fix: detect GEMINI_API_KEY/.env and parse current Gemini stream schema

The benchmark adapter only recognized GOOGLE_API_KEY and parsed the legacy
text/usage event shape. Recognize GEMINI_API_KEY and ~/.gemini/.env, parse
the current content/stats schema, ignore echoed user messages, and run
report-only plan mode with --skip-trust for disposable workspaces.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/gemini-benchmark-adapter.test.ts

@@ -0,0 +1,47 @@
+import { describe, expect, test } from 'bun:test';
+import { parseGeminiStreamJson } from '../lib/model-benchmark/providers/gemini';
+
+describe('parseGeminiStreamJson', () => {
+  test('parses the current Gemini CLI content/stats schema', () => {
+    const raw = [
+      JSON.stringify({ type: 'init', model: 'auto' }),
+      JSON.stringify({ type: 'message', role: 'user', content: 'ignore me' }),
+      JSON.stringify({ type: 'message', role: 'assistant', content: 'real output' }),
+      JSON.stringify({ type: 'tool_use', tool_name: 'read_file' }),
+      JSON.stringify({
+        type: 'result',
+        stats: {
+          input_tokens: 101,
+          output_tokens: 17,
+          models: { 'gemini-3.1-flash-lite': { api: { totalRequests: 1 } } },
+        },
+      }),
+    ].join('\n');
+
+    expect(parseGeminiStreamJson(raw)).toEqual({
+      output: 'real output',
+      tokens: { input: 101, output: 17 },
+      toolCalls: 1,
+      modelUsed: 'gemini-3.1-flash-lite',
+    });
+  });
+
+  test('retains compatibility with legacy text/usage fields', () => {
+    const raw = [
+      JSON.stringify({ type: 'init', model: 'gemini-2.5-pro' }),
+      JSON.stringify({ type: 'message', role: 'assistant', text: 'legacy output' }),
+      JSON.stringify({
+        type: 'result',
+        usage: { input_token_count: 23, output_token_count: 5 },
+      }),
+      '{malformed',
+    ].join('\n');
+
+    expect(parseGeminiStreamJson(raw)).toEqual({
+      output: 'legacy output',
+      tokens: { input: 23, output: 5 },
+      toolCalls: 0,
+      modelUsed: 'gemini-2.5-pro',
+    });
+  });
+});