fix(scout-agent): make context length exceeded error detection more reliable (#223)

Author: hugodutka

packages/scout-agent/lib/compaction.test.ts

@@ -11,7 +11,6 @@ import {
   maxConsecutiveCompactionAttempts,
   createCompactionMarkerPart,
   createCompactionTool,
-  findAPICallError,
   findCompactionSummary,
   isOutOfContextError,
   MAX_CONSECUTIVE_COMPACTION_ATTEMPTS,
@@ -77,60 +76,6 @@ describe("isOutOfContextError", () => {
       true
     );
   });
-
-  test("returns true for APICallError in cause chain", () => {
-    const apiError = createApiError("max_tokens_exceeded");
-    const wrapper = new Error("Gateway error");
-    (wrapper as { cause?: unknown }).cause = apiError;
-    expect(isOutOfContextError(wrapper)).toBe(true);
-  });
-
-  test("returns false for APICallError with unrelated message", () => {
-    expect(isOutOfContextError(createApiError("authentication failed"))).toBe(
-      false
-    );
-  });
-
-  test("returns false for non-APICallError even if message matches pattern", () => {
-    expect(isOutOfContextError(new Error("context_length_exceeded"))).toBe(
-      false
-    );
-    expect(isOutOfContextError("input too long")).toBe(false);
-  });
-});
-
-describe("findAPICallError", () => {
-  const createApiError = (message: string) =>
-    new APICallError({
-      message,
-      url: "https://api.example.com",
-      requestBodyValues: {},
-      statusCode: 400,
-    });
-
-  test("returns the APICallError when provided directly", () => {
-    const error = createApiError("test");
-    expect(findAPICallError(error)).toBe(error);
-  });
-
-  test("returns APICallError from single-level cause", () => {
-    const apiError = createApiError("test");
-    const wrapper = new Error("wrapper");
-    (wrapper as { cause?: unknown }).cause = apiError;
-    expect(findAPICallError(wrapper)).toBe(apiError);
-  });
-
-  test("returns APICallError from deep cause chain", () => {
-    const apiError = createApiError("test");
-    const wrapper = { cause: { cause: apiError } };
-    expect(findAPICallError(wrapper)).toBe(apiError);
-  });
-
-  test("returns null when no APICallError present", () => {
-    expect(findAPICallError(new Error("other"))).toBeNull();
-    expect(findAPICallError("string")).toBeNull();
-    expect(findAPICallError(null)).toBeNull();
-  });
 });
 
 describe("createCompactionTool", () => {

packages/scout-agent/lib/compaction.ts

@@ -1,6 +1,5 @@
 import util from "node:util";
 import {
-  APICallError,
   type StreamTextTransform,
   type TextStreamPart,
   type Tool,
@@ -29,47 +28,32 @@ const OUT_OF_CONTEXT_PATTERNS = [
   /maximum.*tokens/i,
 ];
 
-/**
- * Recursively search for an APICallError in the error's cause chain.
- */
-export function findAPICallError(error: unknown): APICallError | null {
-  if (APICallError.isInstance(error)) {
-    return error;
-  }
-  if (error && typeof error === "object" && "cause" in error) {
-    const cause = (error as { cause?: unknown }).cause;
-    return findAPICallError(cause);
-  }
-  return null;
-}
-
 /**
  * Check if an error is an out-of-context error based on known patterns.
  *
  * TODO: the current patterns only really handle anthropic via the vercel
  * gateway - we need to test with other providers.
  */
 export function isOutOfContextError(error: unknown): boolean {
-  const apiError = findAPICallError(error);
-  if (!apiError) {
-    return false;
-  }
-  let textToTest = apiError.responseBody ?? "";
-  // even though typings say message is always a string, empirically it's not always a string
-  if (!textToTest && typeof apiError.message === "string") {
-    textToTest = apiError.message;
-  }
-  if (!textToTest) {
+  let textToTest = "";
+  if (typeof error === "string") {
+    textToTest = error;
+  } else if (error instanceof Error) {
+    textToTest = error.message;
+  } else {
     try {
-      textToTest = JSON.stringify(apiError);
+      textToTest = JSON.stringify(error, null, 2);
     } catch {
       // note: util.inspect returns different values in Bun and Node.js
       // in Node.js it includes the error message, in Bun it ~sometimes~ doesn't.
       // that's why it's the final fallback
-      textToTest = util.inspect(apiError, { depth: null });
+      textToTest = util.inspect(error, { depth: null });
     }
   }
-  return OUT_OF_CONTEXT_PATTERNS.some((pattern) => pattern.test(textToTest));
+  const lines = textToTest.split("\n");
+  return OUT_OF_CONTEXT_PATTERNS.some((pattern) =>
+    lines.some((line) => pattern.test(line))
+  );
 }
 
 /**