## Issue
Closes https://github.com/langchain4j/langchain4j/issues/4652
## Change
- Add support for `@Tool`-annotated methods to return multimodal content
(images) to the LLM, not just text. Tools can now return `Image`,
`ImageContent`, `Content`, `List<Content>`, `Content[]`, etc.
- Refactor `ToolExecutionResultMessage` to store `List<Content>`
internally instead of a plain `String`, with backward-compatible
`text()` accessor and new `contents()` / `hasSingleText()`
methods.
- Refactor `ToolExecutionResult` to support
`resultContents(List<Content>)` as an alternative to
`resultText(String)` and `resultTextSupplier(Supplier)`.
- Implement multimodal tool result mapping for providers that support
it: Anthropic, Amazon Bedrock, and Google AI Gemini.
- Add `UnsupportedFeatureException` guards in providers that do not
support non-text tool results: Azure OpenAI, GitHub Models, Jlama,
Mistral AI, Ollama, OpenAI (Chat Completions
& Responses), Vertex AI (Anthropic & Gemini), Watsonx, and Workers AI.
- Update `ToolExecutedEvent` / `DefaultToolExecutedEvent` to carry
`resultContents` alongside the existing `resultText` accessor.
- Add comprehensive unit and integration tests
(`should_execute_tool_returning_Image`,
`should_execute_tool_returning_ImageContent`,
`should_execute_tool_returning_ContentList`,
`should_fail_when_tool_returns_image_and_provider_does_not_support_it`).
- Update tools documentation with new "Returning Images and Multimodal
Content" and "Multimodal Tool Results" sections.
## General checklist
- [X] There are no breaking changes (API, behaviour)
- [X] I have added unit and/or integration tests for my change
- [X] The tests cover both positive and negative cases
- [X] I have manually run all the unit and integration tests in the
module I have added/changed, and they are all green
- [X] I have manually run all the unit and integration tests in the
[core](https://github.com/langchain4j/langchain4j/tree/main/langchain4j-core)
and
[main](https://github.com/langchain4j/langchain4j/tree/main/langchain4j)
modules, and they are all green
- [X] I have added/updated the
[documentation](https://github.com/langchain4j/langchain4j/tree/main/docs/docs)
- [ ] I have added an example in the [examples
repo](https://github.com/langchain4j/langchain4j-examples) (only for
"big" features)
- [ ] I have added/updated [Spring Boot
starter(s)](https://github.com/langchain4j/langchain4j-spring) (if
applicable)
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