From dd2fbacda9152de5244e9a1ac800b543b1d29d4e Mon Sep 17 00:00:00 2001
From: Allen Zhou <46854522+allenzhou101@users.noreply.github.com>
Date: Wed, 24 Jun 2026 11:02:37 -0700
Subject: [PATCH] fix(eve): surface gateway rejection details

Signed-off-by: Allen Zhou <46854522+allenzhou101@users.noreply.github.com>
---
 .changeset/gateway-error-detail.md            |  5 ++++
 .../eve/src/harness/model-call-error.test.ts  | 19 ++++++++++++++
 packages/eve/src/harness/model-call-error.ts  | 25 ++++++++++++++++++-
 3 files changed, 48 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/gateway-error-detail.md

diff --git a/.changeset/gateway-error-detail.md b/.changeset/gateway-error-detail.md
new file mode 100644
index 000000000..8903686b2
--- /dev/null
+++ b/.changeset/gateway-error-detail.md
@@ -0,0 +1,5 @@
+---
+"eve": patch
+---
+
+Preserve specific AI Gateway 400 rejection details in model-call failure summaries so channels surface actionable context instead of only a generic request-rejected message.
diff --git a/packages/eve/src/harness/model-call-error.test.ts b/packages/eve/src/harness/model-call-error.test.ts
index b3b3626e1..352145d08 100644
--- a/packages/eve/src/harness/model-call-error.test.ts
+++ b/packages/eve/src/harness/model-call-error.test.ts
@@ -260,6 +260,25 @@ describe("summarizeKnownModelCallRequestError", () => {
       message: "AI Gateway rejected the model request before the agent produced a response.",
     });
   });
+
+  it("keeps specific Gateway 400 rejection details in the summary", () => {
+    const summary = summarizeKnownModelCallRequestError(
+      gatewayModelCallError({
+        gatewayName: "GatewayInvalidRequestError",
+        gatewayType: "invalid_request_error",
+        statusCode: 400,
+        upstreamMessage: "input tokens exceed the model context window",
+        upstreamStatusCode: 400,
+        upstreamType: "invalid_request_error",
+      }),
+    );
+
+    expect(summary).toEqual({
+      name: "AI Gateway model request rejected",
+      message:
+        "AI Gateway rejected the model request before the agent produced a response. Gateway detail: input tokens exceed the model context window",
+    });
+  });
 });
 
 /**
diff --git a/packages/eve/src/harness/model-call-error.ts b/packages/eve/src/harness/model-call-error.ts
index 98936ffe5..cf5e13edb 100644
--- a/packages/eve/src/harness/model-call-error.ts
+++ b/packages/eve/src/harness/model-call-error.ts
@@ -2,6 +2,7 @@ import { isObject } from "#shared/guards.js";
 import type { JsonObject, JsonValue } from "#shared/json.js";
 
 const RESPONSE_BODY_SNIPPET_LIMIT = 1_000;
+const GATEWAY_REQUEST_SUMMARY_DETAIL_LIMIT = 240;
 const GATEWAY_MODEL_REQUEST_REJECTED_MESSAGE =
   "AI Gateway rejected the model request before the agent produced a response.";
 
@@ -131,13 +132,35 @@ export function summarizeKnownModelCallRequestError(
   if (signals.statusCode === 400 && isGatewayErrorSignal(signals)) {
     return {
       name: "AI Gateway model request rejected",
-      message: GATEWAY_MODEL_REQUEST_REJECTED_MESSAGE,
+      message: formatGatewayModelRequestRejectedMessage(signals),
     };
   }
 
   return null;
 }
 
+function formatGatewayModelRequestRejectedMessage(signals: ModelCallErrorSignals): string {
+  const detail = signals.upstreamMessage?.trim();
+  if (detail === undefined || detail.length === 0 || isGenericGatewayRejectionMessage(detail)) {
+    return GATEWAY_MODEL_REQUEST_REJECTED_MESSAGE;
+  }
+
+  return `${GATEWAY_MODEL_REQUEST_REJECTED_MESSAGE} Gateway detail: ${truncateSummaryDetail(
+    detail,
+  )}`;
+}
+
+function isGenericGatewayRejectionMessage(message: string): boolean {
+  return /^(bad request|internal server error)$/i.test(message.trim());
+}
+
+function truncateSummaryDetail(value: string): string {
+  if (value.length <= GATEWAY_REQUEST_SUMMARY_DETAIL_LIMIT) {
+    return value;
+  }
+  return `${value.slice(0, GATEWAY_REQUEST_SUMMARY_DETAIL_LIMIT - 1).trimEnd()}…`;
+}
+
 /**
  * Returns the distinct upstream tool types referenced by any
  * "tool type 'X' is not supported" rejection in an AI Gateway error's