feat: support passing images in Tool results

[anakin87]

Related Issues

• part of Investigate support for images in ToolCallResult #9432

Proposed Changes:

• expand ToolCallResult.result to not only accepts str but also list[TextContent|ImageContent]
• modify OpenAIResponsesChatGenerator to handle this. (Haven't implemented in OpenAIChatGenerator since the Chat Completions API only accept str in Tool results).
• add outputs_to_result initialization parameter to Tool (similar to existing parameters), to allow returning the raw Tool result (instead of stringifying it) and optionally transforming it
• add the same parameter to ComponentTool and PipelineTool
• refactor ToolInvoker to support this feature

How did you test it?

CI, added several tests

A simple end-to-end example can also be found in tests:

haystack/test/components/generators/chat/test_openai_responses.py

Line 885 in 59e38ab

def test_live_run_agent_with_images_in_tool_result(self, test_files_path):

Notes for the reviewer

Opened this PR to get feedback. Something is still missing.

• Tested with Anthropic: wip: Anthropic support imgs tool results haystack-core-integrations#2769. Bedrock should be similar. I am also confident that the current abstractions can work with Gemini and other providers when they support this feature.
• Missing:
  • release note
  • support new ToolCallResult in Jinja2 ChatMessage extension - not needed but in general we tried to keep feature parity between the ChatMessage dataclass and the extension
  • new small section in documentation

Checklist

• I have read the contributors guidelines and the code of conduct.
• I have updated the related issue with new insights and changes.
• I have added unit tests and updated the docstrings.
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test: and added ! in case the PR includes breaking changes.
• I have documented my code.
• I have added a release note file, following the contributors guidelines.
• I have run pre-commit hooks and fixed any issue.

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Project	Deployment	Review	Updated (UTC)
haystack-docs	Ready	Preview, Comment	Jan 21, 2026 2:59pm

[coveralls]

Pull Request Test Coverage Report for Build 21214269984

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 32 unchanged lines in 6 files lost coverage.
• Overall coverage increased (+0.1%) to 92.394%

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Files with Coverage Reduction	New Missed Lines	%
components/generators/chat/openai_responses.py	2	87.38%
dataclasses/chat_message.py	3	99.08%
tools/pipeline_tool.py	5	85.0%
tools/tool.py	6	95.8%
tools/component_tool.py	7	92.78%
components/tools/tool_invoker.py	9	96.45%

Totals
Change from base Build 21212784205:	0.1%
Covered Lines:	14492
Relevant Lines:	15685

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💛 - Coveralls