A composable index template with no `template` defined in the body is mistakingly always assumed to not be a time series template. Even if it refers to a component template that has the `index.mode` setting set to `time_series` and the component template defines mappings with dimension fields or routing paths.

Incorrectly this causes to create a data stream with a tsdb index *without* time series start and end time settings set. The fact that this can happen is another bug and is being tracked #98833.

What should happen in this case is that a tsdb data stream is created with a valid tsdb backing index (with correctly generated time series start and end time settings).

This bug was found as part investigating #98792 and is the cause of that bug.
server/src/main/java/org/elasticsearch/cluster/metadata/Metadata.java
MappingMetadata entry = mappingsByHash.get(digest);
            if (entry != null) {
                indexMetadataBuilder.putMapping(entry);
            } else {
                mappingsByHash.put(digest, indexMetadataBuilder.mapping());
            }
        }
    }
    private static final ToXContent.Params FORMAT_PARAMS;
    static {
        Map<String, String> params = Maps.newMapWithExpectedSize(2);
        params.put("binary", "true");
        params.put(Metadata.CONTEXT_MODE_PARAM, Metadata.CONTEXT_MODE_GATEWAY);
        FORMAT_PARAMS = new ToXContent.MapParams(params);
    }
    /**
     * State format for {@link Metadata} to write to and load from disk
     */
    public static final MetadataStateFormat<Metadata> FORMAT = new MetadataStateFormat<>(GLOBAL_STATE_FILE_PREFIX) {
        @Override
        public void toXContent(XContentBuilder builder, Metadata state) throws IOException {
            ChunkedToXContent.wrapAsToXContent(state).toXContent(builder, FORMAT_PARAMS);
        }
        @Override
        public Metadata fromXContent(XContentParser parser) throws IOException {
            return Builder.fromXContent(parser);
        }
    };
}