diff --git a/changelog.d/unreleased/1617.fixed.md b/changelog.d/unreleased/1617.fixed.md
new file mode 100644
index 0000000000..9b728d6f37
--- /dev/null
+++ b/changelog.d/unreleased/1617.fixed.md
@@ -0,0 +1,20 @@
+---
+category: fixed
+issues:
+  - 1617
+affected:
+  - src/CodeIndex/Cli/GlobalToolLog.cs
+  - src/CodeIndex/Cli/ProgramRunner.cs
+  - src/CodeIndex/Cli/QueryCommandRunner.cs
+  - src/CodeIndex/Mcp/McpServer.cs
+  - src/CodeIndex/Mcp/McpToolHandlers.cs
+  - tests/CodeIndex.Tests/McpServerTests.cs
+---
+
+## English
+
+- **Time-sensitive CLI and MCP paths now use injectable clocks (#1617)** — status age calculations, query trace/log naming, MCP ping timestamps, and MCP suggestion persistence can now be driven by `TimeProvider` for deterministic tests.
+
+## 日本語
+
+- **時刻に依存する CLI / MCP 経路が注入可能な clock を使うようになりました (#1617)** — status の経過時間計算、query trace / log のファイル名、MCP ping の timestamp、MCP suggestion の永続化を `TimeProvider` で決定論的にテストできるようになりました。
diff --git a/changelog.d/unreleased/1618.fixed.md b/changelog.d/unreleased/1618.fixed.md
new file mode 100644
index 0000000000..4872ca681e
--- /dev/null
+++ b/changelog.d/unreleased/1618.fixed.md
@@ -0,0 +1,16 @@
+---
+category: fixed
+issues:
+  - 1618
+affected:
+  - src/CodeIndex/Cli/SuggestionStore.cs
+  - tests/CodeIndex.Tests/SuggestionStoreTests.cs
+---
+
+## English
+
+- **Suggestion `CreatedAt` is now stamped at persistence time (#1618)** — new suggestions receive their creation timestamp inside the store's locked write path, aligning the recorded time with when the suggestion enters the local store.
+
+## 日本語
+
+- **suggestion の `CreatedAt` を永続化時に記録するようになりました (#1618)** — 新規 suggestion の作成時刻は store のロックされた書き込み経路内で付与され、ローカル store に入った時刻と一致するようになりました。
diff --git a/changelog.d/unreleased/2034.fixed.md b/changelog.d/unreleased/2034.fixed.md
new file mode 100644
index 0000000000..f74648aae8
--- /dev/null
+++ b/changelog.d/unreleased/2034.fixed.md
@@ -0,0 +1,17 @@
+---
+category: fixed
+issues:
+  - 2034
+affected:
+  - tests/CodeIndex.Tests/ManualTimeProvider.cs
+  - tests/CodeIndex.Tests/McpServerTests.cs
+  - tests/CodeIndex.Tests/SuggestionStoreTests.cs
+---
+
+## English
+
+- **Time-dependent tests now use an explicit test clock (#2034)** — MCP timestamp and suggestion lifecycle coverage use `ManualTimeProvider` instead of depending on wall-clock time or hardcoded fixture dates.
+
+## 日本語
+
+- **時刻依存テストが明示的な test clock を使うようになりました (#2034)** — MCP timestamp と suggestion lifecycle のカバレッジは wall-clock や固定 fixture 日付に依存せず `ManualTimeProvider` を使うようになりました。
diff --git a/src/CodeIndex/Cli/ConsoleUi.cs b/src/CodeIndex/Cli/ConsoleUi.cs
index 8b012fc2e0..d4cdd9f534 100644
--- a/src/CodeIndex/Cli/ConsoleUi.cs
+++ b/src/CodeIndex/Cli/ConsoleUi.cs
@@ -156,6 +156,23 @@ internal static void EnsureConsoleWritersSynchronized()
         }
     }
 
+    internal static void TryWriteErrorLine(string? value = null)
+    {
+        try
+        {
+            if (value == null)
+                Console.Error.WriteLine();
+            else
+                Console.Error.WriteLine(value);
+        }
+        catch (ObjectDisposedException)
+        {
+        }
+        catch (IOException)
+        {
+        }
+    }
+
     internal static IDisposable SuppressAnsiForJsonOutput(bool enabled)
     {
         if (!enabled)
diff --git a/src/CodeIndex/Cli/GlobalToolLog.cs b/src/CodeIndex/Cli/GlobalToolLog.cs
index 048a415ea2..dff462de5f 100644
--- a/src/CodeIndex/Cli/GlobalToolLog.cs
+++ b/src/CodeIndex/Cli/GlobalToolLog.cs
@@ -18,6 +18,7 @@ internal static class GlobalToolLog
     internal const string LogRetainEnvironmentVariable = "CDIDX_LOG_RETAIN";
     internal const string LogMaxSizeMbEnvironmentVariable = "CDIDX_LOG_MAX_SIZE_MB";
     private const string RedactedValue = "<redacted>";
+    internal static TimeProvider TimeProvider { get; set; } = TimeProvider.System;
     private static readonly AsyncLocal<Session?> CurrentSession = new();
     private static readonly Regex SensitiveAssignmentPattern = new(
         @"^(?<name>--?[^=\s]*(?:token|password|passwd|pwd|secret|auth|apikey|api-key|access-key|credential)[^=\s]*)=(?<value>.+)$",
@@ -377,7 +378,7 @@ private static string GetHomeDirectoryOrOriginal(string original)
 
     private static string ResolveLogPath(string logDirectory, LogOptions options)
     {
-        var date = DateTime.UtcNow.ToString("yyyyMMdd", System.Globalization.CultureInfo.InvariantCulture);
+        var date = TimeProvider.GetUtcNow().UtcDateTime.ToString("yyyyMMdd", System.Globalization.CultureInfo.InvariantCulture);
         if (options.MaxSizeBytes <= 0)
             return Path.Combine(logDirectory, $"stderr-{date}.log");
 
diff --git a/src/CodeIndex/Cli/IndexCommandRunner.FullScan.cs b/src/CodeIndex/Cli/IndexCommandRunner.FullScan.cs
index 64ce35e144..730b60eca7 100644
--- a/src/CodeIndex/Cli/IndexCommandRunner.FullScan.cs
+++ b/src/CodeIndex/Cli/IndexCommandRunner.FullScan.cs
@@ -433,7 +433,7 @@ void WriteJsonLiveness(string message)
             if (!options.Json || options.Quiet)
                 return;
 
