Fix console output synchronization

changelog.d/unreleased/1734.fixed.md

@@ -0,0 +1,17 @@
+---
+category: fixed
+issues:
+  - 1734
+affected:
+  - src/CodeIndex/Cli/ConsoleUi.cs
+  - src/CodeIndex/Program.cs
+  - tests/CodeIndex.Tests/ConsoleUiTests.cs
+---
+
+## English
+
+- **Console output is synchronized before spinner/progress rendering (#1734)** — `cdidx` now wraps stdout and stderr with synchronized writers at startup so spinner frames and main-thread progress lines are emitted as whole writes instead of interleaving characters.
+
+## 日本語
+
+- **スピナー / 進捗表示の前にコンソール出力を同期するようになりました (#1734)** — `cdidx` は起動時に stdout / stderr を同期 writer で包むため、スピナーフレームとメインスレッドの進捗行が文字単位で混ざらず、まとまった書き込みとして出力されます。

src/CodeIndex/Cli/ConsoleUi.cs

@@ -103,6 +103,8 @@ public static string FormatSummaryLine(string label, object? value, int labelWid
     private const int SpinnerStopDelayMs = 20;
     private const int ConsoleLineMargin = 1;
     private static readonly object TerminalLock = new();
+    private static TextWriter? _synchronizedOut;
+    private static TextWriter? _synchronizedError;
     private static readonly string[] ByteUnits = ["bytes", "KiB", "MiB", "GiB", "TiB", "PiB"];
 
     private static readonly string[] DefaultBrailleSpinnerFrames =
@@ -128,6 +130,26 @@ internal static string FoundSummary(int count, string singular, string? plural =
             : $"Found {Counted(count, singular, plural)}.";
     }
 
+    internal static void EnsureConsoleWritersSynchronized()
+    {
+        lock (TerminalLock)
+        {
+            var output = Console.Out;
+            if (!ReferenceEquals(output, _synchronizedOut))
+            {
+                _synchronizedOut = TextWriter.Synchronized(output);
+                Console.SetOut(_synchronizedOut);
+            }
+
+            var error = Console.Error;
+            if (!ReferenceEquals(error, _synchronizedError))
+            {
+                _synchronizedError = TextWriter.Synchronized(error);
+                Console.SetError(_synchronizedError);
+            }
+        }
+    }
+
     // --- Spinner / スピナー ---
 
     public static string FormatDuration(TimeSpan duration, DurationOutputFormat format = DurationOutputFormat.Auto)
@@ -185,6 +207,8 @@ private static string FormatDurationAsHms(TimeSpan duration)
     /// </summary>
     public static CancellationTokenSource? StartSpinner(string message, string[] frames)
     {
+        EnsureConsoleWritersSynchronized();
+
         // Braille frames are single-char; themed frames are longer strings containing the display text
         // ブレイルフレームは1文字、テーマフレームは表示テキストを含む長い文字列
         bool isThemed = frames.Length > 0 && frames[0].Length > 2;

src/CodeIndex/Program.cs

@@ -5,4 +5,5 @@
 // characters (box-drawing, block elements, etc.) to appear as '?'.
 // Windows のコンソールは既定で OEM コードページを使用するため、Unicode 文字が文字化けします。
 Console.OutputEncoding = Encoding.UTF8;
+ConsoleUi.EnsureConsoleWritersSynchronized();
 return ProgramRunner.Run(args);

tests/CodeIndex.Tests/ConsoleUiTests.cs

@@ -219,6 +219,50 @@ public void PrintWarning_FlushesBothConsoleStreams()
         Assert.True(output.FlushCount > 0);
     }
 
+    [Fact]
+    public void EnsureConsoleWritersSynchronized_SerializesConcurrentWholeStringWrites()
+    {
+        using var output = new SlowChunkingTextWriter();
+        using var capture = ConsoleCapture.Start(output, error: null);
+        ConsoleUi.EnsureConsoleWritersSynchronized();
+
+        const int iterations = 40;
+        var left = new Thread(() =>
+        {
+            for (var i = 0; i < iterations; i++)
+                Console.Write("[spinner-frame]\n");
+        });
+        var right = new Thread(() =>
+        {
+            for (var i = 0; i < iterations; i++)
+                Console.Write("[progress-line]\n");
+        });
+
+        left.Start();
+        right.Start();
+        left.Join();
+        right.Join();
+
+        var lines = output.ToString()
+            .Split('\n', StringSplitOptions.RemoveEmptyEntries);
+        Assert.Equal(iterations * 2, lines.Length);
+        Assert.All(lines, line => Assert.True(
+            line is "[spinner-frame]" or "[progress-line]",
+            $"Unexpected interleaved line: {line}"));
+    }
+
+    [Fact]
+    public void StartSpinner_RedirectedOutput_UsesSynchronizedWriterBeforeFallbackLine()
+    {
+        using var output = new StringWriter();
+        using var capture = ConsoleCapture.Start(output, error: null);
+
+        var cts = ConsoleUi.StartSpinner("Indexing...", ["|"]);
+
+        Assert.Null(cts);
+        Assert.Contains("Indexing...", output.ToString());
+    }
+
     [Fact]
     public void GetWindowWidth_ColumnsEnvVarSet_UsesColumnsValue()
     {
@@ -1447,6 +1491,21 @@ public override void Flush()
         }
     }
 
+    private sealed class SlowChunkingTextWriter : TextWriter
+    {
+        private readonly StringBuilder builder = new();
+
+        public override Encoding Encoding => Encoding.UTF8;
+
+        public override void Write(char value)
+        {
+            builder.Append(value);
+            Thread.Sleep(1);
+        }
+
+        public override string ToString() => builder.ToString();
+    }
+
     private static string CaptureUsageOutput(bool showBanner = true)
     {
         using var capture = ConsoleCapture.Start(captureOut: true);