Introduce AI review chat integration with Claude

Change-Id: I8bc4002c6684052c4e3c8379f4e9851538d628a6
diff --git a/ai/ai-review-agent-claude-1.0.groovy b/ai/ai-review-agent-claude-1.0.groovy
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+// Copyright (C) 2026 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+import com.gerritforge.gerrit.plugins.ai.provider.api.*
+
+import com.google.common.flogger.FluentLogger
+import com.google.gerrit.extensions.registration.DynamicSet
+import com.google.inject.*
+
+import org.apache.http.*
+import org.apache.http.message.*
+import org.apache.http.entity.StringEntity
+
+import java.nio.charset.StandardCharsets
+
+import groovy.json.*
+
+@Singleton
+class AiClaudeReviewProvider implements AiReviewProvider {
+    private static final FluentLogger logger = FluentLogger.forEnclosingClass()
+    private static final String CLAUDE_API_URL = 'https://api.anthropic.com/v1'
+    private static final String API_KEY_HEADER = 'x-api-key'
+    private static final Header ANTHROPIC_VERSION_HEADER = new BasicHeader('anthropic-version', '2023-06-01')
+    private static final int MAX_ERROR_LEN = 500
+    /*
+     * Lowest max_tokens for the current Claude models, Claude Sonnet 4.6 / Haiku 4.5
+     * Reference: https://platform.claude.com/docs/en/about-claude/models/overview
+     */
+    private static final int MAX_TOKENS = 65536
+
+    final String displayName = 'Claude'
+
+    @Inject
+    private AiHttpClient http
+
+    @Override
+    Set<String> getModels(String apiKey) {
+        try {
+            http.get(
+                    "${CLAUDE_API_URL}/models",
+                    [http.acceptApplicationJson(), apiKeyHeader(apiKey), ANTHROPIC_VERSION_HEADER] as Header[],
+                    { extractErrorMessage(it) },
+                    { extractResponseModels(it) })
+        } catch (IOException | JsonException e) {
+            logger.atWarning().withCause(e).log('Failed to call Claude API to get the list of models')
+            [] as Set
+        }
+    }
+
+
+    @Override
+    String review(String apiKey, String model, String prompt) {
+        try {
+            http.post("${CLAUDE_API_URL}/messages",
+                    [http.contentTypeApplicationJson(), apiKeyHeader(apiKey), ANTHROPIC_VERSION_HEADER] as Header[],
+                    new StringEntity(new JsonBuilder([
+                            model     : model,
+                            max_tokens: MAX_TOKENS,
+                            messages  : [
+                                    [role: 'user', content: prompt]
+                            ]
+                    ]).toString(), StandardCharsets.UTF_8),
+                    { extractErrorMessage(it) },
+                    { extractResponseText(it) })
+        }
+        catch (IOException | JsonException e) {
+            logger.atWarning().withCause(e).log('Failed to call Claude API (model=%s)', model)
+            throw new IllegalStateException('Failed to call Claude API', e)
+        }
+    }
+
+    private static Header apiKeyHeader(String apiKey) {
+        new BasicHeader(API_KEY_HEADER, apiKey)
+    }
+
+    private static String extractResponseText(String body) {
+        def json = new JsonSlurper().parseText(body)
+
+        def textContent = json.content?.find { it.type == 'text' }?.text
+
+        if (!textContent) {
+            throw new IOException('Claude API response contains no text content')
+        }
+
+        return textContent
+    }
+
+    private static Set<String> extractResponseModels(String body) {
+        def json = new JsonSlurper().parseText(body)
+
+        def modelsIds = json.data?.collect { it.id }
+
+        if (!modelsIds) {
+            throw new IOException('Claude API response contains no models')
+        }
+
+        return modelsIds as Set
+    }
+
+    private static String extractErrorMessage(String body) {
+        try {
+            def json = new JsonSlurper().parseText(body)
+            if (json?.error) return "[${json.error.type}] ${json.error.message}"
+        } catch (Exception e) {
+            logger.atWarning().withCause(e).log('Failed to parse error response')
+        }
+        return body.length() > MAX_ERROR_LEN ? "${body.take(MAX_ERROR_LEN)}..." : body
+    }
+
+}
+
+
+class AiClaudeModule extends AbstractModule {
+    @Override
+    protected void configure() {
+        DynamicSet.bind(binder(), AiReviewProvider).to(AiClaudeReviewProvider)
+    }
+}
+
+module = AiClaudeModule
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diff --git a/ai/ai-review-agent-claude.md b/ai/ai-review-agent-claude.md
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+# Gerrit AI Review Agent for Claude
+
+Implementation of Gerrit's AI Code Review Agent API on top of Anthropic's Claude.
+
+[Install](#install-in-gerrit) this plugin and enable the Gerrit AI chat to enjoy
+a side-by-side collaboration with Claude on the Change screen.
+
+## License
+
+This script is licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+## How to use
+
+### Prerequisites
+
+Gerrit v3.14 or later with the following additional plugins:
+
+- [Groovy scripting provider](https://github.com/GerritForge/groovy-provider/)
+- [GerritForge's AI Review Agent Provider](https://github.com/GerritForge/ai-review-agent-provider)
+
+### [Install in Gerrit](#install-in-gerrit)
+
+Copy the `ai-review-agent-claude-1.0.groovy` script into your Gerrit site (`$GERRIT_SITE`)
+plugins' directory.
+
+```bash
+cp ai-review-agent-claude-1.0.groovy "$GERRIT_SITE/plugins/"
+```
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