[codex] Add display fields to arrivals

[gtokman]

Summary

Adds display-oriented arrival fields to mta-js so clients can render destination labels without decoding raw GTFS direction details.

Changes

• Adds optional destination and displayDirection fields to Arrival.
• Populates those fields for direct subway arrivals from static GTFS trip headsigns.
• Populates those fields for direct BusTime arrivals from DestinationName.
• Normalizes rider-facing L train east/west direction aliases to NYCT realtime south/north, including hosted API requests.
• Documents the preferred arrival rendering fallback.

Why

MTA subway realtime uses NYCT north/south directions even on east-west lines like the L. This makes client UIs easy to get wrong. The SDK should expose destination-ready fields and handle the common L train alias case directly.

Validation

• bun test
• bun run typecheck

[chatgpt-codex-connector]

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[Copilot]

Pull request overview

Adds destination/display-focused metadata to Arrival objects and normalizes direction inputs for the L train so client UIs can render rider-facing labels without having to interpret NYCT realtime direction quirks.

Changes:

• Extends Arrival with optional destination and displayDirection fields and populates them for subway (static GTFS trip headsign) and bus (BusTime DestinationName) arrivals.
• Normalizes L train east/west direction aliases to underlying realtime south/north directions, including hosted API requests.
• Adds README guidance and tests covering the new fields and L alias normalization.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/types.ts	Adds destination and displayDirection to the Arrival type.
README.md	Documents display-oriented arrival rendering and L direction alias behavior.
index.ts	Populates new arrival display fields; normalizes L alias directions before filtering/requests.
index.test.ts	Adds coverage for L alias normalization (local + hosted) and new arrival fields.

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.