From 761177c8c4a8e96ca112ef03e1805ba18bfa3ccf Mon Sep 17 00:00:00 2001
From: mastertyko <11311479+mastertyko@users.noreply.github.com>
Date: Sun, 12 Apr 2026 18:14:03 +0200
Subject: [PATCH] fix(pi-coding-agent): use safe compaction role markers

---
 .../src/core/compaction-utils.test.ts         | 50 +++++++++++++++++++
 .../src/core/compaction/utils.ts              | 10 ++--
 2 files changed, 55 insertions(+), 5 deletions(-)
 create mode 100644 packages/pi-coding-agent/src/core/compaction-utils.test.ts

diff --git a/packages/pi-coding-agent/src/core/compaction-utils.test.ts b/packages/pi-coding-agent/src/core/compaction-utils.test.ts
new file mode 100644
index 000000000..87fd3d3fb
--- /dev/null
+++ b/packages/pi-coding-agent/src/core/compaction-utils.test.ts
@@ -0,0 +1,50 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import type { Message } from "@gsd/pi-ai";
+
+import { serializeConversation } from "./compaction/index.js";
+
+test("serializeConversation uses narrative role markers instead of chat-style delimiters (#4054)", () => {
+	const messages: Message[] = [
+		{ role: "user", content: "Please refactor the parser." } as Message,
+		{
+			role: "assistant",
+			content: [
+				{ type: "thinking", thinking: "I should inspect the parser entry points first." },
+				{ type: "text", text: "I'll start with the parser entry points." },
+				{ type: "toolCall", id: "tool-1", name: "Read", arguments: { path: "src/parser.ts" } },
+			],
+			api: "anthropic-messages",
+			provider: "anthropic",
+			model: "claude-sonnet-4-6",
+			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(),
+		} as Message,
+		{
+			role: "toolResult",
+			content: [{ type: "text", text: "parser contents" }],
+			toolName: "Read",
+			toolCallId: "tool-1",
+		} as Message,
+	];
+
+	const serialized = serializeConversation(messages);
+
+	assert.match(serialized, /\*\*User said:\*\* Please refactor the parser\./);
+	assert.match(serialized, /\*\*Assistant thinking:\*\* I should inspect the parser entry points first\./);
+	assert.match(serialized, /\*\*Assistant responded:\*\* I'll start with the parser entry points\./);
+	assert.match(serialized, /\*\*Assistant tool calls:\*\* Read\(path="src\/parser\.ts"\)/);
+	assert.match(serialized, /\*\*Tool result:\*\* parser contents/);
+	assert.ok(!serialized.includes("[User]:"), "chat-style [User]: markers should not remain");
+	assert.ok(!serialized.includes("[Assistant]:"), "chat-style [Assistant]: markers should not remain");
+	assert.ok(!serialized.includes("[Tool result]:"), "chat-style [Tool result]: markers should not remain");
+});
diff --git a/packages/pi-coding-agent/src/core/compaction/utils.ts b/packages/pi-coding-agent/src/core/compaction/utils.ts
index 86fc21a2d..95cf42555 100644
--- a/packages/pi-coding-agent/src/core/compaction/utils.ts
+++ b/packages/pi-coding-agent/src/core/compaction/utils.ts
@@ -218,7 +218,7 @@ export function serializeConversation(messages: Message[]): string {
 							.filter((c): c is { type: "text"; text: string } => c.type === "text")
 							.map((c) => c.text)
 							.join("");
-			if (content) parts.push(`[User]: ${content}`);
+			if (content) parts.push(`**User said:** ${content}`);
 		} else if (msg.role === "assistant") {
 			const textParts: string[] = [];
 			const thinkingParts: string[] = [];
@@ -239,13 +239,13 @@ export function serializeConversation(messages: Message[]): string {
 			}
 
 			if (thinkingParts.length > 0) {
-				parts.push(`[Assistant thinking]: ${thinkingParts.join("\n")}`);
+				parts.push(`**Assistant thinking:** ${thinkingParts.join("\n")}`);
 			}
 			if (textParts.length > 0) {
-				parts.push(`[Assistant]: ${textParts.join("\n")}`);
+				parts.push(`**Assistant responded:** ${textParts.join("\n")}`);
 			}
 			if (toolCalls.length > 0) {
-				parts.push(`[Assistant tool calls]: ${toolCalls.join("; ")}`);
+				parts.push(`**Assistant tool calls:** ${toolCalls.join("; ")}`);
 			}
 		} else if (msg.role === "toolResult") {
 			const content = msg.content
@@ -253,7 +253,7 @@ export function serializeConversation(messages: Message[]): string {
 				.map((c) => c.text)
 				.join("");
 			if (content) {
-				parts.push(`[Tool result]: ${truncateForSummary(content, TOOL_RESULT_MAX_CHARS)}`);
+				parts.push(`**Tool result:** ${truncateForSummary(content, TOOL_RESULT_MAX_CHARS)}`);
 			}
 		}
 	}