fix(flows): dedupe identical tool calls within an invocation (#3940)

[jayy-77]

Repeated tool execution can happen when the model emits the same function call multiple times (same tool name + same arguments), which is especially painful for slow or expensive tools.

This change introduces an invocation-scoped single-flight cache:

• Adds RunConfig.dedupe_tool_calls (opt-in) to reuse results for identical calls
• Always dedupes BaseTool.is_long_running tools (safer default for long ops)
• Ensures only the first execution applies tool side effects (state/artifacts)
• Emits cached responses with per-call function_response.id and debug metadata

Tests:

• Added unit tests covering duplicate calls across steps and within one step.

Link to Issue or Description of Change

1. Link to an existing issue (if applicable):

• Closes: Tool Call has been called multiple times by ADK #3940
• Related: Tool Call has been called multiple times by ADK #3940

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[gemini-code-assist]

Summary of Changes

Hello @jayy-77, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses the issue of redundant tool executions when a model repeatedly emits the same function call. By implementing an invocation-scoped caching mechanism, it significantly improves efficiency and reduces costs associated with slow or expensive tools. The changes ensure that identical tool calls are executed only once, while still providing the expected responses for all calls, and carefully manage side effects to prevent unintended multiple applications.

Highlights

• Tool Call Deduplication: Introduced an invocation-scoped single-flight cache to prevent redundant execution of identical tool calls (same tool name and arguments) within a single invocation. This is particularly beneficial for slow or expensive tools.
• Configurable Opt-in and Automatic Deduplication: Added a new dedupe_tool_calls boolean flag to RunConfig for opt-in deduplication. Additionally, tools marked as is_long_running will always be deduped by default, ensuring safer handling of long-running operations.
• Side Effect Management: Ensures that tool side effects (state or artifact deltas) are applied only once, from the first successful execution of a tool, even if subsequent identical calls are deduped.
• Cache Hit Metadata: Cached responses will now include adk_tool_call_cache_hit: True in their custom_metadata to indicate that the result was served from the cache.
• New Caching Infrastructure: Implemented a new _tool_call_cache and associated locking mechanism within InvocationContext, along with methods to canonicalize tool arguments for consistent cache keys.
• Comprehensive Unit Tests: Added new unit tests to cover scenarios where identical tool calls occur across different steps and within a single step, verifying the deduplication logic.

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[adk-bot]

Hello @jayy-77, thank you for your contribution!

Before we can merge this PR, you'll need to sign our Contributor License Agreement (CLA). You can do so here: https://cla.developers.google.com/

Response from ADK Triaging Agent

[gemini-code-assist]

Code Review

This pull request introduces a valuable feature for deduplicating identical tool calls within an invocation, which can significantly improve performance and reduce costs for slow or expensive tools. The implementation is robust, employing a single-flight pattern with asyncio.Task and proper locking to handle concurrent requests effectively. The exception handling, which clears the cache on failure, is a thoughtful addition that prevents caching failed states. The changes are well-contained, and the inclusion of unit tests covering both sequential and parallel duplicate calls is excellent. I have a couple of minor suggestions to reduce code duplication, but overall, this is a high-quality contribution.