Fix C# symbol extraction self-index stalls

changelog.d/unreleased/2710.fixed.md

@@ -0,0 +1,18 @@
+---
+category: fixed
+issues:
+  - 2710
+  - 2711
+  - 2717
+affected:
+  - src/CodeIndex/Indexer/Symbols/SymbolExtractor.cs
+  - tests/CodeIndex.Tests/SymbolExtractorTests.cs
+---
+
+## English
+
+- **Full self-indexing no longer stalls while extracting C# symbols (#2710, #2711, #2717)** — C# symbol extraction now reuses the per-line multi-line member candidate during pattern matching, avoiding repeated expensive lookahead on large source files.
+
+## 日本語
+
+- **C# シンボル抽出中に full self-indexing が停止しないようになりました (#2710, #2711, #2717)** — C# シンボル抽出はパターン照合中に行単位の複数行メンバー候補を再利用し、大きなソースファイルで高コストな先読みを繰り返さないようになりました。

src/CodeIndex/Indexer/Symbols/SymbolExtractor.cs

@@ -2447,6 +2447,7 @@ public static List<SymbolRecord> Extract(long fileId, string? lang, string conte
             {
                 var stopAfterFirstPatternMatch = false;
                 var restartPatternScanOffset = -1;
+                CSharpPropertyMatchCandidate? csharpPropertyCandidateForLine = null;
                 foreach (var pattern in patterns)
                 {
                     if (lang == "csharp" && ReferenceEquals(pattern.Regex, CSharpEnumMemberRegex))
@@ -2463,7 +2464,7 @@ public static List<SymbolRecord> Extract(long fileId, string? lang, string conte
                     // function パターンは `CSharpPropertyHeaderPrefixRegex` が `(` や `{` を含む行を
                     // 受け付けないため影響を受けず、merger は元の行をそのまま返す。Closes #355.
                     var csharpPropertyCandidate = lang == "csharp" && pattern.Kind is "property" or "function"
-                        ? BuildCSharpPropertyMatchLine(lines, csharpMatchLines!, i)
+                        ? csharpPropertyCandidateForLine ??= BuildCSharpPropertyMatchLine(lines, csharpMatchLines!, i)
                         : new CSharpPropertyMatchCandidate(matchLine, i, i);
                     var patternMatchLine = csharpPropertyCandidate.MatchLine;
                     if (fortranContinuationCandidate != null)

tests/CodeIndex.Tests/SymbolExtractorTests.cs

@@ -24399,6 +24399,28 @@ public void Extract_CSharp_InstallScriptFixture_CompletesWithinPracticalBudget()
             $"InstallScriptTests.cs extraction took {stopwatch.Elapsed.TotalSeconds:F2}s, expected < {runawayBudget.TotalSeconds:F0}s runaway guard budget.");
     }
 
+    [Fact]
+    public void Extract_CSharp_ReferenceExtractorFixture_CompletesWithinPracticalBudget()
+    {
+        // issue #2710/#2711/#2717 regression: full self-indexing could spend minutes
+        // repeatedly rebuilding the same multi-line C# member candidate while scanning large
+        // extractor sources. Keep this as a broad runaway guard for the realistic file that
+        // reproduced the stall on origin/main.
+        var path = Path.Combine(GetRepositoryRoot(), "src", "CodeIndex", "Indexer", "References", "ReferenceExtractor.cs");
+        var content = File.ReadAllText(path);
+
+        var stopwatch = Stopwatch.StartNew();
+        var symbols = SymbolExtractor.Extract(1, "csharp", content);
+        stopwatch.Stop();
+
+        Assert.Contains(symbols, s => s.Kind == "class" && s.Name == "ReferenceExtractor");
+        Assert.Contains(symbols, s => s.Kind == "function" && s.Name == "Extract");
+        var runawayBudget = TimeSpan.FromSeconds(30);
+        Assert.True(
+            stopwatch.Elapsed < runawayBudget,
+            $"ReferenceExtractor.cs extraction took {stopwatch.Elapsed.TotalSeconds:F2}s, expected < {runawayBudget.TotalSeconds:F0}s runaway guard budget.");
+    }
+
     [Fact]
     public void Extract_Java_SameLineAnnotationsCompactConstructorsAndEnumOverrides_StayIndexed()
     {