KG-487 Add handler for GooglePart.InlineData (#1094)

YouTrack link:
https://youtrack.jetbrains.com/issue/KG-487/GoogleLLMClient-does-not-support-InlineData-part-type
#954

## Motivation and Context

Currently, `GoogleLLMClient` throws an `IllegalStateException: Not
supported part type: InlineData` when processing responses from Gemini
models that return binary content, such as images (e.g., from
`gemini-2.5-flash-image`). This crash occurs because the
`processGoogleCandidate` function lacks a handler for the
`GooglePart.InlineData` type.

This PR adds the necessary logic to correctly parse `InlineData` parts
into `Message.Assistant` messages containing either `ContentPart.Image`
or `ContentPart.File`, allowing the client to support multimodal
responses from Google's API.

## >> Important Note <<
`gemini-2.5-flash-image` is not in GoogleModels.kt and therefor nor
officially supported yet. For that reason there are only unit tests for
the `InlineData` handler in this PR. I would be open to add this Model
but best to open a separate Issue for it and discuss.

## Breaking Changes
None. This change is a non-breaking bug fix that adds support for a
previously unhandled response type. Existing functionality is
unaffected.

Co-authored-by: Malte Heuser <[email protected]>
Co-authored-by: Konstantin Pavlov <[email protected]>

Author: 3 people

prompt/prompt-executor/prompt-executor-clients/prompt-executor-google-client/src/commonMain/kotlin/ai/koog/prompt/executor/clients/google/GoogleLLMClient.kt

@@ -601,7 +601,7 @@ public open class GoogleLLMClient(
      * @return A list of response messages
      */
     @OptIn(ExperimentalUuidApi::class)
-    private fun processGoogleCandidate(candidate: GoogleCandidate, metaInfo: ResponseMetaInfo): List<Message.Response> {
+    internal fun processGoogleCandidate(candidate: GoogleCandidate, metaInfo: ResponseMetaInfo): List<Message.Response> {
         val parts = candidate.content?.parts.orEmpty()
         val responses = mutableListOf<Message.Response>()
         with(responses) {
@@ -646,6 +646,29 @@ public open class GoogleLLMClient(
                         )
                     )
 
+                    is GooglePart.InlineData -> {
+                        val inlineData = part.inlineData
+                        val contentPart = when (val mimeType = inlineData.mimeType) {
+                            "image/png", "image/jpeg", "image/webp" -> ContentPart.Image(
+                                content = AttachmentContent.Binary.Bytes(inlineData.data),
+                                format = mimeType.substringAfter("image/"),
+                                mimeType = mimeType,
+                            )
+                            else -> ContentPart.File(
+                                content = AttachmentContent.Binary.Bytes(inlineData.data),
+                                mimeType = mimeType,
+                                format = mimeType.substringAfterLast('.'),
+                            )
+                        }
+                        add(
+                            Message.Assistant(
+                                parts = listOf(contentPart),
+                                finishReason = candidate.finishReason,
+                                metaInfo = metaInfo
+                            )
+                        )
+                    }
+
                     else -> error("Not supported part type: $part")
                 }
             }

prompt/prompt-executor/prompt-executor-clients/prompt-executor-google-client/src/jvmTest/kotlin/ai/koog/prompt/executor/clients/google/GoogleLLMClientTest.kt

@@ -4,10 +4,19 @@ import ai.koog.agents.core.tools.ToolDescriptor
 import ai.koog.agents.core.tools.ToolParameterDescriptor
 import ai.koog.agents.core.tools.ToolParameterType
 import ai.koog.prompt.dsl.Prompt
+import ai.koog.prompt.executor.clients.google.models.GoogleCandidate
+import ai.koog.prompt.executor.clients.google.models.GoogleContent
+import ai.koog.prompt.executor.clients.google.models.GoogleData
 import ai.koog.prompt.executor.clients.google.models.GoogleFunctionCallingMode
+import ai.koog.prompt.executor.clients.google.models.GooglePart
 import ai.koog.prompt.executor.clients.google.models.GoogleThinkingConfig
+import ai.koog.prompt.message.AttachmentContent
+import ai.koog.prompt.message.ContentPart
+import ai.koog.prompt.message.Message
+import ai.koog.prompt.message.ResponseMetaInfo
 import ai.koog.prompt.params.LLMParams
 import io.kotest.matchers.collections.shouldContain
+import io.kotest.matchers.collections.shouldHaveSize
 import io.kotest.matchers.shouldBe
 import io.kotest.matchers.shouldNotBe
 import kotlinx.serialization.json.JsonObject
@@ -325,4 +334,54 @@ class GoogleLLMClientTest {
         fc!!.mode shouldBe GoogleFunctionCallingMode.ANY
         fc.allowedFunctionNames shouldBe listOf("weather")
     }
+
+    @Test
+    fun `processGoogleCandidate should handle InlineData image part`() {
+        val client = GoogleLLMClient(apiKey = "apiKey")
+        val imageData = "png-bytes".encodeToByteArray()
+        val candidate = GoogleCandidate(
+            content = GoogleContent(
+                role = "model",
+                parts = listOf(
+                    GooglePart.InlineData(
+                        inlineData = GoogleData.Blob("image/png", imageData)
+                    )
+                )
+            )
+        )
+
+        val responses = client.processGoogleCandidate(candidate, ResponseMetaInfo.Empty)
+
+        responses shouldHaveSize 1
+        val assistantMessage = responses.single() as Message.Assistant
+        assistantMessage.parts shouldHaveSize 1
+        val imagePart = assistantMessage.parts.single() as ContentPart.Image
+        imagePart.format shouldBe "png"
+        (imagePart.content as AttachmentContent.Binary.Bytes).asBytes() shouldBe imageData
+    }
+
+    @Test
+    fun `processGoogleCandidate should handle InlineData generic file part`() {
+        val client = GoogleLLMClient(apiKey = "apiKey")
+        val fileData = "pdf-bytes".encodeToByteArray()
+        val candidate = GoogleCandidate(
+            content = GoogleContent(
+                role = "model",
+                parts = listOf(
+                    GooglePart.InlineData(
+                        inlineData = GoogleData.Blob("application/pdf", fileData)
+                    )
+                )
+            )
+        )
+
+        val responses = client.processGoogleCandidate(candidate, ResponseMetaInfo.Empty)
+
+        responses shouldHaveSize 1
+        val assistantMessage = responses.single() as Message.Assistant
+        assistantMessage.parts shouldHaveSize 1
+        val filePart = assistantMessage.parts.single() as ContentPart.File
+        filePart.mimeType shouldBe "application/pdf"
+        (filePart.content as AttachmentContent.Binary.Bytes).asBytes() shouldBe fileData
+    }
 }