fix: Formalize Vite startup validation guarantee and document the plugin contract

apps/www/content/docs/frameworks/tanstack-start.mdx

@@ -8,6 +8,15 @@ or `@arkenv/rsbuild-plugin`, depending on your underlying bundler. ArkEnv
 inlines public keys (`VITE_` or `PUBLIC_`) into the client bundle, keeps server
 secrets inside server functions, and throws if client code reads them.
 
+When the Vite plugin is registered, it discovers and validates `env.ts` during
+Vite config resolution. Missing or invalid values abort the dev server or
+production build before it is ready, and relevant `.env` or schema changes are
+revalidated during HMR. Without the plugin, validation is import-driven and
+starts when a module first imports `env.ts`.
+
+This is the existing fail-fast contract, not a new lazy-validation option.
+ArkEnv does not add a default-off flag for lazy validation.
+
 For high-level architectural trade-offs, see
 [Frameworks](/docs/frameworks).
 

apps/www/content/docs/frameworks/vite.mdx

@@ -7,6 +7,24 @@ description: Learn how to use ArkEnv in a Vite project.
 Transform mode inlines public `VITE_` keys into the client bundle and
 keeps server secrets out.
 
+## When does validation run?
+
+When `@arkenv/vite-plugin` is registered, it discovers and validates `env.ts`
+during Vite config resolution. An invalid or missing value aborts the dev
+server or production build before Vite reports that it is ready. Relevant
+`.env` and schema changes are validated again during HMR.
+
+Without the plugin, validation is import-driven: `env.ts` runs when an
+application module imports it. This distinction applies to both server and
+client graphs; the plugin is what lets Vite validate the schema before the
+graph is ready and transform client imports safely. See the
+[`@arkenv/vite-plugin` reference](/docs/reference/vite-plugin) for the
+plugin contract.
+
+This documents the existing fail-fast behavior. ArkEnv does not add a
+default-off lazy-validation flag; a separate lazy mode would be an
+intentionally scoped feature.
+
 For high-level architectural trade-offs, see
 [Frameworks](/docs/frameworks).
 

apps/www/content/docs/reference/vite-plugin.mdx

@@ -44,6 +44,18 @@ Call `arkenvPlugin()` with no args, or an options object that includes
 transform fields (`schemaPath`, `clientPrefix`, logging). Do not pass a
 schema map or compiled `type()` to the plugin.
 
+## Startup validation
+
+When the plugin is registered, it resolves `env.ts` and validates it during
+Vite config resolution. Missing or invalid environment variables therefore
+abort the dev server or production build before Vite is ready. The plugin
+revalidates the schema when a relevant `.env` file or schema module changes
+during HMR.
+
+Without the plugin, validation is import-driven and runs when a module imports
+`env.ts`. Startup fail-fast is the documented behavior of the existing plugin
+contract; there is no default-off lazy-validation flag.
+
 ## Next steps
 
 <Cards>

packages/vite-plugin/src/env-module.test.ts

@@ -170,6 +170,119 @@ describe("transform mode plugin", () => {
 		}
 	});
 
+	it("fails during config resolution when the environment is invalid", async () => {
+		const root = mkdtempSync(join(tmpdir(), "arkenv-vite-invalid-startup-"));
+		temps.push(root);
+		writeFileSync(
+			join(root, "env.ts"),
+			'import arkenv from "@arkenv/core";\n\nexport const env = arkenv({ REQUIRED_TOKEN: "string" });\n',
+		);
+		const plugin = arkenvPlugin() as any;
+		const context = {} as any;
+
+		if (plugin.config && typeof plugin.config === "function") {
+			plugin.config.call(
+				context,
+				{ root, envDir: root },
+				{ mode: "test", command: "serve" },
+			);
+		}
+
+		await expect(
+			Promise.resolve().then(() =>
+				plugin.configResolved?.call(context, {
+					root,
+					envDir: root,
+					envPrefix: "VITE_",
+				} as any),
+			),
+		).rejects.toMatchObject({ name: "ArkEnvError" });
+		expect(process.env.REQUIRED_TOKEN).toBeUndefined();
+	});
+
+	it("revalidates valid schema and dotenv changes during HMR", async () => {
+		const root = mkdtempSync(join(tmpdir(), "arkenv-vite-hmr-"));
+		temps.push(root);
+		const schemaPath = join(root, "env.ts");
+		const dotenvPath = join(root, ".env.test");
+		writeFileSync(
+			schemaPath,
+			'import arkenv from "@arkenv/core";\n\nexport const env = arkenv({ VITE_API_URL: "string" });\n',
+		);
+		writeFileSync(dotenvPath, "VITE_API_URL=https://example.com\n");
+		const plugin = arkenvPlugin({ schemaPath }) as any;
+		const server = {
+			moduleGraph: {
+				getModulesByFile: () => new Set([{ id: schemaPath }]),
+				invalidateModule: () => {},
+			},
+		} as any;
+		const context = {} as any;
+
+		plugin.config?.call(
+			context,
+			{ root, envDir: root },
+			{ mode: "test", command: "serve" },
+		);
+		await plugin.configResolved?.call(context, {
+			root,
+			envDir: root,
+			envPrefix: "VITE_",
+		} as any);
+
+		const schemaUpdate = plugin.handleHotUpdate?.call(context, {
+			file: schemaPath,
+			server,
+		} as any);
+		expect(schemaUpdate).toHaveLength(1);
+		const dotenvUpdate = plugin.handleHotUpdate?.call(context, {
+			file: dotenvPath,
+			server,
+		} as any);
+		expect(dotenvUpdate).toHaveLength(1);
+	});
+
+	it("propagates invalid dotenv values during HMR", async () => {
+		const root = mkdtempSync(join(tmpdir(), "arkenv-vite-invalid-hmr-"));
+		temps.push(root);
+		const schemaPath = join(root, "env.ts");
+		const dotenvPath = join(root, ".env.test");
+		writeFileSync(
+			schemaPath,
+			'import arkenv from "@arkenv/core";\n\nexport const env = arkenv({ VITE_PORT: "number" });\n',
+		);
+		writeFileSync(dotenvPath, "VITE_PORT=8080\n");
+		const plugin = arkenvPlugin({ schemaPath }) as any;
+		const server = {
+			moduleGraph: {
+				getModulesByFile: () => new Set(),
+				invalidateModule: () => {},
+			},
+		} as any;
+		const context = {} as any;
+
+		plugin.config?.call(
+			context,
+			{ root, envDir: root },
+			{ mode: "test", command: "serve" },
+		);
+		await plugin.configResolved?.call(context, {
+			root,
+			envDir: root,
+			envPrefix: "VITE_",
+		} as any);
+		writeFileSync(dotenvPath, "VITE_PORT=not-a-number\n");
+
+		await expect(
+			Promise.resolve().then(() =>
+				plugin.handleHotUpdate?.call(context, {
+					file: dotenvPath,
+					server,
+				} as any),
+			),
+		).rejects.toMatchObject({ name: "ArkEnvError" });
+	});
+
 	it("passes through the env module unchanged in the SSR graph", async () => {
 		const fixtureDir = join(__dirname, "__fixtures__", "transform-env");
 		const plugin = arkenvPlugin({ schemaPath: join(fixtureDir, "env.ts") });