discover every chunk
+    // the browser can end up loading. Dynamic specifiers themselves aren't
+    // checked against FORBIDDEN — the chunk they target is, on visit.
+    for (const id of [...scanned.static, ...scanned.dynamic]) {
+      if (id.startsWith('./') || id.startsWith('../')) {
+        const next = resolve(dirname(file), id)
+        await visit(next)
+      }
+    }
+  }
+
+  for (const entry of entries)
+    await visit(entry)
+
+  if (violations.length > 0) {
+    const lines: string[] = ['[check-client-dist] Forbidden server-only imports found in client dist:', '']
+    for (const v of violations) {
+      lines.push(`  ${relative(cwd, v.file)}`)
+      lines.push(`    imports ${JSON.stringify(v.specifier)} (matches forbidden rule: ${v.rule})`)
+    }
+    lines.push('')
+    lines.push(`Scanned ${visited.size} chunks reachable from ${entries.length} client entries.`)
+    lines.push('Client chunks must not statically import server-only modules — see packages/core/tsdown.config.ts.')
+    throw new Error(lines.join('\n'))
+  }
+
+  console.log(`[check-client-dist] OK — scanned ${visited.size} chunks reachable from ${entries.length} client entries`)
+}
diff --git a/packages/core/tsdown.config.ts b/packages/core/tsdown.config.ts
index e785a19d..833fe36c 100644
--- a/packages/core/tsdown.config.ts
+++ b/packages/core/tsdown.config.ts
@@ -1,79 +1,120 @@
+import { dirname, resolve } from 'node:path'
+import { fileURLToPath } from 'node:url'
 import { defineConfig } from 'tsdown'
 import Vue from 'unplugin-vue/rolldown'
 
+const here = dirname(fileURLToPath(import.meta.url))
+const distDir = resolve(here, 'dist')
+
 const define = {
   'import.meta.env.VITE_DEVTOOLS_LOCAL_DEV': 'false',
   'process.env.VITE_DEVTOOLS_LOCAL_DEV': 'false',
 }
 
-export default defineConfig({
-  exports: true,
-  plugins: [
-    Vue({
-      isProduction: true,
-    }),
+const deps = {
+  neverBundle: [
+    'vite',
+    '@vitejs/devtools/client/webcomponents',
+    /^node:/,
   ],
-  deps: {
-    neverBundle: [
-      'vite',
-      '@vitejs/devtools/client/webcomponents',
-      /^node:/,
-    ],
-    // @keep-sorted
-    onlyBundle: [
-      '@clack/core',
-      '@clack/prompts',
-      '@json-render/core',
-      '@json-render/vue',
-      '@vue/reactivity',
-      '@vue/runtime-core',
-      '@vue/runtime-dom',
-      '@vue/shared',
-      '@vueuse/core',
-      '@vueuse/shared',
-      '@xterm/addon-fit',
-      '@xterm/xterm',
-      'csstype',
-      'dompurify',
-      'fast-string-truncated-width',
-      'fast-string-width',
-      'fast-wrap-ansi',
-      'fuse.js',
-      'get-port-please',
-      'human-id',
-      'sisteransi',
-      'vue',
-      'zod',
-    ],
+  // @keep-sorted
+  onlyBundle: [
+    '@clack/core',
+    '@clack/prompts',
+    '@json-render/core',
+    '@json-render/vue',
+    '@vue/reactivity',
+    '@vue/runtime-core',
+    '@vue/runtime-dom',
+    '@vue/shared',
+    '@vueuse/core',
+    '@vueuse/shared',
+    '@xterm/addon-fit',
+    '@xterm/xterm',
+    'csstype',
+    'dompurify',
+    'fast-string-truncated-width',
+    'fast-string-width',
+    'fast-wrap-ansi',
+    'fuse.js',
+    'get-port-please',
+    'human-id',
+    'sisteransi',
+    'vue',
+    'zod',
+  ],
+}
+
+const inputOptions = {
+  resolve: {
+    mainFields: ['module', 'main'],
   },
-  clean: true,
-  platform: 'neutral',
-  tsconfig: '../../tsconfig.base.json',
-  entry: {
-    'index': 'src/index.ts',
-    'integration': 'src/integration.ts',
-    'internal': 'src/internal.ts',
-    'dirs': 'src/dirs.ts',
-    'cli': 'src/node/cli.ts',
-    'cli-commands': 'src/node/cli-commands.ts',
-    'config': 'src/node/config.ts',
-    'client/inject': 'src/client/inject/index.ts',
-    'client/webcomponents': 'src/client/webcomponents/index.ts',
+  experimental: {
+    resolveNewUrlToAsset: false,
   },
-  dts: true,
-  inputOptions: {
-    resolve: {
-      mainFields: ['module', 'main'],
+}
+
+const tsconfig = '../../tsconfig.base.json'
+
+// Split into two configs so the client and server entries live in independent
+// rolldown chunk graphs. A single combined build lets rolldown hoist shared
+// helpers (e.g. `__exportAll`) into chunks that mix server-only imports like
+// `devframe/rpc/transports/ws-server`, which then leak into the browser bundle.
+export default defineConfig([
+  // Client build — runs first; `clean: true` clears dist/ before the server
+  // build appends to it. Keep this first in the array.
+  {
+    clean: true,
+    platform: 'browser',
+    tsconfig,
+    plugins: [
+      Vue({
+        isProduction: true,
+      }),
+    ],
+    deps,
+    entry: {
+      'client/inject': 'src/client/inject/index.ts',
+      'client/webcomponents': 'src/client/webcomponents/index.ts',
     },
-    experimental: {
-      resolveNewUrlToAsset: false,
+    dts: true,
+    inputOptions,
+    define,
+    hooks: {
+      'build:before': async function () {
+        const { buildCSS } = await import('./src/client/webcomponents/scripts/build-css')
+        await buildCSS()
+      },
+      'build:done': async function () {
+        const { checkClientDist } = await import('./scripts/check-client-dist')
+        await checkClientDist({
+          entries: [
+            resolve(distDir, 'client/inject.js'),
+            resolve(distDir, 'client/webcomponents.js'),
+          ],
+          cwd: here,
+        })
+      },
     },
   },
-  define,
-  hooks: {
-    'build:before': async function () {
-      const { buildCSS } = await import('./src/client/webcomponents/scripts/build-css')
-      await buildCSS()
+  // Server build — `clean: false` so it appends to the client output. No Vue
+  // plugin (server entries don't import .vue) and no CSS hook.
+  {
+    clean: false,
+    platform: 'neutral',
+    tsconfig,
+    deps,
+    entry: {
+      'index': 'src/index.ts',
+      'integration': 'src/integration.ts',
+      'internal': 'src/internal.ts',
+      'dirs': 'src/dirs.ts',
+      'cli': 'src/node/cli.ts',
+      'cli-commands': 'src/node/cli-commands.ts',
+      'config': 'src/node/config.ts',
     },
+    dts: true,
+    inputOptions,
+    define,
   },
-})
+])