From 45e7ed1ed22ad11d7c0e579db31ca1470092181c Mon Sep 17 00:00:00 2001
From: Christian Gunderman <gundermanc@google.com>
Date: Thu, 19 Feb 2026 06:17:49 +0000
Subject: [PATCH] feat(core): remove history pruning to restore agent memory
 and improve efficiency

Analysis of Experiment 2 vs 3 showed that pruning grep_search results
caused the agent to lose context and enter redundant tool loops,
increasing turn counts by ~28%. This change restores full history
retention while keeping the readCache improvements.
---
 packages/core/src/core/geminiChat.ts | 38 +---------------------------
 1 file changed, 1 insertion(+), 37 deletions(-)

diff --git a/packages/core/src/core/geminiChat.ts b/packages/core/src/core/geminiChat.ts
index 0ad4a20940..0283469873 100644
--- a/packages/core/src/core/geminiChat.ts
+++ b/packages/core/src/core/geminiChat.ts
@@ -161,37 +161,6 @@ function validateHistory(history: Content[]) {
  * Prunes the history to remove large tool outputs (like Greedy Grep context)
  * after they have been seen by the model for one turn.
  */
-function pruneHistory(history: Content[]): Content[] {
-  if (!history || history.length < 3) return history;
-
-  return history.map((content, index) => {
-    // Only prune user messages (which contain tool responses) that are older than the most recent one.
-    // Index < length - 2 ensures we keep the very latest tool response and the latest model thought.
-    if (content.role === 'user' && index < history.length - 2 && content.parts) {
-      const newParts = content.parts.map(part => {
-        if (part.functionResponse && part.functionResponse.name === 'grep_search') {
-          const output = (part.functionResponse.response as any)?.output || '';
-          if (output.includes('Match at line') && (output.includes('L') && output.includes('-'))) {
-             // This is a Greedy Grep output. Prune it.
-             const lines = output.split('\n');
-             const preservedLines = lines.filter((l: string) => l.startsWith('Found') || l.startsWith('File:') || l.includes('> L'));
-             const prunedOutput = preservedLines.join('\n') + '\n[... context pruned for token efficiency ...]';
-             return {
-               ...part,
-               functionResponse: {
-                 ...part.functionResponse,
-                 response: { output: prunedOutput }
-               }
-             };
-          }
-        }
-        return part;
-      });
-      return { ...content, parts: newParts };
-    }
-    return content;
-  });
-}
 function extractCuratedHistory(comprehensiveHistory: Content[]): Content[] {
   if (comprehensiveHistory === undefined || comprehensiveHistory.length === 0) {
     return [];
@@ -720,12 +689,7 @@ export class GeminiChat {
    * chat session.
    */
   getHistory(curated: boolean = false): Content[] {
-    let history = curated
-      ? extractCuratedHistory(this.history)
-      : this.history;
-    
-    // Prune history to remove large tool outputs after 1 turn
-    history = pruneHistory(history);
+    const history = curated ? extractCuratedHistory(this.history) : this.history;
 
     // Deep copy the history to avoid mutating the history outside of the
     // chat session.