Fix AI price check truncation and JSON parse errors

Root cause: MaxTokens=4096 was too low — 25 items at ~250 tokens each hit the
limit mid-array (logged error showed Path: $[17]).

- MaxTokens: 4096 → 8192
- BatchSize: 25 → 15 items (keeps each response well under the limit)
- StripJsonFences → ExtractJsonArray: now also handles prose before/after the
  JSON array, and recovers truncated responses by finding the last complete
  object and closing the array — so partial batches return whatever Claude
  finished rather than nothing
- GET action: added try-catch around ResultsJson deserialization so a bad DB
  row shows a friendly "re-run" warning instead of a raw error page

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Infrastructure/Services/AiCatalogPriceCheckService.cs

@@ -20,7 +20,7 @@ public class AiCatalogPriceCheckService : IAiCatalogPriceCheckService
     private readonly ILogger<AiCatalogPriceCheckService> _logger;
 
     private const string Model = "claude-sonnet-4-6";
-    private const int BatchSize = 25;
+    private const int BatchSize = 15; // 25 items at ~250 tokens each exceeds 4096 output tokens
 
     private static readonly JsonSerializerOptions JsonOpts = new() { PropertyNameCaseInsensitive = true };
 
@@ -37,18 +37,44 @@ public class AiCatalogPriceCheckService : IAiCatalogPriceCheckService
     }
 
     /// <summary>
-    /// Strips optional ```json ... ``` fences that Claude sometimes adds despite instructions.
+    /// Extracts a JSON array from Claude's response, handling three common failure modes:
+    /// (1) ```json ... ``` fences wrapping the array,
+    /// (2) prose text before or after the JSON array,
+    /// (3) truncated responses where the closing ] is missing — in that case we close any
+    ///     open string and append ]} to produce a parseable (though incomplete) array so
+    ///     we recover whatever items Claude did finish.
     /// </summary>
-    private static string StripJsonFences(string text)
+    private static string ExtractJsonArray(string text)
     {
         var trimmed = text.Trim();
+
+        // Strip code fences
         if (trimmed.StartsWith("```"))
         {
             var firstNewline = trimmed.IndexOf('\n');
             if (firstNewline >= 0) trimmed = trimmed[(firstNewline + 1)..];
             if (trimmed.EndsWith("```")) trimmed = trimmed[..^3];
+            trimmed = trimmed.Trim();
         }
-        return trimmed.Trim();
+
+        // Find the outermost [ ... ] even when Claude adds prose around it
+        var arrayStart = trimmed.IndexOf('[');
+        if (arrayStart < 0) return "[]";
+        trimmed = trimmed[arrayStart..];
+
+        var arrayEnd = trimmed.LastIndexOf(']');
+        if (arrayEnd >= 0)
+            return trimmed[..(arrayEnd + 1)];
+
+        // No closing bracket — response was truncated. Patch it so we can recover
+        // whatever complete objects Claude did return.
+        // Strategy: find the last complete },  and close the array after it.
+        var lastComplete = trimmed.LastIndexOf("},");
+        if (lastComplete < 0) lastComplete = trimmed.LastIndexOf('}');
+        if (lastComplete >= 0)
+            return trimmed[..(lastComplete + 1)] + "]";
+
+        return "[]";
     }
 
     private static async Task<MessageResponse> SendAsync(AnthropicClient client, MessageParameters parameters)
@@ -98,7 +124,7 @@ public class AiCatalogPriceCheckService : IAiCatalogPriceCheckService
         var parameters = new MessageParameters
         {
             Model = Model,
-            MaxTokens = 4096,
+            MaxTokens = 8192,
             SystemMessage = systemPrompt,
             Messages = new List<Message>
             {
@@ -110,7 +136,7 @@ public class AiCatalogPriceCheckService : IAiCatalogPriceCheckService
         {
             var response = await SendAsync(client, parameters);
             var raw = response.Content.OfType<TextContent>().FirstOrDefault()?.Text ?? "[]";
-            var json = StripJsonFences(raw);
+            var json = ExtractJsonArray(raw);
 
             var claudeItems = JsonSerializer.Deserialize<List<ClaudePriceCheckItem>>(json, JsonOpts) ?? new();
 

src/PowderCoating.Web/Controllers/CatalogItemsController.cs

@@ -944,9 +944,19 @@ namespace PowderCoating.Web.Controllers
             CatalogPriceCheckReportDto? dto = null;
             if (report != null)
             {
-                var results = JsonSerializer.Deserialize<List<CatalogItemPriceVerdict>>(
+                List<CatalogItemPriceVerdict> results;
-                    report.ResultsJson,
+                try
-                    new JsonSerializerOptions { PropertyNameCaseInsensitive = true }) ?? new();
+                {
+                    results = JsonSerializer.Deserialize<List<CatalogItemPriceVerdict>>(
+                        report.ResultsJson,
+                        new JsonSerializerOptions { PropertyNameCaseInsensitive = true }) ?? new();
+                }
+                catch (Exception ex)
+                {
+                    _logger.LogError(ex, "Failed to deserialize stored price check report {ReportId}", report.Id);
+                    TempData["Warning"] = "The previous report could not be loaded. Please re-run the price check.";
+                    results = new();
+                }
 
                 dto = new CatalogPriceCheckReportDto
                 {