-            Console.Error.WriteLine($"cdidx: {message}");
+            ConsoleUi.TryWriteErrorLine($"cdidx: {message}");
         }
 
         (CancellationTokenSource Cts, Task Task)? StartJsonPhaseHeartbeat(string phase, Func<string?>? detailProvider = null)
@@ -461,7 +461,7 @@ void WriteJsonLiveness(string message)
 
                     var detail = detailProvider?.Invoke();
                     var suffix = string.IsNullOrWhiteSpace(detail) ? string.Empty : $": {detail}";
-                    Console.Error.WriteLine($"cdidx: still {phase}{suffix}...");
+                    ConsoleUi.TryWriteErrorLine($"cdidx: still {phase}{suffix}...");
                 }
             }, token);
             return (cts, task);
@@ -685,7 +685,7 @@ void WriteIndexVerboseStatus(string message)
 
             if (options.Json)
             {
-                Console.Error.WriteLine(message);
+                ConsoleUi.TryWriteErrorLine(message);
                 return;
             }
 
@@ -727,7 +727,7 @@ void ReportJsonIndexProgressIfNeeded()
                 || processed % 100 == 0
                 || Stopwatch.GetElapsedTime(lastJsonProgressAt, now) >= TimeSpan.FromSeconds(5))
             {
-                Console.Error.WriteLine($"cdidx: indexed {processed:N0}/{files.Count:N0} file(s)...");
+                ConsoleUi.TryWriteErrorLine($"cdidx: indexed {processed:N0}/{files.Count:N0} file(s)...");
                 lastJsonProgressAt = now;
             }
         }
@@ -759,7 +759,7 @@ void StartJsonHeartbeatIfNeeded()
                         currentJsonIndexFile,
                         activeJsonExtractionPhases.OrderBy(static kvp => kvp.Key).Select(static kvp => kvp.Value));
                     var fileSuffix = string.IsNullOrEmpty(file) ? string.Empty : $": {file}";
-                    Console.Error.WriteLine($"cdidx: still indexing {processed:N0}/{files.Count:N0} file(s){fileSuffix}...");
+                    ConsoleUi.TryWriteErrorLine($"cdidx: still indexing {processed:N0}/{files.Count:N0} file(s){fileSuffix}...");
                 }
             }, token);
         }
@@ -1108,7 +1108,7 @@ void StopJsonHeartbeat()
                     {
                         PauseIndexSpinnerForConsoleWrite();
                         ConsoleUi.ClearProgressLine();
-                        Console.Error.WriteLine(FormatPerFileErrorLine("ERR ", item.FilePath, ex, errorMessage));
+                        ConsoleUi.TryWriteErrorLine(FormatPerFileErrorLine("ERR ", item.FilePath, ex, errorMessage));
                         ResumeIndexSpinnerAfterConsoleWrite();
                     }
                 }
diff --git a/src/CodeIndex/Cli/ProgramRunner.cs b/src/CodeIndex/Cli/ProgramRunner.cs
index 1bc2966af9..77c6df9ba7 100644
--- a/src/CodeIndex/Cli/ProgramRunner.cs
+++ b/src/CodeIndex/Cli/ProgramRunner.cs
@@ -14,6 +14,7 @@ namespace CodeIndex.Cli;
 internal static class ProgramRunner
 {
     internal const string QuietEnvironmentVariable = "CDIDX_QUIET";
+    internal static TimeProvider TimeProvider { get; set; } = TimeProvider.System;
 
     internal static int Run(
         string[] args,
@@ -87,7 +88,7 @@ internal static int Run(
         using var jsonAnsiScope = ConsoleUi.SuppressAnsiForJsonOutput(ContainsJsonOutputFlag(args));
 
         var commandStopwatch = Stopwatch.StartNew();
-        var commandStartTimestamp = DateTimeOffset.UtcNow;
+        var commandStartTimestamp = TimeProvider.GetUtcNow();
         var versionPinExit = CheckWorkspaceVersionPin(appVersion, configStartDirectory ?? Environment.CurrentDirectory, strictVersion);
         if (versionPinExit != CommandExitCodes.Success)
             return versionPinExit;
@@ -1132,7 +1133,7 @@ private static void EmitQueryTrace(string mode, string commandName, string[] sub
 
             var directory = GlobalToolLog.ResolveLogDirectoryForStatus();
             Directory.CreateDirectory(directory);
-            var path = Path.Combine(directory, $"query-trace-{DateTime.UtcNow:yyyyMMdd}.jsonl");
+            var path = Path.Combine(directory, $"query-trace-{TimeProvider.GetUtcNow().UtcDateTime:yyyyMMdd}.jsonl");
             File.AppendAllText(path, payload + Environment.NewLine);
         }
         catch
diff --git a/src/CodeIndex/Cli/QueryCommandRunner.cs b/src/CodeIndex/Cli/QueryCommandRunner.cs
index 7270bf0b96..dea6997d84 100644
--- a/src/CodeIndex/Cli/QueryCommandRunner.cs
+++ b/src/CodeIndex/Cli/QueryCommandRunner.cs
@@ -21,9 +21,12 @@ public static class QueryCommandRunner
     internal const string DefaultMaxLineWidthEnvironmentVariable = "CDIDX_DEFAULT_MAX_LINE_WIDTH";
     internal const string StaleAfterEnvironmentVariable = "CDIDX_STALE_AFTER";
     internal static readonly TimeSpan DefaultStaleAfter = TimeSpan.FromHours(24);
+    internal static TimeProvider TimeProvider { get; set; } = TimeProvider.System;
     [ThreadStatic]
     private static DbReader? s_batchReader;
 
