feat: Retain oneOf/anyOf branch errors in validator

Author: thced

src/main/java/com/retailsvc/http/validate/DefaultValidator.java

@@ -527,29 +527,39 @@ private Optional<ValidationError> checkAllOf(Object value, List<Schema> parts, S
   }
 
   private Optional<ValidationError> checkAnyOf(Object value, List<Schema> options, String pointer) {
+    List<ValidationError> failures = new ArrayList<>();
     for (Schema o : options) {
-      if (check(value, o, pointer).isEmpty()) {
+      Optional<ValidationError> result = check(value, o, pointer);
+      if (result.isEmpty()) {
         return OK;
       }
+      failures.add(result.get());
     }
-    return err(pointer, "anyOf", "did not match any anyOf branch", value);
+    return Optional.of(
+        new ValidationError(pointer, "anyOf", "did not match any anyOf branch", value, failures));
   }
 
   private Optional<ValidationError> checkOneOf(Object value, List<Schema> options, String pointer) {
     int matched = 0;
+    List<ValidationError> failures = new ArrayList<>();
     for (Schema o : options) {
-      if (check(value, o, pointer).isEmpty()) {
+      Optional<ValidationError> result = check(value, o, pointer);
+      if (result.isEmpty()) {
         matched++;
+      } else {
+        failures.add(result.get());
       }
     }
     if (matched == 1) {
       return OK;
     }
-    return err(
-        pointer,
-        "oneOf",
-        "matched " + matched + " of " + options.size() + " oneOf branches",
-        value);
+    return Optional.of(
+        new ValidationError(
+            pointer,
+            "oneOf",
+            "matched " + matched + " of " + options.size() + " oneOf branches",
+            value,
+            matched == 0 ? failures : List.of()));
   }
 
   private Optional<ValidationError> checkNot(Object value, Schema inner, String pointer) {

src/test/java/com/retailsvc/http/validate/DefaultValidatorDispatchTest.java

@@ -235,4 +235,42 @@ void neverSchemaRejectsNull() {
         .extracting(t -> ((ValidationException) t).error().keyword())
         .isEqualTo("false");
   }
+
+  @Test
+  void oneOfZeroMatchesCapturesEachBranchError() {
+    // "hello" (len 5): branch[0] minLength 100 fails, branch[1] maxLength 2 fails.
+    var schema = new OneOfSchema(List.of(stringSchema(100, null), stringSchema(null, 2)), Map.of());
+    assertThatThrownBy(() -> v.validate("hello", schema, "/v"))
+        .isInstanceOf(ValidationException.class)
+        .satisfies(
+            t -> {
+              var err = ((ValidationException) t).error();
+              assertThat(err.branches())
+                  .extracting(ValidationError::keyword)
+                  .containsExactly("minLength", "maxLength");
+            });
+  }
+
+  @Test
+  void oneOfTwoMatchesHasNoBranchErrors() {
+    // Both branches accept "hello" — ambiguity, not a field error.
+    var schema = new OneOfSchema(List.of(stringSchema(null, 10), stringSchema(1, null)), Map.of());
+    assertThatThrownBy(() -> v.validate("hello", schema, "/v"))
+        .isInstanceOf(ValidationException.class)
+        .satisfies(t -> assertThat(((ValidationException) t).error().branches()).isEmpty());
+  }
+
+  @Test
+  void anyOfNoMatchCapturesEachBranchError() {
+    var schema = new AnyOfSchema(List.of(stringSchema(100, null), stringSchema(null, 2)), Map.of());
+    assertThatThrownBy(() -> v.validate("hello", schema, "/v"))
+        .isInstanceOf(ValidationException.class)
+        .satisfies(
+            t -> {
+              var err = ((ValidationException) t).error();
+              assertThat(err.branches())
+                  .extracting(ValidationError::keyword)
+                  .containsExactly("minLength", "maxLength");
+            });
+  }
 }