feat: harden gemini provider path

apps/cli/src/test/kotlin/dev/diff2test/android/cli/D2tConfigTest.kt

@@ -163,6 +163,27 @@ class D2tConfigTest {
         assertContains(report, "Supported now: yes")
     }
 
+    @Test
+    fun `defaults gemini config to native generate content protocol`() {
+        val configFile = Files.createTempFile("d2t-gemini-config", ".toml")
+        Files.writeString(
+            configFile,
+            """
+            [ai]
+            provider = "gemini"
+            """.trimIndent(),
+        )
+        val loadResult = loadConfig(configFile)
+        val resolved = resolveAiConfiguration(loadResult, mapOf("GEMINI_API_KEY" to "sk-gem"))
+
+        assertEquals(AiProvider.GEMINI, resolved?.provider)
+        assertEquals(AiProtocol.GEMINI_GENERATE_CONTENT, resolved?.protocol)
+        assertEquals("GEMINI_API_KEY", resolved?.apiKeyEnv)
+        assertEquals("gemini-2.5-pro", resolved?.model)
+        assertEquals("https://generativelanguage.googleapis.com/v1beta", resolved?.baseUrl)
+        assertTrue(resolved?.supportedByGenerator == true)
+    }
+
     @Test
     fun `template does not include actual secrets`() {
         val template = defaultConfigTemplate()

docs/providers/gemini.md

@@ -0,0 +1,37 @@
+# Gemini Provider
+
+`d2t` supports the native Gemini GenerateContent API.
+
+## Config
+
+```toml
+[ai]
+enabled = true
+provider = "gemini"
+protocol = "gemini-generate-content"
+api_key_env = "GEMINI_API_KEY"
+model = "gemini-2.5-pro"
+base_url = "https://generativelanguage.googleapis.com/v1beta"
+connect_timeout_seconds = 30
+request_timeout_seconds = 300
+```
+
+## Environment
+
+```bash
+export GEMINI_API_KEY="..."
+```
+
+## Verify
+
+```bash
+d2t doctor
+d2t auto --ai
+```
+
+## Notes
+
+- `d2t` calls `POST /v1beta/models/{model}:generateContent`
+- authentication is sent with `x-goog-api-key`
+- the request asks Gemini for JSON output with the generated test schema
+- use `--strict-ai` if you want the command to fail instead of falling back when AI generation is rejected

modules/test-generator/src/test/kotlin/dev/diff2test/android/testgenerator/OpenAiResponsesTestGeneratorTest.kt

@@ -224,6 +224,30 @@ class OpenAiResponsesTestGeneratorTest {
         assertEquals(listOf("gemini"), payload.warnings)
     }
 
+    @Test
+    fun `gemini generator sends native header to generate content endpoint`() {
+        val capture = RequestCapture()
+        val generator = GeminiGenerateContentTestGenerator(
+            config = GeminiGenerateContentConfig(
+                apiKey = "sk-gem",
+                model = "gemini-2.5-pro",
+                baseUrl = "https://generativelanguage.googleapis.com/v1beta",
+            ),
+            httpClient = capturingHttpClient(capture, 200, geminiResponseBody()),
+        )
+
+        val bundle = generator.generate(plan(), context(), analysis())
+
+        assertContains(bundle.files.single().content, "class SignUpViewModelGeneratedTest")
+        val request = assertNotNull(capture.request)
+        assertEquals(
+            "https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-pro:generateContent",
+            request.uri().toString(),
+        )
+        assertEquals("sk-gem", request.headers().firstValue("x-goog-api-key").orElse(null))
+        assertEquals("application/json", request.headers().firstValue("Accept").orElse(null))
+    }
+
     @Test
     fun `normalizes junit test imports to kotlin test`() {
         val content = """
@@ -677,6 +701,22 @@ class OpenAiResponsesTestGeneratorTest {
         }
     }
 
+    private fun geminiResponseBody(): String = """
+        {
+          "candidates": [
+            {
+              "content": {
+                "parts": [
+                  {
+                    "text": "{\"content\":\"package com.example.auth\\n\\nclass SignUpViewModelGeneratedTest\",\"warnings\":[]}"
+                  }
+                ]
+              }
+            }
+          ]
+        }
+    """.trimIndent()
+
     private fun anthropicResponseBody(): String = """
         {
           "content": [