diff --git a/.changeset/node-22-floor-signals-dedupe.md b/.changeset/node-22-floor-signals-dedupe.md
new file mode 100644
index 0000000..1a626dc
--- /dev/null
+++ b/.changeset/node-22-floor-signals-dedupe.md
@@ -0,0 +1,5 @@
+---
+'@solidjs/vite-plugin': patch
+---
+
+Node floor and a signals dedupe. `engines.node` is now `>=22.12.0` (was `^20.19.0 || >=22.12.0`), matching the `solid-js`, `@solidjs/web` and `@solidjs/signals` 2.0 runtime packages, which have been ESM-only with that floor since rc.8; the README says the same. Under `serve`, `@solidjs/signals` joins `solid-js` and `@solidjs/web` in `resolve.dedupe` when the app root can reach a copy of it (`node_modules/@solidjs/signals`, walking up — an npm-style hoist or a direct dependency): `@solidjs/diagnostics/browser` and `solid-js/attribution` import the signals core directly, so a nested/duplicated install yielded a second engine beside the one `solid-js` loads. The entry is gated on the root copy because `resolve.dedupe` resolves the listed package from the root and Vite's Node-side resolver (`fetchModule` for externalized SSR imports, and the externalize decision) has no importer fallback when that misses — under pnpm's isolated layout, where signals exists only as `solid-js`'s transitive dependency, an unconditional entry turned `import "@solidjs/signals"` from the inlined `solid-js` into `ERR_MODULE_NOT_FOUND` once anything externalized it (vitefu does, when a semi-framework package such as `@solidjs/diagnostics` lists it under `dependencies`). With no root copy there is nothing to dedupe to, so the gate loses nothing. Signals does not join `optimizeDeps.include`: the optimizer already reaches it through `solid-js`, and an include entry that doesn't resolve from the root warns on every start.
diff --git a/README.md b/README.md
index fc11153..b529ec8 100644
--- a/README.md
+++ b/README.md
@@ -28,7 +28,8 @@ Join [solid discord](https://discord.com/invite/solidjs) and check the [troubles
 
 ## Requirements
 
-This module is 100% ESM compatible and requires Node.js `^20.19.0 || >=22.12.0`.
+This module is 100% ESM compatible and requires Node.js `>=22.12.0` (the same
+floor as the `solid-js` 2.0 runtime packages).
 
