fix(runner): drop JSON content-type on bodyless light-run requests

src/runner/LightRunClient.ts

@@ -66,7 +66,7 @@ export class LightRunClient {
       if (!lightRunId) return;
       fetch(`${this.url}/runs/${lightRunId}/cancel`, {
         method: 'POST',
-        headers: this.headers(),
+        headers: this.authHeaders(),
       }).catch(() => {});
     };
 
@@ -236,7 +236,7 @@ export class LightRunClient {
   async deleteNetwork(name: string): Promise<void> {
     const res = await fetch(`${this.url}/networks/${encodeURIComponent(name)}`, {
       method: 'DELETE',
-      headers: this.headers(),
+      headers: this.authHeaders(),
     });
     if (!res.ok && res.status !== 404) {
       const text = await res.text().catch(() => '');
@@ -278,7 +278,7 @@ export class LightRunClient {
   async stopRun(id: string): Promise<void> {
     const res = await fetch(`${this.url}/runs/${id}/stop`, {
       method: 'POST',
-      headers: this.headers(),
+      headers: this.authHeaders(),
     });
     if (!res.ok && res.status !== 404) {
       const text = await res.text().catch(() => '');
@@ -291,4 +291,17 @@ export class LightRunClient {
     if (this.token) h.authorization = `Bearer ${this.token}`;
     return h;
   }
+
+  /*
+   * Headers for a request with NO body (stop, cancel, network delete). A
+   * bodyless request must not declare `content-type: application/json`: Fastify
+   * rejects an empty body under that content-type with 400
+   * (FST_ERR_CTP_EMPTY_JSON_BODY), which silently failed service/network
+   * teardown. Carry only the bearer token.
+   */
+  private authHeaders(): Record<string, string> {
+    const h: Record<string, string> = {};
+    if (this.token) h.authorization = `Bearer ${this.token}`;
+    return h;
+  }
 }