swarm: bash task status keys expire after 72 hours

Nothing deletes the key of a finished task, so the bucket would grow with every
task an agent runs. The shared bucket helper takes an optional max age, applied
when the bucket is created; a live task's republishing keeps its own key.

swarm-queue-client/src/bash_task.rs

@@ -32,16 +32,19 @@ pub(crate) fn output_config(
 }
 
 /// Open the status bucket, creating it if nothing has yet. `history: 1`: a
-/// reader wants each task's current state, not every state it has been in.
+/// reader wants each task's current state, not every state it has been in. A
+/// key expires [`swarm_wire::bash_task::STATUS_MAX_AGE`] after its last write,
+/// since nothing deletes the key of a finished task.
 pub async fn open_status(
     client: &async_nats::Client,
 ) -> Result<async_nats::jetstream::kv::Store, crate::Error> {
     let js = async_nats::jetstream::new(client.clone());
-    crate::kv::open_or_create(
+    crate::kv::open_or_create_expiring(
         &js,
         swarm_wire::bash_task::BUCKET,
         "bash-task-status",
         "The state of each bash task, as its agent's bash MCP last published it".to_owned(),
+        Some(swarm_wire::bash_task::STATUS_MAX_AGE),
     )
     .await
 }

swarm-queue-client/src/kv.rs

@@ -9,6 +9,19 @@ pub(crate) async fn open_or_create(
     bucket: &str,
     label: &str,
     description: String,
+) -> Result<async_nats::jetstream::kv::Store, Error> {
+    open_or_create_expiring(js, bucket, label, description, None).await
+}
+
+/// [`open_or_create`] with a `max_age`: a key nobody writes for that long goes
+/// away, for a bucket whose keys come from a publisher that never deletes. The
+/// age applies to a bucket created here; one that already exists keeps its own.
+pub(crate) async fn open_or_create_expiring(
+    js: &async_nats::jetstream::Context,
+    bucket: &str,
+    label: &str,
+    description: String,
+    max_age: Option<std::time::Duration>,
 ) -> Result<async_nats::jetstream::kv::Store, Error> {
     match js.get_key_value(bucket).await {
         Ok(store) => Ok(store),
@@ -22,6 +35,7 @@ pub(crate) async fn open_or_create(
                 bucket: bucket.to_owned(),
                 description,
                 history: 1,
+                max_age: max_age.unwrap_or_default(),
                 ..Default::default()
             })
             .await