fix(agent-builder): prefill seeded prompt instead of auto-sending

Opening the Agent Builder dock via a contextual action ("New agent",
"Edit configuration", etc.) used to auto-send the seeded prompt, so the
sidebar started a chat on its own. Instead, prefill the composer with the
seeded prompt and let the user review and hit send.

Since prefilling is non-destructive, the start-fresh-vs-continue
confirmation dialog is no longer needed and is removed.

Generated-By: PostHog Code
Task-Id: fc2c5587-1464-4cb1-9116-0e7a34f70734

Author: dmarticus

packages/ui/src/features/agent-applications/agent-builder/AgentBuilderDock.tsx

@@ -23,7 +23,6 @@ import { useAgentChatPendingApproval } from "../hooks/useAgentChatPendingApprova
 import { agentIngressBaseUrl } from "../utils/ingress";
 import { AgentBuilderMcpConnectDialog } from "./AgentBuilderMcpConnectDialog";
 import { AgentBuilderSecretForm } from "./AgentBuilderSecretForm";
-import { AgentBuilderSeedDialog } from "./AgentBuilderSeedDialog";
 import {
   AGENT_BUILDER_CHAT_ID,
   AGENT_BUILDER_SLUG,
@@ -322,37 +321,22 @@ export function AgentBuilderDock() {
     setPendingMcpConnect(null);
   }
 
-  // Edit-with-AI hand-offs: send the seeded prompt once when a new seed lands.
-  // An empty dock starts immediately; if a chat is already in progress, confirm
-  // whether to start fresh or continue (so a deliberate "New agent" / "Edit with
-  // AI" doesn't silently wipe or append onto an unrelated conversation).
+  // Contextual hand-offs ("New agent" / "Edit with AI" / …): prefill the
+  // seeded prompt into the composer when a new seed lands — never send it. The
+  // user reviews and hits send, so opening the dock doesn't fire a chat on its
+  // own. Prefilling is non-destructive, so no start-fresh-vs-continue prompt is
+  // needed: it drops into whatever chat is open, and the header "New chat" (+)
+  // clears first if the user wants a fresh conversation.
   const lastSeedRef = useRef(0);
-  const [seedConfirm, setSeedConfirm] = useState<string | null>(null);
+  const [draft, setDraft] = useState<{ text: string; token: number } | null>(
+    null,
+  );
   useEffect(() => {
     if (!seed || seed.seq === lastSeedRef.current) return;
     lastSeedRef.current = seed.seq;
     consumeSeed(seed.seq);
-    if (chat.messages.length === 0) {
-      chat.send(seed.prompt);
-    } else {
-      setSeedConfirm(seed.prompt);
-    }
-  }, [seed, chat, consumeSeed]);
-
-  function seedStartFresh() {
-    if (!seedConfirm) return;
-    setPendingSecret(null);
-    setPendingMcpConnect(null);
-    chat.newChat();
-    setLastSession(null);
-    chat.send(seedConfirm);
-    setSeedConfirm(null);
-  }
-  function seedContinue() {
-    if (!seedConfirm) return;
-    chat.send(seedConfirm);
-    setSeedConfirm(null);
-  }
+    setDraft({ text: seed.prompt, token: seed.seq });
+  }, [seed, consumeSeed]);
 
   return (
     <Flex
@@ -432,6 +416,7 @@ export function AgentBuilderDock() {
           placeholder={placeholder}
           emptyState={<AgentBuilderEmptyState page={page} onPick={chat.send} />}
           emptyHint="Ask the agent builder to inspect, debug, or edit your agents. It can see what you're looking at and walk you there."
+          draft={draft ?? undefined}
           belowConversation={
             pendingApproval ? (
               <AgentChatPendingApprovalCard
@@ -459,14 +444,6 @@ export function AgentBuilderDock() {
         />
       )}
 
-      <AgentBuilderSeedDialog
-        open={seedConfirm != null}
-        prompt={seedConfirm ?? ""}
-        onStartFresh={seedStartFresh}
-        onContinue={seedContinue}
-        onCancel={() => setSeedConfirm(null)}
-      />
-
       <AgentBuilderMcpConnectDialog
         pending={pendingMcpConnect}
         busy={mcpConnectBusy}

packages/ui/src/features/agent-applications/agent-builder/AgentBuilderSeedDialog.tsx

