Added the visual briefing assistant (#893)

app/MindWork AI Studio/Assistants/VisualBriefing/VisualBriefingPreviewEndpoint.cs

@@ -0,0 +1,74 @@
+namespace AIStudio.Assistants.VisualBriefing;
+
+/// <summary>
+/// Serves committed briefing revisions to the live preview inside the Visual Briefing Assistant.
+/// </summary>
+/// <remarks>
+/// The assistant shows a briefing in an iframe, and an iframe can only load a URL. The exported
+/// artifact is a single self-contained HTML file, so this endpoint streams exactly that file and
+/// nothing else. Two properties make it safe to expose on the local app port: the caller must
+/// present a short-lived token bound to this briefing and revision, and the response repeats the
+/// artifact's own Content Security Policy so the preview runs under the same restrictions as the
+/// exported file.
+/// </remarks>
+internal static class VisualBriefingPreviewEndpoint
+{
+    private const string ROUTE = "/visual-briefing/preview/{briefingId:guid}/{revisionId:guid}";
+
+    /// <summary>
+    /// Maps the visual briefing preview endpoint.
+    /// </summary>
+    /// <param name="app">The web application.</param>
+    public static void MapVisualBriefingPreview(this WebApplication app) => app.MapGet(
+        ROUTE,
+        async (
+            Guid briefingId,
+            Guid revisionId,
+            string? token,
+            HttpContext context,
+            VisualBriefingPreviewTokenService tokenService,
+            VisualBriefingStore store,
+            ILoggerFactory loggerFactory,
+            CancellationToken cancellationToken) =>
+        {
+            var logger = loggerFactory.CreateLogger(nameof(VisualBriefingPreviewEndpoint));
+            if (!tokenService.Validate(token, briefingId, revisionId))
+            {
+                logger.LogWarning(
+                    Event(VisualBriefingLogEventId.PREVIEW_REJECTED),
+                    "Visual briefing preview token rejected. BriefingId={BriefingId} RevisionId={RevisionId}",
+                    briefingId,
+                    revisionId);
+
+                return Results.NotFound();
+            }
+
+            // The store re-validates the stored artifact before handing out a stream, so a manually
+            // modified file on disk never reaches the preview:
+            var preview = await store.OpenIntegrityCheckedVersionAsync(briefingId, revisionId, cancellationToken);
+            if (preview is null)
+            {
+                logger.LogWarning(
+                    Event(VisualBriefingLogEventId.SECURITY_REJECTED),
+                    "Visual briefing preview artifact rejected. BriefingId={BriefingId} RevisionId={RevisionId}",
+                    briefingId,
+                    revisionId);
+
+                return Results.NotFound();
+            }
+
+            context.Response.Headers.CacheControl = "no-store";
+            context.Response.Headers.XContentTypeOptions = "nosniff";
+            context.Response.Headers["Referrer-Policy"] = "no-referrer";
+            context.Response.Headers.ContentSecurityPolicy = VisualBriefingArtifactService.GetContentSecurityPolicy(preview.Value.Parts);
+
+            return Results.File(preview.Value.Stream, "text/html; charset=utf-8", enableRangeProcessing: false);
+        });
+
+    /// <summary>
+    /// Creates the log event ID for one visual briefing log event.
+    /// </summary>
+    /// <param name="eventId">The visual briefing log event.</param>
+    /// <returns>The log event ID.</returns>
+    private static EventId Event(VisualBriefingLogEventId eventId) => new((int)eventId, eventId.ToString());
+}