This function starts progress tracking for a File Manager extract operation.

Note:

• The Fileman::fileop function with op=extract is a single synchronous call to tar that reports no progress of its own. This function brackets that call from the outside so that a caller can show real progress.
• Call this function first, then call the Fileman::fileop function to perform the extract, poll the ExtractInfo::progress function while it runs, and call the ExtractInfo::finish function when it completes.
• The function records the archive's total uncompressed byte size and a baseline snapshot of the destination directory's disk usage, then writes a run-state marker.
• This function returns immediately and extracts nothing itself.

{
  "apiversion": 3,
  "func": "start",
  "module": "ExtractInfo",
  "result": {
    "data": {
      "started": true
    },
    "status": 1
  }
}