feat(multi-run): Agent Selector (#103)

* Add Agent Selector

* Send on Enter

* Allow multi run with 1 Model for Agent Manager

* Update packages/ui/src/stores/useMultiRunStore.ts

* Update Changelog

packages/ui/src/components/views/agent-manager/AgentManagerEmptyState.tsx

@@ -15,6 +15,7 @@ import { Textarea } from '@/components/ui/textarea';
 import { useDirectoryStore } from '@/stores/useDirectoryStore';
 import { ModelMultiSelect, generateInstanceId, type ModelSelectionWithId } from '@/components/multirun/ModelMultiSelect';
 import { BranchSelector, useBranchOptions } from '@/components/multirun/BranchSelector';
+import { AgentSelector } from '@/components/multirun/AgentSelector';
 import type { CreateMultiRunParams, MultiRunFileAttachment } from '@/types/multirun';
 
 /** Max file size in bytes (10MB) */
@@ -47,6 +48,7 @@ export const AgentManagerEmptyState: React.FC<AgentManagerEmptyStateProps> = ({
   const [groupName, setGroupName] = React.useState('');
   const [prompt, setPrompt] = React.useState('');
   const [selectedModels, setSelectedModels] = React.useState<ModelSelectionWithId[]>([]);
+  const [selectedAgent, setSelectedAgent] = React.useState<string>('');
   const [baseBranch, setBaseBranch] = React.useState('HEAD');
   const [attachedFiles, setAttachedFiles] = React.useState<AttachedFile[]>([]);
   const [isSubmitting, setIsSubmitting] = React.useState(false);
@@ -154,6 +156,7 @@ export const AgentManagerEmptyState: React.FC<AgentManagerEmptyStateProps> = ({
         name: groupName.trim(),
         prompt: prompt.trim(),
         models,
+        agent: selectedAgent || undefined,
         worktreeBaseBranch: baseBranch,
         files,
       });
@@ -162,6 +165,7 @@ export const AgentManagerEmptyState: React.FC<AgentManagerEmptyStateProps> = ({
       setGroupName('');
       setPrompt('');
       setSelectedModels([]);
+      setSelectedAgent('');
       setAttachedFiles([]);
       setBaseBranch('HEAD');
     } catch (error) {
@@ -172,6 +176,18 @@ export const AgentManagerEmptyState: React.FC<AgentManagerEmptyStateProps> = ({
     }
   };
 
+  const handleKeyDown = (e: React.KeyboardEvent<HTMLTextAreaElement>) => {
+    // Enter submits if valid, Shift+Enter adds newline
+    if (e.key === 'Enter' && !e.shiftKey) {
+      e.preventDefault();
+      if (isValid && !isSubmittingOrCreating) {
+        handleSubmit(e as unknown as React.FormEvent);
+      }
+      // If not valid, do nothing (no newline, no submit)
+    }
+    // Shift+Enter: default textarea behavior (adds newline)
+  };
+
   return (
     <div className={cn('flex flex-col items-center justify-center h-full w-full p-4', className)}>
       <form onSubmit={handleSubmit} className="w-full max-w-2xl space-y-4">
@@ -208,6 +224,20 @@ export const AgentManagerEmptyState: React.FC<AgentManagerEmptyStateProps> = ({
           </p>
         </div>
 
+        {/* Agent Selection */}
+        <div className="space-y-1.5">
+          <label className="typography-ui-label font-medium text-foreground">
+            Agent
+          </label>
+          <AgentSelector
+            value={selectedAgent}
+            onChange={setSelectedAgent}
+          />
+          <p className="typography-micro text-muted-foreground">
+            Optional agent to use for all runs
+          </p>
+        </div>
+
         {/* Model Selection */}
         <div className="space-y-1.5">
           <label className="typography-ui-label font-medium text-foreground">
@@ -235,6 +265,7 @@ export const AgentManagerEmptyState: React.FC<AgentManagerEmptyStateProps> = ({
               id="prompt"
               value={prompt}
               onChange={(e) => setPrompt(e.target.value)}
+              onKeyDown={handleKeyDown}
               placeholder="Ask anything..."
               className="min-h-[100px] max-h-[300px] resize-none border-0 bg-transparent px-4 py-3 typography-markdown focus-visible:ring-0 focus-visible:ring-offset-0"
             />