Keep new-workspace composer expanded after submit

The new-workspace composer uses preserve-and-lock: it keeps the typed
text through workspace creation so it survives a failure. But the input
minimized its height on every submit, collapsing a multi-line draft to
one line while the text and loading spinner remained — clipped and ugly.

Gate the height-minimize on the same condition that clears the text, so
the box only collapses when the text actually goes away (agent panel),
not when it's preserved (new-workspace).

packages/app/src/composer/index.tsx

@@ -1871,6 +1871,7 @@ export function Composer({
               submitIcon={submitIcon}
               isSubmitDisabled={isSubmitBusy}
               isSubmitLoading={isSubmitBusy}
+              preserveHeightOnSubmit={submitBehavior === "preserve-and-lock"}
               attachments={selectedAttachments}
               cwd={cwd}
               attachmentMenuItems={attachmentMenuItems}

packages/app/src/composer/input/input.tsx

@@ -94,6 +94,8 @@ export interface MessageInputProps {
   submitIcon?: "arrow" | "return";
   isSubmitDisabled?: boolean;
   isSubmitLoading?: boolean;
+  /** When true, keep the grown input height after submit (text is preserved, not cleared). */
+  preserveHeightOnSubmit?: boolean;
   attachments: ComposerAttachment[];
   cwd: string;
   attachmentMenuItems: AttachmentMenuItem[];
@@ -982,6 +984,7 @@ interface SendMessageContext {
   isAgentRunning: boolean;
   onSubmit: (payload: MessagePayload) => void;
   onMinimizeHeight: () => void;
+  preserveHeightOnSubmit: boolean;
 }
 
 function sendMessageImpl(ctx: SendMessageContext): void {
@@ -1000,7 +1003,11 @@ function sendMessageImpl(ctx: SendMessageContext): void {
     cwd: ctx.cwd,
     forceSend: ctx.isAgentRunning || undefined,
   });
-  ctx.onMinimizeHeight();
+  // When the host preserves and locks the composer (e.g. new-workspace creation),
+  // the text stays put — collapsing the height would clip it. Keep it grown.
+  if (!ctx.preserveHeightOnSubmit) {
+    ctx.onMinimizeHeight();
+  }
 }
 
 interface QueueMessageContext {
@@ -1141,6 +1148,7 @@ interface ResolvedMessageInputProps {
   submitIcon: "arrow" | "return";
   isSubmitDisabled: boolean;
   isSubmitLoading: boolean;
+  preserveHeightOnSubmit: boolean;
   attachments: ComposerAttachment[];
   cwd: string;
   attachmentMenuItems: AttachmentMenuItem[];
@@ -1182,6 +1190,7 @@ function resolveMessageInputProps(props: MessageInputProps): ResolvedMessageInpu
     submitIcon: props.submitIcon ?? "arrow",
     isSubmitDisabled: props.isSubmitDisabled ?? false,
     isSubmitLoading: props.isSubmitLoading ?? false,
+    preserveHeightOnSubmit: props.preserveHeightOnSubmit ?? false,
     attachments: props.attachments,
     cwd: props.cwd,
     attachmentMenuItems: props.attachmentMenuItems,
@@ -1231,6 +1240,7 @@ export const MessageInput = forwardRef<MessageInputRef, MessageInputProps>(
       submitIcon,
       isSubmitDisabled,
       isSubmitLoading,
+      preserveHeightOnSubmit,
       attachments,
       cwd,
       attachmentMenuItems,
@@ -1546,6 +1556,7 @@ export const MessageInput = forwardRef<MessageInputRef, MessageInputProps>(
           isAgentRunning,
           onSubmit,
           onMinimizeHeight: minimizeInputHeight,
+          preserveHeightOnSubmit,
         }),
       [
         allowEmptySubmit,
@@ -1555,6 +1566,7 @@ export const MessageInput = forwardRef<MessageInputRef, MessageInputProps>(
         isAgentRunning,
         hasExternalContent,
         minimizeInputHeight,
+        preserveHeightOnSubmit,
       ],
     );