*/
    @Nonnull
    Map<String, String> getSystemProperties();

    /**
     * Returns the properly overlaid map of properties: system + user.
     */
    @Nonnull
    Map<String, String> getEffectiveProperties();

    /**
     * Returns the start time of the session.
     *
     * @return the start time as an Instant object, never {@code null}
     */
    @Nonnull
    Instant getStartTime();

    /**

    /**
     * Default implementation at {@link ProtoSession} level, as the notion of project
     * does not exist there.
     */
    @Nonnull
    default Map<String, String> getEffectiveProperties() {
        return getEffectiveProperties(null);
    }

    /**
     * Each invocation computes a new map of effective properties. To be used in interpolation.
     * <p>