Fix(gateway): Prevent crash on unhandled fetch rejections (close #3974)

src/infra/unhandled-rejections.test.ts

@@ -87,6 +87,18 @@ describe("isTransientNetworkError", () => {
     expect(isTransientNetworkError(error)).toBe(true);
   });
 
+  it("returns true for fetch failed with unknown cause (Regression Test for #3974)", () => {
+    // Simulate Cause with NO code
+    const causeNoCode = new Error("Some obscure network error");
+    const errorNoCode = Object.assign(new TypeError("fetch failed"), { cause: causeNoCode });
+    expect(isTransientNetworkError(errorNoCode)).toBe(true);
+
+    // Simulate Cause with UNKNOWN code
+    const causeUnknown = Object.assign(new Error("Unknown"), { code: "UNKNOWN_123" });
+    const errorUnknown = Object.assign(new TypeError("fetch failed"), { cause: causeUnknown });
+    expect(isTransientNetworkError(errorUnknown)).toBe(true);
+  });
+
   it("returns true for nested cause chain with network error", () => {
     const innerCause = Object.assign(new Error("connection reset"), { code: "ECONNRESET" });
     const outerCause = Object.assign(new Error("wrapper"), { cause: innerCause });

src/infra/unhandled-rejections.ts

@@ -83,8 +83,14 @@ export function isTransientNetworkError(err: unknown): boolean {
 
   // "fetch failed" TypeError from undici (Node's native fetch)
   if (err instanceof TypeError && err.message === "fetch failed") {
+    // Almost all cases of "fetch failed" are network related (DNS, timeout, connection refuse).
+    // If we can't determine otherwise, assume transient to prevent crashing the gateway.
     const cause = getErrorCause(err);
-    if (cause) return isTransientNetworkError(cause);
+    if (cause) {
+      if (isTransientNetworkError(cause)) return true;
+      // If cause exists but isn't explicitly fatal, treat "fetch failed" as transient
+      if (!isFatalError(cause) && !isConfigError(cause)) return true;
+    }
     return true;
   }