Address adversarial suggestion review (#5061)

Author: Widthdom

changelog.d/unreleased/5061.added.md

@@ -11,6 +11,8 @@ affected:
   - tests/CodeIndex.Tests/ProgramCliTests.cs
   - tests/CodeIndex.Tests/CliFlagSchemaTests.cs
   - tests/CodeIndex.Tests/ConsoleUiTests.cs
+  - tests/CodeIndex.Tests/JsonOutputSnapshotTests.cs
+  - tests/CodeIndex.Tests/golden/suggestions-compact.json
   - USER_GUIDE.md
   - DEVELOPER_GUIDE.md
   - TESTING_GUIDE.md

src/CodeIndex/Cli/SuggestionsCommandRunner.cs

@@ -928,7 +928,19 @@ private static bool MatchesAgent(SuggestionRecord record, string agent)
     private static string FormatTitle(string description, int maxLength)
     {
         var firstLine = description.Replace('\r', ' ').Replace('\n', ' ').Trim();
-        return firstLine.Length <= maxLength ? firstLine : firstLine[..(maxLength - 1)] + "...";
+        if (firstLine.Length <= maxLength)
+            return firstLine;
+
+        var end = maxLength - 1;
+        if (end > 0
+            && end < firstLine.Length
+            && char.IsHighSurrogate(firstLine[end - 1])
+            && char.IsLowSurrogate(firstLine[end]))
+        {
+            end--;
+        }
+
+        return firstLine[..end] + "...";
     }
 
     private static SuggestionListItemJsonResult ToListItem(SuggestionRecord record) => new(

tests/CodeIndex.Tests/JsonOutputSnapshotTests.cs

@@ -1,7 +1,9 @@
 using System.Text.Json;
 using System.Text.Json.Nodes;
+using System.Text.Json.Serialization.Metadata;
 using CodeIndex.Cli;
 using CodeIndex.Database;
+using CodeIndex.Models;
 
 namespace CodeIndex.Tests;
 
@@ -22,6 +24,7 @@ public class JsonOutputSnapshotTests
     private readonly JsonSerializerOptions _jsonOptions = new()
     {
         PropertyNamingPolicy = JsonNamingPolicy.SnakeCaseLower,
+        TypeInfoResolver = new DefaultJsonTypeInfoResolver(),
     };
 
     private const string LibSource = @"namespace Demo;
@@ -233,6 +236,52 @@ public void RunExcerpt_JsonOutput_MatchesGolden()
         }
     }
 
+    [Fact]
+    public void RunSuggestionsCompact_JsonOutput_MatchesGolden_Issue5061()
+    {
+        var projectRoot = TestProjectHelper.CreateTempProject("cdidx_snapshot_suggestions_compact");
+        try
+        {
+            var cdidxDir = Path.Combine(projectRoot, ".cdidx");
+            Directory.CreateDirectory(cdidxDir);
+            var dbPath = Path.Combine(cdidxDir, "codeindex.db");
+            var titlePrefix = new string('a', 118);
+            var store = new SuggestionStore(cdidxDir);
+            Assert.True(store.TryAdd(new SuggestionRecord
+            {
+                Id = new string('1', 64),
+                Category = "output_format",
+                Language = "csharp",
+                Description = "Snapshot query description",
+                SampledTitle = titlePrefix + "😀suffix",
+                EvidencePaths = ["src/Snapshot.cs"],
+                CreatedAt = new DateTime(2026, 8, 11, 0, 0, 0, DateTimeKind.Utc),
+            }));
+
+            var (exitCode, stdout, stderr) = CaptureConsole(() => SuggestionsCommandRunner.Run(
+                ["list", "--db", dbPath, "--query", "snapshot query", "--compact"],
+                _jsonOptions));
+
+            Assert.Equal(CommandExitCodes.Success, exitCode);
+            Assert.Equal(string.Empty, stderr);
+            using var document = JsonDocument.Parse(stdout);
+            var item = Assert.Single(document.RootElement.GetProperty("results").EnumerateArray());
+            var compactTitle = item.GetProperty("title").GetString()
+                ?? throw new InvalidOperationException("Compact suggestion title was null.");
+            Assert.Equal(titlePrefix + "...", compactTitle);
+            Assert.DoesNotContain('\uFFFD', compactTitle);
+
+            JsonOutputSnapshotHelper.AssertMatches(
+                "suggestions-compact.json",
+                stdout,
+                BuildPathReplacements(projectRoot));
+        }
+        finally
+        {
+            TestProjectHelper.DeleteDirectory(projectRoot);
+        }
+    }
+
     private static void MarkGraphAndFoldReady(string dbPath)
     {
         using var db = new DbContext(DbOpenIntent.WriteIndex, dbPath);

tests/CodeIndex.Tests/golden/suggestions-compact.json

@@ -0,0 +1,26 @@
+{
+  "api_version": "1",
+  "mode": "compact",
+  "query": "snapshot query",
+  "total_count": 1,
+  "total_count_authoritative": true,
+  "returned_count": 1,
+  "offset": 0,
+  "omitted_count": 0,
+  "pagination_omitted_count": 0,
+  "byte_limit_omitted_count": 0,
+  "projection_omitted_count": 0,
+  "truncated": false,
+  "has_more": false,
+  "next_offset": null,
+  "results": [
+    {
+      "id": "1111111111111111111111111111111111111111111111111111111111111111",
+      "title": "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa...",
+      "status": "draft",
+      "evidence_paths": [
+        "src/Snapshot.cs"
+      ]
+    }
+  ]
+}