Implement velocity-testkit: in-memory reference backend + conformance TCK

velocity-spi/src/main/java/com/codeheadsystems/velocity/spi/CountStore.java

@@ -25,9 +25,17 @@ public interface CountStore extends VelocityBackend {
    * APPLIED|FAILED|SKIPPED} — a {@code SKIPPED} being a backend-owned outcome such as an idempotent
    * replay) alongside the {@link FeatureResult} (ADR 0009, FR-34).
    *
+   * <p>The result cardinality is <strong>one {@link
+   * com.codeheadsystems.velocity.spi.model.PerFeature PerFeature} per {@code (intent × each of the
+   * intent's feature's windows)}</strong>, not one per intent: a feature tracked over several
+   * windows contributes one entry per window, each carrying that window's post-apply value. The
+   * entries are therefore not positionally aligned with {@code intents}; disambiguate by the
+   * entry's feature and its {@link com.codeheadsystems.velocity.spi.model.FeatureValue#window()
+   * window}.
+   *
    * @param ctx the namespace + optional deadline context
    * @param intents the count intents to apply
-   * @return the per-intent apply outcomes, positionally aligned with {@code intents}
+   * @return one apply outcome per {@code (intent × the intent's feature's windows)}
    */
   ApplyResult applyCount(ApplyContext ctx, List<CountIntent> intents);
 

velocity-spi/src/main/java/com/codeheadsystems/velocity/spi/DistinctStore.java

@@ -30,9 +30,17 @@ public interface DistinctStore extends VelocityBackend {
    * com.codeheadsystems.velocity.spi.model.ApplyStatus apply status} ({@code
    * APPLIED|FAILED|SKIPPED}) alongside the {@link FeatureResult} (ADR 0009, FR-34).
    *
+   * <p>The result cardinality is <strong>one {@link
+   * com.codeheadsystems.velocity.spi.model.PerFeature PerFeature} per {@code (intent × each of the
+   * intent's feature's windows)}</strong>, not one per intent: a feature tracked over several
+   * windows contributes one entry per window, each carrying that window's post-apply value. The
+   * entries are therefore not positionally aligned with {@code intents}; disambiguate by the
+   * entry's feature and its {@link com.codeheadsystems.velocity.spi.model.FeatureValue#window()
+   * window}.
+   *
    * @param ctx the namespace + optional deadline context
    * @param intents the distinct intents to apply
-   * @return the per-intent apply outcomes, positionally aligned with {@code intents}
+   * @return one apply outcome per {@code (intent × the intent's feature's windows)}
    */
   ApplyResult applyDistinct(ApplyContext ctx, List<DistinctIntent> intents);
 

velocity-spi/src/main/java/com/codeheadsystems/velocity/spi/SumStore.java

@@ -24,9 +24,17 @@ public interface SumStore extends VelocityBackend {
    * com.codeheadsystems.velocity.spi.model.ApplyStatus apply status} ({@code
    * APPLIED|FAILED|SKIPPED}) alongside the {@link FeatureResult} (ADR 0009, FR-34).
    *
+   * <p>The result cardinality is <strong>one {@link
+   * com.codeheadsystems.velocity.spi.model.PerFeature PerFeature} per {@code (intent × each of the
+   * intent's feature's windows)}</strong>, not one per intent: a feature tracked over several
+   * windows contributes one entry per window, each carrying that window's post-apply value. The
+   * entries are therefore not positionally aligned with {@code intents}; disambiguate by the
+   * entry's feature and its {@link com.codeheadsystems.velocity.spi.model.FeatureValue#window()
+   * window}.
+   *
    * @param ctx the namespace + optional deadline context
    * @param intents the sum intents to apply
-   * @return the per-intent apply outcomes, positionally aligned with {@code intents}
+   * @return one apply outcome per {@code (intent × the intent's feature's windows)}
    */
   ApplyResult applySum(ApplyContext ctx, List<SumIntent> intents);
 

velocity-testkit/build.gradle.kts

@@ -13,13 +13,9 @@ dependencies {
     // contract; both are on the api surface so backend modules inherit them from their tests.
     api(project(":velocity-spi"))
     api(libs.jspecify)
-    api(libs.bundles.jackson)
     // AssertJ is on the api surface because the *Scenarios TCK asserts with `assertThat`; backend
     // modules drive these scenarios from their integration tests and inherit the dependency.
     api(libs.assertj.core)
 
-    implementation(libs.caffeine)
-    implementation(libs.slf4j.api)
-
     testRuntimeOnly(libs.logback.classic)
 }