diff --git a/jouledesk/jouledesk-rs/Cargo.lock b/jouledesk/jouledesk-rs/Cargo.lock
index 5876b5edc..b5eb9e6ff 100644
--- a/jouledesk/jouledesk-rs/Cargo.lock
+++ b/jouledesk/jouledesk-rs/Cargo.lock
@@ -1116,6 +1116,7 @@ dependencies = [
  "hex",
  "jcp-receipt",
  "jcp-schema",
+ "serde",
  "serde_json",
  "thiserror 2.0.20",
 ]
diff --git a/joulehook/joulehook-rs/Cargo.lock b/joulehook/joulehook-rs/Cargo.lock
index c7d87299f..ea9836e82 100644
--- a/joulehook/joulehook-rs/Cargo.lock
+++ b/joulehook/joulehook-rs/Cargo.lock
@@ -412,6 +412,7 @@ dependencies = [
  "hex",
  "jcp-receipt",
  "jcp-schema",
+ "serde",
  "serde_json",
  "thiserror",
 ]
diff --git a/sandbox/sandbox-rs/Cargo.lock b/sandbox/sandbox-rs/Cargo.lock
index 04882f2bf..0777052a6 100644
--- a/sandbox/sandbox-rs/Cargo.lock
+++ b/sandbox/sandbox-rs/Cargo.lock
@@ -1066,6 +1066,7 @@ dependencies = [
  "hex",
  "jcp-receipt",
  "jcp-schema",
+ "serde",
  "serde_json",
  "thiserror 2.0.20",
 ]
diff --git a/sandbox/sandbox-rs/crates/sandbox-meter/tests/tree_energy.rs b/sandbox/sandbox-rs/crates/sandbox-meter/tests/tree_energy.rs
index cdf75aae3..6538ddf51 100644
--- a/sandbox/sandbox-rs/crates/sandbox-meter/tests/tree_energy.rs
+++ b/sandbox/sandbox-rs/crates/sandbox-meter/tests/tree_energy.rs
@@ -106,6 +106,32 @@ fn ps_tree(root: i32) -> Vec<i32> {
     tree
 }
 
+/// `root`'s tree once it has exactly `want` members. Panics after 20 s,
+/// naming the tree it last saw.
+///
+/// A server's reply does not mean its worker is gone. The worker prints and
+/// the parent reads that line while the worker still has its work to do and
+/// its exit and reaping after that, so a tree walked straight after a reply
+/// can still hold it. Waiting for the shape a test assumes is the only way to
+/// assert that shape; asserting it on the first walk asserts a race, and that
+/// race is real — the count came back 62 instead of 61 in 2 runs of 5 on this
+/// host, more often the busier it is.
+fn settled_tree(root: i32, want: usize) -> Vec<i32> {
+    let deadline = Instant::now() + Duration::from_secs(20);
+    loop {
+        let tree = ps_tree(root);
+        if tree.len() == want {
+            return tree;
+        }
+        assert!(
+            Instant::now() < deadline,
+            "the tree of {root} never settled to {want} members; last saw {}: {tree:?}",
+            tree.len()
+        );
+        std::thread::sleep(Duration::from_millis(20));
+    }
+}
+
 /// Each of `pids`' rusage once every one of them is quiet by the oracle's
 /// rule: not running or queued (or exited) at two reads 20 ms apart, with
 /// the same energy at both. Panics after 20 s.
@@ -277,11 +303,14 @@ fn a_worker_reaped_while_its_tree_is_walked_is_never_missed() {
         ],
     );
     let root = s.pid() as u32;
-    // The first round trip runs once all 60 are forked; the tree is quiet
-    // before the first span.
+    // The first round trip runs once all 60 are forked. It does not leave the
+    // tree quiet, though — the worker it forks prints its pid before doing its
+    // work, so the reply arrives while that worker is still running — hence
+    // the wait below rather than a bare walk.
     let _ = s.ask("warm up");
-    let tree = ps_tree(s.pid());
-    assert_eq!(tree.len(), 61, "setup: the server and its 60 idle children: {tree:?}");
+    // Not `ps_tree` + `assert_eq!` here: the warm-up round trip returns while
+    // its worker is still the server's child, so the first walk sees 62.
+    let tree = settled_tree(s.pid(), 61);
     quiet(&tree);
     let meter = s.meter();
     let (mut exited, mut reaped, mut unsettled) = (0, 0, 0);