Rust #325: describe a parent waiting on an activity beside children

docs/rust-server-port-checkpoints/2026-10-29-child-descriptions.md

@@ -28,3 +28,16 @@
   activity, are still described without their wait, pending evidence.
 - **Tests.** `child_descriptions.rs`. On the previous source, two children
   and a child beside a timer were described with a null wait.
+
+## Follow-up: activities and cancellation policies
+
+- **Contract** (published 2.11.5): an open activity is described ahead of
+  open children in either order, as a timer is. A child requesting
+  `cancellation_policy: try_cancel` from a worker that does not declare
+  cooperative cancellation is refused `409
+  child_cancellation_policy_not_supported`; native refuses it the same way.
+- **Fixture.** `child-descriptions` gains three cases: `cancelling_child`,
+  `child_then_activity` and `activity_then_child`.
+- **Native.** An already chosen activity wait, like a timer wait, stays the
+  run's wait while every child is open. On the previous source a child
+  beside an activity was described with a null wait.

docs/rust-server-port.md

@@ -595,9 +595,11 @@ contract fixture before its correction.
   was described with no wait. The `child-descriptions` fixture records five
   cases against published 2.11.5
   ([checkpoint](rust-server-port-checkpoints/2026-10-29-child-descriptions.md)).
-  A child with a cancellation policy other than `abandon`, a retry or
-  timeout policy, or beside an open activity is still described without
-  its wait, pending its own evidence.
+  An open activity is likewise described ahead of open children
+  (October 29). A child with a retry or timeout policy, or a cancellation
+  policy other than `abandon` under a worker that declares cooperative
+  cancellation, is still described without its wait, pending its own
+  evidence.
 - **Trace context (Core 2.10, published in Server 2.11.1).** Core adds
   nullable `observability_context` columns on runs, commands and tasks.
   Native has no carrier: it accepts and ignores a top-level carrier on

rust/src/runtime/child_summary.rs

@@ -169,13 +169,14 @@ where
         if rows.is_empty() {
             return Ok(true);
         }
-        // An open timer wait describes the run ahead of open children, as
-        // PHP's run description does. Other wait families, and a resolved
-        // child beside a timer, retain their separately qualified precedence.
+        // An open timer or activity wait describes the run ahead of open
+        // children, as PHP's run description does, whichever was scheduled
+        // first. Other wait families, and a resolved child beside them,
+        // retain their separately qualified precedence.
         let all_open = rows.iter().all(|row| DB::string(row, "status").is_ok_and(|status| status == "open"));
-        if summary.wait.as_ref().is_some_and(|wait| wait.kind == "timer")
+        if let Some(kind) = summary.wait.as_ref().map(|wait| wait.kind).filter(|kind| matches!(*kind, "timer" | "activity"))
             && all_open
-            && summary.task_type.as_deref().is_none_or(|kind| kind == "timer")
+            && summary.task_type.as_deref().is_none_or(|task| task == kind)
         {
             return Ok(true);
         }

rust/tests/execution/child_descriptions.rs

@@ -18,17 +18,21 @@ async fn a_parent_is_described_by_its_waits_with_several_children() {
     let timer = json!({"type":"start_timer","delay_seconds":3600});
     let child_wait = (json!("child"), json!("Waiting for child workflow echo"));
     let timer_wait = (json!("timer"), json!("Waiting for timer"));
+    let activity = json!({"type":"schedule_activity","activity_type":"echo-activity","arguments":envelope(Payload::Array(vec![]))});
+    let activity_wait = (json!("activity"), json!("Waiting for activity echo-activity"));
     for (id, commands, expected) in [
         ("one-child", json!([child(None)]), child_wait.clone()),
         ("two-children", json!([child(None), child(None)]), child_wait.clone()),
         ("child-then-timer", json!([child(None), timer.clone()]), timer_wait.clone()),
         ("timer-then-child", json!([timer.clone(), child(None)]), timer_wait.clone()),
         ("terminating-child", json!([child(Some("terminate"))]), child_wait.clone()),
+        ("child-then-activity", json!([child(None), activity.clone()]), activity_wait.clone()),
+        ("activity-then-child", json!([activity.clone(), child(None)]), activity_wait.clone()),
     ] {
         let database = TestDatabase::new().await;
         let runtime = database.open().await.unwrap();
         let app = router(runtime.clone());
-        register(&app, "worker", json!(["echo"]), json!([])).await;
+        register(&app, "worker", json!(["echo"]), json!(["echo-activity"])).await;
         start(&app, id).await;
         let task = poll(&app, "worker", "workflow").await;
         let (status, body) = finish_task(&app, &task, commands).await;