+    private static DateTime GetUtcNow() => TimeProvider.GetUtcNow().UtcDateTime;
+
     // Cap OR-joined `symbols` names well below SQLite's 1000 expression-tree depth so oversized
     // batches fail fast with a clear usage error instead of a confusing SQLite exception.
     // OR 結合の `symbols` 名は SQLite の式木深さ上限 1000 を十分下回る値で頭打ちにし、
@@ -2638,7 +2641,7 @@ public static int RunStatus(string[] cmdArgs, JsonSerializerOptions jsonOptions,
                     : null;
                 status.StaleAfterSeconds = (long)Math.Round(staleAfter.Value.TotalSeconds, MidpointRounding.AwayFromZero);
                 if (status.IndexedAt.HasValue)
-                    status.IndexAgeSeconds = Math.Max(0, (long)Math.Round((DateTime.UtcNow - status.IndexedAt.Value).TotalSeconds, MidpointRounding.AwayFromZero));
+                    status.IndexAgeSeconds = Math.Max(0, (long)Math.Round((GetUtcNow() - status.IndexedAt.Value).TotalSeconds, MidpointRounding.AwayFromZero));
             }
             // Attach runtime metadata / ランタイムメタデータを付加
             status.SymbolKinds = reader.GetSymbolKindCounts();
@@ -6150,7 +6153,7 @@ private static void WriteZeroResultHints(QueryCommandOptions options, DbReader r
 
         if (freshness.IndexedAt.HasValue)
         {
-            var age = DateTime.UtcNow - freshness.IndexedAt.Value;
+            var age = GetUtcNow() - freshness.IndexedAt.Value;
             if (age > staleAfter.Value)
                 Console.Error.WriteLine($"Hint: the index is {FormatDuration(age)} old (threshold: {FormatDuration(staleAfter.Value)}). Run 'cdidx index <projectPath>' to refresh.");
         }
@@ -6685,7 +6688,7 @@ private static void WriteStatusAge(StatusResult status, TimeSpan staleAfter)
         if (!status.IndexedAt.HasValue)
             return;
 
-        var age = DateTime.UtcNow - status.IndexedAt.Value;
+        var age = GetUtcNow() - status.IndexedAt.Value;
         if (age < TimeSpan.Zero)
             age = TimeSpan.Zero;
 
diff --git a/src/CodeIndex/Cli/SuggestionStore.cs b/src/CodeIndex/Cli/SuggestionStore.cs
index 6d89abce1a..b686b2216d 100644
--- a/src/CodeIndex/Cli/SuggestionStore.cs
+++ b/src/CodeIndex/Cli/SuggestionStore.cs
@@ -22,6 +22,7 @@ public class SuggestionStore
 {
     private readonly string _filePath;
     private readonly string _lockPath;
+    private readonly TimeProvider _timeProvider;
     private readonly string _archivePath;
     private static readonly TimeSpan s_inFlightSubmitRetryDelay = TimeSpan.FromMinutes(1);
     internal const FileShare StreamingReadFileShare = FileShare.ReadWrite | FileShare.Delete;
@@ -96,12 +97,18 @@ static SuggestionStore()
     /// 拡張子なしのデータベースファイル名（任意、デフォルトは "codeindex"）。
     /// </param>
     public SuggestionStore(string cdidxDir, string? dbName = null)
+        : this(cdidxDir, dbName, TimeProvider.System)
+    {
+    }
+
+    internal SuggestionStore(string cdidxDir, string? dbName, TimeProvider timeProvider)
     {
         // Derive a safe store filename from the DB identity.
         // DB固有の安全なストアファイル名を導出する。
         var safeName = string.IsNullOrWhiteSpace(dbName) ? "codeindex" : dbName;
         _filePath = Path.Combine(cdidxDir, $"suggestions-{safeName}.json");
         _lockPath = Path.Combine(cdidxDir, $"suggestions-{safeName}.lock");
+        _timeProvider = timeProvider;
         _archivePath = Path.Combine(cdidxDir, $"suggestions-{safeName}.archive.jsonl");
     }
 
@@ -144,6 +151,7 @@ record = RedactRecordForPersistence(record);
                 return false;
             }
 
+            StampCreatedAt(record);
             existing.Add(record);
             PruneUnlocked(existing);
             SaveUnlocked(existing);
@@ -220,6 +228,7 @@ record = RedactRecordForPersistence(record);
 
             if (isNew)
             {
+                StampCreatedAt(record);
                 existing.Add(record);
                 PruneUnlocked(existing);
                 SaveUnlocked(existing);
@@ -229,7 +238,7 @@ record = RedactRecordForPersistence(record);
             var current = found!;
             if (!alreadySubmitted && submitToGitHub != null && ShouldAttemptSubmit(current))
             {
-                var attemptedAt = DateTime.UtcNow;
+                var attemptedAt = GetUtcNow();
                 StampSubmitAttempt(current, attemptedAt, null, attemptedAt.Add(s_inFlightSubmitRetryDelay));
                 SaveUnlocked(existing);
                 return new SubmitReservation(
@@ -403,7 +412,7 @@ public void MarkSubmitted(string hash, string issueUrl)
             if (record == null)
                 return;
 
-            MarkSubmitted(record, issueUrl, DateTime.UtcNow);
+            MarkSubmitted(record, issueUrl, GetUtcNow());
             SaveUnlocked(all);
         });
     }
@@ -756,19 +765,23 @@ private static void MarkSubmitted(SuggestionRecord record, string issueUrl, Date
         record.GitHubIssueUrl = null;
     }
 
-    private static bool ShouldAttemptSubmit(SuggestionRecord record)
+    private bool ShouldAttemptSubmit(SuggestionRecord record)
     {
         if (record.NextRetryAt == null)
             return true;
 
-        return record.NextRetryAt.Value <= DateTime.UtcNow;
+        return record.NextRetryAt.Value <= GetUtcNow();
     }
 
