delete c0re-side reminder plumbing (#2635 inc 1 commit 6)

hive-c0re/src/questions.rs

@@ -186,14 +186,15 @@ pub fn handle_cancel_loose_end(
             Ok(())
         }
         hive_sh4re::CancelLooseEndKind::Reminder => {
-            // Agent-socket path: ownership-only (cancel your own reminder).
-            let owner = coord
-                .broker
-                .cancel_reminder_as(id, canceller, false)
-                .map_err(|e| format!("{e:#}"))?;
-            tracing::info!(%id, %canceller, %owner, "reminder cancelled");
-            coord.emit_reminders_snapshot();
-            Ok(())
+            // Reminders are now agent-local (in-container store) — the
+            // agent-mcp `cancel_loose_end` tool branches on this kind and
+            // dials the agent's own socket directly, never forwarding to
+            // hive-c0re. This arm should be unreachable in practice; kept
+            // only so the match stays exhaustive.
+            Err(format!(
+                "reminder {id}: reminders are handled locally by the agent, \
+                 not by hive-c0re"
+            ))
         }
         hive_sh4re::CancelLooseEndKind::Approval => {
             // Withdrawing an approval needs the grantable `approvals`