The specific question is, what triggers should I be attaching my import functions to?  Putting that first, so we don't get side-tracked on other issues.  Obvious keyword searches on the list of triggers didn't find anything that looked right, and checking the facetag plugin didn't show me how to do this.

What the plugin is supposed to do is, whenever an image is initially imported or resynchronized (either by FTP resync or by HTML upload including automatic resync when the image is replaced), it will create tags based on various fields in the IPTC or EXIF data (in addition to the tags core code already creates from the keywords field in the IPTC data).  These should then get stored in the database, and appear whenever a list of tags is extracted, and be searchable in searches like other tags, and so forth, just like "real" keywords.  If I can get control at the right point, and add my new virtual keywords into the existing list of keywords, this should work, right? 

So...does somebody know off the top of their head the trigger I should be hooking myself to, or have ideas for how to find out?  I'll find it eventually just from the code, but saving time would be nice.  I suppose there might be two, three, or four triggers (could be resync, initial html upload, html replacement, say, separately) I needed to hook to?

    Piwigo 2.9.5
    Operating system: Linux
    PHP: 7.0.33 (Show info) [2019-08-13 16:03:14]
    MySQL: 5.7.25-log [2019-08-13 16:03:14]
    Graphics Library: ImageMagick 6.9.7-4