refactor: dedupe provider usage fetch logic and tests

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

@@ -0,0 +1,39 @@
+import { describe, expect, it } from "vitest";
+import { createProviderUsageFetch, makeResponse } from "../test-utils/provider-usage-fetch.js";
+import { fetchGeminiUsage } from "./provider-usage.fetch.gemini.js";
+
+describe("fetchGeminiUsage", () => {
+  it("returns HTTP errors for failed requests", async () => {
+    const mockFetch = createProviderUsageFetch(async () =>
+      makeResponse(429, { error: "rate_limited" }),
+    );
+    const result = await fetchGeminiUsage("token", 5000, mockFetch, "google-gemini-cli");
+
+    expect(result.error).toBe("HTTP 429");
+    expect(result.windows).toHaveLength(0);
+  });
+
+  it("selects the lowest remaining fraction per model family", async () => {
+    const mockFetch = createProviderUsageFetch(async (_url, init) => {
+      const headers = (init?.headers as Record<string, string> | undefined) ?? {};
+      expect(headers.Authorization).toBe("Bearer token");
+
+      return makeResponse(200, {
+        buckets: [
+          { modelId: "gemini-pro", remainingFraction: 0.8 },
+          { modelId: "gemini-pro-preview", remainingFraction: 0.3 },
+          { modelId: "gemini-flash", remainingFraction: 0.7 },
+          { modelId: "gemini-flash-latest", remainingFraction: 0.9 },
+          { modelId: "gemini-unknown", remainingFraction: 0.5 },
+        ],
+      });
+    });
+
+    const result = await fetchGeminiUsage("token", 5000, mockFetch, "google-gemini-cli");
+
+    expect(result.windows).toHaveLength(2);
+    expect(result.windows[0]).toEqual({ label: "Pro", usedPercent: 70 });
+    expect(result.windows[1]?.label).toBe("Flash");
+    expect(result.windows[1]?.usedPercent).toBeCloseTo(30, 6);
+  });
+});