feat(anthropic): add anthropic_server_tools to AnthropicChatGenerator

[Aftabbs]

Summary

Closes #2724

AnthropicChatGenerator currently validates that all items in tools are Tool or Toolset instances, which prevents users from passing Anthropic's native server-side tools (web search, computer use, etc.). This PR adds an anthropic_server_tools parameter that accepts raw dicts and forwards them directly to the Anthropic API alongside any function tools.

Root Cause

Anthropic's messages.create API accepts two categories of tools:

1. Custom function tools — validated and converted by haystack's Tool/Toolset machinery
2. Built-in server-side tools (e.g. {"type": "web_search_20250305"}) — these bypass function-call dispatch and are handled entirely by the Anthropic backend

The existing tools parameter only supports category 1. Users who tried to pass raw dicts got a TypeError: Items in the tools list must be Tool or Toolset instances.

Changes

File	What changed
chat_generator.py	Added anthropic_server_tools: list[dict[str, Any]] | None = None parameter; stored, serialized, and appended to the tools list in _prepare_request_params
test_chat_generator.py	Updated 3 existing serde tests to include the new param; added 5 new unit tests

Usage

from haystack_integrations.components.generators.anthropic import AnthropicChatGenerator

generator = AnthropicChatGenerator(
    model="claude-sonnet-4-5",
    anthropic_server_tools=[{"type": "web_search_20250305"}],
)
result = generator.run(messages=[...])

Function tools and server-side tools can also be combined:

generator = AnthropicChatGenerator(
    tools=[my_function_tool],
    anthropic_server_tools=[{"type": "web_search_20250305"}],
)

Testing

• Existing tests pass (updated test_to_dict_default, test_to_dict_with_parameters, test_serde_in_pipeline for new param)
• New test: test_init_with_anthropic_server_tools — verifies parameter is stored
• New test: test_to_dict_with_anthropic_server_tools — verifies serialization round-trip
• New test: test_from_dict_with_anthropic_server_tools — verifies deserialization
• New test: test_run_with_anthropic_server_tools — verifies server tools are passed to messages.create
• New test: test_run_with_tools_and_anthropic_server_tools — verifies mixed function + server tools

Impact

Users can now use Anthropic's native web search and other built-in tools directly in Haystack pipelines without hacks. The parameter is fully serializable, so pipelines that use it can be saved and reloaded via pipeline.to_dict() / Pipeline.from_dict().

[github-actions]

Heads-up for maintainers

This PR is from a fork and touches integrations whose integration tests require API keys.
Those tests are skipped in CI because fork PRs don't have access to repo secrets for security reasons.

Affected integrations:

• anthropic

Please run the integration tests locally (hatch run test:integration inside each folder) before approving.

[davidsbatista]

@Aftabbs, I see you have three PRs open, I was reviewing one, which is still under review with failing tests and with changes requests. I kindly ask you to focus on that PR before opening new ones.

[anakin87]

Thanks for this PR!

Tests are failing.
Please make them pass then ping me to get a review.