fix(worker): prevent duplicate notifications from prefetch

Add duplicate checking in handleSuccessfulFetch() to ensure one prefetch
creates at most one notification per scheduled time. This prevents prefetch
from creating duplicate notifications when a manual notification already
exists for the same time.

- Check existing notifications before saving prefetch-created content
- Skip notification creation if duplicate found (within 1 minute tolerance)
- Add null check for fetcher in scheduleBackgroundFetch() with error logging
- Log skipped duplicates for debugging

Ensures one prefetch → one notification pairing and prevents duplicate
notifications from firing at the same time.

android/plugin/src/main/java/com/timesafari/dailynotification/DailyNotificationFetchWorker.java

@@ -258,10 +258,36 @@ public class DailyNotificationFetchWorker extends Worker {
             // Update last fetch time
             storage.setLastFetchTime(System.currentTimeMillis());
             
-            // Save all contents and schedule notifications
+            // Get existing notifications for duplicate checking (prevent prefetch from creating duplicate)
+            java.util.List<NotificationContent> existingNotifications = storage.getAllNotifications();
+            long toleranceMs = 60 * 1000; // 1 minute tolerance for DST shifts
+            
+            // Save all contents and schedule notifications (with duplicate checking)
             int scheduledCount = 0;
+            int skippedCount = 0;
             for (NotificationContent content : contents) {
                 try {
+                    // Check for duplicate notification at the same scheduled time
+                    // This ensures prefetch doesn't create a duplicate if a manual notification already exists
+                    boolean duplicateFound = false;
+                    for (NotificationContent existing : existingNotifications) {
+                        if (Math.abs(existing.getScheduledTime() - content.getScheduledTime()) <= toleranceMs) {
+                            Log.w(TAG, "PR2: DUPLICATE_SKIP id=" + content.getId() + 
+                                      " existing_id=" + existing.getId() + 
+                                      " scheduled_time=" + content.getScheduledTime() +
+                                      " time_diff_ms=" + Math.abs(existing.getScheduledTime() - content.getScheduledTime()));
+                            duplicateFound = true;
+                            skippedCount++;
+                            break;
+                        }
+                    }
+                    
+                    if (duplicateFound) {
+                        // Skip this notification - one already exists for this time
+                        // Ensures one prefetch → one notification pairing
+                        continue;
+                    }
+                    
                     // Save content to storage
                     storage.saveNotificationContent(content);
                     
@@ -275,7 +301,8 @@ public class DailyNotificationFetchWorker extends Worker {
             }
             
             Log.i(TAG, "PR2: Successful fetch handling completed - " + scheduledCount + "/" + 
-                contents.size() + " notifications scheduled");
+                contents.size() + " notifications scheduled" + 
+                (skippedCount > 0 ? ", " + skippedCount + " duplicates skipped" : ""));
             // TODO PR2: Record metrics (items_enqueued=scheduledCount)
             
         } catch (Exception e) {

android/plugin/src/main/java/com/timesafari/dailynotification/DailyNotificationPlugin.java

@@ -145,6 +145,97 @@ public class DailyNotificationPlugin extends Plugin {
         return nativeFetcher;
     }
     
