Optimize CI caching for Blacksmith runners, fix SNMP bulk walk on Mikrotik

- Dockerfile: add BuildKit cache mounts for Go module and build caches,
  pin both stages to Alpine 3.23
- CI: replace BUILDKIT_INLINE_CACHE with registry-based layer caching
  (mode=max) for branch and release builds
- .dockerignore: exclude test files, Rust legacy, nix, and other
  non-build artifacts from Docker context
- SNMP: lower MaxRepetitions from default 50 to 10 to prevent Mikrotik
  routers from timing out during bulk walks

.dockerignore

@@ -1,11 +1,24 @@
 .git/
+.github/
 .gitignore
+.direnv/
+.envrc
+.cargo/
+.claude/
+.conductor/
 Dockerfile
 .dockerignore
 README.md
+docker-compose.example.yml
+flake.nix
+flake.lock
+cover.out
+coverage/
+proto/
 *.db
 *.db-shm
 *.db-wal
+*_test.go
 src/
 native/
 target/

.github/workflows/ci.yml

@@ -86,8 +86,8 @@ jobs:
           context: .
           push: true
           provenance: false
-          build-args: |
-            BUILDKIT_INLINE_CACHE=1
+          cache-from: type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:buildcache
+          cache-to: type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:buildcache,mode=max
           tags: |
             ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:${{ steps.branch.outputs.name }}
             ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:sha-${{ github.sha }}
@@ -170,7 +170,8 @@ jobs:
           provenance: false
           build-args: |
             VERSION=${{ needs.version.outputs.version }}
-            BUILDKIT_INLINE_CACHE=1
+          cache-from: type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:buildcache-${{ matrix.arch }}
+          cache-to: type=registry,ref=${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:buildcache-${{ matrix.arch }},mode=max
           tags: |
             ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:${{ needs.version.outputs.version }}-${{ matrix.arch }}
             docker.io/${{ env.DOCKERHUB_IMAGE }}:${{ needs.version.outputs.version }}-${{ matrix.arch }}

Dockerfile

@@ -1,12 +1,15 @@
-FROM golang:1.25-alpine AS builder
+FROM golang:1.25-alpine3.23 AS builder
 WORKDIR /app
 COPY go.mod go.sum ./
-RUN go mod download
+RUN --mount=type=cache,target=/go/pkg/mod \
+    go mod download
 COPY . .
 ARG VERSION=dev
-RUN CGO_ENABLED=0 go build -ldflags="-s -w -X main.version=${VERSION}" -o towerops-agent .
+RUN --mount=type=cache,target=/go/pkg/mod \
+    --mount=type=cache,target=/root/.cache/go-build \
+    CGO_ENABLED=0 go build -ldflags="-s -w -X main.version=${VERSION}" -o towerops-agent .
 
-FROM alpine:3.21
+FROM alpine:3.23
 RUN apk add --no-cache ca-certificates iputils
 COPY --from=builder /app/towerops-agent /usr/local/bin/towerops-agent
 RUN adduser -D -u 1000 towerops && chown towerops /usr/local/bin/towerops-agent

snmp.go

@@ -10,6 +10,21 @@ import (
 	"github.com/towerops-app/towerops-agent/pb"
 )
 
+// snmpQuerier abstracts SNMP operations for testability.
+type snmpQuerier interface {
+	Get(oids []string) (*gosnmp.SnmpPacket, error)
+	BulkWalkAll(rootOid string) ([]gosnmp.SnmpPDU, error)
+}
+
+// snmpDial connects to an SNMP device and returns a querier + close function.
+var snmpDial = func(dev *pb.SnmpDevice) (snmpQuerier, func(), error) {
+	conn, err := newSnmpConn(dev)
+	if err != nil {
+		return nil, nil, err
+	}
+	return conn, func() { _ = conn.Conn.Close() }, nil
+}
+
 // executeSnmpJob runs SNMP GET/WALK queries for a job and sends results.
 func executeSnmpJob(job *pb.AgentJob, resultCh chan<- *pb.SnmpResult) {
 	dev := job.SnmpDevice
@@ -18,12 +33,12 @@ func executeSnmpJob(job *pb.AgentJob, resultCh chan<- *pb.SnmpResult) {
 		return
 	}
 
-	conn, err := newSnmpConn(dev)
+	conn, closeFn, err := snmpDial(dev)
 	if err != nil {
 		slog.Error("snmp connect", "job_id", job.JobId, "device", dev.Ip, "error", err)
 		return
 	}
-	defer func() { _ = conn.Conn.Close() }()
+	defer closeFn()
 
 	oidValues := make(map[string]string)
 
@@ -85,7 +100,7 @@ func executeCredentialTest(job *pb.AgentJob, resultCh chan<- *pb.CredentialTestR
 		return
 	}
 
-	conn, err := newSnmpConn(dev)
+	conn, closeFn, err := snmpDial(dev)
 	timestamp := time.Now().Unix()
 
 	if err != nil {
@@ -97,7 +112,7 @@ func executeCredentialTest(job *pb.AgentJob, resultCh chan<- *pb.CredentialTestR
 		}
 		return
 	}
-	defer func() { _ = conn.Conn.Close() }()
+	defer closeFn()
 
 	result, err := conn.Get([]string{"1.3.6.1.2.1.1.1.0"})
 	if err != nil {
@@ -126,10 +141,11 @@ func executeCredentialTest(job *pb.AgentJob, resultCh chan<- *pb.CredentialTestR
 // newSnmpConn creates a gosnmp.GoSNMP connection from protobuf device config.
 func newSnmpConn(dev *pb.SnmpDevice) (*gosnmp.GoSNMP, error) {
 	conn := &gosnmp.GoSNMP{
-		Target:  dev.Ip,
-		Port:    uint16(dev.Port),
-		Timeout: 10 * time.Second,
-		Retries: 2,
+		Target:         dev.Ip,
+		Port:           uint16(dev.Port),
+		Timeout:        10 * time.Second,
+		Retries:        2,
+		MaxRepetitions: 10,
 	}
 
 	// Transport