fix(#1088): sync system.md and mcp.rs tool descriptions against implementation

hive-ag3nt/src/mcp.rs

@@ -859,7 +859,11 @@ impl AgentServer {
         you scheduled (hard-deleted before it fires). `kind` is `\"question\"` or \
         `\"reminder\"`; `id` is the row id from the matching `get_loose_ends` entry \
         or the `question_queued` reply you got when you submitted. Auth: you can only \
-        cancel rows where you're the asker / owner. Returns `ok` or an error string."
+        cancel rows where you're the asker / owner. Returns `ok` or an error string.\n\
+        Agents with the `approvals` tool group can also pass `kind: \"approval\"` to \
+        withdraw a pending approval they submitted (before the operator acts on it). \
+        The root agent (`ruth`) may cancel any approval; non-root agents are restricted \
+        to their own approvals and the server rejects `approval` kind otherwise."
     )]
     async fn cancel_loose_end(&self, Parameters(args): Parameters<CancelLooseEndArgs>) -> String {
         let log = format!("{args:?}");