Add test coverage for indexer/export-csv.mjs

[Spagero763]

Context

The CSV export script has no tests. See indexer/export-csv.mjs and the existing test style in indexer/index.test.mjs.

Acceptance criteria

• A test runs the export against a small fixture of indexed events and asserts the CSV output (header, row count, correct field values).

Per CONTRIBUTING.md: one concern, tests required for behaviour changes. CI gate: cargo fmt / cargo clippy --all-targets -- -D warnings / cargo test for Rust, npm run build for the sdk/app.

[mxrtins04]

Hi maintainer, can i be assigned this issue pleasee?

[Bug00Joe]

Hi, I will like to take this on.

I have experience with Node.js testing and data pipeline validation, so this seems like a good fit.

Plan: add tests for export-csv.mjs, following the existing style in index.test.mjs. I'll run the export against a small fixture of indexed events and assert the CSV output — correct header, row count, and field values.

Will follow CONTRIBUTING.md (one concern per PR, tests for behavior changes) and make sure npm run build passes as part of CI. Would appreciate being assigned this one. Thanks!

[grantfox-oss]

🦊 GrantFox — @Bug00Joe has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #335)
2. Your PR will be reviewed by the tributary-protocol maintainers

Good luck! Track your progress on GrantFox.