Fixes

Jiten.Api/Controllers/AdminController.cs

@@ -906,6 +906,37 @@ public async Task<IActionResult> ReaggregateParentDifficulty(int deckId)
         return Ok(new { Message = "Queued difficulty reaggregation", DeckId = deckId });
     }
 
+    /// <summary>
+    /// Backstop sweep: find leaf decks that have raw text but no computed difficulty (e.g. children left at 0 by a
+    /// transient RunPod failure) and re-enqueue them, then schedule re-aggregation for any affected parents.
+    /// </summary>
+    [HttpPost("recompute-missing-difficulties")]
+    public async Task<IActionResult> RecomputeMissingDifficulties()
+    {
+        var missing = await dbContext.Decks
+            .Where(d => d.RawText != null && d.DeckDifficulty == null && !d.Children.Any())
+            .Select(d => new { d.DeckId, d.ParentDeckId })
+            .ToListAsync();
+
+        foreach (var m in missing)
+            backgroundJobs.Enqueue<DifficultyComputationJob>(
+                job => job.ComputeDeckDifficulty(m.DeckId, false));
+
+        var parentIds = missing
+            .Where(m => m.ParentDeckId != null)
+            .Select(m => m.ParentDeckId!.Value)
+            .Distinct()
+            .ToList();
+
+        foreach (var parentId in parentIds)
+            backgroundJobs.Schedule<DifficultyComputationJob>(
+                job => job.ReaggregateParentDifficulty(parentId), TimeSpan.FromMinutes(45));
+
+        logger.LogInformation("Admin queued {Count} missing-difficulty recomputations across {ParentCount} parents",
+            missing.Count, parentIds.Count);
+        return Ok(new { Message = $"Queued {missing.Count} missing-difficulty recomputations", Count = missing.Count, AffectedParents = parentIds.Count });
+    }
+
     [HttpGet("issues")]
     public async Task<IActionResult> GetIssues()
     {

Jiten.Api/Jobs/DifficultyComputationJob.cs

@@ -10,6 +10,7 @@ public class DifficultyComputationJob(
     IDbContextFactory<JitenDbContext> contextFactory,
     IHttpClientFactory httpClientFactory,
     IConfiguration configuration,
+    IBackgroundJobClient backgroundJobs,
     ILogger<DifficultyComputationJob> logger)
 {
     private record DifficultyResponse(
@@ -128,6 +129,7 @@ private async Task ComputeParentWithChildren(JitenDbContext context, Deck parent
             parent.DeckId, children.Count, forceRecompute);
 
         var computedCount = 0;
+        var failedChildren = new List<int>();
         foreach (var child in children)
         {
             if (!forceRecompute && child.DeckDifficulty != null)
@@ -151,7 +153,10 @@ private async Task ComputeParentWithChildren(JitenDbContext context, Deck parent
             }
             catch (Exception ex)
             {
-                logger.LogError(ex, "Failed to compute difficulty for child deck {DeckId}, skipping", child.DeckId);
+                // Usually a transient RunPod worker failure (e.g. CUDA "no kernel image"). Re-enqueue the child
+                // below as its own job so it inherits the per-deck delayed-retry policy and lands on a fresh worker.
+                logger.LogError(ex, "Failed to compute difficulty for child deck {DeckId}, will re-enqueue", child.DeckId);
+                failedChildren.Add(child.DeckId);
             }
         }
 
@@ -162,8 +167,22 @@ private async Task ComputeParentWithChildren(JitenDbContext context, Deck parent
             .OrderBy(d => d.DeckOrder)
             .ToListAsync();
 
-        // Aggregate parent difficulty from children
+        // Aggregate parent difficulty from whatever succeeded so the parent is never blocked by a few failures
         await AggregateParentDifficulty(context, parent, childrenWithDifficulty);
+
+        // Self-heal stragglers: re-enqueue each failed child (leaf → 3× delayed retry) and schedule a single
+        // delayed re-aggregation so the parent picks up the recovered children once their retries complete.
+        if (failedChildren.Count > 0)
+        {
+            logger.LogWarning("Re-enqueueing {Count} failed children for parent {ParentId}: {ChildIds}",
+                failedChildren.Count, parent.DeckId, string.Join(",", failedChildren));
+
+            foreach (var childId in failedChildren)
+                backgroundJobs.Enqueue<DifficultyComputationJob>(j => j.ComputeDeckDifficulty(childId, false));
+
+            backgroundJobs.Schedule<DifficultyComputationJob>(
+                j => j.ReaggregateParentDifficulty(parent.DeckId), TimeSpan.FromMinutes(45));
+        }
     }
 
     private async Task ComputeSingleDeckDifficulty(JitenDbContext context, Deck deck)

Jiten.Core/JitenHelper.cs

@@ -13,9 +13,38 @@ public static class JitenHelper
 {
     // Cap concurrent PostgreSQL COPY operations to reduce server pressure/timeouts
     private static readonly SemaphoreSlim CopySemaphore = new SemaphoreSlim(6);
+
+    private static string? StripNul(string? value) =>
+        value != null && value.Contains('\0') ? value.Replace("\0", "") : value;
+
+    private static void SanitizeDeckStrings(Deck deck)
+    {
+        deck.OriginalTitle = StripNul(deck.OriginalTitle) ?? deck.OriginalTitle;
+        deck.RomajiTitle = StripNul(deck.RomajiTitle);
+        deck.EnglishTitle = StripNul(deck.EnglishTitle);
+        deck.Description = StripNul(deck.Description);
+
+        foreach (var title in deck.Titles)
+            title.Title = StripNul(title.Title) ?? title.Title;
+
+        foreach (var link in deck.Links)
+            link.Url = StripNul(link.Url) ?? link.Url;
+
+        if (deck.RawText != null)
+            deck.RawText.RawText = StripNul(deck.RawText.RawText) ?? deck.RawText.RawText;
+
+        if (deck.ExampleSentences != null)
+            foreach (var sentence in deck.ExampleSentences)
+                sentence.Text = StripNul(sentence.Text) ?? sentence.Text;
+
+        foreach (var child in deck.Children)
+            SanitizeDeckStrings(child);
+    }
+
     public static async Task InsertDeck(IDbContextFactory<JitenDbContext> contextFactory, Deck deck, byte[] cover, bool update = false)
     {
         var totalTimer = Stopwatch.StartNew();
+        SanitizeDeckStrings(deck);
         Console.WriteLine($"[{DateTime.UtcNow:O}] Inserting deck {deck.OriginalTitle}...");
 
         byte[]? optimizedCoverBytes = null;
@@ -204,7 +233,10 @@ public static async Task InsertDeck(IDbContextFactory<JitenDbContext> contextFac
                 /* ignore */
             }
 
-            Console.WriteLine($"[{DateTime.UtcNow:O}] Error inserting deck: {ex.Message}");
+            var detail = ex.Message;
+            for (var inner = ex.InnerException; inner != null; inner = inner.InnerException)
+                detail += $"\n  -> {inner.GetType().Name}: {inner.Message}";
+            Console.WriteLine($"[{DateTime.UtcNow:O}] Error inserting deck: {detail}");
             return;
         }
     }