Validate essential files early

Source/AppScaffolding/LibationScaffolding.cs

@@ -294,6 +294,10 @@ public static class LibationScaffolding
 		// begin logging session with a form feed
 		Log.Logger.Information("\r\n\f");
 
+		// Validate log file was created and is writable (OS may delay availability)
+		var logFilePath = Path.Combine(config.LibationFiles.Location, "Log.log");
+		EssentialFileValidator.ValidateCreatedAndReport(logFilePath);
+
 		static int fileCount(FileManager.LongPath? longPath)
 		{
 			if (longPath is null)
@@ -389,8 +393,8 @@ public static class LibationScaffolding
 		}
 		catch (Exception ex)
 		{
-            // different text to make it easier to identify in logs, vs the AggregateException case above
-            Log.Logger.Error(ex, "Version check failed. General exception");
+			// different text to make it easier to identify in logs, vs the AggregateException case above
+			Log.Logger.Error(ex, "Version check failed. General exception");
 		}
 		return (null, null, null, false, false);
 	}

Source/ApplicationServices/DbContexts.cs

@@ -7,6 +7,8 @@ namespace ApplicationServices;
 
 public static class DbContexts
 {
+	private static bool _sqliteDbValidated;
+
 	/// <summary>Use for fully functional context, incl. SaveChanges(). For query-only, use the other method</summary>
 	public static LibationContext GetContext()
 	{
@@ -14,6 +16,14 @@ public static class DbContexts
 			? LibationContextFactory.CreatePostgres(Configuration.Instance.PostgresqlConnectionString)
 			: LibationContextFactory.CreateSqlite(SqliteStorage.ConnectionString);
 		context.Database.Migrate();
+
+		// Validate SQLite DB file was created and is accessible (once per process; OS may delay availability)
+		if (!_sqliteDbValidated && string.IsNullOrEmpty(Configuration.Instance.PostgresqlConnectionString))
+		{
+			EssentialFileValidator.ValidateCreatedAndReport(SqliteStorage.DatabasePath);
+			_sqliteDbValidated = true;
+		}
+
 		return context;
 	}
 

Source/LibationAvalonia/Program.cs

@@ -6,6 +6,7 @@ using Avalonia.Threading;
 using FileManager;
 using LibationAvalonia.Dialogs;
 using LibationFileManager;
+using LibationUiBase.Forms;
 using ReactiveUI.Avalonia;
 using System;
 using System.Diagnostics;
@@ -40,6 +41,9 @@ static class Program
 		}
 		AppDomain.CurrentDomain.UnhandledException += CurrentDomain_UnhandledException;
 
+		// When essential file validation fails and the error cannot be written to the log, show the user
+		EssentialFileValidator.ShowUserWhenLogUnavailable = msg => Dispatcher.UIThread.Post(() => _ = MessageBoxBase.Show(null, msg, "Libation - Essential File Error", MessageBoxButtons.OK, MessageBoxIcon.Warning));
+
 		//***********************************************//
 		//                                               //
 		//   do not use Configuration before this line   //

