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/**
 * Derived-key utilities for integrating hybrid KEX output with streaming
 * builders.
 *
 * <p>
 * This package provides a thin, SDK-level integration layer between hybrid key
 * exchange ({@link zeroecho.sdk.hybrid.kex.HybridKexContext} /
 * {@link zeroecho.sdk.hybrid.kex.HybridKexExporter}) and streaming data-content
 * builders (for example AES/ChaCha/HMAC builders in
 * {@link zeroecho.sdk.builders.alg}).
 * </p>
 *
 * <p>
 * The central concept is <b>derived material</b>: purpose-separated keying
 * bytes (key, optional IV/nonce, optional AAD) derived via HKDF labels. The
 * material is then applied to an existing builder via {@code applyTo(...)}
 * which returns the same builder instance to preserve fluent pipeline
 * construction.
 * </p>
 *
 * <h2>Design goals</h2>
 * <ul>
 * <li>Keep cryptographic primitives unchanged; only inject derived
 * parameters.</li>
 * <li>Provide safe-by-construction key separation using labels and transcript
 * binding.</li>
 * <li>Preserve fluent builder usage by returning the original builder from
 * {@code applyTo(...)}.</li>
 * </ul>
 *
 * @since 1.0
 */
package zeroecho.sdk.hybrid.derived;
