fix(coding-agent): truncate tool results in compaction summarization to prevent overflow, fixes #1796

packages/coding-agent/test/compaction-serialization.test.ts

@@ -0,0 +1,79 @@
+import type { Message } from "@mariozechner/pi-ai";
+import { describe, expect, it } from "vitest";
+import { serializeConversation } from "../src/core/compaction/utils.js";
+
+describe("serializeConversation", () => {
+	it("should truncate long tool results", () => {
+		const longContent = "x".repeat(5000);
+		const messages: Message[] = [
+			{
+				role: "toolResult",
+				toolCallId: "tc1",
+				toolName: "read",
+				content: [{ type: "text", text: longContent }],
+				isError: false,
+				timestamp: Date.now(),
+			},
+		];
+
+		const result = serializeConversation(messages);
+
+		expect(result).toContain("[Tool result]:");
+		expect(result).toContain("[... 3000 more characters truncated]");
+		expect(result).not.toContain("x".repeat(3000));
+		// First 2000 chars should be present
+		expect(result).toContain("x".repeat(2000));
+	});
+
+	it("should not truncate short tool results", () => {
+		const shortContent = "x".repeat(1500);
+		const messages: Message[] = [
+			{
+				role: "toolResult",
+				toolCallId: "tc1",
+				toolName: "read",
+				content: [{ type: "text", text: shortContent }],
+				isError: false,
+				timestamp: Date.now(),
+			},
+		];
+
+		const result = serializeConversation(messages);
+
+		expect(result).toBe(`[Tool result]: ${shortContent}`);
+		expect(result).not.toContain("truncated");
+	});
+
+	it("should not truncate assistant or user messages", () => {
+		const longText = "y".repeat(5000);
+		const messages: Message[] = [
+			{
+				role: "user",
+				content: [{ type: "text", text: longText }],
+				timestamp: Date.now(),
+			},
+			{
+				role: "assistant",
+				content: [{ type: "text", text: longText }],
+				api: "anthropic",
+				provider: "anthropic",
+				model: "test",
+				usage: {
+					input: 0,
+					output: 0,
+					cacheRead: 0,
+					cacheWrite: 0,
+					totalTokens: 0,
+					cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+				},
+				stopReason: "stop",
+				timestamp: Date.now(),
+			},
+		];
+
+		const result = serializeConversation(messages);
+
+		expect(result).not.toContain("truncated");
+		expect(result).toContain(longText);
+	});
+});