LlmChatView dispose() does not cancel pending streaming response, causing setState on disposed widget

Start in llm_chat_view.dart at _LlmChatViewState.dispose() and compare its lifecycle handling with _onCancelMessage(), which already uses LlmResponse.cancel(). Reproduce navigation away during streaming, then verify that the pending response no longer reaches the update callback or triggers setState after disposal.

Description

_LlmChatViewState.dispose() does not cancel _pendingPromptResponse, causing a Null check operator used on a null value crash when the user navigates away from the chat while the AI is still streaming a response.

Steps to Reproduce

1. Open a chat with an LLM using LlmChatView
2. Send a message that triggers a streaming response
3. Navigate away (pop the page) before the response finishes streaming

Error

_TypeError: Null check operator used on a null value

Stack trace:
State.setState (package:flutter/src/widgets/framework.dart:1219)
_LlmChatViewState._onSendMessage.<fn> (package:flutter_ai_toolkit/src/views/llm_chat_view/llm_chat_view.dart:257)
FirebaseProvider._sendMessageStream (package:flutter_ai_toolkit/src/providers/implementations/firebase_provider.dart)

Root Cause

In llm_chat_view.dart, the _onSendMessage method creates an LlmResponse with an onUpdate callback that calls setState:

// line 253-258
_pendingPromptResponse = LlmResponse(
  stream: sendMessageStream(prompt, attachments: attachments),
  onUpdate: (_) => setState(() {}),
  onDone: _onPromptDone,
);

But dispose() (line 174) does not cancel this response:

@override
void dispose() {
  super.dispose();
  widget.viewModel.provider.removeListener(_onHistoryChanged);
}

When the widget is disposed while streaming is active, the LlmResponse subscription continues to receive data and calls setState on the disposed state, crashing at _element! inside State.setState.

Suggested Fix

Cancel the pending response in dispose():

@override
void dispose() {
  _pendingPromptResponse?.cancel();
  super.dispose();
  widget.viewModel.provider.removeListener(_onHistoryChanged);
}

The cancel() method already exists on LlmResponse and is used by _onCancelMessage() — it just needs to also be called during disposal.

Impact

• 588 occurrences across 124 users in our production app (CraftNote)
• Affects any app using LlmChatView where users can navigate away during streaming
• Package version: flutter_ai_toolkit 1.0.0

Environment

• Flutter AI Toolkit: 1.0.0
• Flutter: 3.27+
• Platform: iOS (but likely affects all platforms)