fix(mobile): give React Native's AbortSignal throwIfAborted

apps/mobile/index.ts

@@ -1,4 +1,5 @@
 import "./src/platform/installCrypto";
+import "./src/platform/installAbortSignal";
 import "./src/background/defineNavigationTask";
 import { registerRootComponent } from "expo";
 import { App } from "./src/App";

apps/mobile/src/platform/installAbortSignal.test.ts

@@ -0,0 +1,30 @@
+import { installAbortSignal } from "./installAbortSignal";
+
+class BareSignal {
+  aborted = false;
+  reason?: unknown;
+}
+type Throwing = BareSignal & { throwIfAborted(): void };
+
+describe("installAbortSignal", () => {
+  it("adds throwIfAborted to a signal class without it", () => {
+    installAbortSignal(BareSignal);
+    const signal = new BareSignal() as Throwing;
+    expect(() => signal.throwIfAborted()).not.toThrow();
+    signal.aborted = true;
+    expect(() => signal.throwIfAborted()).toThrow(expect.objectContaining({ name: "AbortError" }));
+    const reason = new Error("timeout");
+    signal.reason = reason;
+    expect(() => signal.throwIfAborted()).toThrow(reason);
+  });
+
+  it("keeps an existing implementation", () => {
+    const own = () => undefined;
+    class Native {
+      throwIfAborted = own;
+    }
+    Object.defineProperty(Native.prototype, "throwIfAborted", { value: own });
+    installAbortSignal(Native);
+    expect(Native.prototype.throwIfAborted).toBe(own);
+  });
+});

apps/mobile/src/platform/installAbortSignal.ts

@@ -0,0 +1,28 @@
+/**
+ * Gives React Native's `AbortSignal` the `throwIfAborted()` method it lacks.
+ *
+ * The shared API client calls `signal.throwIfAborted()` after reading a
+ * response, so without it every directions, reroute and transit refresh
+ * request from the shell fails with "undefined is not a function". A runtime
+ * that already has the method keeps it.
+ */
+export function installAbortSignal(
+  ctor: { prototype: object } | undefined = globalThis.AbortSignal,
+): void {
+  if (!ctor) return;
+  const prototype = ctor.prototype as { throwIfAborted?: unknown };
+  if (typeof prototype.throwIfAborted === "function") return;
+  Object.defineProperty(prototype, "throwIfAborted", {
+    configurable: true,
+    writable: true,
+    value(this: { aborted: boolean; reason?: unknown }) {
+      if (!this.aborted) return;
+      if (this.reason !== undefined) throw this.reason;
+      const error = new Error("This operation was aborted");
+      error.name = "AbortError";
+      throw error;
+    },
+  });
+}
+
+installAbortSignal();