perf: use stable sha256 cache keys for summarizer requests

JobTrackerApi.Tests/AttachmentsControllerTests.cs

@@ -1,5 +1,6 @@
 using System.Reflection;
 using JobTrackerApi.Controllers;
+using JobTrackerApi.Services;
 using Xunit;
 
 namespace JobTrackerApi.Tests;
@@ -20,4 +21,12 @@ public sealed class AttachmentsControllerTests
         Assert.Contains(".png", values);
         Assert.DoesNotContain(".exe", values);
     }
+
+    [Fact]
+    public void Max_file_size_limit_is_10_mb()
+    {
+        var field = typeof(AttachmentsController).GetField("MaxFileSizeBytes", BindingFlags.NonPublic | BindingFlags.Static);
+        Assert.NotNull(field);
+        Assert.Equal(10 * 1024 * 1024, (long)field!.GetValue(null)!);
+    }
 }

JobTrackerApi.Tests/OwnershipGuardTests.cs

@@ -1,5 +1,6 @@
 using System.Reflection;
 using JobTrackerApi.Controllers;
+using JobTrackerApi.Services;
 using Xunit;
 
 namespace JobTrackerApi.Tests;
@@ -19,4 +20,19 @@ public sealed class OwnershipGuardTests
         var method = typeof(CorrespondenceController).GetMethod("FindOwnedMessageAsync", BindingFlags.NonPublic | BindingFlags.Instance);
         Assert.NotNull(method);
     }
+
+    [Fact]
+    public void Summarizer_service_uses_sha256_cache_key_builder()
+    {
+        var method = typeof(SummarizerService).GetMethod("BuildCacheKey", BindingFlags.NonPublic | BindingFlags.Static);
+        Assert.NotNull(method);
+
+        var first = (string)method!.Invoke(null, new object[] { "example text", 150, 30 })!;
+        var second = (string)method.Invoke(null, new object[] { "example text", 150, 30 })!;
+        var different = (string)method.Invoke(null, new object[] { "different text", 150, 30 })!;
+
+        Assert.Equal(first, second);
+        Assert.StartsWith("summ:", first);
+        Assert.NotEqual(first, different);
+    }
 }

JobTrackerApi/Services/SummarizerService.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Diagnostics;
 using System.Net.Http;
+using System.Security.Cryptography;
 using System.Text;
 using System.Text.Json;
 using System.Threading;
@@ -63,11 +64,20 @@ namespace JobTrackerApi.Services
             _cache = cache;
         }
 
+        private static string BuildCacheKey(string text, int maxLength, int minLength)
+        {
+            var payload = $"{text}\n::{maxLength}:{minLength}";
+            var hash = Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(payload))).ToLowerInvariant();
+            return $"summ:{hash}";
+        }
+
         public async Task<string?> SummarizeAsync(string text, int maxLength = 150, int minLength = 30)
         {
             if (string.IsNullOrWhiteSpace(text)) return null;
 
-            var key = $"summ:{text.GetHashCode()}:{maxLength}:{minLength}";
+            // Use a deterministic content hash instead of string.GetHashCode() so cache keys
+            // are collision-resistant and stable across process restarts.
+            var key = BuildCacheKey(text, maxLength, minLength);
             Interlocked.Increment(ref _requests);
 
             if (_cache.TryGetValue<string>(key, out var cached))