fix: gate previousConversation array format for older servers (#400)

* fix: gate previousConversation array format behind BrowserOS 0.41.0.0

Older servers reject the array format for previousConversation with a
ZodError ("Expected string, received array"). Gate the feature behind
BrowserOS >= 0.41.0.0 which bundles server >= 0.0.64 that accepts both
array and string formats.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: use minServerVersion 0.0.64 for previousConversation gate

Server version is the direct indicator of schema support, more accurate
than using BrowserOS version as a proxy.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: fall back to string format for previousConversation on old servers

Instead of omitting previousConversation entirely on servers < 0.0.64,
serialize the conversation history as a "role: content" string which
old servers accept via their z.string() schema.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

apps/agent/entrypoints/sidepanel/index/useChatSession.ts

@@ -5,6 +5,7 @@ import { useEffect, useRef, useState } from 'react'
 import { useSearchParams } from 'react-router'
 import useDeepCompareEffect from 'use-deep-compare-effect'
 import type { Provider } from '@/components/chat/chatComponentTypes'
+import { Capabilities, Feature } from '@/lib/browseros/capabilities'
 import { useAgentServerUrl } from '@/lib/browseros/useBrowserOSProviders'
 import type { ChatAction } from '@/lib/chat-actions/types'
 import {
@@ -256,12 +257,20 @@ export const useChatSession = () => {
           }[]
         }
 
-        // Format previous messages from ref (messagesRef doesn't include current message yet)
+        const supportsArrayConversation = await Capabilities.supports(
+          Feature.PREVIOUS_CONVERSATION_ARRAY,
+        )
+
         const previousMessages = messagesRef.current
-        const previousConversation =
+        const history =
           previousMessages.length > 0
             ? formatConversationHistory(previousMessages)
             : undefined
+        const previousConversation = history?.length
+          ? supportsArrayConversation
+            ? history
+            : history.map((m) => `${m.role}: ${m.content}`).join('\n')
+          : undefined
 
         return {
           api: `${agentUrlRef.current}/chat`,

apps/agent/lib/browseros/capabilities.ts

@@ -33,6 +33,8 @@ export enum Feature {
   PROXY_SUPPORT = 'PROXY_SUPPORT',
   // Workflows feature
   WORKFLOW_SUPPORT = 'WORKFLOW_SUPPORT',
+  // previousConversation as structured array (older servers only accept string)
+  PREVIOUS_CONVERSATION_ARRAY = 'PREVIOUS_CONVERSATION_ARRAY',
 }
 
 /**
@@ -54,6 +56,7 @@ const FEATURE_CONFIG: { [K in Feature]: FeatureConfig } = {
   [Feature.WORKSPACE_FOLDER_SUPPORT]: { minBrowserOSVersion: '0.36.4.0' },
   [Feature.PROXY_SUPPORT]: { minBrowserOSVersion: '0.39.0.1' },
   [Feature.WORKFLOW_SUPPORT]: { minServerVersion: '0.0.41' },
+  [Feature.PREVIOUS_CONVERSATION_ARRAY]: { minServerVersion: '0.0.64' },
 }
 
 function parseVersion(version: string): number[] {