From f5f39f08f1c3914c43e009fd864f1bd72ef2aa07 Mon Sep 17 00:00:00 2001
From: Mario Zechner <badlogicgames@gmail.com>
Date: Mon, 29 Dec 2025 21:34:50 +0100
Subject: [PATCH] Use token-based maxTokens instead of fraction-based
 reserveFraction

- BranchSummarySettings.maxTokens (default 100000) instead of reserveFraction
- More intuitive and consistent with CompactionSettings.keepRecentTokens
---
 packages/coding-agent/src/core/agent-session.ts      |  2 +-
 .../src/core/compaction/branch-summarization.ts      | 12 ++++--------
 packages/coding-agent/src/core/settings-manager.ts   |  6 +++---
 3 files changed, 8 insertions(+), 12 deletions(-)

diff --git a/packages/coding-agent/src/core/agent-session.ts b/packages/coding-agent/src/core/agent-session.ts
index 24f182c6..eaca341c 100644
--- a/packages/coding-agent/src/core/agent-session.ts
+++ b/packages/coding-agent/src/core/agent-session.ts
@@ -1656,7 +1656,7 @@ export class AgentSession {
 				apiKey,
 				signal: this._branchSummaryAbortController.signal,
 				customInstructions: options.customInstructions,
-				reserveFraction: branchSummarySettings.reserveFraction,
+				maxTokens: branchSummarySettings.maxTokens,
 			});
 			this._branchSummaryAbortController = undefined;
 			if (result.aborted) {
diff --git a/packages/coding-agent/src/core/compaction/branch-summarization.ts b/packages/coding-agent/src/core/compaction/branch-summarization.ts
index f621518e..c303ca08 100644
--- a/packages/coding-agent/src/core/compaction/branch-summarization.ts
+++ b/packages/coding-agent/src/core/compaction/branch-summarization.ts
@@ -53,8 +53,8 @@ export interface GenerateBranchSummaryOptions {
 	signal: AbortSignal;
 	/** Optional custom instructions for summarization */
 	customInstructions?: string;
-	/** Reserve this fraction of context window for summary (default 0.2) */
-	reserveFraction?: number;
+	/** Maximum tokens to include in summary context (default 100000) */
+	maxTokens?: number;
 }
 
 // ============================================================================
@@ -321,13 +321,9 @@ export async function generateBranchSummary(
 	entries: SessionEntry[],
 	options: GenerateBranchSummaryOptions,
 ): Promise<BranchSummaryResult> {
-	const { model, apiKey, signal, customInstructions, reserveFraction = 0.2 } = options;
+	const { model, apiKey, signal, customInstructions, maxTokens = 100000 } = options;
 
-	// Calculate token budget (leave room for summary generation)
-	const contextWindow = model.contextWindow || 128000;
-	const tokenBudget = Math.floor(contextWindow * (1 - reserveFraction));
-
-	const { messages, fileOps } = prepareBranchEntries(entries, tokenBudget);
+	const { messages, fileOps } = prepareBranchEntries(entries, maxTokens);
 
 	if (messages.length === 0) {
 		return { summary: "No content to summarize" };
diff --git a/packages/coding-agent/src/core/settings-manager.ts b/packages/coding-agent/src/core/settings-manager.ts
index b957fd51..737a812e 100644
--- a/packages/coding-agent/src/core/settings-manager.ts
+++ b/packages/coding-agent/src/core/settings-manager.ts
@@ -9,7 +9,7 @@ export interface CompactionSettings {
 }
 
 export interface BranchSummarySettings {
-	reserveFraction?: number; // default: 0.2 (fraction of context window reserved for summary)
+	maxTokens?: number; // default: 100000 (max tokens to include in branch summary context)
 }
 
 export interface RetrySettings {
@@ -260,9 +260,9 @@ export class SettingsManager {
 		};
 	}
 
-	getBranchSummarySettings(): { reserveFraction: number } {
+	getBranchSummarySettings(): { maxTokens: number } {
 		return {
-			reserveFraction: this.settings.branchSummary?.reserveFraction ?? 0.2,
+			maxTokens: this.settings.branchSummary?.maxTokens ?? 100000,
 		};
 	}