api: throttle streaming admin read polls

crates/crank-registry/src/postgres/mod.rs

@@ -2027,6 +2027,15 @@ mod tests {
             .unwrap();
         assert_eq!(closed.status, StreamStatus::Stopped);
 
+        let touched = registry
+            .touch_stream_session_poll(&session.id, &timestamp("2026-04-06T12:00:20Z"))
+            .await
+            .unwrap();
+        assert_eq!(
+            touched.last_poll_at,
+            Some(timestamp("2026-04-06T12:00:20Z"))
+        );
+
         let updated = registry
             .update_stream_session_state(UpdateStreamSessionStateRequest {
                 session_id: &session.id,

crates/crank-registry/src/postgres/stream.rs

@@ -198,6 +198,43 @@ impl PostgresRegistry {
         }
     }
 
+    pub async fn touch_stream_session_poll(
+        &self,
+        id: &StreamSessionId,
+        now: &OffsetDateTime,
+    ) -> Result<StreamSession, RegistryError> {
+        let row = sqlx::query(
+            "update stream_sessions
+                set last_poll_at = $2::timestamptz
+              where id = $1
+            returning
+                id,
+                workspace_id,
+                agent_id,
+                operation_id,
+                protocol,
+                mode,
+                status,
+                cursor_json,
+                state_json,
+                expires_at,
+                last_poll_at,
+                created_at,
+                closed_at",
+        )
+        .bind(id.as_str())
+        .bind(now)
+        .fetch_optional(&self.pool)
+        .await?;
+
+        match row.as_ref() {
+            Some(row) => map_stream_session(row),
+            None => Err(RegistryError::StreamSessionNotFound {
+                session_id: id.as_str().to_owned(),
+            }),
+        }
+    }
+
     pub async fn list_stream_sessions(
         &self,
         filter: StreamSessionFilter<'_>,