From 29e0ff50b6f1040ce193b8a92d72f500a2700336 Mon Sep 17 00:00:00 2001
From: Eva <eva@100yen.org>
Date: Fri, 1 May 2026 14:49:21 +0700
Subject: [PATCH] perf(context-engine): defer precheck history snapshot

---
 src/agents/pi-embedded-runner/run/attempt.ts | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/agents/pi-embedded-runner/run/attempt.ts b/src/agents/pi-embedded-runner/run/attempt.ts
index 8741ac4fade..f0d105a16a1 100644
--- a/src/agents/pi-embedded-runner/run/attempt.ts
+++ b/src/agents/pi-embedded-runner/run/attempt.ts
@@ -2074,7 +2074,7 @@ export async function runEmbeddedAttempt(
 
         if (activeContextEngine) {
           try {
-            unwindowedContextEngineMessagesForPrecheck = activeSession.messages.slice();
+            const preassemblyContextEngineMessagesForPrecheck = activeSession.messages;
             const assembled = await assembleAttemptContextEngine({
               contextEngine: activeContextEngine,
               sessionId: params.sessionId,
@@ -2093,6 +2093,10 @@ export async function runEmbeddedAttempt(
               activeSession.agent.state.messages = assembled.messages;
             }
             contextEnginePromptAuthority = assembled.promptAuthority ?? "assembled";
+            if (contextEnginePromptAuthority === "preassembly_may_overflow") {
+              unwindowedContextEngineMessagesForPrecheck =
+                preassemblyContextEngineMessagesForPrecheck.slice();
+            }
             if (assembled.systemPromptAddition) {
               systemPromptText = prependSystemPromptAddition({
                 systemPrompt: systemPromptText,