 You can check your current Node.js version by running `node -v`. Use a version
 manager such as [Volta](https://volta.sh/) or [nvm](https://github.com/nvm-sh/nvm)
diff --git a/examples/start-ssr/package.json b/examples/start-ssr/package.json
index 8fcb0bf..866607b 100644
--- a/examples/start-ssr/package.json
+++ b/examples/start-ssr/package.json
@@ -6,7 +6,7 @@
     "dev": "vite",
     "build": "vite build",
     "serve": "NODE_ENV=production node server.js",
-    "test": "node test/run.mjs && node test/http-bridge.mjs && node test/components-warning.mjs && node test/webworker-warning.mjs"
+    "test": "node test/run.mjs && node test/http-bridge.mjs && node test/components-warning.mjs && node test/webworker-warning.mjs && node test/dedupe.mjs"
   },
   "devDependencies": {
     "jsdom": "^26.1.0",
diff --git a/examples/start-ssr/test/dedupe.mjs b/examples/start-ssr/test/dedupe.mjs
new file mode 100644
index 0000000..5349547
--- /dev/null
+++ b/examples/start-ssr/test/dedupe.mjs
@@ -0,0 +1,125 @@
+// Config-level test for the dev `resolve.dedupe` list:
+//   - `solid-js` and `@solidjs/web` are always deduped under `serve`,
+//   - `@solidjs/signals` joins them only when the app root can reach a copy
+//     (`<root>/node_modules/@solidjs/signals`, walking up). Dedupe resolves
+//     the listed package from the root and Vite's Node-side resolver
+//     (`fetchModule`, the externalize decision) has no importer fallback,
+//     so under pnpm's isolated layout — signals present only as `solid-js`'s
+//     transitive dependency, which is this example's own layout — the entry
+//     would turn `import "@solidjs/signals"` from the inlined `solid-js` into
+//     ERR_MODULE_NOT_FOUND once anything externalizes signals,
+//   - `@solidjs/signals` never rides into `optimizeDeps.include` (an include
+//     entry that doesn't resolve from the root warns on every start),
+//   - under `build` the list is empty (dev-only fix).
+//
+// Pure resolveConfig — no dev server, no browser. Requires the plugin built
+// (pnpm build at the repo root). Usage: node test/dedupe.mjs
+
+import { fileURLToPath } from 'node:url';
+import path from 'node:path';
+import fs from 'node:fs';
+import os from 'node:os';
+import { resolveConfig } from 'vite';
+import solidPlugin from '@solidjs/vite-plugin';
+
+const exampleDir = path.dirname(path.dirname(fileURLToPath(import.meta.url)));
+
+const results = [];
+function record(name, ok, detail = '') {
+  results.push({ name, ok, detail });
+  console.log(`  ${ok ? 'PASS' : 'FAIL'} ${name}${detail && !ok ? ` — ${detail}` : ''}`);
+}
+
+function findUp(root, name) {
+  let dir = root;
+  while (true) {
+    if (fs.existsSync(path.join(dir, 'node_modules', name, 'package.json'))) return dir;
+    const parent = path.dirname(dir);
+    if (parent === dir) return undefined;
+    dir = parent;
+  }
+}
+
+async function resolveWith(root, command) {
+  return resolveConfig(
+    { root, configFile: false, logLevel: 'error', plugins: [solidPlugin({ ssr: true })] },
+    command,
+  );
+}
+
+// ---- this example: pnpm isolated layout, signals is transitive only -------
+{
+  const reachable = findUp(exampleDir, '@solidjs/signals');
+  record(
+    'precondition: @solidjs/signals is not reachable from the example root',
+    reachable === undefined,
+    `found under ${reachable}`,
+  );
+  const config = await resolveWith(exampleDir, 'serve');
+  record(
+    'serve: solid-js and @solidjs/web deduped',
+    config.resolve.dedupe.includes('solid-js') && config.resolve.dedupe.includes('@solidjs/web'),
+    config.resolve.dedupe.join(', '),
+  );
+  record(
+    'serve, no root copy: @solidjs/signals NOT in resolve.dedupe',
+    !config.resolve.dedupe.includes('@solidjs/signals'),
+    config.resolve.dedupe.join(', '),
+  );
+  record(
+    'serve: @solidjs/signals not in optimizeDeps.include',
+    !config.optimizeDeps.include.includes('@solidjs/signals'),
+    config.optimizeDeps.include.join(', '),
+  );
+}
+
+// ---- a root that CAN reach a copy (npm-style hoist / direct dependency) ----
+{
+  const root = fs.mkdtempSync(path.join(os.tmpdir(), 'solid-dedupe-'));
+  try {
+    fs.writeFileSync(
+      path.join(root, 'package.json'),
+      JSON.stringify({ name: 'dedupe-probe', private: true, type: 'module' }),
+    );
+    const stub = path.join(root, 'node_modules', '@solidjs', 'signals');
+    fs.mkdirSync(stub, { recursive: true });
+    fs.writeFileSync(
+      path.join(stub, 'package.json'),
+      JSON.stringify({ name: '@solidjs/signals', version: '0.0.0-stub' }),
+    );
+
+    const serve = await resolveWith(root, 'serve');
+    record(
+      'serve, root copy present: @solidjs/signals in resolve.dedupe',
+      serve.resolve.dedupe.includes('@solidjs/signals'),
+      serve.resolve.dedupe.join(', '),
+    );
+    record(
+      'serve, root copy present: solid-js and @solidjs/web still deduped',
+      serve.resolve.dedupe.includes('solid-js') && serve.resolve.dedupe.includes('@solidjs/web'),
+      serve.resolve.dedupe.join(', '),
+    );
+    record(
+      'serve, root copy present: @solidjs/signals still not in optimizeDeps.include',
+      !serve.optimizeDeps.include.includes('@solidjs/signals'),
+      serve.optimizeDeps.include.join(', '),
+    );
+
+    const build = await resolveWith(root, 'build');
+    record(
+      'build: resolve.dedupe is empty (dev-only fix)',
+      build.resolve.dedupe.length === 0,
+      build.resolve.dedupe.join(', '),
+    );
+  } finally {
+    fs.rmSync(root, { recursive: true, force: true });
+  }
+}
+
+const failed = results.filter((r) => !r.ok);
+console.log(`\n${results.length - failed.length}/${results.length} assertions passed`);
+if (failed.length) {
+  console.log('\nFailures:');
+  for (const f of failed) console.log(`  ${f.name} — ${f.detail}`);
+  process.exit(1);
+}
diff --git a/package.json b/package.json
index 9bed622..c741420 100644
--- a/package.json
+++ b/package.json
@@ -4,7 +4,7 @@
   "description": "solid-js integration plugin for Vite",
   "type": "module",
   "engines": {
-    "node": "^20.19.0 || >=22.12.0"
+    "node": ">=22.12.0"
   },
   "files": [
     "dist",
diff --git a/src/index.ts b/src/index.ts
index affac6f..f7b48cf 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1287,6 +1287,30 @@ export default function solidPlugin(options: Partial<Options> = {}): Plugin[] {
 
