From 20db67b89b3e2054ab365fe44fbe5dfc5c4164a5 Mon Sep 17 00:00:00 2001
From: Nicolas Meienberger <github@thisprops.com>
Date: Sat, 21 Mar 2026 20:37:13 +0100
Subject: [PATCH] refactor: limit stderr length to 50 lines

---
 app/server/utils/__tests__/spawn.test.ts | 11 ++++++++++-
 packages/core/src/utils/spawn.ts         | 13 +++++++++----
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/app/server/utils/__tests__/spawn.test.ts b/app/server/utils/__tests__/spawn.test.ts
index 66164c42..8066a442 100644
--- a/app/server/utils/__tests__/spawn.test.ts
+++ b/app/server/utils/__tests__/spawn.test.ts
@@ -206,7 +206,7 @@ describe("safeSpawn", () => {
 			expect(result.error).toBe("err_last");
 		});
 
-		test("stderr keeps the full stderr output", async () => {
+		test("stderr keeps the captured stderr output", async () => {
 			const result = await safeSpawn({
 				command: "sh",
 				args: ["-c", "echo err_first >&2 && echo err_last >&2 && exit 1"],
@@ -215,6 +215,15 @@ describe("safeSpawn", () => {
 			expect(result.stderr).toBe("err_first\nerr_last");
 		});
 
+		test("stderr keeps only the last 50 stderr lines", async () => {
+			const result = await safeSpawn({
+				command: "sh",
+				args: ["-c", "i=1; while [ $i -le 55 ]; do echo err_$i >&2; i=$((i+1)); done; exit 1"],
+			});
+
+			expect(result.stderr).toBe(Array.from({ length: 50 }, (_, index) => `err_${index + 6}`).join("\n"));
+		});
+
 		test("returns exitCode -1 when the command is not found", async () => {
 			const result = await safeSpawn({
 				command: "this-command-does-not-exist-zerobyte",
diff --git a/packages/core/src/utils/spawn.ts b/packages/core/src/utils/spawn.ts
index 5d173b23..618ee7ac 100644
--- a/packages/core/src/utils/spawn.ts
+++ b/packages/core/src/utils/spawn.ts
@@ -62,6 +62,8 @@ export type SpawnResult = {
 	stderr?: string;
 };
 
+const MAX_STDERR_LINES = 50;
+
 export function safeSpawn(params: SafeSpawnParamsLines): Promise<SpawnResult>;
 export function safeSpawn(params: SafeSpawnParamsRaw): Promise<SpawnResult>;
 export function safeSpawn(params: SafeSpawnParams): Promise<SpawnResult> {
@@ -71,7 +73,7 @@ export function safeSpawn(params: SafeSpawnParams): Promise<SpawnResult> {
 
 	let lastStdout = "";
 	let lastStderr = "";
-	let stderr = "";
+	const stderrLines: string[] = [];
 
 	return new Promise<SpawnResult>((resolve) => {
 		const child = spawn(command, args, {
@@ -103,7 +105,10 @@ export function safeSpawn(params: SafeSpawnParams): Promise<SpawnResult> {
 
 		rlErr.on("line", (line) => {
 			if (onStderr) onStderr(line);
-			stderr += `${line}\n`;
+			stderrLines.push(line);
+			if (stderrLines.length > MAX_STDERR_LINES) {
+				stderrLines.shift();
+			}
 			const trimmed = line.trim();
 			if (trimmed.length > 0) {
 				lastStderr = line;
@@ -118,7 +123,7 @@ export function safeSpawn(params: SafeSpawnParams): Promise<SpawnResult> {
 				exitCode: -1,
 				summary: lastStdout,
 				error: err.message || lastStderr,
-				stderr: stderr.trim(),
+				stderr: stderrLines.join("\n"),
 			});
 		});
 
@@ -127,7 +132,7 @@ export function safeSpawn(params: SafeSpawnParams): Promise<SpawnResult> {
 				exitCode: code ?? -1,
 				summary: lastStdout,
 				error: lastStderr,
-				stderr: stderr.trim(),
+				stderr: stderrLines.join("\n"),
 			});
 		});
 	});