Add retry mechanism for CloudKit authentication

Implement exponential backoff retry logic to handle intermittent CloudKit authentication failures, particularly 421 status codes and UNKNOWN_ERROR responses. The mechanism retries up to 3 times with increasing delays (1s, 2s, 4s) to improve the reliability of CloudKit integration.

- Add a retry loop with exponential backoff in the setupAuth function
- Handle specific error types (421 status, UNKNOWN_ERROR)
- Preserve original authentication flow for successful cases
- Add wide error logging and final error handling

Author: MotyRose

src/components/Cloudkit.ts

@@ -37,16 +37,50 @@ export function useCloudkit() {
 
   useEffect(() => {
     const setupAuth = async (ck: CloudKit) => {
-      const appleId = await ck.getDefaultContainer().setUpAuth();
-      if (appleId) {
-        setAppleSignedIn(true);
-      } else {
-        setAppleSignedIn(false);
+      // CloudKit authentication with retry mechanism
+      const MAX_RETRIES = 3;
+      const MAX_DELAY = 8000; // Cap at 8 seconds
+      let attempt = 0;
+      let delay = 1000; // Start with 1 second
+
+      while (attempt < MAX_RETRIES) {
+        attempt++;
+        try {
+          const appleId = await ck.getDefaultContainer().setUpAuth();
+          if (appleId) {
+            setAppleSignedIn(true);
+            return; // Success
+          }
+          // If appleId is null but no error, it's a valid state (user not signed in)
+          setAppleSignedIn(false);
+          return;
+        } catch (error: any) {
+          const isRetryableError = error?.status === 421 || error?.ckErrorCode === "UNKNOWN_ERROR";
+          const isLastAttempt = attempt >= MAX_RETRIES;
+
+          console.warn(`CloudKit auth attempt ${attempt}/${MAX_RETRIES} failed:`, error);
+
+          if (isRetryableError && !isLastAttempt) {
+            console.log(`Retrying CloudKit auth in ${delay}ms due to transient error...`);
+            await new Promise((resolve) => setTimeout(resolve, delay));
+            delay = Math.min(delay * 2, MAX_DELAY); // Exponential backoff with cap
+          } else {
+            // Either non-retryable error or last attempt failed, re-throw the error to be handled elsewhere if needed
+            setAppleSignedIn(false);
+            throw error;
+          }
+        }
       }
+      // Fallback: should never reach here, but defensive programming
+      setAppleSignedIn(false);
+      throw new Error("CloudKit authentication failed");
     };
 
     if (cloudkit) {
-      setupAuth(cloudkit);
+      setupAuth(cloudkit).catch((err) => {
+        console.error("CloudKit authentication failed after all retries:", err);
+        // Optionally set an error state here to show in the UI
+      });
     }
   }, [cloudkit]);