diff --git a/src/process/ProviderDeadline.test.ts b/src/process/ProviderDeadline.test.ts
index ca83d98ab7..6f26c870e1 100644
--- a/src/process/ProviderDeadline.test.ts
+++ b/src/process/ProviderDeadline.test.ts
@@ -1,8 +1,106 @@
-import { afterEach, expect, it, vi } from "vitest";
+import { afterEach, beforeEach, expect, it, vi } from "vitest";
 import { ProviderStartupDeadline } from "./ProviderDeadline.js";
 
+beforeEach(() => {
+  vi.useFakeTimers({
+    toFake: ["setTimeout", "clearTimeout", "Date", "performance"],
+  });
+});
+
 afterEach(() => {
   vi.restoreAllMocks();
+  vi.useRealTimers();
+});
+
+it.each([-3_600_000, 3_600_000])(
+  "keeps the elapsed budget when the wall clock jumps by %i ms",
+  async (jump) => {
+    const deadline = new ProviderStartupDeadline(1000);
+    try {
+      await vi.advanceTimersByTimeAsync(250);
+      vi.setSystemTime(Date.now() + jump);
+      expect(deadline.remainingMs()).toBe(750);
+      expect(deadline.interruption).toBeUndefined();
+      expect(deadline.signal.aborted).toBe(false);
+      const waiting = deadline.wait(2000);
+      await vi.advanceTimersByTimeAsync(749);
+      expect(deadline.interruption).toBeUndefined();
+      await vi.advanceTimersByTimeAsync(1);
+      await expect(waiting).resolves.toBe("aborted");
+      expect(deadline.interruption).toBe("timeout");
+      expect(deadline.remainingMs()).toBe(0);
+      expect(vi.getTimerCount()).toBe(0);
+    } finally {
+      deadline.dispose();
+    }
+  },
+);
+
+it("preserves caller cancellation after a forward wall-clock correction", async () => {
+  const controller = new AbortController();
+  const reason = new Error("caller cancelled");
+  const deadline = new ProviderStartupDeadline(1000, controller.signal);
+  try {
+    const waiting = deadline.wait(1000);
+    await vi.advanceTimersByTimeAsync(100);
+    vi.setSystemTime(Date.now() + 3_600_000);
+    controller.abort(reason);
+    await expect(waiting).resolves.toBe("aborted");
+    expect(deadline.interruption).toBe("cancelled");
+    expect(deadline.signal.reason).toBe(reason);
+    expect(vi.getTimerCount()).toBe(0);
+  } finally {
+    deadline.dispose();
+  }
+});
+
+it("does not revive an expired budget after the wall clock moves backward", async () => {
+  const deadline = new ProviderStartupDeadline(1000);
+  try {
+    await vi.advanceTimersByTimeAsync(1000);
+    vi.setSystemTime(Date.now() - 3_600_000);
+    expect(deadline.remainingMs()).toBe(0);
+    expect(deadline.interruption).toBe("timeout");
+    await expect(deadline.wait(1000)).resolves.toBe("aborted");
+    expect(vi.getTimerCount()).toBe(0);
+  } finally {
+    deadline.dispose();
+  }
+});
+
+it("classifies elapsed time before a delayed timer callback and a later abort", () => {
+  const controller = new AbortController();
+  const deadline = new ProviderStartupDeadline(1000, controller.signal);
+  try {
+    // Model an event-loop stall: elapsed time advanced, but timers have not run.
+    vi.spyOn(performance, "now").mockReturnValue(1001);
+    vi.setSystemTime(Date.now() - 3_600_000);
+    expect(deadline.interruption).toBe("timeout");
+    expect(deadline.remainingMs()).toBe(0);
+    controller.abort();
+    expect(deadline.interruption).toBe("timeout");
+    expect(deadline.signal.reason).toMatchObject({ name: "TimeoutError" });
+    expect(vi.getTimerCount()).toBe(0);
+  } finally {
+    deadline.dispose();
+  }
+});
+
+it("keeps remaining milliseconds integral for downstream request budgets", () => {
+  const now = vi.spyOn(performance, "now").mockReturnValue(10.25);
+  const deadline = new ProviderStartupDeadline(1000);
+  try {
+    now.mockReturnValue(260.5);
+    expect(deadline.remainingMs()).toBe(750);
+    now.mockReturnValue(1010.2);
+    expect(deadline.remainingMs()).toBe(1);
+    expect(deadline.interruption).toBeUndefined();
+    now.mockReturnValue(1010.25);
+    expect(deadline.remainingMs()).toBe(0);
+    expect(deadline.interruption).toBe("timeout");
+  } finally {
+    deadline.dispose();
+  }
 });
 
 it("keeps remaining time and cancellation classification stable across wall-clock jumps", () => {
@@ -24,6 +122,7 @@ it("keeps remaining time and cancellation classification stable across wall-cloc
 });
 
 it("aborts a bounded wait when its real monotonic deadline expires", async () => {
+  vi.useRealTimers();
   const deadline = new ProviderStartupDeadline(40);
   try {
     await expect(deadline.wait(500)).resolves.toBe("aborted");