feat(core): share API request assembly between both transports

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/core/src/api-request.ts

@@ -0,0 +1,36 @@
+/**
+ * Assemble an API request from a block's declared input.
+ *
+ * Shared by both transports on purpose. The browser and the in-process server
+ * caller must send the same thing for the same call; two copies of these rules
+ * would drift, and the drift would be invisible because each side is tested
+ * separately.
+ */
+export interface BuiltApiRequest {
+  url: string;
+  body?: string;
+  contentType?: string;
+}
+
+export function buildApiRequest(
+  path: string,
+  method: string,
+  input: Record<string, unknown> | undefined,
+): BuiltApiRequest {
+  const verb = String(method || "GET").toUpperCase();
+  const values = input ?? {};
+
+  if (verb === "GET" || verb === "HEAD") {
+    const query: string[] = [];
+
+    for (const [key, value] of Object.entries(values)) {
+      // 0 and false are legitimate values and must survive.
+      if (value === undefined || value === null || value === "") continue;
+      query.push(`${encodeURIComponent(key)}=${encodeURIComponent(String(value))}`);
+    }
+
+    return { url: query.length ? `${path}?${query.join("&")}` : path };
+  }
+
+  return { url: path, body: JSON.stringify(values), contentType: "application/json" };
+}