feat(arena): forward chat history to spawned agents

Add stripStartupContext to remove env-info from parent history and pass
chatHistory through ArenaManager → InProcessBackend → AgentInteractive →
AgentCore. This allows arena agents to start with conversational context
from the main session.

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

packages/cli/src/ui/commands/arenaCommand.ts

@@ -21,6 +21,7 @@ import {
   ArenaSessionStatus,
   AuthType,
   createDebugLogger,
+  stripStartupContext,
   type Config,
   type ArenaModelConfig,
   type ArenaAgentErrorEvent,
@@ -171,6 +172,18 @@ function executeArenaCommand(
   ui: CommandContext['ui'],
   input: ArenaExecutionInput,
 ): void {
+  // Capture the main session's chat history so arena agents start with
+  // conversational context. Strip the leading startup context (env info
+  // user message + model ack) because each agent generates its own for
+  // its worktree directory — keeping the parent's would duplicate it.
+  let chatHistory;
+  try {
+    const fullHistory = config.getGeminiClient().getHistory();
+    chatHistory = stripStartupContext(fullHistory);
+  } catch {
+    debugLogger.debug('Could not retrieve chat history for arena agents');
+  }
+
   const manager = new ArenaManager(config);
   const emitter = manager.getEventEmitter();
   const detachListeners: Array<() => void> = [];
@@ -331,6 +344,7 @@ function executeArenaCommand(
       cols,
       rows,
       approvalMode: input.approvalMode,
+      chatHistory,
     })
     .then(
       () => {

packages/cli/src/ui/components/agent-view/AgentChatView.tsx

@@ -155,6 +155,7 @@ export const AgentChatView = ({ agentId }: AgentChatViewProps) => {
       ),
     // eslint-disable-next-line react-hooks/exhaustive-deps
     [
+      agentId,
       messages.length,
       pendingApprovals?.size,
       liveOutputs?.size,