Fuellarbeit: zeitlich flexible Arbeit fuellt ungenutztes Budget (#717, Stufe 1)

Eine einmalige Aufgabe mit fill_by (spaetestens bis) statt Termin laeuft,
wenn der Tag Budget uebrig laesst: nach regulaerer und nachgeholter Arbeit,
nur wenn nichts vom Agenten wartet, bevorzugt ab 18 Uhr, und nur wenn ihre
eigene Schaetzung in den Spielraum aus #716 passt. Kurz vor der Frist wird
einmal ein Mensch gefragt; nach der Frist laeuft sie als regulaere Arbeit.

Ehrliche Schaetzung (TaskCostEstimator): eigene Laeufe, dann Geschwister
unter derselben Elternaufgabe, dann die Angabe des Autors (als Schaetzung
gekennzeichnet), zuletzt das Mittel des Agenten.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ClawdDotNet.App/Services/TaskAdministration.cs

@@ -21,7 +21,10 @@ public sealed record TaskInput(
     string? TimeZone = null,
     string Acceptance = "",
     int Priority = 3,
-    string ParentId = "");
+    string ParentId = "",
+    // #717: fill work — at the latest by (ISO or yyyy-MM-dd), and the author's estimate per run.
+    string? FillBy = null,
+    decimal? EstimateUsd = null);
 
 /// <summary>
 /// Das Taskboard fuer die Oberflaechen (#594): anlegen, aendern, pausieren, sofort ausfuehren,
@@ -88,6 +91,8 @@ public sealed class TaskAdministration(
             return AdminResult.Failure(fehler);
         if (await CheckParentAsync(null, input.ParentId, ct) is { } parentProblem)
             return AdminResult.Failure(parentProblem);
+        if (CheckFill(input, when, out var fillBy) is { } fillProblem)
+            return AdminResult.Failure(fillProblem);
 
         var created = await board.CreateAsync(new TaskItem
         {
@@ -99,7 +104,9 @@ public sealed class TaskAdministration(
             When = when,
             Status = TaskItemStatus.Todo,
             Type = TaskItemType.Work,
-            ParentId = input.ParentId.Trim()
+            ParentId = input.ParentId.Trim(),
+            FillBy = fillBy,
+            EstimateUsd = input.EstimateUsd
         }, ct);
 
         return AdminResult.Success(MitHinweis($"Aufgabe '{created.Title}' angelegt ({created.Id}).", created));
@@ -114,6 +121,8 @@ public sealed class TaskAdministration(
             return AdminResult.Failure(fehler);
         if (await CheckParentAsync(id, input.ParentId, ct) is { } parentProblem)
             return AdminResult.Failure(parentProblem);
+        if (CheckFill(input, when, out var fillBy) is { } fillProblem)
+            return AdminResult.Failure(fillProblem);
 
         var updated = await board.UpdateAsync(id, current => current with
         {
@@ -123,7 +132,9 @@ public sealed class TaskAdministration(
             Priority = Math.Clamp(input.Priority, 1, 5),
             Assignee = assignee,
             When = when,
-            ParentId = input.ParentId.Trim()
+            ParentId = input.ParentId.Trim(),
+            FillBy = fillBy,
+            EstimateUsd = input.EstimateUsd
         }, ct);
 
         return updated is null
@@ -131,6 +142,27 @@ public sealed class TaskAdministration(
             : AdminResult.Success(MitHinweis($"Aufgabe '{updated.Title}' gespeichert.", updated));
     }
 
+    /// <summary>
+    /// #717: Fill work is one-time, and its deadline lies ahead — a recurring schedule and a
+    /// deadline contradict each other.
+    /// </summary>
+    private static string? CheckFill(TaskInput input, TaskWhen? when, out DateTime? fillBy)
+    {
+        fillBy = null;
+        if (input.EstimateUsd is < 0)
+            return "The estimate cannot be negative.";
+        if (string.IsNullOrWhiteSpace(input.FillBy))
+            return null;
+        if (TaskFrontmatter.ParseUtc(input.FillBy) is not { } parsed)
+            return $"'{input.FillBy}' is not a point in time. Use a date (yyyy-MM-dd) or an ISO timestamp.";
+        if (when is { Kind: TaskWhenKind.Cron or TaskWhenKind.Every })
+            return "Fill work is one-time: a deadline and a recurring schedule do not go together.";
+        if (parsed <= DateTime.UtcNow)
+            return "The deadline of fill work has to lie ahead.";
+        fillBy = parsed;
+        return null;
+    }
+
     /// <summary>#714: The parent must exist and must not lie below the task itself.</summary>
     private async Task<string?> CheckParentAsync(string? taskId, string parentId, CancellationToken ct)
     {