fix(gateway): treat all fetch failed TypeErrors as transient

When a TypeError("fetch failed") from undici had a cause with an
unrecognized error code, isTransientNetworkError() would recurse into
the cause, fail to match, and return false — causing the gateway to
exit via process.exit(1).

Since the outer TypeError("fetch failed") already indicates a
network-level failure, treat it as transient unconditionally regardless
of the cause chain contents.

Added tests for fetch failures with unrecognized cause and no cause.

Fixes #4425

src/infra/unhandled-rejections.fatal-detection.test.ts

@@ -114,6 +114,32 @@ describe("installUnhandledRejectionHandler - fatal detection", () => {
       );
     });
 
+    it("does NOT exit on undici fetch failures with unrecognized cause", () => {
+      const fetchErr = Object.assign(new TypeError("fetch failed"), {
+        cause: new Error("some unknown undici error"),
+      });
+
+      process.emit("unhandledRejection", fetchErr, Promise.resolve());
+
+      expect(exitCalls).toEqual([]);
+      expect(consoleWarnSpy).toHaveBeenCalledWith(
+        "[openclaw] Non-fatal unhandled rejection (continuing):",
+        expect.stringContaining("fetch failed"),
+      );
+    });
+
+    it("does NOT exit on undici fetch failures without cause", () => {
+      const fetchErr = new TypeError("fetch failed");
+
+      process.emit("unhandledRejection", fetchErr, Promise.resolve());
+
+      expect(exitCalls).toEqual([]);
+      expect(consoleWarnSpy).toHaveBeenCalledWith(
+        "[openclaw] Non-fatal unhandled rejection (continuing):",
+        expect.stringContaining("fetch failed"),
+      );
+    });
+
     it("does NOT exit on DNS resolution failures", () => {
       const dnsErr = Object.assign(new Error("DNS resolve failed"), {
         code: "UND_ERR_DNS_RESOLVE_FAILED",

src/infra/unhandled-rejections.ts

@@ -81,10 +81,10 @@ export function isTransientNetworkError(err: unknown): boolean {
   const code = extractErrorCodeWithCause(err);
   if (code && TRANSIENT_NETWORK_CODES.has(code)) return true;
 
-  // "fetch failed" TypeError from undici (Node's native fetch)
+  // "fetch failed" TypeError from undici (Node's native fetch).
+  // Always treat as transient — the cause may carry an unknown code
+  // but the outer TypeError already indicates a network-level failure.
   if (err instanceof TypeError && err.message === "fetch failed") {
-    const cause = getErrorCause(err);
-    if (cause) return isTransientNetworkError(cause);
     return true;
   }