feat: Add Request.pathParam(name) convenience accessor

Mirrors Request.queryParam(name); avoids the round-trip through
pathParams().get(name) for the common single-lookup case.

Author: thced

README.md

@@ -44,7 +44,7 @@ public class PostDataHandler implements RequestHandler {
     // Or get the already-parsed object (Map / List) produced by the registered TypeMapper.
     Object parsed = request.parsed();
     // Path parameters, query parameters, and headers are also available.
-    String id = request.pathParams().get("id");
+    String id = request.pathParam("id");
     String filter = request.queryParam("filter");
     String corr = request.header("correlation-id");
 
@@ -218,7 +218,7 @@ A handler in this setup is just business logic:
 public class GetPromotionHandler implements RequestHandler {
   @Override
   public Response handle(Request request) {
-    String id = request.pathParams().get("id");
+    String id = request.pathParam("id");
     String tenant = TENANT_ID.get();
     return promotionService
         .find(tenant, id)
@@ -257,7 +257,7 @@ public final class App {
     Spec spec = Spec.fromPath(Path.of("openapi.yaml"));         // SnakeYAML parses the spec
 
     RequestHandler getPromotion = req -> {
-      String id = req.pathParams().get("id");
+      String id = req.pathParam("id");
       return PromotionService.find(TENANT.get(), id)            // uses bound tenant
           .<Response>map(p -> Response.of(HTTP_OK, p))           // 200 + JSON via Gson
           .orElseGet(() -> Response.status(HTTP_NOT_FOUND));     // 404, no body

src/main/java/com/retailsvc/http/Request.java

@@ -49,6 +49,11 @@ public Map<String, String> pathParams() {
     return pathParameters;
   }
 
+  /** Value of the path parameter {@code name}, or {@code null} if absent. */
+  public String pathParam(String name) {
+    return pathParameters.get(name);
+  }
+
   public String header(String name) {
     return exchange.getRequestHeaders().getFirst(name);
   }

src/test/java/com/retailsvc/http/RequestTest.java

@@ -41,6 +41,15 @@ void readsBoundContext() throws Exception {
     assertThat(seenPathParams.get()).containsEntry("id", "42");
   }
 
+  @Test
+  void pathParamReturnsValueOrNull() {
+    HttpExchange exchange = mock(HttpExchange.class);
+    Request req = new Request(exchange, new byte[0], null, "op", Map.of("id", "42"));
+
+    assertThat(req.pathParam("id")).isEqualTo("42");
+    assertThat(req.pathParam("missing")).isNull();
+  }
+
   @Test
   void exposesQueryParams() {
     HttpExchange exchange = mock(HttpExchange.class);