[gemini] Fix HTTP 400 when using tool calling with thinking models (#21097)

* [gemini] Fix HTTP 400 when using tool calling with thinking models

Signed-off-by: Florian Hotze <dev@florianhotze.com>

bundles/org.openhab.binding.gemini/src/main/java/org/openhab/binding/gemini/internal/api/GeminiApiClient.java

@@ -51,7 +51,6 @@ import org.openhab.binding.gemini.internal.api.dto.response.GeminiModelsResponse
 import org.openhab.binding.gemini.internal.api.dto.response.GeminiResponse;
 import org.openhab.core.voice.text.conversation.Conversation;
 import org.openhab.core.voice.text.interpreter.llm.LLMTool;
-import org.openhab.core.voice.text.interpreter.llm.LLMToolCall;
 import org.openhab.core.voice.text.interpreter.llm.LLMToolParam;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -105,7 +104,7 @@ public class GeminiApiClient {
         GeminiContent systemInstruction = createSystemInstruction(systemMessage);
 
         // Contents
-        GeminiPart userPart = new GeminiPart(prompt, null, null, null);
+        GeminiPart userPart = new GeminiPart(prompt, null, null, null, null);
         GeminiContent userContent = new GeminiContent(ROLE_USER, List.of(userPart));
 
         // Config
@@ -141,21 +140,21 @@ public class GeminiApiClient {
         for (Conversation.Message msg : history) {
             switch (msg.role()) {
                 case USER: {
-                    GeminiPart part = new GeminiPart(msg.content(), null, null, null);
+                    GeminiPart part = new GeminiPart(msg.content(), null, null, null, null);
-                    contents.add(new GeminiContent(ROLE_USER, List.of(part)));
+                    contents.add(new GeminiContent(ROLE_USER, new ArrayList<>(List.of(part))));
                     break;
                 }
                 case OPENHAB: {
-                    GeminiPart part = new GeminiPart(msg.content(), null, null, null);
+                    GeminiPart part = new GeminiPart(msg.content(), null, null, null, null);
-                    contents.add(new GeminiContent(ROLE_MODEL, List.of(part)));
+                    contents.add(new GeminiContent(ROLE_MODEL, new ArrayList<>(List.of(part))));
                     break;
                 }
                 case TOOL_CALL: {
-                    LLMToolCall toolCall = LLMToolCall.fromJson(msg.content());
+                    GeminiLLMToolCall toolCall = GeminiLLMToolCall.fromJson(msg.content());
-                    String name = toolCall.tool().replaceAll("[^a-zA-Z0-9_-]", "_");
+                    String name = toolCall.tool.replaceAll("[^a-zA-Z0-9_-]", "_");
                     pendingToolCallNames.add(name);
-                    GeminiFunctionCall fc = new GeminiFunctionCall(name, toolCall.params());
+                    GeminiFunctionCall fc = new GeminiFunctionCall(name, toolCall.params, toolCall.id);
-                    GeminiPart part = new GeminiPart(null, fc, null, null);
+                    GeminiPart part = new GeminiPart(null, fc, null, null, toolCall.thoughtSignature);
                     contents.add(new GeminiContent(ROLE_MODEL, List.of(part)));
                     break;
                 }
@@ -166,8 +165,21 @@ public class GeminiApiClient {
                         break; // TOOL_RETURN without preceding TOOL_CALL - ignore
                     }
                     GeminiFunctionResponse fr = new GeminiFunctionResponse(name, Map.of("result", msg.content()));
-                    GeminiPart part = new GeminiPart(null, null, fr, null);
+                    GeminiPart part = new GeminiPart(null, null, fr, null, null);
-                    contents.add(new GeminiContent(ROLE_USER, List.of(part)));
+
+                    // Consolidate consecutive TOOL_RETURNs into the same ROLE_USER content
+                    if (!contents.isEmpty() && ROLE_USER.equals(contents.getLast().role())) {
+                        GeminiContent lastContent = contents.getLast();
+                        List<GeminiPart> lastParts = lastContent.parts();
+                        if (lastParts != null && !lastParts.isEmpty()
+                                && lastParts.getFirst().functionResponse() != null) {
+                            lastParts.add(part);
+                        } else {
+                            contents.add(new GeminiContent(ROLE_USER, new ArrayList<>(List.of(part))));
+                        }
+                    } else {
+                        contents.add(new GeminiContent(ROLE_USER, new ArrayList<>(List.of(part))));
+                    }
                     break;
                 }
                 case THINKING:
@@ -356,7 +368,7 @@ public class GeminiApiClient {
 
     private @Nullable GeminiContent createSystemInstruction(@Nullable String systemMessage) {
         if (systemMessage != null && !systemMessage.isBlank()) {
-            GeminiPart sysPart = new GeminiPart(systemMessage, null, null, null);
+            GeminiPart sysPart = new GeminiPart(systemMessage, null, null, null, null);
             return new GeminiContent(null, List.of(sysPart));
         }
         return null;

