+ * Exports from pageantc.c.
+ *
+ * agent_query returns 1 for here's-a-response, and 0 for query-in-
+ * progress. In the latter case there will be a call to `callback'
+ * at some future point, passing callback_ctx as the first
+ * parameter and the actual reply data as the second and third.
+ *
+ * The response may be a NULL pointer (in either of the synchronous
+ * or asynchronous cases), which indicates failure to receive a
+ * response.