fix(amazonq): duplicate messages in flare chat (aws#7097)

## Problem
when the flare chat panel refreshes on log in/log out, the message
listener never gets disposed of, causing the next webview instantiation
to have two message listeners that are forwarding messages to the ui

## Solution
dispose of the message listener when the webview gets disposed

---

- Treat all work as PUBLIC. Private `feature/x` branches will not be
squash-merged at release time.
- Your code changes must meet the guidelines in
[CONTRIBUTING.md](https://github.com/aws/aws-toolkit-vscode/blob/master/CONTRIBUTING.md#guidelines).
- License: I confirm that my contribution is made under the terms of the
Apache 2.0 license.

Author: jpinkney-aws

packages/amazonq/src/lsp/chat/activation.ts

@@ -15,12 +15,14 @@ import { AuthUtil } from 'aws-core-vscode/codewhisperer'
 import { updateConfigurationRequestType } from '@aws/language-server-runtimes/protocol'
 
 export async function activate(languageClient: LanguageClient, encryptionKey: Buffer, mynahUIPath: string) {
+    const disposables = globals.context.subscriptions
+
     // Make sure we've sent an auth profile to the language server before even initializing the UI
     await updateProfile(languageClient)
 
     const provider = new AmazonQChatViewProvider(mynahUIPath)
 
-    globals.context.subscriptions.push(
+    disposables.push(
         window.registerWebviewViewProvider(AmazonQChatViewProvider.viewType, provider, {
             webviewOptions: {
                 retainContextWhenHidden: true,
@@ -36,12 +38,18 @@ export async function activate(languageClient: LanguageClient, encryptionKey: Bu
     registerLanguageServerEventListener(languageClient, provider)
 
     provider.onDidResolveWebview(() => {
-        if (provider.webview) {
-            DefaultAmazonQAppInitContext.instance.getAppsToWebViewMessageListener().onMessage((msg) => {
-                provider.webview?.postMessage(msg).then(undefined, (e) => {
-                    getLogger().error('webView.postMessage failed: %s', (e as Error).message)
-                })
+        const disposable = DefaultAmazonQAppInitContext.instance.getAppsToWebViewMessageListener().onMessage((msg) => {
+            provider.webview?.postMessage(msg).then(undefined, (e) => {
+                getLogger().error('webView.postMessage failed: %s', (e as Error).message)
             })
+        })
+
+        if (provider.webviewView) {
+            disposables.push(
+                provider.webviewView.onDidDispose(() => {
+                    disposable.dispose()
+                })
+            )
         }
 
         registerMessageListeners(languageClient, provider, encryptionKey)
@@ -50,7 +58,7 @@ export async function activate(languageClient: LanguageClient, encryptionKey: Bu
     // register event listeners from the legacy agent flow
     await registerLegacyChatListeners(globals.context)
 
-    globals.context.subscriptions.push(
+    disposables.push(
         AuthUtil.instance.regionProfileManager.onDidChangeRegionProfile(async () => {
             void updateProfile(languageClient)
             await provider.refreshWebview()

packages/amazonq/src/lsp/chat/webviewProvider.ts

@@ -6,11 +6,11 @@
 import {
     EventEmitter,
     CancellationToken,
-    Webview,
     WebviewView,
     WebviewViewProvider,
     WebviewViewResolveContext,
     Uri,
+    Webview,
 } from 'vscode'
 import * as path from 'path'
 import {
@@ -29,7 +29,8 @@ export class AmazonQChatViewProvider implements WebviewViewProvider {
     private readonly onDidResolveWebviewEmitter = new EventEmitter<void>()
     public readonly onDidResolveWebview = this.onDidResolveWebviewEmitter.event
 
-    webview: Webview | undefined
+    webviewView?: WebviewView
+    webview?: Webview
 
     connectorAdapterPath?: string
     uiPath?: string
@@ -41,8 +42,6 @@ export class AmazonQChatViewProvider implements WebviewViewProvider {
         context: WebviewViewResolveContext,
         _token: CancellationToken
     ) {
-        this.webview = webviewView.webview
-
         const lspDir = Uri.parse(LanguageServerResolver.defaultDir())
         const dist = Uri.joinPath(globals.context.extensionUri, 'dist')
 
@@ -77,7 +76,16 @@ export class AmazonQChatViewProvider implements WebviewViewProvider {
 
         webviewView.webview.html = await this.getWebviewContent()
 
+        this.webviewView = webviewView
+        this.webview = this.webviewView.webview
+
         this.onDidResolveWebviewEmitter.fire()
+        globals.context.subscriptions.push(
+            this.webviewView.onDidDispose(() => {
+                this.webviewView = undefined
+                this.webview = undefined
+            })
+        )
         performance.mark(amazonqMark.open)
     }