fix(app): synchronize chat submission and keyboard state

Render optimistic turn feedback before host acknowledgement and roll it back on rejection. Reconcile iOS keyboard offsets from the native transition end event so JS contention cannot leave the composer displaced.

packages/app/src/composer/index.tsx

@@ -1095,6 +1095,7 @@ export function Composer({
     buildOutgoingAttachments,
     removeAttachment,
     openAttachment,
+    beginSubmit,
     clearSentAttachments,
     completeSubmit,
     resetSuppression,
@@ -1372,6 +1373,9 @@ export function Composer({
           queueMessage(queuedText, queuedAttachments);
         },
         submitMessage: async ({ message: submitText, attachments: submitAttachments }) => {
+          if (submitBehavior !== "preserve-and-lock") {
+            beginSubmit(submitAttachments);
+          }
           await submitMessage(submitText, submitAttachments);
         },
         clearDraft,
@@ -1393,6 +1397,7 @@ export function Composer({
     },
     [
       allowEmptySubmit,
+      beginSubmit,
       clearDraft,
       completeSubmit,
       hasExternalContent,