refactor: extract serverless warning to static constant, improve JSDoc

Address code review feedback:
- Extract duplicated warning message to static SERVERLESS_PERSISTENCE_WARNING constant
- Add JSDoc note about process/env unavailability in non-Node.js runtimes

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

packages/plugins/driver-memory/src/memory-driver.ts

@@ -947,6 +947,9 @@ export class InMemoryDriver implements DriverInterface {
    * - `K_SERVICE` — Google Cloud Run / Cloud Functions
    * - `FUNCTION_TARGET` — Google Cloud Functions (Node.js)
    * - `DENO_DEPLOYMENT_ID` — Deno Deploy
+   *
+   * Returns `false` when `process` or `process.env` is unavailable
+   * (e.g. browser or edge runtimes without a Node.js process object).
    */
   private isServerlessEnvironment(): boolean {
     if (typeof globalThis.process === 'undefined' || !globalThis.process.env) {
@@ -965,6 +968,12 @@ export class InMemoryDriver implements DriverInterface {
     );
   }
 
+  private static readonly SERVERLESS_PERSISTENCE_WARNING =
+    'Serverless environment detected — file-system persistence is disabled in auto mode. ' +
+    'Data will NOT be persisted across function invocations. ' +
+    'Set persistence: false to silence this warning, or provide a custom adapter ' +
+    '(e.g. Upstash Redis, Vercel KV) via persistence: { adapter: yourAdapter }.';
+
   /**
    * Initialize the persistence adapter based on configuration.
    * Defaults to 'auto' when persistence is not specified.
@@ -985,12 +994,7 @@ export class InMemoryDriver implements DriverInterface {
           this.persistenceAdapter = new LocalStoragePersistenceAdapter();
           this.logger.debug('Auto-detected browser environment, using localStorage persistence');
         } else if (this.isServerlessEnvironment()) {
-          this.logger.warn(
-            'Serverless environment detected — file-system persistence is disabled in auto mode. ' +
-            'Data will NOT be persisted across function invocations. ' +
-            'Set persistence: false to silence this warning, or provide a custom adapter ' +
-            '(e.g. Upstash Redis, Vercel KV) via persistence: { adapter: yourAdapter }.'
-          );
+          this.logger.warn(InMemoryDriver.SERVERLESS_PERSISTENCE_WARNING);
         } else {
           const { FileSystemPersistenceAdapter } = await import('./persistence/file-adapter.js');
           this.persistenceAdapter = new FileSystemPersistenceAdapter();
@@ -1016,12 +1020,7 @@ export class InMemoryDriver implements DriverInterface {
           });
           this.logger.debug('Auto-detected browser environment, using localStorage persistence');
         } else if (this.isServerlessEnvironment()) {
-          this.logger.warn(
-            'Serverless environment detected — file-system persistence is disabled in auto mode. ' +
-            'Data will NOT be persisted across function invocations. ' +
-            'Set persistence: false to silence this warning, or provide a custom adapter ' +
-            '(e.g. Upstash Redis, Vercel KV) via persistence: { adapter: yourAdapter }.'
-          );
+          this.logger.warn(InMemoryDriver.SERVERLESS_PERSISTENCE_WARNING);
         } else {
           const { FileSystemPersistenceAdapter } = await import('./persistence/file-adapter.js');
           this.persistenceAdapter = new FileSystemPersistenceAdapter({