diff --git a/.changeset/vitest-client-inline-runtime.md b/.changeset/vitest-client-inline-runtime.md
new file mode 100644
index 0000000..6245ff3
--- /dev/null
+++ b/.changeset/vitest-client-inline-runtime.md
@@ -0,0 +1,5 @@
+---
+'@solidjs/vite-plugin': patch
+---
+
+In the Vitest client posture (jsdom, happy-dom), the plugin now inlines `solid-js`, `@solidjs/web` and the packages that import them without a `solid` export condition, such as `@solidjs/testing-library`. Before, they stayed external, and the host runtime resolved their own imports. Node gets the `browser` condition from Vitest's worker `--conditions`, but Deno does not apply it in worker threads (the `threads` pool) and resolves `deno`/`node`. Under Deno, `@solidjs/testing-library` loaded the server build of `@solidjs/web` and `render` failed with `isServer` true (#369). Inlining sends these imports through Vite's `browser` condition and loads one client-build instance. A `test.server.deps.inline` list is merged with the plugin's, and a `test.server.deps.external` entry for `solid-js` still opts out.
diff --git a/README.md b/README.md
index 74508fc..537b1a0 100644
--- a/README.md
+++ b/README.md
@@ -1152,7 +1152,7 @@ For other breaking changes, check [the migration guide of vite](https://vitejs.d
 
 If you are using [vitest](https://vitest.dev/), this plugin already injects the necessary configuration for you. It even automatically detects if you have `@testing-library/jest-dom` installed in your project and automatically adds it to the `setupFiles`. All you need to add (if you want) is `globals`, `coverage`, and other testing configuration of your choice. If you can live without those, enjoy using vitest without the need to configure it yourself.
 
-Tests default to the client posture, regardless of the app's `ssr` flag: DOM codegen, non-hydratable (nothing hydrates in a test), browser export conditions, and a `jsdom` default `test.environment`. A server-rendered app needs no `ssr: mode !== 'test'` workaround — DOM component tests just work.
+Tests default to the client posture, regardless of the app's `ssr` flag: DOM codegen, non-hydratable (nothing hydrates in a test), browser export conditions, and a `jsdom` default `test.environment`. `solid-js`, `@solidjs/web` and the packages that import them (such as `@solidjs/testing-library`) are inlined, so their imports resolve the browser build through Vite on any host runtime, Deno included. A server-rendered app needs no `ssr: mode !== 'test'` workaround — DOM component tests just work.
 
 Server-runtime unit tests (server functions, sessions, `renderToString` — anything that needs `isServer` to be `true` and the real server build of the framework) opt out per [vitest project](https://vitest.dev/guide/projects) by setting `test.environment: 'node'` (or `'edge-runtime'`) explicitly. That project gets the server posture end to end: server export conditions, ssr codegen, and the framework inlined so the whole graph — request-event storage included — resolves into one server-build instance. No inline/alias configuration needed. Both postures coexist in one workspace:
 
@@ -1172,7 +1172,7 @@ test: {
 },
 ```
 
-The posture is chosen while each project resolves its own Vite config. Vitest 5 lets inline projects reuse the root Vite server instead (`test.sharedViteServer`, on by default), which skips that step, so the plugin sets `sharedViteServer: false` when the root config declares `test.projects` — trading Vitest 5's shared-server optimization for the per-project resolution Vitest 4 always did. Setting the option yourself overrides this; with `true`, every shared project runs with the root config's posture, without the injected `jest-dom` setup file, and without the plugin's `server.deps` handling (the framework inlined for the server posture, externalized for the client one).
+The posture is chosen while each project resolves its own Vite config. Vitest 5 lets inline projects reuse the root Vite server instead (`test.sharedViteServer`, on by default), which skips that step, so the plugin sets `sharedViteServer: false` when the root config declares `test.projects` — trading Vitest 5's shared-server optimization for the per-project resolution Vitest 4 always did. Setting the option yourself overrides this; with `true`, every shared project runs with the root config's posture, without the injected `jest-dom` setup file, and without the plugin's `server.deps` handling (the framework inlined in both postures, together with its consumers such as `@solidjs/testing-library` in the client one).
 
 # Credits
 
diff --git a/examples/start-ssr/package.json b/examples/start-ssr/package.json
index fb275b1..177579c 100644
--- a/examples/start-ssr/package.json
+++ b/examples/start-ssr/package.json
@@ -9,6 +9,7 @@
     "test": "node test/run.mjs && node test/http-bridge.mjs && node test/components-warning.mjs && node test/webworker-warning.mjs && node test/dedupe.mjs && node test/ssr-inline.mjs"
   },
   "devDependencies": {
+    "@solidjs/testing-library": "^1.0.0-beta.2",
     "jsdom": "^26.1.0",
     "vite": "^8.2.1",
     "@solidjs/vite-plugin": "workspace:*",
diff --git a/examples/start-ssr/src/testing-library.test.tsx b/examples/start-ssr/src/testing-library.test.tsx
new file mode 100644
index 0000000..b715966
--- /dev/null
+++ b/examples/start-ssr/src/testing-library.test.tsx
@@ -0,0 +1,41 @@
+// Client-posture regression test for runtime-consuming packages (#369). The
+// vitest mode of test/run.mjs runs it with test/deno-conditions.mjs
+// preloaded. `@solidjs/testing-library` has no `solid` export condition.
