refactor: dedupe provider usage fetch logic and tests

src/infra/provider-usage.fetch.copilot.test.ts

@@ -0,0 +1,37 @@
+import { describe, expect, it } from "vitest";
+import { createProviderUsageFetch, makeResponse } from "../test-utils/provider-usage-fetch.js";
+import { fetchCopilotUsage } from "./provider-usage.fetch.copilot.js";
+
+describe("fetchCopilotUsage", () => {
+  it("returns HTTP errors for failed requests", async () => {
+    const mockFetch = createProviderUsageFetch(async () => makeResponse(500, "boom"));
+    const result = await fetchCopilotUsage("token", 5000, mockFetch);
+
+    expect(result.error).toBe("HTTP 500");
+    expect(result.windows).toHaveLength(0);
+  });
+
+  it("parses premium/chat usage from remaining percentages", async () => {
+    const mockFetch = createProviderUsageFetch(async (_url, init) => {
+      const headers = (init?.headers as Record<string, string> | undefined) ?? {};
+      expect(headers.Authorization).toBe("token token");
+      expect(headers["X-Github-Api-Version"]).toBe("2025-04-01");
+
+      return makeResponse(200, {
+        quota_snapshots: {
+          premium_interactions: { percent_remaining: 20 },
+          chat: { percent_remaining: 75 },
+        },
+        copilot_plan: "pro",
+      });
+    });
+
+    const result = await fetchCopilotUsage("token", 5000, mockFetch);
+
+    expect(result.plan).toBe("pro");
+    expect(result.windows).toEqual([
+      { label: "Premium", usedPercent: 80 },
+      { label: "Chat", usedPercent: 25 },
+    ]);
+  });
+});