fix(usage): read Gemini usageMetadata out of the antigravity response envelope

Antigravity and gemini-cli wrap their payload in { response: {...} }.
extractUsageFromResponse only tested top-level usageMetadata, so every
non-streaming antigravity request logged zero usage (IN 0 | OUT 0) and
zeroed rows in the usage dashboard. Read the envelope the same way
usageTracking.js and nonStreamingHandler.js already do; top-level
metadata keeps priority and the OpenAI/Claude branches are untouched.

Fixes #3260

open-sse/handlers/chatCore/requestDetail.js

@@ -44,13 +44,14 @@ export function extractUsageFromResponse(responseBody) {
     };
   }
 
-  // Gemini format
-  if (responseBody.usageMetadata) {
+  // Gemini format. Antigravity / gemini-cli wrap the payload in { response: {...} }.
+  const usageMetadata = responseBody.usageMetadata || responseBody.response?.usageMetadata;
+  if (usageMetadata) {
     return {
-      prompt_tokens: responseBody.usageMetadata.promptTokenCount || 0,
-      completion_tokens: responseBody.usageMetadata.candidatesTokenCount || 0,
-      cached_tokens: responseBody.usageMetadata.cachedContentTokenCount || 0,
-      reasoning_tokens: responseBody.usageMetadata.thoughtsTokenCount || 0
+      prompt_tokens: usageMetadata.promptTokenCount || 0,
+      completion_tokens: usageMetadata.candidatesTokenCount || 0,
+      cached_tokens: usageMetadata.cachedContentTokenCount || 0,
+      reasoning_tokens: usageMetadata.thoughtsTokenCount || 0
     };
   }
 

tests/unit/antigravity-nonstream-usage-3260.test.js

@@ -0,0 +1,54 @@
+import { describe, expect, it, vi } from "vitest";
+
+vi.mock("@/lib/usageDb.js", () => ({
+  appendRequestLog: vi.fn(async () => {}),
+  saveRequestDetail: vi.fn(async () => {}),
+  saveRequestUsage: vi.fn(async () => {})
+}));
+
+const { extractUsageFromResponse } = await import("../../open-sse/handlers/chatCore/requestDetail.js");
+
+const USAGE_METADATA = {
+  promptTokenCount: 1234,
+  candidatesTokenCount: 56,
+  cachedContentTokenCount: 78,
+  thoughtsTokenCount: 90,
+};
+
+const EXPECTED = {
+  prompt_tokens: 1234,
+  completion_tokens: 56,
+  cached_tokens: 78,
+  reasoning_tokens: 90,
+};
+
+describe("#3260 non-streaming usage extraction for enveloped Gemini responses", () => {
+  it("reads usageMetadata out of the antigravity { response } envelope", () => {
+    expect(extractUsageFromResponse({ response: { usageMetadata: USAGE_METADATA } })).toEqual(EXPECTED);
+  });
+
+  it("still reads a top-level usageMetadata", () => {
+    expect(extractUsageFromResponse({ usageMetadata: USAGE_METADATA })).toEqual(EXPECTED);
+  });
+
+  it("prefers the top-level metadata when both are present", () => {
+    const enveloped = { ...USAGE_METADATA, promptTokenCount: 1 };
+    const out = extractUsageFromResponse({
+      usageMetadata: USAGE_METADATA,
+      response: { usageMetadata: enveloped },
+    });
+    expect(out.prompt_tokens).toBe(1234);
+  });
+
+  it("leaves the OpenAI and Claude shapes alone", () => {
+    expect(extractUsageFromResponse({ usage: { prompt_tokens: 10, completion_tokens: 2 } }))
+      .toMatchObject({ prompt_tokens: 10, completion_tokens: 2 });
+    expect(extractUsageFromResponse({ usage: { input_tokens: 10, output_tokens: 2 } }))
+      .toMatchObject({ prompt_tokens: 10, completion_tokens: 2 });
+  });
+
+  it("returns null when there is no usage anywhere", () => {
+    expect(extractUsageFromResponse({ response: { candidates: [] } })).toBeNull();
+    expect(extractUsageFromResponse(null)).toBeNull();
+  });
+});