Add active-turn steering (#3394)

* feat(agents): add active-turn steering

Let users choose whether an immediate prompt interrupts or joins the active turn. The daemon owns exact-turn admission, provider delivery, safe fallback, and canonical timeline identity while queueing remains client-side.

* fix(agents): stabilize steering history and replay QA

* fix(agents): preserve steering timeline order

* fix(agents): reconcile resumed provider history

* fix(agents): serialize steering with cancellation

* test(agents): prove Claude multi-tool steering

* test(agents): force explicit history hydration

* fix(agents): flush output before steer admission

packages/app/src/screens/settings-screen.tsx

@@ -249,6 +249,7 @@ function selectedSidebarItemStyle({ hovered }: PressableStateCallbackType & { ho
 function getSendBehaviorOptions(t: TFunction) {
   return [
     { value: "interrupt" as const, label: t("settings.general.defaultSend.options.interrupt") },
+    { value: "steer" as const, label: t("settings.general.defaultSend.options.steer") },
     { value: "queue" as const, label: t("settings.general.defaultSend.options.queue") },
   ];
 }
@@ -340,10 +341,7 @@ function GeneralSection({
   const { t, i18n } = useTranslation();
   const activeLocale = getActiveLocale(i18n.language);
   const sendBehaviorOptions = useMemo(() => getSendBehaviorOptions(t), [t]);
-  const sendBehaviorDescriptionKey =
-    settings.sendBehavior === "interrupt"
-      ? "settings.general.defaultSend.descriptions.interrupt"
-      : "settings.general.defaultSend.descriptions.queue";
+  const sendBehaviorDescriptionKey = `settings.general.defaultSend.descriptions.${settings.sendBehavior}`;
   const selectedLanguageOption = LANGUAGE_OPTIONS.find(
     (option) => option.value === settings.language,
   );