fix: ensure variables passed to subgraph requests

[rawkode]

• Forward collected operation variables to each subgraph fetch.
• Previously execute_fetch_node always built HttpExecutionRequest with variables: None, so any resolver that expected arguments saw them missing, threw Variable \… not provided, and the federated response ended up as invalid JSON ({"data":,"errors":[…]}).
• Build the borrowed HashMap<&str, &sonic_rs::Value> from the query plan’s variable_values before invoking the executor so subgraphs receive the inputs they need.

[gemini-code-assist]

Summary of Changes

Hello @rawkode, 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 resolves a critical issue in the executor where subgraph requests were not correctly receiving operation variables. Previously, all subgraph fetches were initiated without variables, causing resolvers to fail and resulting in malformed federated responses. The change introduces proper forwarding of collected variables to each subgraph, ensuring that all necessary arguments are passed, thereby enabling correct execution of federated queries and maintaining the integrity of the JSON responses.

Highlights

• Variable Forwarding: Ensured that operation variables are correctly forwarded to each subgraph fetch request, resolving issues where subgraphs were not receiving necessary arguments.
• Resolver Argument Fix: Addressed a bug where resolvers expecting arguments would fail due to HttpExecutionRequest always being built with variables: None, leading to Variable ... not provided errors.
• Valid Federated Responses: Prevented federated responses from becoming invalid JSON by ensuring that subgraphs receive the inputs they need for successful execution.

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[Copilot]

Pull Request Overview

This PR fixes a critical bug where GraphQL variables were not being passed to subgraph requests during federated query execution, causing resolvers to fail with missing variable errors.

• Forward collected operation variables to each subgraph fetch request
• Replace hardcoded None variables with properly mapped variable references
• Build borrowed HashMap from query plan's variable_values for subgraph consumption

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[gemini-code-assist]

Code Review

This pull request correctly fixes an issue where variables were not being passed to subgraph requests. The change introduces logic to build and forward the operation variables to each subgraph fetch. My review includes a suggestion to optimize the creation of these variables to avoid redundant work for query plans with multiple fetch nodes.

[Copilot]

Pull Request Overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

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[rawkode]

@ardatan I've changed the select helper to return None when usages is None. This along side the correct application when usages has keys should be the behaviour we expect.

Sorry for the iterations, but I do hope this is correct now.

[ardatan]

Thanks for the PR! 🙏
The changes look good to me! After others approve, we can merge and release!