fix: Case-insensitive Content-Type matching

Per RFC 9110/2045 media types are case-insensitive. Lower-case the
result of ContentTypeHeader.subtype() and lower-case spec content-type
keys at parse time so headers like "Application/JSON" or
"Text/Plain" match requestBody.content entries regardless of casing.

Also fixes a compile error in FormUrlEncodedParser.decodeComponent
which referenced a non-existent ValidationException constructor; the
URLDecoder failure path now wraps the IllegalArgumentException as a
proper ValidationError(/body, decode, ...).

Author: thced

src/main/java/com/retailsvc/http/internal/ContentTypeHeader.java

@@ -8,14 +8,17 @@ public final class ContentTypeHeader {
 
   private ContentTypeHeader() {}
 
-  /** Returns the bare media type, stripping parameters. {@code null} → {@code application/json}. */
+  /**
+   * Returns the bare media type, stripping parameters and lower-casing for case-insensitive
+   * matching (RFC 9110 / 2045). {@code null} → {@code application/json}.
+   */
   public static String subtype(String header) {
     if (header == null) {
       return "application/json";
     }
     int semi = header.indexOf(';');
     String bare = (semi < 0 ? header : header.substring(0, semi));
-    return bare.trim();
+    return bare.trim().toLowerCase(Locale.ROOT);
   }
 
   /** Returns the named parameter value (e.g. {@code charset}), or empty if absent. */

src/main/java/com/retailsvc/http/internal/FormUrlEncodedParser.java

@@ -1,8 +1,10 @@
 package com.retailsvc.http.internal;
 
+import com.retailsvc.http.ValidationException;
 import com.retailsvc.http.spec.schema.ArraySchema;
 import com.retailsvc.http.spec.schema.ObjectSchema;
 import com.retailsvc.http.spec.schema.Schema;
+import com.retailsvc.http.validate.ValidationError;
 import java.net.URLDecoder;
 import java.nio.charset.Charset;
 import java.nio.charset.IllegalCharsetNameException;
@@ -42,7 +44,9 @@ private static String decodeComponent(String value, Charset charset) {
     try {
       return URLDecoder.decode(value, charset);
     } catch (IllegalArgumentException ex) {
-      throw new ValidationException("/body", "decode", "Malformed form URL encoding", ex);
+      throw new ValidationException(
+          new ValidationError(
+              "/body", "decode", "malformed form URL encoding: " + ex.getMessage(), value));
     }
   }
 

src/main/java/com/retailsvc/http/spec/Spec.java

@@ -203,7 +203,7 @@ private static RequestBody parseRequestBody(Map<String, Object> raw) {
     for (var e : contentRaw.entrySet()) {
       Map<String, Object> mt = (Map<String, Object>) e.getValue();
       content.put(
-          e.getKey(),
+          e.getKey().toLowerCase(java.util.Locale.ROOT),
           new MediaType(SchemaParser.parse(mt.getOrDefault(SCHEMA_KEY, Map.of("type", "object")))));
     }
     return new RequestBody(Boolean.TRUE.equals(raw.get("required")), Map.copyOf(content));
@@ -219,7 +219,9 @@ private static Map<String, Response> parseResponses(Map<String, Object> raw) {
       for (var ce : contentRaw.entrySet()) {
         Map<String, Object> mt = (Map<String, Object>) ce.getValue();
         if (mt.containsKey(SCHEMA_KEY)) {
-          content.put(ce.getKey(), new MediaType(SchemaParser.parse(mt.get(SCHEMA_KEY))));
+          content.put(
+              ce.getKey().toLowerCase(java.util.Locale.ROOT),
+              new MediaType(SchemaParser.parse(mt.get(SCHEMA_KEY))));
         }
       }
       out.put(e.getKey(), new Response(Map.copyOf(content)));

src/test/java/com/retailsvc/http/internal/ContentTypeHeaderTest.java

@@ -26,6 +26,12 @@ void subtypeDefaultsToApplicationJsonWhenNull() {
     assertThat(ContentTypeHeader.subtype(null)).isEqualTo("application/json");
   }
 
+  @Test
+  void subtypeLowerCasesMediaType() {
+    assertThat(ContentTypeHeader.subtype("Application/JSON")).isEqualTo("application/json");
+    assertThat(ContentTypeHeader.subtype("Text/Plain; charset=UTF-8")).isEqualTo("text/plain");
+  }
+
   @Test
   void parameterReturnsValue() {
     assertThat(ContentTypeHeader.parameter("text/plain; charset=iso-8859-1", "charset"))