Fixed attached files silently reaching the AI as empty documents (#904)

app/MindWork AI Studio/Tools/FileExtractionResult.cs

@@ -0,0 +1,47 @@
+namespace AIStudio.Tools;
+
+/// <summary>
+/// The result of reading a file through the Rust runtime.
+/// </summary>
+/// <remarks>
+/// Content and failure travel together on purpose. When reading a file returns a bare string, a
+/// failed extraction is indistinguishable from an empty document, and the empty document reaches
+/// the AI as if that were the content of the user's file.
+/// </remarks>
+/// <param name="Outcome">How the extraction ended.</param>
+/// <param name="Content">The extracted content. Empty when the extraction failed.</param>
+/// <param name="ErrorCode">Why the extraction failed or lost parts of the file.</param>
+/// <param name="ErrorMessage">The technical failure description, meant for logs and diagnostics.</param>
+/// <param name="FailedPages">The pages which could not be read, when known.</param>
+/// <param name="DetectedFormat">The format the runtime identified by looking at the content, when it is worth naming.</param>
+public readonly record struct FileExtractionResult(FileExtractionOutcome Outcome, string Content, FileExtractionErrorCode ErrorCode, string? ErrorMessage, IReadOnlyList<int> FailedPages, string? DetectedFormat)
+{
+    private static readonly int[] NO_FAILED_PAGES = [];
+
+    public static FileExtractionResult Success(string content, string? detectedFormat = null) => new(FileExtractionOutcome.SUCCESS, content, FileExtractionErrorCode.NONE, null, NO_FAILED_PAGES, detectedFormat);
+
+    public static FileExtractionResult Partial(string content, IReadOnlyList<int> failedPages, string? detectedFormat = null) => new(FileExtractionOutcome.PARTIAL, content, FileExtractionErrorCode.PAGE_EXTRACTION_FAILED, null, failedPages, detectedFormat);
+
+    public static FileExtractionResult Failed(FileExtractionErrorCode errorCode, string? errorMessage, string? detectedFormat = null) => new(FileExtractionOutcome.FAILED, string.Empty, errorCode, errorMessage, NO_FAILED_PAGES, detectedFormat);
+
+    /// <summary>
+    /// Gets a value indicating whether the whole file was read.
+    /// </summary>
+    public bool IsSuccess => this.Outcome is FileExtractionOutcome.SUCCESS;
+
+    /// <summary>
+    /// Gets a value indicating whether the content may be handed to the AI, i.e. the extraction
+    /// either succeeded or lost only parts of the file.
+    /// </summary>
+    public bool HasUsableContent => this.Outcome is FileExtractionOutcome.SUCCESS or FileExtractionOutcome.PARTIAL;
+
+    /// <summary>
+    /// Gets a value indicating whether the file was read, but its content did not match its file
+    /// extension.
+    /// </summary>
+    /// <remarks>
+    /// On a readable file, only the mismatch notice names a detected format, which is why no
+    /// separate flag is needed here.
+    /// </remarks>
+    public bool HasExtensionMismatch => this.HasUsableContent && this.DetectedFormat is not null;
+}