       // fix for bundling dev in production
       const nestedDeps = replaceDev ? ['solid-js', '@solidjs/web'] : [];
+      // `@solidjs/signals` is the reactive core `solid-js` depends on.
+      // `@solidjs/diagnostics/browser` and `solid-js/attribution` import it
+      // directly, so a nested/duplicated install (npm nesting a second copy
+      // under a package that lists it as a dependency) yields a second
+      // engine beside the one `solid-js` loads — the same two-engines
+      // symptom the `optimizeDeps.include` entries below guard against on
+      // the pre-bundle path. Dedupe it to the app's copy — but only when the
+      // app root can reach one. `resolve.dedupe` resolves the listed package
+      // from the root, and Vite's Node-side resolver (`fetchModule` for
+      // externalized SSR imports, and the externalize decision itself) has
+      // no importer fallback when that misses. Under pnpm's isolated layout
+      // signals exists only as `solid-js`'s transitive dependency, so with
+      // the entry always on, `import "@solidjs/signals"` from the inlined
+      // `solid-js` fails with ERR_MODULE_NOT_FOUND as soon as anything
+      // externalizes it (vitefu does, once a semi-framework package such as
+      // `@solidjs/diagnostics` lists it under `dependencies`). With no root
+      // copy there is nothing to dedupe TO, so the gate loses nothing. Not
+      // added to `optimizeDeps.include`: the optimizer already reaches
+      // signals through `solid-js`, and an include entry that doesn't
+      // resolve from the root logs a warning on every start.
+      const dedupe =
+        replaceDev && findPackageDir('@solidjs/signals', path.resolve(projectRoot || process.cwd()))
+          ? [...nestedDeps, '@solidjs/signals']
+          : nestedDeps;
 
       const userTest = (userConfig as any).test ?? {};
       const test = {} as any;
@@ -1361,7 +1385,7 @@ export default function solidPlugin(options: Partial<Options> = {}): Plugin[] {
         // esbuild: { include: /\.ts$/ },
         // resolve.conditions is handled per-environment in configEnvironment.
         resolve: {
-          dedupe: nestedDeps,
+          dedupe,
         },
         optimizeDeps: {
           extensions: ['.tsrx'],