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/**
 * Adapters and generic contexts for key agreement built on the core SPI.
 *
 * <p>
 * This package provides a generic JCA-backed agreement context and a thin
 * adapter that exposes a KEM as a message-based agreement primitive. The goal
 * is to keep provider-specific details encapsulated while presenting clear
 * roles and lifecycles that higher layers can compose.
 * </p>
 *
 * <h2>Scope and responsibilities</h2>
 * <ul>
 * <li>Expose a generic agreement context that delegates to the JCA
 * {@code KeyAgreement} API for algorithms such as ECDH and XDH.</li>
 * <li>Adapt KEM contexts to a two-message agreement API suitable for initiator/
 * responder protocols.</li>
 * <li>Preserve clear separation between algorithm descriptors, runtime
 * contexts, and higher-level composition utilities.</li>
 * </ul>
 *
 * <h2>Components</h2>
 * <ul>
 * <li><b>GenericJcaAgreementContext</b>: an
 * {@link zeroecho.core.context.AgreementContext} backed by
 * {@link javax.crypto.KeyAgreement}; constructed with a local private key and
 * configured using a JCA algorithm name and optional provider.</li>
 * <li><b>KemMessageAgreementAdapter</b>: a
 * {@link zeroecho.core.context.MessageAgreementContext} built on a
 * {@link zeroecho.core.context.KemContext}, modeling initiator/responder roles
 * and exchanging a single peer message (ciphertext) when required.</li>
 * </ul>
 *
 * <h2>Lifecycle and usage notes</h2>
 * <ul>
 * <li>Agreement contexts should be created with the correct local key and
 * configured before deriving secrets; KDF application remains the caller's
 * responsibility.</li>
 * <li>KEM-based adapters encapsulate or decapsulate depending on role and
 * memoize results for repeated reads within a single exchange.</li>
 * <li>Instances are not thread-safe; synchronize externally if they are
 * shared.</li>
 * </ul>
 *
 * @since 1.0
 */
package zeroecho.core.alg.common.agreement;