scripts/conformance/server-parity/child-descriptions-probe.php

@@ -41,7 +41,7 @@ function finishHttpChildDescriptions(Client $admin, array $fixture, string $work
         $worker = $id.'-worker';
         $registered = $raw('POST', 'worker/register', ['worker_id' => $worker, 'task_queue' => $queue, 'runtime' => 'php',
             'sdk_version' => 'raw-http', 'supported_workflow_types' => [$definition['workflow_type'], $definition['child_type']],
-            'supported_activity_types' => [],
+            'supported_activity_types' => [$definition['activity_type']],
             'capability_manifest' => array_fill_keys(['local_activities', 'worker_sessions', 'sticky_execution'],
                 ['supported' => false, 'minimum_protocol_version' => '1.18', 'reason' => 'raw_http'])]);
         $started = $raw('POST', 'workflows', ['workflow_id' => $id, 'workflow_type' => $definition['workflow_type'],

tests/Fixtures/ServerParity/child-descriptions.json

@@ -2,7 +2,7 @@
   "schema": "durable-workflow.server-parity-fixture/v1",
   "id": "child-descriptions",
   "review_state": "reviewed",
-  "contract": "A parent run's description while its children are open (published Server 2.11.5 WorkflowController::show with Workflow 2.15.1 RunWaitView), over raw worker HTTP on protocol 1.20 in a fresh namespace. Each case completes the parent's first workflow task with child and timer commands and records the description. A parent with two open children is described as waiting for a child; with an open child and an open timer, in either order, as waiting for the timer; and a child under parent_close_policy terminate is described like any other. Embedded applications have no worker protocol.",
+  "contract": "A parent run's description while its children are open (published Server 2.11.5 WorkflowController::show with Workflow 2.15.1 RunWaitView), over raw worker HTTP on protocol 1.20 in a fresh namespace. Each case completes the parent's first workflow task with child and timer commands and records the description. A parent with two open children is described as waiting for a child; with an open child and an open timer, in either order, as waiting for the timer; and a child under parent_close_policy terminate is described like any other. An open activity is likewise described ahead of open children, in either order. A child requesting cancellation_policy try_cancel from a worker that does not declare cooperative cancellation is refused 409 child_cancellation_policy_not_supported. Embedded applications have no worker protocol.",
   "workflow_type": "parity.v1.echo",
   "input": {
     "message": "continue transfers λ",
@@ -112,6 +112,53 @@
           },
           "parent_close_policy": "terminate"
         }
+      ],
+      "cancelling_child": [
+        {
+          "type": "start_child_workflow",
+          "workflow_type": "parity.v1.child_descriptions_child",
+          "arguments": {
+            "codec": "avro",
+            "blob": "wwHioz3/VYAiNwwA"
+          },
+          "cancellation_policy": "try_cancel"
+        }
+      ],
+      "child_then_activity": [
+        {
+          "type": "start_child_workflow",
+          "workflow_type": "parity.v1.child_descriptions_child",
+          "arguments": {
+            "codec": "avro",
+            "blob": "wwHioz3/VYAiNwwA"
+          }
+        },
+        {
+          "type": "schedule_activity",
+          "activity_type": "parity.v1.child_descriptions_activity",
+          "arguments": {
+            "codec": "avro",
+            "blob": "wwHioz3/VYAiNwwA"
+          }
+        }
+      ],
+      "activity_then_child": [
+        {
+          "type": "schedule_activity",
