fix(ui): preserve draft across prompt history

Stop resetting history navigation on input so editing recalled entries doesn't wipe the bottom draft. Allow ArrowDown navigation while in history and persist the session draft only for fresh prompts.

packages/ui/src/components/prompt-input/usePromptPicker.ts

@@ -17,7 +17,6 @@ type PromptPickerOptions = {
 
   prompt: Accessor<string>
   setPrompt: (value: string) => void
-  resetHistoryNavigation?: () => void
   getTextarea: () => HTMLTextAreaElement | null
 
   instanceAgents: Accessor<Agent[]>
@@ -53,7 +52,6 @@ export function usePromptPicker(options: PromptPickerOptions): PromptPickerContr
     const target = e.target as HTMLTextAreaElement
     const value = target.value
     options.setPrompt(value)
-    options.resetHistoryNavigation?.()
 
     const cursorPos = target.selectionStart