+    private void StampCreatedAt(SuggestionRecord record) => record.CreatedAt = GetUtcNow();
+
+    private DateTime GetUtcNow() => _timeProvider.GetUtcNow().UtcDateTime;
+
     private bool PruneUnlocked(List<SuggestionRecord> records)
     {
         var maxAge = ResolveMaxAge();
         var maxCount = ResolveMaxCount();
-        var cutoff = DateTime.UtcNow.Subtract(maxAge);
+        var cutoff = GetUtcNow().Subtract(maxAge);
         var pruned = records
             .Where(record => record.CreatedAt != default && record.CreatedAt < cutoff)
             .ToList();
@@ -794,7 +807,7 @@ private bool PruneUnlocked(List<SuggestionRecord> records)
         ArchivePrunedRecords(pruned);
         try
         {
-            Console.Error.WriteLine($"[cdidx] Pruned {pruned.Count} stale suggestion record(s) to {_archivePath}.");
+            ConsoleUi.TryWriteErrorLine($"[cdidx] Pruned {pruned.Count} stale suggestion record(s) to {_archivePath}.");
         }
         catch (ObjectDisposedException)
         {
diff --git a/src/CodeIndex/Mcp/McpServer.cs b/src/CodeIndex/Mcp/McpServer.cs
index 6864093f9e..0ce2cf7a9c 100644
--- a/src/CodeIndex/Mcp/McpServer.cs
+++ b/src/CodeIndex/Mcp/McpServer.cs
@@ -33,6 +33,7 @@ public partial class McpServer : IDisposable
     private readonly Func<JsonNode, string> _serializeResponse;
     private readonly IMcpAuthenticator _authenticator;
     private readonly McpToolFilter _toolFilter;
+    private readonly TimeProvider _timeProvider;
     // Bounds the number of MCP tool calls in flight at once so an unbounded burst of
     // requests cannot exhaust memory or wedge the SQLite reader lock (#1567). The
     // stdio / HTTP loop today only ever has one frame in flight, but the gate
@@ -173,17 +174,17 @@ public partial class McpServer : IDisposable
     internal static readonly TimeSpan DefaultEofPostCancelDrainTimeout = TimeSpan.FromSeconds(5);
 
     public McpServer(string dbPath, string version, bool dbPathExplicit = false)
-        : this(dbPath, version, dbPathExplicit, null, null, null, null, DefaultMaxConcurrency)
+        : this(dbPath, version, dbPathExplicit, null, null, null, null, DefaultMaxConcurrency, null)
     {
     }
 
     public McpServer(string dbPath, string version, bool dbPathExplicit, IMcpAuthenticator authenticator)
-        : this(dbPath, version, dbPathExplicit, null, authenticator, null, null, DefaultMaxConcurrency)
+        : this(dbPath, version, dbPathExplicit, null, authenticator, null, null, DefaultMaxConcurrency, null)
     {
     }
 
     public McpServer(string dbPath, string version, bool dbPathExplicit, McpToolFilter? toolFilter)
-        : this(dbPath, version, dbPathExplicit, null, null, toolFilter, null, DefaultMaxConcurrency)
+        : this(dbPath, version, dbPathExplicit, null, null, toolFilter, null, DefaultMaxConcurrency, null)
     {
     }
 
@@ -191,22 +192,22 @@ public McpServer(string dbPath, string version, bool dbPathExplicit, McpToolFilt
     // do not need a custom authenticator or tool filter.
     // serializer 注入だけが必要な既存テスト向けの内部互換 entry。
     internal McpServer(string dbPath, string version, bool dbPathExplicit, Func<JsonNode, string>? serializeResponse)
-        : this(dbPath, version, dbPathExplicit, serializeResponse, null, null, null, DefaultMaxConcurrency)
+        : this(dbPath, version, dbPathExplicit, serializeResponse, null, null, null, DefaultMaxConcurrency, null)
     {
     }
 
     internal McpServer(string dbPath, string version, bool dbPathExplicit, AuditLogSink? auditLog)
-        : this(dbPath, version, dbPathExplicit, null, null, null, auditLog, DefaultMaxConcurrency)
+        : this(dbPath, version, dbPathExplicit, null, null, null, auditLog, DefaultMaxConcurrency, null)
     {
     }
 
     internal McpServer(string dbPath, string version, bool dbPathExplicit, Func<JsonNode, string>? serializeResponse, IMcpAuthenticator? authenticator)
-        : this(dbPath, version, dbPathExplicit, serializeResponse, authenticator, null, null, DefaultMaxConcurrency)
+        : this(dbPath, version, dbPathExplicit, serializeResponse, authenticator, null, null, DefaultMaxConcurrency, null)
     {
     }
 
     internal McpServer(string dbPath, string version, bool dbPathExplicit, Func<JsonNode, string>? serializeResponse, IMcpAuthenticator? authenticator, McpToolFilter? toolFilter)
-        : this(dbPath, version, dbPathExplicit, serializeResponse, authenticator, toolFilter, null, DefaultMaxConcurrency)
+        : this(dbPath, version, dbPathExplicit, serializeResponse, authenticator, toolFilter, null, DefaultMaxConcurrency, null)
     {
     }
 
@@ -214,7 +215,7 @@ internal McpServer(string dbPath, string version, bool dbPathExplicit, Func<Json
     // with a null AuditLogSink so the maxConcurrency tests do not need to thread an audit log.
     // #1567 由来の maxConcurrency 注入用 overload。auditLog は null 固定で master に流す。
     internal McpServer(string dbPath, string version, bool dbPathExplicit, Func<JsonNode, string>? serializeResponse, IMcpAuthenticator? authenticator, McpToolFilter? toolFilter, int maxConcurrency)
-        : this(dbPath, version, dbPathExplicit, serializeResponse, authenticator, toolFilter, null, maxConcurrency)
+        : this(dbPath, version, dbPathExplicit, serializeResponse, authenticator, toolFilter, null, maxConcurrency, null)
     {
     }
 