+          "activity_type": "parity.v1.child_descriptions_activity",
+          "arguments": {
+            "codec": "avro",
+            "blob": "wwHioz3/VYAiNwwA"
+          }
+        },
+        {
+          "type": "start_child_workflow",
+          "workflow_type": "parity.v1.child_descriptions_child",
+          "arguments": {
+            "codec": "avro",
+            "blob": "wwHioz3/VYAiNwwA"
+          }
+        }
       ]
     },
     "expected": {
@@ -194,7 +241,56 @@
           "wait_kind": "child",
           "wait_reason": "Waiting for child workflow parity.v1.child_descriptions_child"
         }
+      },
+      "cancelling_child": {
+        "completed": {
+          "status": 409,
+          "reason": "child_cancellation_policy_not_supported",
+          "run_status": null
+        },
+        "described": {
+          "status": "pending",
+          "status_bucket": "running",
+          "is_terminal": false,
+          "resume_step_sequence": null,
+          "recovery_kind": null,
+          "wait_kind": "workflow-task",
+          "wait_reason": "Workflow task leased to worker"
+        }
+      },
+      "child_then_activity": {
+        "completed": {
+          "status": 200,
+          "reason": null,
+          "run_status": "waiting"
+        },
+        "described": {
+          "status": "waiting",
+          "status_bucket": "running",
+          "is_terminal": false,
+          "resume_step_sequence": null,
+          "recovery_kind": null,
+          "wait_kind": "activity",
+          "wait_reason": "Waiting for activity parity.v1.child_descriptions_activity"
+        }
+      },
+      "activity_then_child": {
+        "completed": {
+          "status": 200,
+          "reason": null,
+          "run_status": "waiting"
+        },
+        "described": {
+          "status": "waiting",
+          "status_bucket": "running",
+          "is_terminal": false,
+          "resume_step_sequence": null,
+          "recovery_kind": null,
+          "wait_kind": "activity",
+          "wait_reason": "Waiting for activity parity.v1.child_descriptions_activity"
+        }
       }
-    }
+    },
+    "activity_type": "parity.v1.child_descriptions_activity"
   }
 }

tests/Unit/ServerParityChildDescriptionsContractTest.mjs

@@ -20,12 +20,16 @@ test('embedded applications have no worker protocol', () => {
 
 test('children and timers are described by the published precedence', () => {
   assert.deepStrictEqual(Object.fromEntries(Object.entries(expected).map(([name, run]) => [name, run.described.wait_kind])),
-    {one_child: 'child', two_children: 'child', child_then_timer: 'timer', timer_then_child: 'timer', terminating_child: 'child'});
+    {one_child: 'child', two_children: 'child', child_then_timer: 'timer', timer_then_child: 'timer', terminating_child: 'child',
+      cancelling_child: 'workflow-task', child_then_activity: 'activity', activity_then_child: 'activity'});
+  assert.deepStrictEqual([expected.cancelling_child.completed.status, expected.cancelling_child.completed.reason],
+    [409, 'child_cancellation_policy_not_supported']);
 });
 
 for (const [name, mutate] of [
   ['two children described without a wait', state => { state.two_children.described.wait_kind = null; }],
   ['a child ahead of an open timer', state => { state.child_then_timer.described.wait_kind = 'child'; }],
+  ['a child beside an activity described without a wait', state => { state.child_then_activity.described.wait_kind = null; }],
   ['an unexpected case', state => { state.extra = {}; }],
 ]) test(`the contract rejects ${name}`, () => {
   const raw = observation(); mutate(raw.child_descriptions);