Fix a2amcp login error reporting

src/api.ts

@@ -24,8 +24,11 @@ export class ControlPlaneClient {
   }
 
   private headers(): Record<string, string> {
-    const h: Record<string, string> = { "content-type": "application/json" };
-    if (this.token) h["authorization"] = `bearer ${this.token}`;
+    const h: Record<string, string> = {
+      accept: "application/json",
+      "content-type": "application/json",
+    };
+    if (this.token) h["authorization"] = `Bearer ${this.token}`;
     return h;
   }
 
@@ -35,18 +38,12 @@ export class ControlPlaneClient {
       headers: this.headers(),
       body: body !== undefined ? JSON.stringify(body) : undefined,
     });
+    const text = await resp.text();
     if (!resp.ok) {
-      let detail: string;
-      try {
-        const j: any = await resp.json();
-        detail = j?.detail ?? JSON.stringify(j);
-      } catch {
-        detail = await resp.text();
-      }
-      throw new ApiError(resp.status, detail);
+      throw new ApiError(resp.status, errorDetail(text, resp.statusText));
     }
     if (resp.status === 204) return undefined as T;
-    return (await resp.json()) as T;
+    return (text ? JSON.parse(text) : undefined) as T;
   }
 
   me() {
@@ -61,3 +58,16 @@ export class ControlPlaneClient {
     return this.request<AgentRow>("GET", `/v1/agents/${encodeURIComponent(name)}`);
   }
 }
+
+function errorDetail(text: string, fallback: string): string {
+  if (!text.trim()) return fallback;
+  try {
+    const parsed = JSON.parse(text);
+    const detail = parsed?.detail;
+    if (typeof detail === "string") return detail;
+    if (detail !== undefined) return JSON.stringify(detail);
+    return JSON.stringify(parsed);
+  } catch {
+    return text;
+  }
+}