feat(copilot): support prompt-in-URL for shareable prompt links (#12406)

Requested by @torantula

Add support for shareable AutoPilot URLs that contain a prompt in the
URL hash fragment, inspired by [Lovable's
implementation](https://docs.lovable.dev/integrations/build-with-url).

**URL format:**
- `/copilot#prompt=URL-encoded-text` — pre-fills the input for the user
to review before sending
- `/copilot?autosubmit=true#prompt=...` — auto-creates a session and
sends the prompt immediately

**Example:**
```
https://platform.agpt.co/copilot#prompt=Create%20a%20todo%20app
https://platform.agpt.co/copilot?autosubmit=true#prompt=Create%20a%20todo%20app
```

**Key design decisions:**
- Uses URL fragment (`#`) instead of query params — fragments never hit
the server, so prompts stay client-side only (better for privacy, no
backend URL length limits)
- URL is cleaned via `history.replaceState` immediately after extraction
to prevent re-triggering on navigation/reload
- Leverages existing `pendingMessage` + `createSession()` flow for
auto-submit — no new backend APIs needed
- For populate-only mode, passes `initialPrompt` down through component
tree to pre-fill the chat input

**Files changed:**
- `useCopilotPage.ts` — URL hash extraction logic + `initialPrompt`
state
- `CopilotPage.tsx` — passes `initialPrompt` to `ChatContainer`
- `ChatContainer.tsx` — passes `initialPrompt` to `EmptySession`
- `EmptySession.tsx` — passes `initialPrompt` to `ChatInput`
- `ChatInput.tsx` / `useChatInput.ts` — accepts `initialValue` to
pre-fill the textarea

Fixes SECRT-2119

---
Co-authored-by: Toran Bruce Richards (@Torantulino) <toran@agpt.co>

autogpt_platform/frontend/src/app/(platform)/copilot/components/ChatInput/useChatInput.ts

@@ -1,3 +1,4 @@
+import { useCopilotUIStore } from "@/app/(platform)/copilot/store";
 import { ChangeEvent, FormEvent, useEffect, useState } from "react";
 
 interface Args {
@@ -16,6 +17,16 @@ export function useChatInput({
 }: Args) {
   const [value, setValue] = useState("");
   const [isSending, setIsSending] = useState(false);
+  const { initialPrompt, setInitialPrompt } = useCopilotUIStore();
+
+  useEffect(
+    function consumeInitialPrompt() {
+      if (!initialPrompt) return;
+      setValue((prev) => (prev.length === 0 ? initialPrompt : prev));
+      setInitialPrompt(null);
+    },
+    [initialPrompt, setInitialPrompt],
+  );
 
   useEffect(
     function focusOnMount() {

autogpt_platform/frontend/src/app/(platform)/copilot/store.ts

@@ -7,6 +7,10 @@ export interface DeleteTarget {
 }
 
 interface CopilotUIState {
+  /** Prompt extracted from URL hash (e.g. /copilot#prompt=...) for input prefill. */
+  initialPrompt: string | null;
+  setInitialPrompt: (prompt: string | null) => void;
+
   sessionToDelete: DeleteTarget | null;
   setSessionToDelete: (target: DeleteTarget | null) => void;
 
@@ -31,6 +35,9 @@ interface CopilotUIState {
 }
 
 export const useCopilotUIStore = create<CopilotUIState>((set) => ({
+  initialPrompt: null,
+  setInitialPrompt: (prompt) => set({ initialPrompt: prompt }),
+
   sessionToDelete: null,
   setSessionToDelete: (target) => set({ sessionToDelete: target }),
 

autogpt_platform/frontend/src/app/(platform)/copilot/useCopilotPage.ts

@@ -19,6 +19,42 @@ import { useCopilotStream } from "./useCopilotStream";
 const TITLE_POLL_INTERVAL_MS = 2_000;
 const TITLE_POLL_MAX_ATTEMPTS = 5;
 
+/**
+ * Extract a prompt from the URL hash fragment.
+ * Supports: /copilot#prompt=URL-encoded-text
+ * Optionally auto-submits if ?autosubmit=true is in the query string.
+ * Returns null if no prompt is present.
+ */
+function extractPromptFromUrl(): {
+  prompt: string;
+  autosubmit: boolean;
+} | null {
+  if (typeof window === "undefined") return null;
+
+  const hash = window.location.hash;
+  if (!hash) return null;
+
+  const hashParams = new URLSearchParams(hash.slice(1));
+  const prompt = hashParams.get("prompt");
+
+  if (!prompt || !prompt.trim()) return null;
+
+  const searchParams = new URLSearchParams(window.location.search);
+  const autosubmit = searchParams.get("autosubmit") === "true";
+
+  // Clean up hash + autosubmit param only (preserve other query params)
+  const cleanURL = new URL(window.location.href);
+  cleanURL.hash = "";
+  cleanURL.searchParams.delete("autosubmit");
+  window.history.replaceState(
+    null,
+    "",
+    `${cleanURL.pathname}${cleanURL.search}`,
+  );
+
+  return { prompt: prompt.trim(), autosubmit };
+}
+
 interface UploadedFile {
   file_id: string;
   name: string;
@@ -127,6 +163,28 @@ export function useCopilotPage() {
     }
   }, [sessionId, pendingMessage, sendMessage]);
 
+  // --- Extract prompt from URL hash on mount (e.g. /copilot#prompt=Hello) ---
+  const { setInitialPrompt } = useCopilotUIStore();
+  const hasProcessedUrlPrompt = useRef(false);
+  useEffect(() => {
+    if (hasProcessedUrlPrompt.current) return;
+
+    const urlPrompt = extractPromptFromUrl();
+    if (!urlPrompt) return;
+
+    hasProcessedUrlPrompt.current = true;
+
+    if (urlPrompt.autosubmit) {
+      setPendingMessage(urlPrompt.prompt);
+      void createSession().catch(() => {
+        setPendingMessage(null);
+        setInitialPrompt(urlPrompt.prompt);
+      });
+    } else {
+      setInitialPrompt(urlPrompt.prompt);
+    }
+  }, [createSession, setInitialPrompt]);
+
   async function uploadFiles(
     files: File[],
     sid: string,