Harden stderr tee logging (#2730)

Author: Widthdom

changelog.d/unreleased/2730.fixed.md

@@ -0,0 +1,16 @@
+---
+category: fixed
+issues:
+  - 2730
+affected:
+  - src/CodeIndex/Cli/GlobalToolLog.cs
+  - tests/CodeIndex.Tests/GlobalToolLogTests.cs
+---
+
+## English
+
+- **Persistent stderr mirroring no longer cascades disposed-writer failures (#2730)** — the global tool log tee now treats closed console/log writers as best-effort failures instead of throwing `ObjectDisposedException` back into test or CLI callers.
+
+## 日本語
+
+- **永続 stderr mirror が閉じた writer の失敗を連鎖させなくなりました (#2730)** — global tool log の tee は、閉じた console/log writer をベストエフォートの失敗として扱い、`ObjectDisposedException` をテストや CLI 呼び出し元へ投げ返さないようになりました。

src/CodeIndex/Cli/GlobalToolLog.cs

@@ -638,26 +638,39 @@ private sealed class TeeTextWriter(TextWriter primary, TextWriter secondary) : T
 
         public override void Flush()
         {
-            primary.Flush();
-            secondary.Flush();
+            TryWrite(primary.Flush);
+            TryWrite(secondary.Flush);
         }
 
         public override void Write(char value)
         {
-            primary.Write(value);
-            secondary.Write(value);
+            TryWrite(() => primary.Write(value));
+            TryWrite(() => secondary.Write(value));
         }
 
         public override void Write(string? value)
         {
-            primary.Write(value);
-            secondary.Write(value);
+            TryWrite(() => primary.Write(value));
+            TryWrite(() => secondary.Write(value));
         }
 
         public override void WriteLine(string? value)
         {
-            primary.WriteLine(value);
-            secondary.WriteLine(value);
+            TryWrite(() => primary.WriteLine(value));
+            TryWrite(() => secondary.WriteLine(value));
+        }
+
+        private static void TryWrite(Action write)
+        {
+            try
+            {
+                write();
+            }
+            catch (Exception ex) when (ex is IOException or ObjectDisposedException)
+            {
+                // Best-effort mirror: a disposed console writer must not cascade into callers.
+                // mirror はベストエフォート。閉じた console writer が呼び出し側へ波及しないようにする。
+            }
         }
     }
 }

tests/CodeIndex.Tests/GlobalToolLogTests.cs

@@ -1,4 +1,5 @@
 using System.Globalization;
+using System.Text;
 using System.Text.RegularExpressions;
 using CodeIndex.Cli;
 
@@ -117,6 +118,52 @@ public void TryStart_WritesInvariantUtcTimestampAndStackTrace()
         }
     }
 
+    [Fact]
+    public void TryStart_ErrorMirrorIgnoresDisposedOriginalConsoleWriter()
+    {
+        var logRoot = Path.Combine(Path.GetTempPath(), $"cdidx_global_log_disposed_{Guid.NewGuid():N}");
+        var originalError = Console.Error;
+        try
+        {
+            using var env = EnvironmentVariableScope.Capture(
+                "CDIDX_FORCE_GLOBAL_TOOL_LOG",
+                "CDIDX_DISABLE_PERSISTENT_LOG",
+                "CDIDX_GLOBAL_TOOL_LOG_DIR");
+            env.Set("CDIDX_FORCE_GLOBAL_TOOL_LOG", "1");
+            env.Set("CDIDX_DISABLE_PERSISTENT_LOG", null);
+            env.Set("CDIDX_GLOBAL_TOOL_LOG_DIR", logRoot);
+
+            using var session = GlobalToolLog.TryStartForTesting(
+                ["status"],
+                "test",
+                afterWriterCreated: () => Console.SetError(new ThrowingTextWriter()));
+
+            var exception = Record.Exception(() => Console.Error.WriteLine("mirrored error"));
+
+            Assert.NotNull(session);
+            Assert.Null(exception);
+        }
+        finally
+        {
+            Console.SetError(originalError);
+            if (Directory.Exists(logRoot))
+                Directory.Delete(logRoot, recursive: true);
+        }
+    }
+
     private static void ThrowForGlobalToolLogTest() =>
         throw new InvalidOperationException("global log stack trace test");
+
+    private sealed class ThrowingTextWriter : TextWriter
+    {
+        public override Encoding Encoding => Encoding.UTF8;
+
+        public override void Flush() => throw new ObjectDisposedException(nameof(ThrowingTextWriter));
+
+        public override void Write(char value) => throw new ObjectDisposedException(nameof(ThrowingTextWriter));
+
+        public override void Write(string? value) => throw new ObjectDisposedException(nameof(ThrowingTextWriter));
+
+        public override void WriteLine(string? value) => throw new ObjectDisposedException(nameof(ThrowingTextWriter));
+    }
 }