fix(api): surface non-json error messages

lib/api/http.ts

@@ -6,14 +6,14 @@ type JsonRequestInit = Omit<RequestInit, "body" | "headers"> & {
   json?: unknown
 }
 
-async function readJsonBody(res: Response): Promise<unknown | null> {
+async function readJsonBody(res: Response): Promise<{ json: unknown | null; text: string }> {
   const text = await res.text()
-  if (!text) return null
+  if (!text) return { json: null, text: "" }
 
   try {
-    return JSON.parse(text) as unknown
+    return { json: JSON.parse(text) as unknown, text }
   } catch {
-    return null
+    return { json: null, text }
   }
 }
 
@@ -64,7 +64,7 @@ export async function httpJson<T>(path: string, init?: JsonRequestInit): Promise
     body,
   })
 
-  const data = await readJsonBody(res)
+  const { json: data, text } = await readJsonBody(res)
 
   if (res.ok) {
     return data as T
@@ -83,5 +83,8 @@ export async function httpJson<T>(path: string, init?: JsonRequestInit): Promise
     throw apiError
   }
 
-  throw { code: res.status, msg: res.statusText || "Request failed" } satisfies ApiError
+  throw {
+    code: res.status,
+    msg: text || res.statusText || "Request failed",
+  } satisfies ApiError
 }