@@ -224,16 +225,21 @@ internal McpServer(string dbPath, string version, bool dbPathExplicit, Func<Json
     // ProgramRunner が authenticator (#1559) と audit log (#1562) を同時に注入できる
     // 経路。それ以外の組み合わせは上の個別 overload で済む。
     internal McpServer(string dbPath, string version, bool dbPathExplicit, IMcpAuthenticator? authenticator, AuditLogSink? auditLog)
-        : this(dbPath, version, dbPathExplicit, null, authenticator, null, auditLog, DefaultMaxConcurrency)
+        : this(dbPath, version, dbPathExplicit, null, authenticator, null, auditLog, DefaultMaxConcurrency, null)
     {
     }
 
     internal McpServer(string dbPath, string version, bool dbPathExplicit, Func<JsonNode, string>? serializeResponse, IMcpAuthenticator? authenticator, McpToolFilter? toolFilter, AuditLogSink? auditLog)
-        : this(dbPath, version, dbPathExplicit, serializeResponse, authenticator, toolFilter, auditLog, DefaultMaxConcurrency)
+        : this(dbPath, version, dbPathExplicit, serializeResponse, authenticator, toolFilter, auditLog, DefaultMaxConcurrency, null)
     {
     }
 
     internal McpServer(string dbPath, string version, bool dbPathExplicit, Func<JsonNode, string>? serializeResponse, IMcpAuthenticator? authenticator, McpToolFilter? toolFilter, AuditLogSink? auditLog, int maxConcurrency)
+        : this(dbPath, version, dbPathExplicit, serializeResponse, authenticator, toolFilter, auditLog, maxConcurrency, null)
+    {
+    }
+
+    internal McpServer(string dbPath, string version, bool dbPathExplicit, Func<JsonNode, string>? serializeResponse, IMcpAuthenticator? authenticator, McpToolFilter? toolFilter, AuditLogSink? auditLog, int maxConcurrency, TimeProvider? timeProvider)
     {
         if (maxConcurrency < 1)
             throw new ArgumentOutOfRangeException(nameof(maxConcurrency), maxConcurrency, "MCP concurrency cap must be at least 1.");
@@ -249,6 +255,7 @@ internal McpServer(string dbPath, string version, bool dbPathExplicit, Func<Json
         _serializeResponse = serializeResponse ?? (node => node.ToJsonString(_jsonOptions));
         _authenticator = authenticator ?? LocalStdioAuthenticator.Instance;
         _toolFilter = toolFilter ?? McpToolFilter.FromEnvironment();
+        _timeProvider = timeProvider ?? TimeProvider.System;
         _auditLog = auditLog;
         RateLimiter = new RateLimiter(RateLimiterOptions.FromEnvironment());
         _concurrencyGate = new SemaphoreSlim(maxConcurrency, maxConcurrency);
@@ -304,6 +311,8 @@ internal void OverrideRateLimiterForTests(RateLimiter limiter)
     /// </summary>
     internal int MaxConcurrency { get; }
 
+    private DateTime GetUtcNow() => _timeProvider.GetUtcNow().UtcDateTime;
+
     internal TimeSpan RequestTimeout
     {
         get => _requestTimeout;
@@ -427,7 +436,7 @@ internal async Task RunAsync(IMcpTransport transport, CancellationToken cancella
 
         // Use stderr for logging so stdout stays clean for JSON-RPC
         // stdoutをJSON-RPC用にクリーンに保つため、ログはstderrに出力
-        Console.Error.WriteLine($"[cdidx-mcp] Starting MCP server v{_version} (db: {_dbPath}, transport: {transport.Name} @ {transport.Endpoint}, max in-flight: {MaxConcurrency})");
+        ConsoleUi.TryWriteErrorLine($"[cdidx-mcp] Starting MCP server v{_version} (db: {_dbPath}, transport: {transport.Name} @ {transport.Endpoint}, max in-flight: {MaxConcurrency})");
 
