There's a little buglet in #85387 (which was the PR that closed #84046), specifically, it doesn't account for the possibility that there's both a default/request **and** and a final pipeline, and that they can both touch the `@timestamp` field.

`IngestService#postIngest` was added in #85387, and it's intended that the logic there only runs **once**, after all the pipelines associated with the request have been executed. But as it's currently written, the logic actually runs after each individual pipeline runs.

The consequence of that is that if there's a default/request and a final pipeline in use for a document, and the final pipeline changes the timestamp field, the `rawTimestamp` recorded for the `IndexRequest` associated with the document will mistakenly use the value it sees after the default/request pipeline runs, and **not** the most correct one (from after when the final pipeline runs).

/cc @martijnvg 
server/src/main/java/org/elasticsearch/ingest/IngestDocument.java
if (index >= 0 && index < list.size()) {
                    return true;
                } else {
                    if (failOutOfRange) {
                        throw new IllegalArgumentException(
                            "[" + index + "] is out of bounds for array with length [" + list.size() + "] as part of path [" + path + "]"
                        );
                    } else {
                        return false;
                    }
                }
            } catch (NumberFormatException e) {
                return false;
            }
        }
        return false;
    }
    /**
     * Removes the field identified by the provided path.
     * @param fieldPathTemplate Resolves to the path with dot-notation within the document
     * @throws IllegalArgumentException if the path is null, empty, invalid or if the field doesn't exist.
     */
    public void removeField(TemplateScript.Factory fieldPathTemplate) {
        removeField(renderTemplate(fieldPathTemplate));
    }
    /**
     * Removes the field identified by the provided path.
     * @param path the path of the field to be removed
     * @throws IllegalArgumentException if the path is null, empty, invalid or if the field doesn't exist.
     */