@@ -27,7 +27,8 @@ export type AgentBuilderPageContext =
   | { kind: "agent-chat"; slug: string }
   | { kind: "unknown" };
 
-/** A pending "Edit with AI" hand-off: open the dock and send `prompt`. */
+/** A pending contextual hand-off: open the dock and prefill the composer with
+ *  `prompt` (the user reviews and sends — it is never auto-sent). */
 export interface AgentBuilderSeed {
   /** Monotonic id so a consumer can mark exactly one seed handled. */
   seq: number;
@@ -113,7 +114,7 @@ interface AgentBuilderStore {
   setVisible: (visible: boolean) => void;
   setFollowMode: (followMode: boolean) => void;
   setPage: (page: AgentBuilderPageContext) => void;
-  /** Open the dock and queue a prompt to send. */
+  /** Open the dock and prefill the composer with a prompt (not sent). */
   startAgentBuilder: (prompt: string, agentSlug?: string | null) => void;
   /** Mark a seed handled (no-op if a newer seed has since replaced it). */
   consumeSeed: (seq: number) => void;

packages/ui/src/features/agent-applications/agent-builder/agentBuilderStore.ts

@@ -8,7 +8,13 @@ import {
 import type { AcpMessage } from "@posthog/shared";
 import { ThreadView } from "@posthog/ui/features/sessions/components/ThreadView";
 import { Flex, Text, Tooltip } from "@radix-ui/themes";
-import { type KeyboardEvent, type ReactNode, useState } from "react";
+import {
+  type KeyboardEvent,
+  type ReactNode,
+  useEffect,
+  useRef,
+  useState,
+} from "react";
 
 /**
  * The conversation + composer half of a deployed-agent chat, shared by the
@@ -28,6 +34,7 @@ export function AgentChatSurface({
   composerDisabledReason,
   scrollX = true,
   placeholder = "Message this agent…",
+  draft,
   onSend,
   onCancel,
 }: {
@@ -50,6 +57,10 @@ export function AgentChatSurface({
   scrollX?: boolean;
   /** Composer placeholder. */
   placeholder?: string;
+  /** When set, prefills the composer with `text` (without sending). Bump
+   * `token` each time a new draft should repopulate the input — the same text
+   * re-applies on a fresh token so re-triggering a seeded prompt works. */
+  draft?: { text: string; token: number };
   onSend: (text: string) => void;
   onCancel: () => void;
 }) {
@@ -84,6 +95,7 @@ export function AgentChatSurface({
         isStreaming={isStreaming}
         placeholder={placeholder}
         disabledReason={composerDisabledReason}
+        draft={draft}
         onSend={onSend}
         onCancel={onCancel}
       />
@@ -95,17 +107,31 @@ function Composer({
   isStreaming,
   placeholder,
   disabledReason,
+  draft,
   onSend,
   onCancel,
 }: {
   isStreaming: boolean;
   placeholder: string;
   disabledReason?: string;
+  draft?: { text: string; token: number };
   onSend: (text: string) => void;
   onCancel: () => void;
 }) {
   const [text, setText] = useState("");
   const parked = !!disabledReason;
+  const textareaRef = useRef<HTMLTextAreaElement>(null);
+
+  // Prefill (but don't send) when a new draft lands — a seeded prompt drops into
+  // the composer for the user to review, edit, and send. Keyed on `token` so the
+  // same prompt re-applies on a fresh trigger.
+  const lastDraftToken = useRef<number | null>(null);
+  useEffect(() => {
+    if (!draft || draft.token === lastDraftToken.current) return;
+    lastDraftToken.current = draft.token;
+    setText(draft.text);
+    textareaRef.current?.focus();
+  }, [draft]);
 
   function submit() {
     if (parked) return;
@@ -132,6 +158,7 @@ function Composer({
     <div className="shrink-0 px-3 pt-2 pb-3">
       <InputGroup className="h-auto cursor-text bg-card focus-within:ring-1 focus-within:ring-purple-9">
         <InputGroupTextarea
+          ref={textareaRef}
           value={text}
           onChange={(e) => setText(e.target.value)}
           onKeyDown={onKeyDown}