From 043756bc024afbd77aba7dbccfd5a8b86da5d6d9 Mon Sep 17 00:00:00 2001
From: diegosouzapw <8016841+diegosouzapw@users.noreply.github.com>
Date: Sat, 25 Jul 2026 18:27:58 -0300
Subject: [PATCH] feat(sse): selective upstream 4xx error passthrough util

---
 open-sse/utils/upstreamErrorPassthrough.ts    | 38 +++++++++++++++
 tests/unit/upstream-error-passthrough.test.ts | 46 +++++++++++++++++++
 2 files changed, 84 insertions(+)
 create mode 100644 open-sse/utils/upstreamErrorPassthrough.ts
 create mode 100644 tests/unit/upstream-error-passthrough.test.ts

diff --git a/open-sse/utils/upstreamErrorPassthrough.ts b/open-sse/utils/upstreamErrorPassthrough.ts
new file mode 100644
index 0000000000..651aa2f77a
--- /dev/null
+++ b/open-sse/utils/upstreamErrorPassthrough.ts
@@ -0,0 +1,38 @@
+/**
+ * Selective upstream 4xx error passthrough (Claude Code auto-recover contract).
+ *
+ * Claude Code matches the upstream error WORDING to auto-disable capabilities
+ * (thinking / output_config) for the rest of the conversation. Wrapping the body
+ * via buildErrorBody() truncates the message and breaks that recovery. For
+ * upstream-originated 4xx errors the body is the provider's public API message —
+ * not our internals — so it is safe and required to relay it verbatim.
+ * OmniRoute-generated errors MUST keep using buildErrorBody() (Hard Rule #12).
+ */
+const PASSTHROUGH_MIN = 400;
+const PASSTHROUGH_MAX = 499;
+// 401/403/407: auth-adjacent — our own credential context may leak via provider
+// echoes; keep those sanitized. 400/404/408/413/422/429 carry the capability and
+// quota wording the client needs.
+const EXCLUDED_STATUSES = new Set([401, 403, 407]);
+const INTERNAL_LEAK_RE = /\sat\s\/|node_modules|omniroute\//i;
+
+export function shouldPassthroughUpstreamError(statusCode: number, upstreamBody: unknown): boolean {
+  if (statusCode < PASSTHROUGH_MIN || statusCode > PASSTHROUGH_MAX) return false;
+  if (EXCLUDED_STATUSES.has(statusCode)) return false;
+  if (!upstreamBody || typeof upstreamBody !== "object") return false;
+  const text = JSON.stringify(upstreamBody);
+  if (INTERNAL_LEAK_RE.test(text)) return false;
+  return true;
+}
+
+export function buildPassthroughErrorResponse(
+  statusCode: number,
+  upstreamBody: unknown,
+  headers?: Record<string, string>
+): Response | null {
+  if (!shouldPassthroughUpstreamError(statusCode, upstreamBody)) return null;
+  return new Response(JSON.stringify(upstreamBody), {
+    status: statusCode,
+    headers: { "Content-Type": "application/json", ...(headers || {}) },
+  });
+}
diff --git a/tests/unit/upstream-error-passthrough.test.ts b/tests/unit/upstream-error-passthrough.test.ts
new file mode 100644
index 0000000000..cedfdfb9ea
--- /dev/null
+++ b/tests/unit/upstream-error-passthrough.test.ts
@@ -0,0 +1,46 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import {
+  shouldPassthroughUpstreamError,
+  buildPassthroughErrorResponse,
+} from "../../open-sse/utils/upstreamErrorPassthrough.ts";
+
+test("upstream error passthrough", async (t) => {
+  await t.test("4xx com corpo JSON de erro do provider é elegível", () => {
+    const body = {
+      type: "error",
+      error: { type: "invalid_request_error", message: "thinking.type: adaptive is not supported" },
+    };
+    assert.equal(shouldPassthroughUpstreamError(400, body), true);
+  });
+  await t.test("5xx NÃO é elegível (segue sanitizado)", () => {
+    assert.equal(shouldPassthroughUpstreamError(500, { error: { message: "x" } }), false);
+  });
+  await t.test("corpo com cara de vazamento interno (stack trace) NÃO é elegível", () => {
+    assert.equal(
+      shouldPassthroughUpstreamError(400, {
+        error: { message: "Error\n    at /usr/lib/node_modules/omniroute/x.js:1" },
+      }),
+      false
+    );
+  });
+  await t.test(
+    "401/407 NÃO são elegíveis (credencial nossa pode vazar em www-authenticate)",
+    () => {
+      assert.equal(shouldPassthroughUpstreamError(401, { error: { message: "bad key" } }), false);
+    }
+  );
+  await t.test("buildPassthroughErrorResponse preserva corpo byte-a-byte", async () => {
+    const body = {
+      type: "error",
+      error: { type: "invalid_request_error", message: "thinking.type: nope" },
+    };
+    const res = buildPassthroughErrorResponse(400, body);
+    assert.ok(res);
+    assert.equal(res.status, 400);
+    assert.deepEqual(await res.json(), body);
+  });
+  await t.test("retorna null quando inelegível", () => {
+    assert.equal(buildPassthroughErrorResponse(500, {}), null);
+  });
+});