feat(anthropic): add fine-grained tool streaming support

docs/providers/anthropic.md

@@ -235,6 +235,29 @@ foreach ($stream as $event) {
 }
 ```
 
+### Fine-grained tool streaming
+
+Anthropic’s [fine-grained tool streaming](https://docs.anthropic.com/en/docs/agents-and-tools/tool-use/fine-grained-tool-streaming) lets tool-use input arrive incrementally (with lower latency for large arguments) instead of waiting for a complete JSON payload. Enable it on each tool that should use this behavior with the `eager_input_streaming` provider option:
+
+```php
+use Prism\Prism\Facades\Prism;
+use Prism\Prism\Tool;
+
+$weatherTool = Tool::as('get_weather')
+    ->for('Get current weather for a location')
+    ->withStringParameter('location', 'The city and state')
+    ->withProviderOptions(['eager_input_streaming' => true])
+    ->using(fn (string $location): string => "Weather in {$location}: 72°F, sunny");
+
+$stream = Prism::text()
+    ->using('anthropic', 'claude-sonnet-4-5-20250929')
+    ->withTools([$weatherTool])
+    ->withPrompt('What is the weather in San Francisco?')
+    ->asStream();
+```
+
+Use this together with a streaming entrypoint (`asStream()`, `asEventStreamResponse()`, etc.). While the model is still emitting a tool call, streamed input may be partial JSON; only treat tool arguments as final once the stream indicates the tool input is complete.
+
 For complete streaming documentation including Vercel Data Protocol and WebSocket broadcasting, see [Streaming Output](/core-concepts/streaming-output).
 
 ## Documents

src/Providers/Anthropic/Maps/ToolMap.php

@@ -30,6 +30,7 @@ public static function map(array $tools): array
                 ],
                 'cache_control' => self::normalizeCacheControl($tool),
                 'strict' => (bool) $tool->providerOptions('strict'),
+                'eager_input_streaming' => (bool) $tool->providerOptions('eager_input_streaming'),
             ]);
         }, $tools);
     }

tests/Providers/Anthropic/ToolMapTest.php

@@ -58,3 +58,45 @@
     'ephemeral',
     AnthropicCacheType::Ephemeral->value,
 ]);
+
+it('sets eager_input_streaming when eager_input_streaming provider option is true on tool', function (): void {
+    $tool = (new Tool)
+        ->as('search')
+        ->for('Searching the web')
+        ->withStringParameter('query', 'the detailed search query')
+        ->using(fn (): string => '[Search results]')
+        ->withProviderOptions(['eager_input_streaming' => true]);
+
+    expect(ToolMap::map([$tool]))->toBe([[
+        'name' => 'search',
+        'description' => 'Searching the web',
+        'input_schema' => [
+            'type' => 'object',
+            'properties' => [
+                'query' => [
+                    'description' => 'the detailed search query',
+                    'type' => 'string',
+                ],
+            ],
+            'required' => ['query'],
+        ],
+        'eager_input_streaming' => true,
+    ]]);
+});
+
+it('omits eager_input_streaming when eager_input_streaming provider option is omitted or false', function (?bool $eagerInputStreaming): void {
+    $tool = (new Tool)
+        ->as('search')
+        ->for('Searching the web')
+        ->withStringParameter('query', 'the detailed search query')
+        ->using(fn (): string => '[Search results]');
+
+    if ($eagerInputStreaming !== null) {
+        $tool = $tool->withProviderOptions(['eager_input_streaming' => $eagerInputStreaming]);
+    }
+
+    expect(ToolMap::map([$tool])[0])->not->toHaveKey('eager_input_streaming');
+})->with([
+    'omitted' => [null],
+    'false' => [false],
+]);