diff --git a/tests/stack_flows.rs b/tests/stack_flows.rs
index 7fce414..54bde10 100644
--- a/tests/stack_flows.rs
+++ b/tests/stack_flows.rs
@@ -1820,3 +1820,66 @@ fn view_says_how_many_commits_each_member_holds() {
     assert_eq!(members[0]["commits"], 1, "{json:#}");
     assert_eq!(members[1]["commits"], 2, "{json:#}");
 }
+
+/// `stack sync --json` is *one* object, carrying both halves.
+///
+/// Rule 1 of `--json` is one value on stdout, and this is the command most
+/// able to break it: it runs a rebase and a reconcile, each of which used to
+/// emit its own object. The two were refactored to return their reports for
+/// exactly this reason, and nothing checked it until now — `.json()` parses
+/// the whole of stdout, so a second object fails here rather than in
+/// somebody's `jq`.
+#[test]
+fn sync_json_is_one_object_describing_both_halves() {
+    let world = published_stack("sync-json");
+    world.checkout.git(&["checkout", "-q", "main"]);
+    world
+        .checkout
+        .commit("unrelated.txt", "theirs\n", "feat: landed meanwhile", None);
+    world.checkout.sync_remote("main");
+    world.checkout.git(&["checkout", "-q", "feature"]);
+    world.checkout.amend_file("three.txt", "three, revised\n");
+
+    let report = world.run(&["stack", "sync", "--json"]).success().json();
+
+    assert_eq!(report["rebase"]["rebased"], true, "{report:#}");
+    assert_ne!(
+        report["rebase"]["was"], report["rebase"]["now"],
+        "a rebase that moved nothing is not a rebase: {report:#}"
+    );
+    assert_eq!(report["reconcile"]["changed"], true, "{report:#}");
+    assert_eq!(report["reconcile"]["total"], 3, "{report:#}");
+}
+
+/// `stack rebase --json` on a branch already on top of its target says so
+/// and moves nothing.
+#[test]
+fn rebase_json_reports_an_up_to_date_branch() {
+    let world = published_stack("rebase-json-noop");
+    let tip = world.checkout.head();
+
+    let report = world.run(&["stack", "rebase", "--json"]).success().json();
+
+    assert_eq!(report["rebased"], false, "{report:#}");
+    assert_eq!(report["was"], report["now"], "{report:#}");
+    assert_eq!(world.checkout.head(), tip, "the branch moved anyway");
+}
+
+/// `stack mark --json` lists the marks, their positions, and the subjects
+/// they end.
+#[test]
+fn mark_json_lists_positions_and_subjects() {
+    let world = Scenario::new("mark-json");
+    three_commit_branch(&world);
+    world.run(&["stack", "mark", "part1", "HEAD~1"]).success();
+
+    let report = world.run(&["stack", "mark", "--json"]).success().json();
+
+    assert_eq!(report["branch"], "feature", "{report:#}");
+    assert_eq!(report["commits"], 3, "{report:#}");
+    let marks = report["marks"].as_array().expect("marks array");
+    assert_eq!(marks.len(), 1, "{report:#}");
+    assert_eq!(marks[0]["name"], "part1", "{report:#}");
+    assert_eq!(marks[0]["position"], 2, "{report:#}");
+    assert_eq!(marks[0]["subject"], "feat: middle", "{report:#}");
+}