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
* Returns the value contained in the document for the provided path
     * @param path The path within the document in dot-notation
     * @param clazz The expected class of the field value
     * @return the value for the provided path if existing
     * @throws IllegalArgumentException if the path is null, empty, invalid, if the field doesn't exist
     * or if the field that is found at the provided path is not of the expected type.
     */
    public <T> T getFieldValue(String path, Class<T> clazz) {
        return getFieldValue(path, clazz, false);
    }
    /**
     * Returns the value contained in the document for the provided path
     *
     * @param path The path within the document in dot-notation
     * @param clazz The expected class of the field value
     * @param ignoreMissing The flag to determine whether to throw an exception when `path` is not found in the document.
     * @return the value for the provided path if existing, null otherwise.
     * @throws IllegalArgumentException only if ignoreMissing is false and the path is null, empty, invalid, if the field doesn't exist
     * or if the field that is found at the provided path is not of the expected type.
     */
    public <T> T getFieldValue(String path, Class<T> clazz, boolean ignoreMissing) {
        FieldPath fieldPath = new FieldPath(path);
        Object context = fieldPath.initialContext;
        for (String pathElement : fieldPath.pathElements) {
            ResolveResult result = resolve(pathElement, path, context);
            if (result.wasSuccessful) {
                context = result.resolvedObject;
            } else if (ignoreMissing && hasField(path) == false) {
                return null;
            } else {