PPOM file uploads ignore ppom_file_upload_chunk_size and use 2mb chunks

[pirate-bot]

Summary

The ppom_file_upload_chunk_size filter (default 1mb) has no effect — the uploader always splits files into 2 MB chunks. Stores cannot control the chunk threshold.

Root cause

js/file-upload.js hardcodes chunk_size: '2mb' in the plupload config and never reads the PHP-provided file_input.chunk_size. The render path computes the filter value (templates/render-fields.php:641) but the JS ignores it. Introduced by the fields-modal refactor (#572, 34742e0); present in the 34.0.x line.

Impact

• The expected ability to tune the chunk size via the filter doesn't work.
• Notably blocks the workaround for the separate multi-chunk upload failure (Multi-chunk file uploads fail: nonce refreshed mid-upload rejects every chunk after the first (regression) #660) — raising the chunk size above the max file size to force a single-request upload has no effect while this bug exists.

Proposed fix

Use the PHP-provided value: chunk_size: file_input.chunk_size || '2mb' in js/file-upload.js.

Note

This issue was originally filed conflated with a separate multi-chunk upload failure. That is a distinct regression (different root cause and commit) tracked in #660; this issue now covers only the chunk-size configuration defect.