+// Left external, its own `import "@solidjs/web"` is resolved by the host
+// runtime, and under Deno that is the server build, so `render` ran with
+// `isServer` true. The plugin inlines it with the runtime, so its imports go
+// through Vite's `browser` condition and share the test file's instance.
+import { expect, it } from 'vitest';
+import { createSignal } from 'solid-js';
+import { isServer } from '@solidjs/web';
+import { render } from '@solidjs/testing-library';
+
+function Counter() {
+  const [count, setCount] = createSignal(0);
+  return (
+    <button type="button" onClick={() => setCount(count() + 1)}>
+      count: {count()}
+    </button>
+  );
+}
+
+const nextTick = () => new Promise((resolve) => setTimeout(resolve, 0));
+
+it('resolves the browser build in the test file', () => {
+  expect(isServer).toBe(false);
+});
+
+it('renders and updates through @solidjs/testing-library', async () => {
+  const { getByRole, unmount } = render(() => <Counter />);
+  try {
+    const button = getByRole('button');
+    expect(button.textContent).toContain('count: 0');
+    button.click();
+    for (let i = 0; i < 20 && !button.textContent!.includes('count: 1'); i++) {
+      await nextTick();
+    }
+    expect(button.textContent).toContain('count: 1');
+  } finally {
+    unmount();
+  }
+});
diff --git a/examples/start-ssr/test/deno-conditions.mjs b/examples/start-ssr/test/deno-conditions.mjs
new file mode 100644
index 0000000..b0b2f95
--- /dev/null
+++ b/examples/start-ssr/test/deno-conditions.mjs
@@ -0,0 +1,29 @@
+// Preloaded into the vitest workers (NODE_OPTIONS=--import) by the vitest
+// mode of test/run.mjs. It makes Node resolve bare imports the way Deno does.
+// In worker threads, Deno does not apply the `browser` condition that vitest
+// passes to the workers as `--conditions`, so an externalized package's own
+// `import "@solidjs/web"` resolves `deno`/`node`, which is the server build
+// (#369).
+import module from 'node:module';
+
+const denoConditions = (context) => ({
+  ...context,
+  conditions: [...context.conditions.filter((c) => c !== 'browser'), 'deno'],
+});
+
+if (module.registerHooks) {
+  module.registerHooks({
+    resolve: (specifier, context, next) => next(specifier, denoConditions(context)),
+  });
+} else {
+  // Node < 22.15 has only the async loader API.
+  module.register(
+    'data:text/javascript,' +
+      encodeURIComponent(`
+        export async function resolve(specifier, context, next) {
+          const conditions = context.conditions.filter((c) => c !== 'browser');
+          return next(specifier, { ...context, conditions: [...conditions, 'deno'] });
+        }
+      `),
+  );
+}
diff --git a/examples/start-ssr/test/run.mjs b/examples/start-ssr/test/run.mjs
index d20091a..73e659d 100644
--- a/examples/start-ssr/test/run.mjs
+++ b/examples/start-ssr/test/run.mjs
@@ -6352,6 +6352,44 @@ async function runVitestMode() {
     testPass ? undefined : out.slice(-2000),
   );
 
+  // Runtime-consuming packages in the client posture (#369). An externalized
+  // package's own imports are resolved by the host runtime, not by Vite.
+  // Node gets the `browser` condition from vitest's worker `--conditions`;
+  // Deno does not, and `@solidjs/testing-library` then loaded the server
+  // build of `@solidjs/web`. test/deno-conditions.mjs makes the workers
+  // resolve the way Deno does, so this fails unless the plugin inlines the
+  // runtime and its consumers.
