Observe source-string changes

pom_translate_string_changed fires after a source string is inserted or updated:

($string_id, $subject_type, $subject_id, $field, $block_key, $original_text, $placeholder_map)

Use it to invalidate integration caches or synchronize a bounded derived index. POM Translate itself uses it for rendering caches and machine-translation queue decisions.

Do not call the registration API again from this action without a recursion guard. Do not perform remote translation synchronously in the callback.

Standalone registration remains pom_translate_register_string(); there is no filter that can replace a source value before every database write.