Longrange custom tracks throw "Symbol.iterator, e is undefined" error (works in legacy browser)

[DatViseR]

Description

When attempting to load a custom bgzipped and tabix-indexed longrange interaction track via URL, the modern WashU Epigenome Browser fails to parse the file and throws a JavaScript error.

The identical file, hosted from the identical local CORS/Range-enabled server, loads and visualizes perfectly in the Legacy WashU Epigenome Browser. Other track types (e.g., .hic and .bigwig) hosted on the exact same server load perfectly in the modern browser, ruling out CORS, preflight, or byte-range server configuration issues.

Error Message (Browser Console)

can't access property Symbol.iterator, e is undefined

Steps to Reproduce

1. Format a valid custom WashU longrange file (e.g., chr1 x1 x2 chr2:y1-y2,score).
2. Compress and index the file using standard tools (bgzip -c file.txt > file.gz and tabix -p bed file.gz).
3. Host the files (.gz and .tbi) via a local HTTP server that fully supports CORS (OPTIONS, Access-Control-Allow-*) and HTTP 206 Partial Content byte-range requests.
4. Open the Modern WashU Epigenome Browser.
5. Click Tracks -> Custom Tracks -> Add Custom Track.
6. Select longrange as the track type and provide the URL.
7. Result: Track fails to load, throwing the Symbol.iterator error.

Data Format Used

chr1	41000000	41010000	chr1:41500000-41510000,1
chr1	42000000	42010000	chr1:42500000-42510000,1

Key Diagnostic Context

• Legacy Browser: Works 100% correctly with the exact same data and URL.
• The issue appears to be a regression in the modern React/JavaScript parser, specifically handling the byte-range chunks or internal tokenisation of the longrange (or interact) format when parsing remote .gz files. --> I have no clue but this is what gemini suggests:)

Expected Behavior

The modern browser should parse the strictly formatted longrange file and render the structural arcs, identical to the correct behavior in the Legacy browser.