+  let consumersOut = '';
+  let consumersOk = false;
+  try {
+    consumersOut = execSync('pnpm exec vitest run src/testing-library.test.tsx --pool=forks', {
+      cwd: exampleDir,
+      stdio: 'pipe',
+      timeout: 180000,
+      env: {
+        ...process.env,
+        NO_COLOR: '1',
+        NODE_OPTIONS: [
+          process.env.NODE_OPTIONS,
+          `--import=${pathToFileURL(path.join(exampleDir, 'test', 'deno-conditions.mjs')).href}`,
+        ]
+          .filter(Boolean)
+          .join(' '),
+      },
+    }).toString();
+    consumersOk = true;
+  } catch (e) {
+    consumersOut = String(e.stdout || '') + String(e.stderr || '');
+  }
+  const consumersPass = consumersOk && /2 passed/.test(consumersOut);
+  record(
+    mode,
+    'runtime-consumers',
+    '@solidjs/testing-library renders with the browser build when the host runtime ignores `browser`',
+    consumersPass,
+    consumersPass ? undefined : consumersOut.slice(-2000),
+  );
+
   // Both postures in ONE workspace (VITEST_PROJECTS=1 adds test.projects to
   // the config): the jsdom project keeps the client posture while the node
   // project gets the server posture end to end just by writing
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 134fa9f..28e2249 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -191,6 +191,9 @@ importers:
         specifier: 'catalog:'
         version: 2.0.0-rc.14
     devDependencies:
+      '@solidjs/testing-library':
+        specifier: ^1.0.0-beta.2
+        version: 1.0.0-beta.2(@solidjs/web@2.0.0-rc.14(solid-js@2.0.0-rc.14))(solid-js@2.0.0-rc.14)
       '@solidjs/vite-plugin':
         specifier: workspace:*
         version: link:../..
diff --git a/src/index.ts b/src/index.ts
index 7b9ab11..02db8ea 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1260,6 +1260,10 @@ export default function solidPlugin(options: Partial<Options> = {}): Plugin[] {
   // Names of the packages `isSemiFrameworkPkgByJson` classified, so their
   // dependencies can be taken back out of `optimizeDeps.include` (see below).
   const semiFrameworkPkgs = new Set<string>();
+  // Packages that import the Solid runtime without a `solid` export
+  // condition, found by the same crawl in the vitest client posture. They are
+  // inlined there with the runtime (see `test.server.deps` below).
+  const testRuntimeConsumers = new Set<string>();
   const tsrxCss = new Map<string, string>();
 
   // The client build's manifest, read back by SSR builds. In builder-mode
@@ -1469,10 +1473,20 @@ export default function solidPlugin(options: Partial<Options> = {}): Plugin[] {
           // the same way `development` does, and an externalized consumer
           // would split it just the same), never vitest (it manages inlining
           // via test.server.deps).
-          if (!(replaceDev || observe) || isTestMode) return false;
           const semi = SOLID_RUNTIME_PKGS.some(
             (name) => pkgJson.dependencies?.[name] || pkgJson.peerDependencies?.[name],
           );
+          if (isTestMode) {
+            // Client test posture: record the runtime consumers so
+            // `test.server.deps.inline` below can inline them, without
+            // handing them to vitefu (its `ssr.external` for their
+            // dependencies would reach vitest's `server.deps.external`).
+            if (semi && !serverTestPosture && typeof pkgJson.name === 'string') {
+              testRuntimeConsumers.add(pkgJson.name);
+            }
+            return false;
+          }
+          if (!(replaceDev || observe)) return false;
           if (semi && typeof pkgJson.name === 'string') semiFrameworkPkgs.add(pkgJson.name);
           return semi;
         },
@@ -1581,11 +1595,36 @@ export default function solidPlugin(options: Partial<Options> = {}): Plugin[] {
             test.server = { deps: { inline: [/solid-js/, /@solidjs[+/]web/] } };
           }
         } else if (
+          // `inline: true` inlines everything already (and Vite's config
+          // merge would turn it into `[true, ...]`, which vitest can't read).
+          // A user list is merged with this one; a user who externalizes
+          // solid-js keeps it external.
+          userTest.server?.deps?.inline !== true &&
           !userTest.server?.deps?.external?.find((item: string | RegExp) =>
             /solid-js/.test(item.toString()),
           )
         ) {
-          test.server = { deps: { external: [/solid-js/] } };
+          // An externalized package is imported natively, and its own imports
+          // are resolved by the host runtime, not by Vite. Node gets the
+          // `browser` condition from vitest's worker `--conditions`, but Deno
+          // does not apply them in worker threads. It resolves `deno`/`node`
+          // and lands on the server build (`isServer` true inside
+          // `@solidjs/testing-library`'s `render`, #369). Inline the runtime and the packages that consume it, so
+          // every import of `solid-js` and `@solidjs/web` goes through Vite's
+          // `browser` condition and loads one client-build instance. A
+          // consumer left external would load a second, native copy, so the
+          // consumers found by the crawl are inlined with the runtime.
+          // Packages with a `solid` export condition are inlined already
+          // through vitefu's `ssr.noExternal`.
+          test.server = {
+            deps: {
+              inline: [
+                /[\\/]node_modules[\\/]solid-js[\\/]/,
+                /[\\/]node_modules[\\/]@solidjs[\\/]web[\\/]/,
+                ...testRuntimeConsumers,
+              ],
+            },
+          };
         }
         // jest-dom's DOM matchers have no place in a server-posture project;
         // vitest browser mode already has bundled jest-dom assertions