test(runtime-e2e): runtime-e2e/x-client-id/ proves SDK emits v9 header

Per CLAUDE.md HARD RULE #0: gate requires runtime-e2e/<feature>/ test
for user-facing surface changes. Adds the v9 X-Client-ID counterpart
to x-axonflow-client/ runner — spawns an in-process forwarding proxy
(JDK HttpServer + HttpClient) that captures the outbound X-Client-ID
off the wire and forwards to the real agent. Asserts captured value
equals the configured clientId. Prereqs: AXONFLOW_AGENT_URL,
AXONFLOW_TENANT_ID, AXONFLOW_TENANT_SECRET.

Signed-off-by: Saurabh Jain <saurabh.jain@getaxonflow.com>

Author: saurabhjain1592

runtime-e2e/x-client-id/SdkXClientIdTest.java

@@ -0,0 +1,99 @@
+/*
+ * runtime-e2e/x-client-id/SdkXClientIdTest.java
+ *
+ * Per CLAUDE.md HARD RULE #0: real-wire test of the SDK's v9 X-Client-ID
+ * header emission to a real running AxonFlow agent.
+ *
+ * Approach: the SDK does not expose its internal OkHttpClient, so we
+ * run a tiny in-process forwarding proxy (Java's HttpServer + the JDK's
+ * built-in HttpClient) that inspects every request, captures the
+ * X-Client-ID header, and forwards to the real agent. The SDK is
+ * pointed at the proxy. Bytes flow real → real.
+ *
+ * Run:
+ *   AXONFLOW_AGENT_URL=http://localhost:8080 \
+ *     AXONFLOW_TENANT_ID=cs_... AXONFLOW_TENANT_SECRET=... \
+ *     java -cp "<sdk-jar>:<deps>" runtime-e2e/x-client-id/SdkXClientIdTest.java
+ */
+import com.getaxonflow.sdk.AxonFlow;
+import com.getaxonflow.sdk.AxonFlowConfig;
+import com.getaxonflow.sdk.types.MCPCheckInputResponse;
+import com.sun.net.httpserver.HttpServer;
+import java.net.InetSocketAddress;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.util.concurrent.atomic.AtomicReference;
+
+public class SdkXClientIdTest {
+  public static void main(String[] args) throws Exception {
+    String endpoint = System.getenv().getOrDefault("AXONFLOW_AGENT_URL", "http://localhost:8080");
+    String tenant = System.getenv("AXONFLOW_TENANT_ID");
+    String secret = System.getenv("AXONFLOW_TENANT_SECRET");
+    if (tenant == null || secret == null) {
+      System.err.println(
+          "AXONFLOW_TENANT_ID + AXONFLOW_TENANT_SECRET must be set; see ../README.md");
+      System.exit(2);
+    }
+
+    final URI target = URI.create(endpoint);
+    final HttpClient forwarder = HttpClient.newHttpClient();
+    final AtomicReference<String> sawClientId = new AtomicReference<>("");
+
+    HttpServer server = HttpServer.create(new InetSocketAddress("127.0.0.1", 0), 0);
+    server.createContext(
+        "/",
+        ex -> {
+          sawClientId.set(ex.getRequestHeaders().getFirst("X-Client-ID"));
+          byte[] body = ex.getRequestBody().readAllBytes();
+          HttpRequest.Builder b =
+              HttpRequest.newBuilder(target.resolve(ex.getRequestURI()))
+                  .method(ex.getRequestMethod(), HttpRequest.BodyPublishers.ofByteArray(body));
+          ex.getRequestHeaders()
+              .forEach(
+                  (k, vs) -> {
+                    if (!k.equalsIgnoreCase("host") && !k.equalsIgnoreCase("content-length")) {
+                      vs.forEach(v -> b.header(k, v));
+                    }
+                  });
+          try {
+            HttpResponse<byte[]> resp =
+                forwarder.send(b.build(), HttpResponse.BodyHandlers.ofByteArray());
+            byte[] respBody = resp.body();
+            ex.sendResponseHeaders(resp.statusCode(), respBody.length);
+            ex.getResponseBody().write(respBody);
+            ex.getResponseBody().close();
+          } catch (Exception e) {
+            ex.sendResponseHeaders(502, 0);
+            ex.close();
+          }
+        });
+    server.start();
+    String proxyUrl = "http://127.0.0.1:" + server.getAddress().getPort();
+
+    AxonFlow client =
+        AxonFlow.create(
+            AxonFlowConfig.builder()
+                .agentUrl(proxyUrl)
+                .clientId(tenant)
+                .clientSecret(secret)
+                .build());
+
+    System.out.println("Asserting wire X-Client-ID = " + tenant);
+    try {
+      MCPCheckInputResponse r = client.mcpCheckInput("postgres", "SELECT 1");
+      // outcome doesn't matter; only the captured header
+    } catch (Exception ignored) {
+      // outcome doesn't matter; only the captured header
+    }
+    server.stop(0);
+
+    String got = sawClientId.get();
+    if (!tenant.equals(got)) {
+      System.err.println("FAIL: wire X-Client-ID = \"" + got + "\", want \"" + tenant + "\"");
+      System.exit(1);
+    }
+    System.out.println("PASS: wire X-Client-ID = \"" + got + "\"");
+  }
+}