Desk: a read of an oversize fork is 422 fork_too_large (#42)

src/Bifrost.Web/Features/Desk/DeskDocuments.cs

@@ -151,7 +151,7 @@ public static class DeskRefusals
         [RequestIdConflict] = (409, "request_id_conflict: this request_id was used for a different body"),
     };
 
-    // fork_too_large (Libby's ruling) is list-only and names its fork, so it is built here, not read from the table.
+    // fork_too_large (Libby's ruling) names its fork, so it is built here, not read from the table.
     // Not a literal const: the pinned vectors' doorRefusals do not name it yet, and the schema test pins literals to them.
     public static string ForkTooLarge => "fork_too_large";
 
@@ -164,6 +164,10 @@ public static class DeskRefusals
             ? $"fork_too_large: fork {forkId} (order {order}) is too large for a page; continue with cursor c{order}"
             : $"fork_too_large: fork {forkId} (order {order}) is too large for a page; the list has reached its end");
 
+    // A read of an oversize fork: the same permanent refusal, naming the fork and nothing to page.
+    public static DeskRefusal ForkTooLargeDocument(string forkId) => new(
+        DeskSchemas.Refusal, ForkTooLarge, $"fork_too_large: fork {forkId} is too large to return");
+
     public static bool IsKnown(string code) => Table.ContainsKey(code);
 
     public static int StatusOf(string code) => Table[code].Status;

src/Bifrost.Web/Features/Desk/DeskEndpoints.cs

@@ -189,6 +189,10 @@ public static class DeskEndpoints
                     {
                         await WriteJsonAsync(http, 200, IsDecider(context) ? entry : DeskNotes.Strip(entry));
                     }
+                    else if (found is DeskReadOutcome.ForkTooLarge(var largeFork))
+                    {
+                        await WriteJsonAsync(http, DeskRefusals.ForkTooLargeStatus, DeskRefusals.ForkTooLargeDocument(largeFork));
+                    }
                     else if (found is DeskReadOutcome.NotFound(var readCode) && DoorMayRefuse(readCode) && readCode != DeskRefusals.RequestIdConflict)
                     {
                         await WriteRefusalAsync(http, ReadListCode(readCode));

src/Bifrost.Web/Features/Desk/DeskPorts.cs

@@ -35,6 +35,9 @@ public abstract record DeskReadOutcome
     public sealed record Found(ForkEntry Entry) : DeskReadOutcome;
 
     public sealed record NotFound(string Code) : DeskReadOutcome;
+
+    // The fork is too large to return: permanent, and nothing to page, so no order or cursor.
+    public sealed record ForkTooLarge(string ForkId) : DeskReadOutcome;
 }
 
 // The list request the desk's query string stands for. Mind is the route's, resolved against the configured list.
@@ -47,7 +50,7 @@ public abstract record DeskListOutcome
     public sealed record NotListed(string Code) : DeskListOutcome;
 
     // The next fork is too large for any page: the page holds nothing past the cursor. The client continues with
-    // cursor c<Order>; at Order 0 it has reached the end. List only: no other call can be refused this way.
+    // cursor c<Order>; at Order 0 it has reached the end. A read of such a fork has its own outcome (no order).
     public sealed record ForkTooLarge(string ForkId, int Order) : DeskListOutcome;
 }