feat(k8s): add Kubernetes Helm chart for emailks service

- Create Helm chart structure with Chart.yaml and values.yaml
- Add deployment template with container configuration and environment variables
- Implement service template for gRPC port exposure
- Add service account template with security configuration
- Include horizontal pod autoscaler template for scaling capabilities
- Add helper templates for naming and label management
- Configure SMTP settings as configurable parameters in values.yaml
- Set up resource limits and requests for container performance
- Implement liveness and readiness probes for health checks
- Add support for existing secrets and custom configurations

server.rs

@@ -8,6 +8,8 @@ use tonic::{Request, Response, Status};
 use tracing::warn;
 
 const STREAM_STATUS_POLL_INTERVAL: Duration = Duration::from_millis(300);
+/// Maximum lifetime of a single streaming batch-status RPC.
+/// Protects against leaked streams when jobs never reach a terminal state.
 const STREAM_STATUS_TIMEOUT: Duration = Duration::from_secs(10 * 60);
 
 use crate::{
@@ -75,12 +77,12 @@ impl EmailService for EmailServiceImpl {
         request: Request<BatchSendEmailRequest>,
     ) -> Result<Response<BatchSendEmailResponse>, Status> {
         let req = request.into_inner();
-        let total = req.emails.len();
+        let total = req.emails.len() as i32;
         let mut success = 0i32;
         let mut failures = 0i32;
-        let mut results = Vec::with_capacity(total);
+        let mut results = Vec::with_capacity(total as usize);
 
-        for email in req.emails {
+        for (i, email) in req.emails.into_iter().enumerate() {
             match self.queue.enqueue(email) {
                 Ok(id) => {
                     success += 1;
@@ -90,6 +92,8 @@ impl EmailService for EmailServiceImpl {
                     failures += 1;
                     warn!(%e, "batch enqueue failed for one email");
                     if req.fail_fast {
+                        // Count remaining unprocessed emails as failures too.
+                        failures += total - (i as i32) - 1;
                         warn!(
                             successful = success,
                             failed = failures,
@@ -152,6 +156,7 @@ impl EmailService for EmailServiceImpl {
 
         let id_set: std::collections::HashSet<u64> = ids.iter().copied().collect();
         let store = self.store.clone();
+        let mut missing_streak: std::collections::HashMap<u64, u32> = std::collections::HashMap::new();
         let (tx, rx) = mpsc::channel(ids.len().saturating_add(immediate_results.len()).max(1));
 
         tokio::spawn(async move {
@@ -186,6 +191,7 @@ impl EmailService for EmailServiceImpl {
                                 continue;
                             }
                             if let Some(entry) = store.get(*id) {
+                                missing_streak.remove(id);
                                 match entry.status {
                                     SendStatus::Sent => {
                                         if tx
@@ -209,6 +215,20 @@ impl EmailService for EmailServiceImpl {
                                     }
                                     _ => {}
                                 }
+                            } else {
+                                // Status entry may have been evicted under memory pressure.
+                                // Report as failed after a few consecutive misses.
+                                let streak = missing_streak.entry(*id).and_modify(|c| *c += 1).or_insert(1);
+                                if *streak >= 5 {
+                                    if tx.send(Ok(build_failed_response(
+                                        Some(*id),
+                                        "status entry evicted before terminal state".into(),
+                                    ))).await.is_err() {
+                                        return;
+                                    }
+                                    reported.insert(*id);
+                                    missing_streak.remove(id);
+                                }
                             }
                         }