Input processor for removing empty toolcall list from input

[przepeck]

🛠 Summary

CVS-190935
We are removing empty tool call lists from messages to prevent rendering it in input e.g.

[...]
<role>assistant
<|tool_call_start|>[]<|tool_call_end|>
[...]

It will help us, to not implement the same workaround in chat templates.

🧪 Checklist

• Unit tests added.
• The documentation updated.
• Change follows security best practices.
  ``

[Copilot]

Pull request overview

This PR adds an input-processing step to sanitize chat messages by removing empty "tool_calls": [] entries from ov::genai::ChatHistory, preventing empty tool-call blocks from being rendered downstream (e.g., by chat templates).

Changes:

• Added EmptyToolCallsArrayRemovingProcessor to remove empty tool_calls arrays from chat-history messages.
• Wired the new processor into the chat-path InputProcessor chain early in processing.
• Added a new gtest suite covering empty vs non-empty tool_calls behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/test/llm/input_processing/empty_tool_calls_array_removing_processor_test.cpp	Adds unit tests for the new processor behavior.
src/llm/io_processing/input_processors/empty_tool_calls_array_removing_processor.hpp	Declares the new processor (doc comment currently mismatches implementation).
src/llm/io_processing/input_processors/empty_tool_calls_array_removing_processor.cpp	Implements removal of empty tool_calls arrays from ChatHistory.
src/llm/io_processing/input_processor.cpp	Inserts the new processor into the chat-path processing chain.
src/llm/BUILD	Adds the new processor sources/headers to the Bazel target.

[mzegla]

Do we want this processor to be unconditional? Like not tied to chat template caps?
I wonder if resolving this won't introduce another problem when we get chat template that always expects something in the tool calls and empty array would be somewhat expected.

[przepeck]

Do we want this processor to be unconditional? Like not tied to chat template caps? I wonder if resolving this won't introduce another problem when we get chat template that always expects something in the tool calls and empty array would be somewhat expected.

In that scenario usual curl request e.g. {type:"text", content:"Hello"} would fail, I don't think that is possible for chat template to be that bad.

[mzegla]

Okay, we can always adjust if such template appears. Let's move forward.