feat(nodes): remote ingress via Traefik file provider

Remote replicas publish an ephemeral host port; the agent reports the
assigned binding back in the create_container result and the backend
renders a per-service file-provider config into TRAEFIK_DYNAMIC_DIR
pointing Traefik at the node's mesh IP + port. Routes are rewritten on
every remote reconcile and removed on teardown or local placement.

Also: RetireService retires remote leftovers when a service returns to
local placement; remove_container is idempotent agent-side; tombstoned
replicas skip remove dispatch; the domains-stay-local ceiling is gone.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/backend/internal/api/ingress.go

@@ -0,0 +1,171 @@
+package api
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+
+	"containr/internal/database"
+	"containr/internal/database/sqlcdb"
+	"containr/internal/deployment"
+)
+
+// Remote ingress: replicas on node agents aren't on the hub's
+// containr-network, so Traefik's Docker provider can't see them. Instead
+// the backend renders one file-provider config per service into
+// TRAEFIK_DYNAMIC_DIR (a directory Traefik watches), pointing the
+// loadbalancer at the node's reachable IP + the ephemeral host port the
+// agent reported back after `create_container`.
+//
+// Empty dir → feature off (bare-metal dev). Files are best-effort: a
+// failed write never fails a reconcile.
+
+func ingressDir() string { return os.Getenv("TRAEFIK_DYNAMIC_DIR") }
+
+func ingressFile(serviceID string) string {
+	return filepath.Join(ingressDir(), "containr-"+serviceID+".yml")
+}
+
+// jsonInt coerces JSON-ish numbers (int/int32/int64/float64) to int —
+// spec fields arrive as int32, agent payloads unmarshal as float64.
+func jsonInt(v interface{}) int {
+	switch n := v.(type) {
+	case int:
+		return n
+	case int32:
+		return int(n)
+	case int64:
+		return int(n)
+	case float64:
+		return int(n)
+	}
+	return 0
+}
+
+// reportedHostPorts parses the agent's create_container result —
+// {"name": ..., "host_ports": {"80/tcp": "32768"}}. Older agents return a
+// bare name string; JSON parse failure means no port info.
+func reportedHostPorts(result string) map[string]string {
+	var out struct {
+		HostPorts map[string]string `json:"host_ports"`
+	}
+	if json.Unmarshal([]byte(result), &out) != nil {
+		return nil
+	}
+	return out.HostPorts
+}
+
+// nodeIngressIP picks the address the hub can reach the node on. Mesh
+// overlays first — the agent operator joined a mesh precisely so the hub
+// can reach it — then the reported primary IP as a LAN fallback.
+func nodeIngressIP(agent sqlcdb.NodeAgent) string {
+	var meta struct {
+		Mesh map[string]string `json:"mesh"`
+	}
+	_ = json.Unmarshal(agent.Metadata.RawMessage, &meta)
+	for _, prefix := range []string{"tailscale", "netbird", "wg", "zt"} {
+		var keys []string
+		for name := range meta.Mesh {
+			keys = append(keys, name)
+		}
+		sort.Strings(keys)
+		for _, name := range keys {
+			if strings.HasPrefix(name, prefix) && meta.Mesh[name] != "" {
+				return meta.Mesh[name]
+			}
+		}
+	}
+	return agent.IpAddress
+}
+
+// syncRemoteIngress rewrites the service's file-provider config from the
+// live remote replica set. Called after every remote reconcile so replica
+// adds/removals and node retargets converge the upstream list.
+func syncRemoteIngress(ctx context.Context, db *database.DB, spec deployment.RuntimeSpec) {
+	if ingressDir() == "" {
+		return
+	}
+	domains := spec.Domains
+	if len(domains) == 0 && spec.Domain != "" {
+		domains = []string{spec.Domain}
+	}
+	if len(domains) == 0 || spec.Port <= 0 {
+		removeServiceIngress(spec.ServiceID)
+		return
+	}
+
+	q := sqlcdb.New(db.DB)
+	rows, err := q.ListServiceContainers(ctx, spec.ServiceID)
+	if err != nil {
+		return
+	}
+	type upstream struct{ ip, port string }
+	var servers []upstream
+	for _, row := range rows {
+		var st struct {
+			State string `json:"state"`
+		}
+		_ = json.Unmarshal(row.Status.RawMessage, &st)
+		if st.State != "running" {
+			continue
+		}
+		var port string
+		var plist []map[string]interface{}
+		if err := json.Unmarshal(row.Ports.RawMessage, &plist); err == nil {
+			for _, p := range plist {
+				if hp, ok := p["host_port"].(float64); ok && hp > 0 {
+					port = fmt.Sprintf("%d", int(hp))
+				}
+			}
+		}
+		if port == "" {
+			continue
+		}
+		agent, err := q.GetAgent(ctx, row.NodeAgentID)
+		if err != nil {
+			continue
+		}
+		if ip := nodeIngressIP(agent); ip != "" {
+			servers = append(servers, upstream{ip, port})
+		}
+	}
+	if len(servers) == 0 {
+		removeServiceIngress(spec.ServiceID)
+		return
+	}
+
+	router := "svc-" + spec.ServiceID[:8]
+	rules := make([]string, 0, len(domains))
+	for _, d := range domains {
+		rules = append(rules, "Host(`"+d+"`)")
+	}
+	var b strings.Builder
+	b.WriteString("http:\n  routers:\n    " + router + ":\n")
+	b.WriteString("      rule: \"" + strings.Join(rules, " || ") + "\"\n")
+	b.WriteString("      entrypoints: [web]\n")
+	b.WriteString("      service: " + router + "\n")
+	b.WriteString("  services:\n    " + router + ":\n      loadBalancer:\n        servers:\n")
+	for _, s := range servers {
+		b.WriteString("          - url: \"http://" + s.ip + ":" + s.port + "\"\n")
+	}
+	// Atomic-ish: write temp then rename so Traefik's watcher never reads a
+	// truncated file.
+	tmp := ingressFile(spec.ServiceID) + ".tmp"
+	if err := os.WriteFile(tmp, []byte(b.String()), 0o644); err != nil {
+		return
+	}
+	_ = os.Rename(tmp, ingressFile(spec.ServiceID))
+}
+
+// removeServiceIngress deletes the service's remote route. Called on
+// remote teardown and when a service returns to local placement.
+func removeServiceIngress(serviceID string) {
+	if ingressDir() == "" {
+		return
+	}
+	_ = os.Remove(ingressFile(serviceID))
+}