What's the best way to verify this?

To verify:

• Open Developer Tools > Network Tab and filter for extensionquery requests
• Open Extensions View and Search for GitHub.copilot-chat
• In the Network tab, expand preview of extensionquery request and look for Microsoft.VisualStudio.Code.EnabledApiProposals key in results[0].extensions[0].versions[0].properties
• Make sure the value of this key contains all proposals copilot chat extension is using.

The value:

extensionsAny,newSymbolNamesProvider,interactive,codeActionAI,contribCommentThreadAdditionalMenu,contribCommentsViewThreadMenus,documentFiltersExclusive,embeddings,findTextInFiles,findFiles2,textSearchProvider,terminalDataWriteEvent,terminalExecuteCommandEvent,terminalSelection,terminalQuickFixProvider,mappedEditsProvider,aiRelatedInformation,chatParticipantAdditions,defaultChatParticipant,chatVariableResolver,contribSourceControlInputBoxMenu,authLearnMore,testObserver,aiTextSearchProvider,chatParticipantPrivate,chatProvider,lmTools@2

Looks good to me!