diff --git a/docs/rust-server-port-checkpoints/2026-10-22-cleanup-finished-at.md b/docs/rust-server-port-checkpoints/2026-10-22-cleanup-finished-at.md
new file mode 100644
index 000000000..3e7346910
--- /dev/null
+++ b/docs/rust-server-port-checkpoints/2026-10-22-cleanup-finished-at.md
@@ -0,0 +1,30 @@
+# October 22, cancellation cleanup finish time
+
+- **Found by.** The Shared Server fixtures workflow on main. Since the merge
+  of #561 it has failed in `codec-deadline-health` on every database,
+  `execution-and-codec`, `mysql-execution` and `postgres-storage`. These are
+  not required checks, so merges continued. Main run 39671560431 shows the
+  same assertion in each of them, `cleanup closes at persisted terminal
+  time`:
+  - expected `2026-10-21T23:12:52.433000Z`, the run's `closed_at`;
+  - actual `2026-10-21T23:12:52.433Z`, the `WorkflowCancelled` payload's
+    `cancellation_cleanup.finished_at`.
+- **Cause.** Native wrote `finished_at` as a raw chrono time, which serde
+  prints with as few fractional digits as the value needs. Its
+  `cleanup_deadline_at` and `requested_at` beside it, and the run's
+  `closed_at`, use six digits. Published Workflow writes the cleanup's
+  `finished_at` as the run's `closed_at->toISOString()`, and
+  `CancellationCascadeView` treats a different string as a mismatch.
+- **Source.** `finished_at` now uses the same six-digit form as the other
+  cancellation times.
+- **Verification.** The cooperative cleanup integration test compared the two
+  values as parsed instants. It now also compares them as text. It fails
+  without the change (`…22.519Z` against `…22.519000Z`) and passes with it.
+  The SQLite cleanup, cancellation and cooperative tests pass (54).
+- **Still open.** In the same run, `postgres-storage (postgres-17)` stopped
+  earlier, in the operator metrics `waiting_after_redispatch` stage. Its
+  health snapshot warned `durable_resume_paths`, but the metrics snapshot
+  taken just before it counted no run needing repair. The two are separate
+  requests, so the run's summary changed between them. That is a timing
+  difference in the fixture or a native summary refresh. It is diagnosed
+  separately once this assertion no longer hides it.
diff --git a/rust/src/runtime/cooperative.rs b/rust/src/runtime/cooperative.rs
index 52158880e..adbdfa476 100644
--- a/rust/src/runtime/cooperative.rs
+++ b/rust/src/runtime/cooperative.rs
@@ -558,7 +558,7 @@ where
             "workflow_instance_id":DB::string(run,"workflow_instance_id")?,"workflow_run_id":run_id,"failure_id":failure_id,
             "failure_category":"cancelled","closed_reason":"cancelled","exception_class":EXCEPTION,"message":message,"reason":reason,
             "cancellation_cleanup":{"request_id":request_id,"outcome":outcome,"cleanup_deadline_at":timestamp(deadline),
-                "delivery_history_event_id":delivery_id,"delivery_sequence":delivery_sequence,"finished_at":at}});
+                "delivery_history_event_id":delivery_id,"delivery_sequence":delivery_sequence,"finished_at":timestamp(at)}});
         Self::append(
             tx,
             &run_id,
diff --git a/rust/tests/execution.rs b/rust/tests/execution.rs
index 89fa3a9cd..0da1c4e39 100644
--- a/rust/tests/execution.rs
+++ b/rust/tests/execution.rs
@@ -3848,6 +3848,9 @@ async fn cooperative_delivery_cleanup_and_original_deadline_survive_fresh_runtim
         assert_eq!(described.1["output_envelope"], Value::Null);
         let instant = |value: &Value| chrono::DateTime::parse_from_rfc3339(value.as_str().unwrap()).unwrap();
         assert_eq!(instant(&cleanup["finished_at"]), instant(&described.1["closed_at"]));
+        // PHP writes the cleanup's `finished_at` as the run's `closed_at`
+        // string (`CancellationCascadeView`), so the two are equal as text.
+        assert_eq!(cleanup["finished_at"], described.1["closed_at"]);
         if !cleanup_activity.is_null() {
             let observed = request_protocol(&app,"POST",
                 &format!("/api/worker/activity-tasks/{}/status",cleanup_activity["task_id"].as_str().unwrap()),