         if (transport is HttpMcpTransport httpTransport)
         {
diff --git a/src/CodeIndex/Mcp/McpToolHandlers.cs b/src/CodeIndex/Mcp/McpToolHandlers.cs
index d4a8191fa5..fecf4d0972 100644
--- a/src/CodeIndex/Mcp/McpToolHandlers.cs
+++ b/src/CodeIndex/Mcp/McpToolHandlers.cs
@@ -2717,7 +2717,7 @@ private JsonNode ExecutePing(JsonNode? id)
         var payload = new JsonObject
         {
             ["version"] = _version,
-            ["timestamp"] = DateTime.UtcNow.ToString("O"),
+            ["timestamp"] = GetUtcNow().ToString("O"),
             ["db_path"] = _dbPath,
             ["db_exists"] = File.Exists(LongPath.EnsureWindowsPrefix(_dbPath)),
         };
@@ -3114,7 +3114,7 @@ void WriteProjectRootOnce()
             {
                 var headBranch = GitHelper.TryGetHeadBranch(projectPath);
                 var timestamp = currentHeadCommit != null
-                    ? DateTime.UtcNow.ToString("o", System.Globalization.CultureInfo.InvariantCulture)
+                    ? GetUtcNow().ToString("o", System.Globalization.CultureInfo.InvariantCulture)
                     : null;
                 writer.SetMeta(DbContext.IndexedHeadShaMetaKey, currentHeadCommit);
                 writer.SetMeta(DbContext.IndexedHeadBranchMetaKey, headBranch);
@@ -3340,7 +3340,7 @@ private async Task<JsonNode> ExecuteSuggestImprovementAsync(JsonNode? id, JsonNo
         // Derive DB identity for scoped suggestion storage.
         // スコープ付き提案蓄積のため DB identity を導出。
         var dbName = Path.GetFileNameWithoutExtension(_dbPath);
-        var store = new SuggestionStore(cdidxDir, dbName);
+        var store = new SuggestionStore(cdidxDir, dbName, _timeProvider);
         var record = new SuggestionRecord
         {
             Category = category,
@@ -3348,7 +3348,6 @@ private async Task<JsonNode> ExecuteSuggestImprovementAsync(JsonNode? id, JsonNo
             Description = description,
             Context = context,
             Hash = hash,
-            CreatedAt = DateTime.UtcNow,
             CreatedByAgent = ResolveSuggestionAgent(),
             SessionId = _sessionId,
             ClientVersion = _version,
diff --git a/tests/CodeIndex.Tests/ConcurrencyTests.cs b/tests/CodeIndex.Tests/ConcurrencyTests.cs
index e2863a93c9..c2920c072f 100644
--- a/tests/CodeIndex.Tests/ConcurrencyTests.cs
+++ b/tests/CodeIndex.Tests/ConcurrencyTests.cs
@@ -32,7 +32,7 @@ public async Task ConcurrentReads_DoNotBlock()
         var fileId = writer.UpsertFile(new FileRecord
         {
             Path = "src/app.cs", Lang = "csharp", Size = 100, Lines = 10,
-            Modified = new DateTime(2025, 1, 1, 0, 0, 0, DateTimeKind.Utc),
+            Modified = ManualTimeProvider.FixtureUtcNow.UtcDateTime,
             Checksum = "abc",
         });
         writer.InsertChunks([new ChunkRecord { FileId = fileId, ChunkIndex = 0, StartLine = 1, EndLine = 10, Content = "public class App { }" }]);
@@ -126,7 +126,7 @@ public async Task GetStatus_ReferencesAndFilesStaySnapshotConsistent_UnderConcur
             var fileId = writer.UpsertFile(new FileRecord
             {
                 Path = $"src/seed{seedIndex}.cs", Lang = "csharp", Size = 100, Lines = 10,
-                Modified = new DateTime(2025, 1, 1, 0, 0, 0, DateTimeKind.Utc),
+                Modified = ManualTimeProvider.FixtureUtcNow.UtcDateTime,
                 Checksum = $"seed{seedIndex}",
             });
             writer.InsertReferences(BuildReferenceBatch(fileId, $"seed{seedIndex}", refsPerFile));
@@ -155,7 +155,7 @@ public async Task GetStatus_ReferencesAndFilesStaySnapshotConsistent_UnderConcur
                 var fileId = w.UpsertFile(new FileRecord
                 {
                     Path = $"src/added{extra}.cs", Lang = "csharp", Size = 100, Lines = 10,
-                    Modified = new DateTime(2025, 1, 1, 0, 0, 0, DateTimeKind.Utc),
+                    Modified = ManualTimeProvider.FixtureUtcNow.UtcDateTime,
                     Checksum = $"added{extra}",
                 });
                 w.InsertReferences(BuildReferenceBatch(fileId, $"added{extra}", refsPerFile));
@@ -217,8 +217,8 @@ public async Task AnalyzeSymbol_RefsCallersAndFreshnessStaySnapshotConsistent_Un
         //      file A のみで freshness = T0、2 refs なら file B も存在し modified = T1 > T0
         //      なので freshness = T1。`SearchReferences` / `GetCallers` と
         //      `GetWorkspaceFreshness` の間で writer が commit すると食い違う。
-        var fileAModified = new DateTime(2025, 1, 1, 0, 0, 0, DateTimeKind.Utc);
-        var fileBModified = new DateTime(2026, 6, 1, 0, 0, 0, DateTimeKind.Utc);
+        var fileAModified = ManualTimeProvider.FixtureUtcNow.UtcDateTime;
+        var fileBModified = ManualTimeProvider.FixtureUtcNow.AddDays(1).UtcDateTime;
         var writer = new DbWriter(_db.Connection);
         var fileAId = writer.UpsertFile(new FileRecord
         {
@@ -362,7 +362,7 @@ public async Task GetRepoMap_FreshnessAndEntrypointsStaySnapshotConsistent_Under
         //   2. `src/Program.cs`（`Main()` 関数を持つ）の存在は freshness と整合する。
         //      `getFreshness` と `GetEntrypoints` の torn read で破れる。
         var writer = new DbWriter(_db.Connection);
-        var baselineModified = new DateTime(2025, 1, 1, 0, 0, 0, DateTimeKind.Utc);
+        var baselineModified = ManualTimeProvider.FixtureUtcNow.UtcDateTime;
         for (var seedIndex = 0; seedIndex < 3; seedIndex++)
         {
             writer.UpsertFile(new FileRecord
@@ -543,7 +543,7 @@ public async Task BeginTransaction_SharedWriterSerializesConcurrentScopes()
                         Lang = "csharp",
                         Size = 10,
                         Lines = 1,
-                        Modified = new DateTime(2025, 1, 1, 0, 0, 0, DateTimeKind.Utc),
+                        Modified = ManualTimeProvider.FixtureUtcNow.UtcDateTime,
                         Checksum = $"{worker}_{i}",
                     });
                     txn.Commit();
diff --git a/tests/CodeIndex.Tests/ConsoleUiTests.cs b/tests/CodeIndex.Tests/ConsoleUiTests.cs
index 047c04ba8c..fa39a9f4ed 100644
--- a/tests/CodeIndex.Tests/ConsoleUiTests.cs
+++ b/tests/CodeIndex.Tests/ConsoleUiTests.cs
@@ -25,6 +25,51 @@ public class ConsoleUiTests
         .Select(field => (OpCode)field.GetValue(null)!)
         .ToDictionary(opCode => (short)(opCode.Value & 0xff));
 
+    [Fact]
+    public void TryWriteErrorLine_IgnoresClosedErrorWriter()
+    {
+        lock (TestConsoleLock.Gate)
+        {
+            var originalError = Console.Error;
+            var closedError = new StringWriter();
+            closedError.Dispose();
+            Console.SetError(closedError);
+            try
+            {
+                ConsoleUi.TryWriteErrorLine("diagnostic");
+            }
+            finally
+            {
+                Console.SetError(originalError);
+            }
+        }
+    }
+
+    [Fact]
+    public void TryWriteErrorLine_IgnoresErrorWriterIoFailures()
+    {
+        lock (TestConsoleLock.Gate)
+        {
+            var originalError = Console.Error;
+            Console.SetError(new ThrowingTextWriter());
+            try
+            {
+                ConsoleUi.TryWriteErrorLine("diagnostic");
+            }
+            finally
+            {
+                Console.SetError(originalError);
+            }
+        }
+    }
+
+    private sealed class ThrowingTextWriter : TextWriter
+    {
+        public override Encoding Encoding => Encoding.UTF8;
+
+        public override void WriteLine(string? value) => throw new IOException("closed pipe");
+    }
+
     [Fact]
     public void StartSpinner_BackgroundLoop_DoesNotBlockOnTaskWait()
     {
diff --git a/tests/CodeIndex.Tests/LegacySchemaMigrationTests.cs b/tests/CodeIndex.Tests/LegacySchemaMigrationTests.cs
index 779be59dc3..26ad8c04a5 100644
--- a/tests/CodeIndex.Tests/LegacySchemaMigrationTests.cs
+++ b/tests/CodeIndex.Tests/LegacySchemaMigrationTests.cs
@@ -91,7 +91,8 @@ line        INTEGER
 
