From 50c5f7590449dd01145f0d30e7ace48b41307576 Mon Sep 17 00:00:00 2001
From: Tak Hoffman <781889+Takhoffman@users.noreply.github.com>
Date: Sun, 22 Feb 2026 20:13:21 -0600
Subject: [PATCH] Compaction: sanitize token split accounting (#24058)

* Compaction: sanitize token split accounting

* Tests/Compaction: type sanitize token estimate callback
---
 src/agents/compaction.token-sanitize.test.ts | 52 ++++++++++++++++++++
 src/agents/compaction.ts                     |  8 ++-
 2 files changed, 58 insertions(+), 2 deletions(-)
 create mode 100644 src/agents/compaction.token-sanitize.test.ts

diff --git a/src/agents/compaction.token-sanitize.test.ts b/src/agents/compaction.token-sanitize.test.ts
new file mode 100644
index 000000000..f7fad927f
--- /dev/null
+++ b/src/agents/compaction.token-sanitize.test.ts
@@ -0,0 +1,52 @@
+import type { AgentMessage } from "@mariozechner/pi-agent-core";
+import { describe, expect, it, vi } from "vitest";
+
+const piCodingAgentMocks = vi.hoisted(() => ({
+  estimateTokens: vi.fn((_message: unknown) => 1),
+  generateSummary: vi.fn(async () => "summary"),
+}));
+
+vi.mock("@mariozechner/pi-coding-agent", async () => {
+  const actual = await vi.importActual<typeof import("@mariozechner/pi-coding-agent")>(
+    "@mariozechner/pi-coding-agent",
+  );
+  return {
+    ...actual,
+    estimateTokens: piCodingAgentMocks.estimateTokens,
+    generateSummary: piCodingAgentMocks.generateSummary,
+  };
+});
+
+import { chunkMessagesByMaxTokens, splitMessagesByTokenShare } from "./compaction.js";
+
+describe("compaction token accounting sanitization", () => {
+  it("does not pass toolResult.details into per-message token estimates", () => {
+    const messages: AgentMessage[] = [
+      {
+        role: "toolResult",
+        toolCallId: "call_1",
+        toolName: "browser",
+        isError: false,
+        content: [{ type: "text", text: "ok" }],
+        details: { raw: "x".repeat(50_000) },
+        timestamp: 1,
+        // oxlint-disable-next-line typescript/no-explicit-any
+      } as any,
+      {
+        role: "user",
+        content: "next",
+        timestamp: 2,
+      },
+    ];
+
+    splitMessagesByTokenShare(messages, 2);
+    chunkMessagesByMaxTokens(messages, 16);
+
+    const calledWithDetails = piCodingAgentMocks.estimateTokens.mock.calls.some((call) => {
+      const message = call[0] as { details?: unknown } | undefined;
+      return Boolean(message?.details);
+    });
+
+    expect(calledWithDetails).toBe(false);
+  });
+});
diff --git a/src/agents/compaction.ts b/src/agents/compaction.ts
index ba9870afe..da83723c3 100644
--- a/src/agents/compaction.ts
+++ b/src/agents/compaction.ts
@@ -23,6 +23,10 @@ export function estimateMessagesTokens(messages: AgentMessage[]): number {
   return safe.reduce((sum, message) => sum + estimateTokens(message), 0);
 }
 
+function estimateCompactionMessageTokens(message: AgentMessage): number {
+  return estimateMessagesTokens([message]);
+}
+
 function normalizeParts(parts: number, messageCount: number): number {
   if (!Number.isFinite(parts) || parts <= 1) {
     return 1;
@@ -49,7 +53,7 @@ export function splitMessagesByTokenShare(
   let currentTokens = 0;
 
   for (const message of messages) {
-    const messageTokens = estimateTokens(message);
+    const messageTokens = estimateCompactionMessageTokens(message);
     if (
       chunks.length < normalizedParts - 1 &&
       current.length > 0 &&
@@ -93,7 +97,7 @@ export function chunkMessagesByMaxTokens(
   let currentTokens = 0;
 
   for (const message of messages) {
-    const messageTokens = estimateTokens(message);
+    const messageTokens = estimateCompactionMessageTokens(message);
     if (currentChunk.length > 0 && currentTokens + messageTokens > effectiveMax) {
       chunks.push(currentChunk);
       currentChunk = [];