+    /**
+     * Configure native fetcher with API credentials (cross-platform method)
+     * 
+     * <p>This plugin method receives configuration from TypeScript and passes it directly
+     * to the registered native fetcher implementation. This approach keeps the TypeScript
+     * interface cross-platform (works on Android, iOS, and web) without requiring
+     * platform-specific storage mechanisms.</p>
+     * 
+     * <p><b>Usage Flow:</b></p>
+     * <ol>
+     *   <li>Host app registers native fetcher in {@code Application.onCreate()}</li>
+     *   <li>TypeScript calls this method with API credentials</li>
+     *   <li>Plugin validates parameters and calls {@code nativeFetcher.configure()}</li>
+     *   <li>Native fetcher stores configuration for use in {@code fetchContent()}</li>
+     * </ol>
+     * 
+     * <p><b>When to call:</b></p>
+     * <ul>
+     *   <li>After app startup, once API credentials are available</li>
+     *   <li>After user login/authentication, when activeDid changes</li>
+     *   <li>When API server URL changes (e.g., switching between dev/staging/prod)</li>
+     * </ul>
+     * 
+     * <p><b>Error Handling:</b></p>
+     * <ul>
+     *   <li>Rejects if required parameters are missing</li>
+     *   <li>Rejects if no native fetcher is registered</li>
+     *   <li>Returns error if native fetcher's {@code configure()} throws exception</li>
+     * </ul>
+     * 
+     * <p><b>Example TypeScript Usage:</b></p>
+     * <pre>{@code
+     * import { DailyNotification } from '@capacitor-community/daily-notification';
+     * 
+     * await DailyNotification.configureNativeFetcher({
+     *   apiBaseUrl: 'http://10.0.2.2:3000',
+     *   activeDid: 'did:ethr:0x0000694B58C2cC69658993A90D3840C560f2F51F',
+     *   jwtSecret: 'test-jwt-secret-for-development'
+     * });
+     * }</pre>
+     * 
+     * @param call Plugin call containing configuration parameters:
+     *             <ul>
+     *               <li>{@code apiBaseUrl} (required): Base URL for API server.
+     *                   Android emulator: "http://10.0.2.2:3000" (maps to host localhost:3000).
+     *                   iOS simulator: "http://localhost:3000".
+     *                   Production: "https://api.timesafari.com"</li>
+     *               <li>{@code activeDid} (required): Active DID for authentication.
+     *                   Format: "did:ethr:0x..."</li>
+     *               <li>{@code jwtSecret} (required): JWT secret for signing tokens.
+     *                   Keep secure in production.</li>
+     *             </ul>
+     * 
+     * @throws PluginException if configuration fails (rejected via call.reject())
+     * 
+     * @see NativeNotificationContentFetcher#configure(String, String, String)
+     */
+    @PluginMethod
+    public void configureNativeFetcher(PluginCall call) {
+        try {
+            String apiBaseUrl = call.getString("apiBaseUrl");
+            String activeDid = call.getString("activeDid");
+            String jwtSecret = call.getString("jwtSecret");
+            
+            if (apiBaseUrl == null || activeDid == null || jwtSecret == null) {
+                call.reject("Missing required parameters: apiBaseUrl, activeDid, and jwtSecret are required");
+                return;
+            }
+            
+            NativeNotificationContentFetcher fetcher = getNativeFetcher();
+            if (fetcher == null) {
+                call.reject("No native fetcher registered. Register one in Application.onCreate() before configuring.");
+                return;
+            }
+            
+            Log.d(TAG, "SPI: Configuring native fetcher - apiBaseUrl: " + 
+                apiBaseUrl.substring(0, Math.min(50, apiBaseUrl.length())) + 
+                "... activeDid: " + activeDid.substring(0, Math.min(30, activeDid.length())) + "...");
+            
+            // Call configure on the native fetcher (defaults to no-op if not implemented)
+            fetcher.configure(apiBaseUrl, activeDid, jwtSecret);
+            
+            Log.i(TAG, "SPI: Native fetcher configured successfully");
+            call.resolve();
+            
+        } catch (Exception e) {
+            Log.e(TAG, "SPI: Error configuring native fetcher", e);
+            call.reject("Failed to configure native fetcher: " + e.getMessage());
+        }
+    }
+    
     /**
      * Initialize the plugin and create notification channel
      */
@@ -962,6 +1053,12 @@ public class DailyNotificationPlugin extends Plugin {
         try {
             Log.i(TAG, "DN|SCHEDULE_FETCH_START time=" + scheduledTime + " current=" + System.currentTimeMillis());
             
+            // Check if fetcher is initialized
+            if (fetcher == null) {
+                Log.e(TAG, "DN|SCHEDULE_FETCH_ERR fetcher is null - cannot schedule prefetch. Plugin may not be fully loaded.");
+                return;
+            }
+            
             // Schedule fetch 5 minutes before notification
             long fetchTime = scheduledTime - TimeUnit.MINUTES.toMillis(5);
             long currentTime = System.currentTimeMillis();