         // Seed one file and a handful of symbols on the legacy schema.
         // レガシースキーマに対してファイル1つとシンボルを数件投入。
-        Exec(conn, "INSERT INTO files (id, path, lang, size, lines, modified) VALUES (1, 'src/Legacy.cs', 'csharp', 200, 20, '2025-06-01 00:00:00')");
+        var modified = ManualTimeProvider.FixtureUtcNow.UtcDateTime.ToString("yyyy-MM-dd HH:mm:ss", System.Globalization.CultureInfo.InvariantCulture);
+        Exec(conn, $"INSERT INTO files (id, path, lang, size, lines, modified) VALUES (1, 'src/Legacy.cs', 'csharp', 200, 20, '{modified}')");
         Exec(conn, @"INSERT INTO chunks (file_id, chunk_index, start_line, end_line, content) VALUES
                      (1, 0, 1, 20, 'class Legacy' || char(10) ||
                                    '{' || char(10) ||
diff --git a/tests/CodeIndex.Tests/ManualTimeProvider.cs b/tests/CodeIndex.Tests/ManualTimeProvider.cs
new file mode 100644
index 0000000000..c0135b32dc
--- /dev/null
+++ b/tests/CodeIndex.Tests/ManualTimeProvider.cs
@@ -0,0 +1,16 @@
+namespace CodeIndex.Tests;
+
+internal sealed class ManualTimeProvider : TimeProvider
+{
+    internal static readonly DateTimeOffset FixtureUtcNow = DateTimeOffset.UnixEpoch.AddDays(20_000);
+    private DateTimeOffset _utcNow;
+
+    public ManualTimeProvider(DateTimeOffset utcNow)
+    {
+        _utcNow = utcNow.ToUniversalTime();
+    }
+
+    public override DateTimeOffset GetUtcNow() => _utcNow;
+
+    public void SetUtcNow(DateTimeOffset utcNow) => _utcNow = utcNow.ToUniversalTime();
+}
diff --git a/tests/CodeIndex.Tests/McpServerTests.cs b/tests/CodeIndex.Tests/McpServerTests.cs
index 87076292a0..d243daa874 100644
--- a/tests/CodeIndex.Tests/McpServerTests.cs
+++ b/tests/CodeIndex.Tests/McpServerTests.cs
@@ -44,7 +44,7 @@ public McpServerTests()
             Lang = "csharp",
             Size = 200,
             Lines = 10,
-            Modified = new DateTime(2024, 1, 1),
+            Modified = ManualTimeProvider.FixtureUtcNow.UtcDateTime,
             Checksum = "abc123",
         });
         writer.InsertChunks([new ChunkRecord
@@ -155,7 +155,7 @@ private void InsertIndexedFile(string path, string lang, string content, bool ge
             Lang = lang,
             Size = normalized.Length,
             Lines = lines.Length,
-            Modified = new DateTime(2024, 1, 1),
+            Modified = ManualTimeProvider.FixtureUtcNow.UtcDateTime,
             Checksum = Guid.NewGuid().ToString("N"),
             Generated = generated,
         });
@@ -6058,14 +6058,16 @@ public void ToolsCall_Status_ExplicitExternalCodeIndexDb_UsesPersistedProjectRoo
     [Fact]
     public void ToolsCall_Ping_ReturnsVersionAndTimestamp()
     {
+        var clock = new ManualTimeProvider(new DateTimeOffset(2032, 4, 5, 6, 7, 8, TimeSpan.Zero));
+        using var server = new McpServer(_dbPath, ConsoleUi.LoadVersion(), false, null, null, null, null, McpServer.DefaultMaxConcurrency, clock);
         var request = JsonNode.Parse("""{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"ping","arguments":{}}}""")!;
-        var response = _server.HandleMessage(request)!;
+        var response = server.HandleMessage(request)!;
 
         var text = response["result"]!["content"]![0]!["text"]!.GetValue<string>();
         Assert.Contains("cdidx v", text);
         Assert.Contains("is ready", text);
         Assert.NotNull(response["result"]!["structuredContent"]!["version"]);
-        Assert.NotNull(response["result"]!["structuredContent"]!["timestamp"]);
+        Assert.Equal(clock.GetUtcNow().UtcDateTime.ToString("O"), response["result"]!["structuredContent"]!["timestamp"]!.GetValue<string>());
         Assert.NotNull(response["result"]!["structuredContent"]!["db_exists"]);
     }
 
diff --git a/tests/CodeIndex.Tests/SuggestionStoreTests.cs b/tests/CodeIndex.Tests/SuggestionStoreTests.cs
index bf7e3e9945..d82ddeb5d2 100644
--- a/tests/CodeIndex.Tests/SuggestionStoreTests.cs
+++ b/tests/CodeIndex.Tests/SuggestionStoreTests.cs
@@ -90,6 +90,20 @@ public void TryAdd_NewSuggestion_ReturnsTrue()
         Assert.True(_store.TryAdd(record));
     }
 
+    [Fact]
+    public void TryAdd_StampsCreatedAtFromInjectedClockWhenPersisted()
+    {
+        var clock = new ManualTimeProvider(new DateTimeOffset(2030, 2, 3, 4, 5, 6, TimeSpan.Zero));
+        var store = new SuggestionStore(_tempDir, null, clock);
+        var record = MakeRecord("symbol_extraction", "csharp", "Missing record support");
+        record.CreatedAt = new DateTime(1999, 1, 1, 0, 0, 0, DateTimeKind.Utc);
+
+        Assert.True(store.TryAdd(record));
+
+        var saved = Assert.Single(store.LoadAll());
+        Assert.Equal(clock.GetUtcNow().UtcDateTime, saved.CreatedAt);
+    }
+
     [Fact]
     public void TryAdd_Duplicate_ReturnsFalse()
     {
@@ -141,6 +155,22 @@ public void TryAddAndSubmit_FuzzyDuplicate_ReturnsMatchedHashAndScore()
         Assert.True(second.DuplicateScore >= SuggestionStore.DefaultDedupThreshold);
     }
 
