docs: annotate safe delete and truncate operations with SAFETY comments

YKanBan.Tests/TestUtilities/TempDirectory.cs

@@ -25,6 +25,9 @@ public sealed class TempDirectory : IDisposable
     {
         try
         {
+            // SAFETY: Recursive directory delete is safe: FullPath is the
+            // read-only, GUID-named directory this instance created under the
+            // OS temp folder, so it can never target user data or the temp root.
             Directory.Delete(FullPath, recursive: true);
         }
         catch (IOException)
@@ -32,6 +35,8 @@ public sealed class TempDirectory : IDisposable
             Thread.Sleep(100);
             try
             {
+                // SAFETY: Retry of the same recursive delete, still confined to
+                // this instance's own temp directory.
                 Directory.Delete(FullPath, recursive: true);
             }
             catch (IOException)

YKanBan/Storage/Workspace/WorkspaceLock.cs

@@ -39,6 +39,9 @@ public sealed class WorkspaceLock : IDisposable
         try
         {
             // FileShare.None gives the exclusive semantics; FileMode.Create empties any stale file.
+            // SAFETY: FileMode.Create truncates a pre-existing file, but the lock
+            // file is empty by design and the path always comes from
+            // WorkspacePaths.LockFile, so no user data is ever affected.
             stream = new FileStream(lockFilePath, FileMode.Create, FileAccess.Write, FileShare.None);
         }
         catch (DirectoryNotFoundException)