Source/LibationFileManager/EssentialFileValidator.cs

@@ -0,0 +1,119 @@
+using Serilog;
+using System;
+using System.IO;
+using System.Threading;
+
+namespace LibationFileManager;
+
+/// <summary>
+/// Validates that essential files were created correctly after creation, with retries to allow for OS delay.
+/// Callers should use <see cref="ReportValidationFailure"/> to log errors and show the user when the log cannot be written.
+/// </summary>
+public static class EssentialFileValidator
+{
+	/// <summary>
+	/// Called when an essential file validation fails and the error could not be written to the log.
+	/// Set by the host (e.g. LibationAvalonia, LibationWinForms) to display the message to the user.
+	/// </summary>
+	public static Action<string>? ShowUserWhenLogUnavailable { get; set; }
+
+	/// <summary>
+	/// Default retry total duration (ms) when checking that a file is available after creation.
+	/// </summary>
+	public const int DefaultMaxRetriesMs = 1000;
+
+	/// <summary>
+	/// Default delay (ms) between retries.
+	/// </summary>
+	public const int DefaultDelayMs = 50;
+
+	/// <summary>
+	/// Validates that the file at <paramref name="path"/> exists and is readable and writable,
+	/// with retries to allow for OS delay between create and availability.
+	/// Error messages use the file name portion of <paramref name="path"/>.
+	/// </summary>
+	/// <param name="path">Full path to the file.</param>
+	/// <param name="maxRetriesMs">Total time to retry (ms).</param>
+	/// <param name="delayMs">Delay between retries (ms).</param>
+	/// <returns>(true, null) if valid; (false, errorMessage) if validation failed.</returns>
+	public static (bool success, string? errorMessage) ValidateCreated(
+		string path,
+		int maxRetriesMs = DefaultMaxRetriesMs,
+		int delayMs = DefaultDelayMs)
+	{
+		if (string.IsNullOrWhiteSpace(path))
+			return (false, "(unknown file): path is null or empty.");
+
+		var displayName = Path.GetFileName(path);
+		if (string.IsNullOrWhiteSpace(displayName))
+			displayName = path;
+
+		var stopAt = DateTime.UtcNow.AddMilliseconds(maxRetriesMs);
+		Exception? lastEx = null;
+
+		while (DateTime.UtcNow < stopAt)
+		{
+			try
+			{
+				if (!File.Exists(path))
+				{
+					lastEx = new FileNotFoundException($"File not found after creation: {path}");
+					Thread.Sleep(delayMs);
+					continue;
+				}
+
+				using (var fs = new FileStream(path, FileMode.Open, FileAccess.ReadWrite, FileShare.Read))
+				{
+					// ensure we can open for read and write
+				}
+
+				return (true, null);
+			}
+			catch (Exception ex)
+			{
+				lastEx = ex;
+				Thread.Sleep(delayMs);
+			}
+		}
+
+		var msg = lastEx is not null
+			? $"{displayName} could not be validated at \"{path}\": {lastEx.Message}"
+			: $"{displayName} could not be validated at \"{path}\" (file not found or not accessible).";
+		return (false, msg);
+	}
+
+	/// <summary>
+	/// Validates that the file was created correctly and, if validation fails, reports the failure (log and optionally user).
+	/// Equivalent to calling <see cref="ValidateCreated"/> then <see cref="ReportValidationFailure"/> when the result is not valid.
+	/// </summary>
+	/// <returns>True if the file is valid; false if validation failed (and failure has been reported).</returns>
+	public static bool ValidateCreatedAndReport(
+		string path,
+		int maxRetriesMs = DefaultMaxRetriesMs,
+		int delayMs = DefaultDelayMs)
+	{
+		var (success, errorMessage) = ValidateCreated(path, maxRetriesMs, delayMs);
+		if (!success && errorMessage is not null)
+			ReportValidationFailure(errorMessage);
+		return success;
+	}
+
+	/// <summary>
+	/// Reports a validation failure: tries to log the error; if logging fails, invokes <see cref="ShowUserWhenLogUnavailable"/>.
+	/// The message is prefixed with a strongly worded error notice for both log and user display.
+	/// </summary>
+	/// <param name="errorMessage">Message to log and optionally show to the user.</param>
+	public static void ReportValidationFailure(string errorMessage)
+	{
+		var fullMessage = $"Critical error! Essential file validation failed: {errorMessage}";
+		try
+		{
+			// Maybe change log level to Fatal later to stand out more
+			Log.Logger.Error(fullMessage);
+		}
+		catch
+		{
+			ShowUserWhenLogUnavailable?.Invoke(fullMessage);
+		}
+	}
+}

Source/LibationFileManager/LibationFiles.cs

@@ -133,6 +133,7 @@ public class LibationFiles
 				try
 				{
 					File.WriteAllText(settingsFile, "{}");
+					EssentialFileValidator.ValidateCreatedAndReport(settingsFile);
 				}
 				catch (Exception createEx)
 				{
@@ -221,6 +222,7 @@ public class LibationFiles
 			{
 				Directory.CreateDirectory(dir);
 				File.WriteAllText(appsettingsFile, endingContents);
+				EssentialFileValidator.ValidateCreatedAndReport(appsettingsFile);
 				return appsettingsFile;
 			}
 			catch (Exception ex)

Source/LibationUiBase/LibationSetup.cs

@@ -237,5 +237,7 @@ public class LibationSetup
 		};
 		var contents = JsonConvert.SerializeObject(jObj, Formatting.Indented);
 		File.WriteAllText(settingsFilePath, contents);
+
+		EssentialFileValidator.ValidateCreatedAndReport(settingsFilePath);
 	}
 }

Source/LibationWinForms/Program.cs

@@ -36,6 +36,9 @@ static class Program
 
 			ApplicationConfiguration.Initialize();
 
+			// When essential file validation fails and the error cannot be written to the log, show the user
+			EssentialFileValidator.ShowUserWhenLogUnavailable = msg => MessageBox.Show(msg, "Libation - Essential File Error", MessageBoxButtons.OK, MessageBoxIcon.Warning);
+
 			//***********************************************//
 			//                                               //
 			//   do not use Configuration before this line   //