+    [Fact]
+    public void TryAddAndSubmit_UsesInjectedClockForRetryAndSubmissionTimestamps()
+    {
+        var clock = new ManualTimeProvider(new DateTimeOffset(2031, 3, 4, 5, 6, 7, TimeSpan.Zero));
+        var store = new SuggestionStore(_tempDir, null, clock);
+        var record = MakeRecord("other", null, "submit me");
+
+        var result = store.TryAddAndSubmit(record, _ => SuggestionStore.SubmitAttemptResult.Success("https://github.com/Widthdom/CodeIndex/issues/1"));
+
+        Assert.True(result.IsNew);
+        var saved = Assert.Single(store.LoadAll());
+        Assert.Equal(clock.GetUtcNow().UtcDateTime, saved.CreatedAt);
+        Assert.Equal(clock.GetUtcNow().UtcDateTime, saved.LastSubmitAttempt);
+        Assert.Equal(clock.GetUtcNow().UtcDateTime, saved.LastSyncedAt);
+    }
+
     [Fact]
     public void TryAddAndSubmit_FuzzyDuplicate_IgnoresClosedDiagnosticStderr()
     {
@@ -481,18 +511,19 @@ public void LoadByStatus_ReturnsOnlyMatchingLifecycleState()
     [Fact]
     public void LoadSince_ReturnsSuggestionsAtOrAfterThreshold()
     {
+        var clock = new ManualTimeProvider(new DateTimeOffset(2031, 5, 1, 9, 0, 0, TimeSpan.Zero));
+        var store = new SuggestionStore(_tempDir, null, clock);
         var older = MakeRecord("other", null, "Older suggestion");
-        older.CreatedAt = new DateTime(2026, 5, 1, 9, 0, 0, DateTimeKind.Utc);
         var boundary = MakeRecord("other", null, "Boundary suggestion");
-        boundary.CreatedAt = new DateTime(2026, 5, 2, 9, 0, 0, DateTimeKind.Utc);
         var newer = MakeRecord("other", null, "Newer suggestion");
-        newer.CreatedAt = new DateTime(2026, 5, 3, 9, 0, 0, DateTimeKind.Utc);
 
-        _store.TryAdd(older);
-        _store.TryAdd(boundary);
-        _store.TryAdd(newer);
+        store.TryAdd(older);
+        clock.SetUtcNow(new DateTimeOffset(2031, 5, 2, 9, 0, 0, TimeSpan.Zero));
+        store.TryAdd(boundary);
+        clock.SetUtcNow(new DateTimeOffset(2031, 5, 3, 9, 0, 0, TimeSpan.Zero));
+        store.TryAdd(newer);
 
-        var loaded = _store.LoadSince(new DateTimeOffset(2026, 5, 2, 9, 0, 0, TimeSpan.Zero));
+        var loaded = store.LoadSince(new DateTimeOffset(2031, 5, 2, 9, 0, 0, TimeSpan.Zero));
 
         Assert.Equal(new[] { boundary.Hash, newer.Hash }, loaded.Select(s => s.Hash));
     }
@@ -754,14 +785,16 @@ public void AtomicWrite_SurvivesAddAfterCorruption()
     [Fact]
     public void TryAdd_PrunesStaleRecordsToArchive()
     {
+        var clock = new ManualTimeProvider(new DateTimeOffset(2031, 1, 1, 0, 0, 0, TimeSpan.Zero));
+        var store = new SuggestionStore(_tempDir, null, clock);
         var old = MakeRecord("other", null, "Old suggestion");
-        old.CreatedAt = DateTime.UtcNow.AddDays(-400);
-        Assert.True(_store.TryAdd(old));
+        Assert.True(store.TryAdd(old));
 
+        clock.SetUtcNow(new DateTimeOffset(2032, 2, 5, 0, 0, 0, TimeSpan.Zero));
         var fresh = MakeRecord("other", null, "Fresh suggestion");
-        Assert.True(_store.TryAdd(fresh));
+        Assert.True(store.TryAdd(fresh));
 
-        var all = _store.LoadAll();
+        var all = store.LoadAll();
         Assert.Single(all);
         Assert.Equal("Fresh suggestion", all[0].Description);
 
@@ -795,15 +828,17 @@ public void TryAdd_PrunesOldestRecordsOverConfiguredMaxCount()
     [Fact]
     public void TryAdd_DuplicateStillPersistsPrunedRecords()
     {
+        var clock = new ManualTimeProvider(new DateTimeOffset(2031, 1, 1, 0, 0, 0, TimeSpan.Zero));
+        var store = new SuggestionStore(_tempDir, null, clock);
         var old = MakeRecord("other", null, "Old suggestion");
-        old.CreatedAt = DateTime.UtcNow.AddDays(-400);
         var duplicate = MakeRecord("other", null, "Duplicate suggestion");
-        Assert.True(_store.TryAdd(old));
-        Assert.True(_store.TryAdd(duplicate));
+        Assert.True(store.TryAdd(old));
+        clock.SetUtcNow(new DateTimeOffset(2032, 2, 5, 0, 0, 0, TimeSpan.Zero));
+        Assert.True(store.TryAdd(duplicate));
 
-        Assert.False(_store.TryAdd(MakeRecord("other", null, "Duplicate suggestion")));
+        Assert.False(store.TryAdd(MakeRecord("other", null, "Duplicate suggestion")));
 
-        var all = _store.LoadAll();
+        var all = store.LoadAll();
         Assert.Single(all);
         Assert.Equal("Duplicate suggestion", all[0].Description);
         var archivePath = Path.Combine(_tempDir, "suggestions-codeindex.archive.jsonl");