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
hashesOfConsistentSettings.writeTo(out);
        }
        
        
        if (out.getTransportVersion().onOrAfter(MAPPINGS_AS_HASH_VERSION)) {
            out.writeMapValues(mappingsByHash);
        }
        out.writeVInt(indices.size());
        final boolean writeMappingsHash = out.getTransportVersion().onOrAfter(MAPPINGS_AS_HASH_VERSION);
        for (IndexMetadata indexMetadata : this) {
            indexMetadata.writeTo(out, writeMappingsHash);
        }
        out.writeCollection(templates.values());
        VersionedNamedWriteable.writeVersionedWritables(out, customs);
        if (out.getTransportVersion().onOrAfter(TransportVersion.V_8_4_0)) {
            out.writeCollection(reservedStateMetadata.values());
        }
    }
    public static Builder builder() {
        return new Builder();
    }
    public static Builder builder(Metadata metadata) {
        return new Builder(metadata);
    }
    public Metadata copyAndUpdate(Consumer<Builder> updater) {
        var builder = builder(this);
        updater.accept(builder);
        return builder.build();
    }
    public static class Builder {