feat(worker): Handler-Session vor dem Usage-Limit warnen und Handoff bis zum Reset zurueckhalten

Eine PowerUse-Handler-Session soll am 5h-Limit nicht mehr mitten im Merge
sterben, sondern vorher selbst sauber uebergeben:

- HandlerUsageGuard (neu) warnt die laufende Session genau einmal pro Runde,
  sobald FiveHour.Utilization den Schwellwert PowerUseHandoffPct erreicht.
  Die Warnung wird per HandlerUsageWarning-Broadcast an Mission Control
  geschickt und dort in das Pane der Handler-TaskId getippt.
- handoff_list_handler broadcastet den Handoff dann nicht sofort, sondern parkt
  ihn bis ResetsAt + 60 s; das Ergebnis traegt deferredUntil. Ohne ResetsAt
  wird wie bisher sofort gesendet.
- Der geparkte Handoff liegt im HandlerRoundState (handler-rounds.json) und
  wird vom Guard-Tick ausgeloest, also auch nach einem Worker-Neustart wieder
  eingeplant bzw. sofort gesendet, wenn er ueberfaellig ist.
- Review-Befund aus #272: HandlerRestartCoordinator wartet nicht mehr selbst
  bis ResetsAt, sondern parkt den Neustart im selben Slot. AutoRestartUsed wird
  erst gesetzt, wenn der Broadcast wirklich rausging - ein Worker-Absturz
  waehrend der Wartezeit laesst die Runde nicht mehr dauerhaft tot zurueck.
  Zurueckgehaltener Handoff und Auto-Neustart teilen sich einen Slot, also
  oeffnet nie beides dieselbe Runde. UsageLimitProofPct entfaellt zugunsten von
  PowerUseHandoffPct.
- PtyTerminalSession.SendLineAsync schreibt in die laufende Session. Gegen eine
  echte claude-Session verifiziert: Text und Enter muessen zwei getrennte
  Writes sein, die Enter-Bytes kommen von Terminal.GenerateKeyInput.

src/ClaudeDo.Ui/Services/PtyTerminalSession.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Reflection;
 using System.Threading;
 using System.Threading.Tasks;
 using Iciclecreek.Terminal;
@@ -93,6 +94,56 @@ public sealed class PtyTerminalSession : IDisposable
         ProcessExited?.Invoke(this, e.ExitCode);
     }
 
+    /// <summary>
+    /// Types <paramref name="text"/> into the running session and submits it, exactly as if the user
+    /// had typed it — used to warn a list-handler session before the usage limit
+    /// (<c>HandlerUsageWarning</c>). Verified against a real `claude` TUI, including while it was
+    /// mid-turn (the message is queued and acted on when the turn ends).
+    ///
+    /// Three non-obvious details, all established by that spike:
+    /// • <see cref="TerminalControl"/> exposes no public write path at all — its only public paste is
+    ///   <c>TerminalView.PasteAsync()</c>, which takes no argument and reads the clipboard. The
+    ///   private <c>SendToPtyAsync</c> on the inner view is the write seam, hence the reflection.
+    /// • The text and the Enter must be TWO writes. A single <c>text + "\r"</c> chunk lands in
+    ///   claude's composer but is never submitted — a chunk carrying an embedded CR reads as pasted
+    ///   text, not as a keypress.
+    /// • The Enter bytes come from the emulator (<c>GenerateKeyInput</c>) rather than a literal
+    ///   "\r", because claude turns Win32 input mode on and the emulator owns that encoding.
+    ///
+    /// Best-effort by design: a package upgrade that renames the private member costs a warning that
+    /// never arrives, never a crashed Mission Control.
+    /// </summary>
+    public async Task<bool> SendLineAsync(string text)
+    {
+        if (_control is not { } control || !IsRunning || string.IsNullOrEmpty(text)) return false;
+        try
+        {
+            await SendRawAsync(control, text);
+            await Task.Delay(SubmitDelay);
+            await SendRawAsync(control, control.Terminal.GenerateKeyInput(XTerm.Input.Key.Enter, XTerm.Input.KeyModifiers.None));
+            return true;
+        }
+        catch (Exception)
+        {
+            return false;
+        }
+    }
+
+    // Long enough that the two writes can't be read as one chunk by the child's stdin reader.
+    private static readonly TimeSpan SubmitDelay = TimeSpan.FromMilliseconds(150);
+
+    private static readonly FieldInfo? s_terminalViewField =
+        typeof(TerminalControl).GetField("_terminalView", BindingFlags.Instance | BindingFlags.NonPublic);
+    private static readonly MethodInfo? s_sendToPty =
+        typeof(TerminalView).GetMethod("SendToPtyAsync", BindingFlags.Instance | BindingFlags.NonPublic);
+
+    private static Task SendRawAsync(TerminalControl control, string data)
+    {
+        if (s_terminalViewField?.GetValue(control) is not TerminalView view || s_sendToPty is null)
+            throw new InvalidOperationException("Iciclecreek.Avalonia.Terminal no longer exposes a PTY write seam.");
+        return (Task)s_sendToPty.Invoke(view, new object[] { data, CancellationToken.None })!;
+    }
+
     public void Kill()
     {
         try { _control?.Kill(); }