feat: replace SerpApi web search with Mistral native web_search tool

MistralClient gains generateWithWebSearch() which uses Mistral's built-in
web_search tool, handling the multi-turn tool-call loop server-side.
SerpApiWebSearch and WebSearchInterface are removed — no longer needed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/Infrastructure/AI/MistralClient.php

@@ -66,6 +66,59 @@ final class MistralClient implements OllamaClientInterface
         return $data['choices'][0]['message']['content'];
     }
 
+    /**
+     * Chat completion with Mistral's built-in web_search tool enabled.
+     * Mistral executes searches server-side; we handle the multi-turn loop if needed.
+     */
+    public function generateWithWebSearch(string $model, string $prompt): string
+    {
+        $messages = [['role' => 'user', 'content' => $prompt]];
+
+        $response = $this->httpClient->request('POST', $this->mistralBaseUrl.'/v1/chat/completions', [
+            'headers' => ['Authorization' => 'Bearer '.$this->mistralApiKey],
+            'json' => [
+                'model' => $model,
+                'tools' => [['type' => 'web_search']],
+                'messages' => $messages,
+            ],
+            'timeout' => 120,
+        ]);
+
+        /** @var array{choices: array{0: array{finish_reason: string, message: array{content: ?string, tool_calls?: list<array{id: string, function: array{name: string, arguments: string}}>}}}} $data */
+        $data = $response->toArray();
+        $choice = $data['choices'][0];
+
+        if ('tool_calls' !== $choice['finish_reason']) {
+            return (string) $choice['message']['content'];
+        }
+
+        // Append assistant's tool call turn, then return empty tool results so
+        // Mistral's servers can complete the search and produce the final answer.
+        $messages[] = $choice['message'];
+        foreach ($choice['message']['tool_calls'] ?? [] as $toolCall) {
+            $messages[] = [
+                'role' => 'tool',
+                'tool_call_id' => $toolCall['id'],
+                'content' => '',
+            ];
+        }
+
+        $final = $this->httpClient->request('POST', $this->mistralBaseUrl.'/v1/chat/completions', [
+            'headers' => ['Authorization' => 'Bearer '.$this->mistralApiKey],
+            'json' => [
+                'model' => $model,
+                'tools' => [['type' => 'web_search']],
+                'messages' => $messages,
+            ],
+            'timeout' => 120,
+        ]);
+
+        /** @var array{choices: array{0: array{message: array{content: string}}}} $finalData */
+        $finalData = $final->toArray();
+
+        return $finalData['choices'][0]['message']['content'];
+    }
+
     private function guessMimeType(string $path): string
     {
         return match (strtolower(pathinfo($path, PATHINFO_EXTENSION))) {

src/Infrastructure/Search/SerpApiWebSearch.php

@@ -1,48 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace App\Infrastructure\Search;
-
-use Symfony\Contracts\HttpClient\HttpClientInterface;
-
-final class SerpApiWebSearch implements WebSearchInterface
-{
-    public function __construct(
-        private readonly HttpClientInterface $httpClient,
-        private readonly string $serpApiKey,
-    ) {
-    }
-
-    public function search(string $query): string
-    {
-        $response = $this->httpClient->request('GET', 'https://serpapi.com/search', [
-            'query' => [
-                'q' => $query,
-                'api_key' => $this->serpApiKey,
-                'num' => 5,
-                'hl' => 'de',
-            ],
-            'timeout' => 15,
-        ]);
-
-        /** @var array{organic_results?: list<array{title?: string, snippet?: string}>} $data */
-        $data = $response->toArray();
-
-        $results = $data['organic_results'] ?? [];
-        if ([] === $results) {
-            return '';
-        }
-
-        $texts = [];
-        foreach ($results as $result) {
-            $title = $result['title'] ?? '';
-            $snippet = $result['snippet'] ?? '';
-            if ('' !== $title || '' !== $snippet) {
-                $texts[] = $title."\n".$snippet;
-            }
-        }
-
-        return implode("\n\n", $texts);
-    }
-}

src/Infrastructure/Search/WebSearchInterface.php

@@ -1,10 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace App\Infrastructure\Search;
-
-interface WebSearchInterface
-{
-    public function search(string $query): string;
-}