bundles/org.openhab.binding.gemini/src/main/java/org/openhab/binding/gemini/internal/api/GeminiLLMToolCall.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright (c) 2010-2026 Contributors to the openHAB project
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.openhab.binding.gemini.internal.api;
+
+import java.util.Map;
+
+import org.eclipse.jdt.annotation.NonNullByDefault;
+import org.eclipse.jdt.annotation.Nullable;
+import org.openhab.core.voice.text.interpreter.llm.LLMToolCall;
+
+import com.google.gson.JsonSyntaxException;
+
+/**
+ * A DTO to store information about a Gemini tool call.
+ * Extends {@link LLMToolCall} with additional fields required by the Gemini API.
+ *
+ * @author Florian Hotze - Initial contribution
+ */
+@NonNullByDefault
+public class GeminiLLMToolCall extends LLMToolCall {
+    public final @Nullable String id;
+    public final @Nullable String thoughtSignature;
+
+    public GeminiLLMToolCall(String tool, Map<String, Object> params, @Nullable String id,
+            @Nullable String thoughtSignature) {
+        super(tool, params);
+        this.id = id;
+        this.thoughtSignature = thoughtSignature;
+    }
+
+    public static GeminiLLMToolCall fromJson(String json) throws JsonSyntaxException {
+        GeminiLLMToolCall call = GSON.fromJson(json, GeminiLLMToolCall.class);
+        if (call == null) {
+            throw new JsonSyntaxException("Deserialized GeminiLLMToolCall is null.");
+        }
+        if (call.tool == null || call.params == null) {
+            throw new JsonSyntaxException("Deserialized GeminiLLMToolCall has null tool or params.");
+        }
+        return call;
+    }
+}

bundles/org.openhab.binding.gemini/src/main/java/org/openhab/binding/gemini/internal/api/dto/GeminiFunctionCall.java

@@ -27,5 +27,5 @@ import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
  */
 @JsonIgnoreProperties(ignoreUnknown = true)
 @NonNullByDefault
-public record GeminiFunctionCall(@Nullable String name, @Nullable Map<String, Object> args) {
+public record GeminiFunctionCall(@Nullable String name, @Nullable Map<String, Object> args, @Nullable String id) {
 }

bundles/org.openhab.binding.gemini/src/main/java/org/openhab/binding/gemini/internal/api/dto/GeminiPart.java

@@ -27,5 +27,6 @@ import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
 @JsonIgnoreProperties(ignoreUnknown = true)
 @NonNullByDefault
 public record GeminiPart(@Nullable String text, @Nullable GeminiFunctionCall functionCall,
-        @Nullable GeminiFunctionResponse functionResponse, @Nullable Boolean thought) {
+        @Nullable GeminiFunctionResponse functionResponse, @Nullable Boolean thought,
+        @Nullable String thoughtSignature) {
 }

bundles/org.openhab.binding.gemini/src/main/java/org/openhab/binding/gemini/internal/hli/GeminiHLIService.java

@@ -28,6 +28,7 @@ import org.openhab.binding.gemini.internal.GeminiConfiguration;
 import org.openhab.binding.gemini.internal.GeminiHandler;
 import org.openhab.binding.gemini.internal.api.GeminiApiClient;
 import org.openhab.binding.gemini.internal.api.GeminiApiException;
+import org.openhab.binding.gemini.internal.api.GeminiLLMToolCall;
 import org.openhab.binding.gemini.internal.api.dto.GeminiContent;
 import org.openhab.binding.gemini.internal.api.dto.GeminiFunctionCall;
 import org.openhab.binding.gemini.internal.api.dto.GeminiPart;
@@ -43,7 +44,6 @@ import org.openhab.core.voice.text.conversation.Conversation;
 import org.openhab.core.voice.text.conversation.ConversationException;
 import org.openhab.core.voice.text.conversation.ConversationRole;
 import org.openhab.core.voice.text.interpreter.llm.LLMTool;
-import org.openhab.core.voice.text.interpreter.llm.LLMToolCall;
 import org.openhab.core.voice.text.interpreter.llm.LLMToolException;
 import org.osgi.framework.Bundle;
 import org.osgi.framework.BundleContext;
@@ -252,8 +252,8 @@ public class GeminiHLIService implements ThingHandlerService, HumanLanguageInter
                         String toolName = fc.name();
                         Map<String, Object> args = fc.args();
 
-                        LLMToolCall llmToolCall = new LLMToolCall(toolName != null ? toolName : "",
+                        GeminiLLMToolCall llmToolCall = new GeminiLLMToolCall(toolName != null ? toolName : "",
-                                args != null ? args : new HashMap<>());
+                                args != null ? args : new HashMap<>(), fc.id(), part.thoughtSignature());
                         try {
                             conversation.addMessage(ConversationRole.TOOL_CALL, llmToolCall.toJson());
                         } catch (ConversationException e) {