A node's bucket opens under its own deadline, so a per-node page is ended by its budget too (issue 1966)

Review round 3: the open on the first key of a node ran on the listing's context,
whose deadline is spent before the page's budget.

Claude-Session: https://claude.ai/code/session_01NcbgfFSnn24M3GcqttoU7i

node-tools/internal/bus/state.go

@@ -166,6 +166,7 @@ func (c *Conn) StatePage(module, name, after string, maxBytes int, budget time.D
 	}
 	// The bind and the listing have a StateTimeout of their own, and each get another: the page's time budget is what
 	// ends a slow page (with Next), never a deadline spread over the whole of it.
+	// ctx covers the bind and the listing alone; every bus request inside the loop takes each().
 	ctx, cancel := context.WithTimeout(context.Background(), StateTimeout)
 	defer cancel()
 	each := func() (context.Context, context.CancelFunc) {
@@ -186,7 +187,10 @@ func (c *Conn) StatePage(module, name, after string, maxBytes int, budget time.D
 			}
 			kv, bound := buckets[node]
 			if !bound {
-				if kv, err = fam.Open(ctx, node); err != nil {
+				octx, ocancel := each() // the open is a bus request in the loop: its own deadline, never ctx's
+				kv, err = fam.Open(octx, node)
+				ocancel()
+				if err != nil {
 					return nil, err
 				}
 				buckets[node] = kv