Clarify StatusCodePages ProblemDetails docs (#66172)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mikekistler

src/Middleware/Diagnostics/src/StatusCodePage/StatusCodePagesExtensions.cs

@@ -20,6 +20,9 @@ public static class StatusCodePagesExtensions
     /// <summary>
     /// Adds a StatusCodePages middleware with the given options that checks for responses with status codes
     /// between 400 and 599 that do not have a body.
+    /// If <see cref="StatusCodePagesOptions.HandleAsync"/> uses its default value, it attempts to generate a
+    /// <see cref="Microsoft.AspNetCore.Mvc.ProblemDetails"/> response using <see cref="IProblemDetailsService"/>
+    /// and falls back to a plain text response that includes the status code.
     /// </summary>
     /// <param name="app"></param>
     /// <param name="options"></param>
@@ -33,8 +36,11 @@ public static IApplicationBuilder UseStatusCodePages(this IApplicationBuilder ap
     }
 
     /// <summary>
-    /// Adds a StatusCodePages middleware with a default response handler that checks for responses with status codes
-    /// between 400 and 599 that do not have a body.
+    /// Adds a <see cref="StatusCodePagesMiddleware"/> with the default response handler.
+    /// The middleware checks for responses with status codes between 400 and 599 that do not have a body and,
+    /// when an <see cref="IProblemDetailsService"/> is available, attempts to generate a
+    /// <see cref="Microsoft.AspNetCore.Mvc.ProblemDetails"/> response. If the service is unavailable or cannot write the response,
+    /// it generates a plain text response that includes the status code.
     /// </summary>
     /// <param name="app"></param>
     /// <returns></returns>

src/Middleware/Diagnostics/src/StatusCodePage/StatusCodePagesOptions.cs

@@ -15,8 +15,10 @@ namespace Microsoft.AspNetCore.Builder;
 public class StatusCodePagesOptions
 {
     /// <summary>
-    /// Creates a default <see cref="StatusCodePagesOptions"/> which produces a plaintext response
-    /// containing the status code and the reason phrase.
+    /// Creates a default <see cref="StatusCodePagesOptions"/> whose handler attempts to generate a
+    /// <see cref="Microsoft.AspNetCore.Mvc.ProblemDetails"/> response using <see cref="IProblemDetailsService"/>, and falls back
+    /// to a plaintext response containing the status code and reason phrase when that service is unavailable
+    /// or cannot write a response.
     /// </summary>
     public StatusCodePagesOptions()
     {
@@ -52,7 +54,10 @@ private static string BuildResponseBody(int httpStatusCode)
     }
 
     /// <summary>
-    /// The handler that generates the response body for the given <see cref="StatusCodeContext"/>. By default this produces a plain text response that includes the status code.
+    /// The handler that generates the response body for the given <see cref="StatusCodeContext"/>.
+    /// By default this attempts to generate a <see cref="Microsoft.AspNetCore.Mvc.ProblemDetails"/> response
+    /// using <see cref="IProblemDetailsService"/> and falls back to a plain text response that includes the
+    /// status code.
     /// </summary>
     public Func<StatusCodeContext, Task> HandleAsync { get; set; }