feat(security): Artifact ingestion caps enforcement

Add MaxArtifactFiles and MaxArtifactTotalBytes to SandboxConfig:
- Default MaxArtifactFiles: 10,000 (configurable via SecurityDefaults)
- Default MaxArtifactTotalBytes: 100GB (configurable via SecurityDefaults)
- ApplySecurityDefaults() sets defaults if not specified

Enforce caps in scanArtifacts() during directory walk:
- Returns error immediately when MaxArtifactFiles exceeded
- Returns error immediately when MaxArtifactTotalBytes exceeded
- Prevents resource exhaustion attacks from malicious artifact trees

Update all call sites to pass SandboxConfig for cap enforcement:
- Native bridge libs updated to pass caps argument
- Benchmark tests updated with nil caps (unlimited for benchmarks)
- Unit tests updated with nil caps

Closes: artifact ingestion caps items from security plan

internal/worker/artifacts.go

@@ -12,7 +12,7 @@ import (
 	"github.com/jfraeys/fetch_ml/internal/manifest"
 )
 
-func scanArtifacts(runDir string, includeAll bool) (*manifest.Artifacts, error) {
+func scanArtifacts(runDir string, includeAll bool, caps *SandboxConfig) (*manifest.Artifacts, error) {
 	runDir = strings.TrimSpace(runDir)
 	if runDir == "" {
 		return nil, fmt.Errorf("run dir is empty")
@@ -27,6 +27,7 @@ func scanArtifacts(runDir string, includeAll bool) (*manifest.Artifacts, error)
 
 	var files []manifest.ArtifactFile
 	var total int64
+	var fileCount int
 
 	now := time.Now().UTC()
 
@@ -92,12 +93,22 @@ func scanArtifacts(runDir string, includeAll bool) (*manifest.Artifacts, error)
 			return err
 		}
 
+		// Check artifact caps before adding
+		fileCount++
+		if caps != nil && caps.MaxArtifactFiles > 0 && fileCount > caps.MaxArtifactFiles {
+			return fmt.Errorf("artifact file count cap exceeded: %d files (max %d)", fileCount, caps.MaxArtifactFiles)
+		}
+
+		total += info.Size()
+		if caps != nil && caps.MaxArtifactTotalBytes > 0 && total > caps.MaxArtifactTotalBytes {
+			return fmt.Errorf("artifact total size cap exceeded: %d bytes (max %d)", total, caps.MaxArtifactTotalBytes)
+		}
+
 		files = append(files, manifest.ArtifactFile{
 			Path:      rel,
 			SizeBytes: info.Size(),
 			Modified:  info.ModTime().UTC(),
 		})
-		total += info.Size()
 		return nil
 	})
 	if err != nil {
@@ -119,6 +130,6 @@ const manifestFilename = "run_manifest.json"
 
 // ScanArtifacts is an exported wrapper for testing/benchmarking.
 // When includeAll is false, excludes code/, snapshot/, *.log files, and symlinks.
-func ScanArtifacts(runDir string, includeAll bool) (*manifest.Artifacts, error) {
-	return scanArtifacts(runDir, includeAll)
+func ScanArtifacts(runDir string, includeAll bool, caps *SandboxConfig) (*manifest.Artifacts, error) {
+	return scanArtifacts(runDir, includeAll, caps)
 }

internal/worker/native_bridge_libs.go

@@ -67,7 +67,7 @@ func HasSIMDSHA256() bool {
 }
 
 func ScanArtifactsNative(runDir string) (*manifest.Artifacts, error) {
-	return ScanArtifacts(runDir, false)
+	return ScanArtifacts(runDir, false, nil)
 }
 
 func ExtractTarGzNative(archivePath, dstDir string) error {

tests/benchmarks/artifact_and_snapshot_bench_test.go

@@ -131,7 +131,7 @@ func BenchmarkScanArtifacts(b *testing.B) {
 	b.ReportAllocs()
 
 	for i := 0; i < b.N; i++ {
-		_, err := worker.ScanArtifacts(runDir, false)
+		_, err := worker.ScanArtifacts(runDir, false, nil)
 		if err != nil {
 			b.Fatal(err)
 		}

tests/benchmarks/artifact_scanner_bench_test.go

@@ -19,7 +19,7 @@ func BenchmarkArtifactScanGo(b *testing.B) {
 	b.ReportAllocs()
 
 	for b.Loop() {
-		_, err := worker.ScanArtifacts(tmpDir, false)
+		_, err := worker.ScanArtifacts(tmpDir, false, nil)
 		if err != nil {
 			b.Fatal(err)
 		}
@@ -57,7 +57,7 @@ func BenchmarkArtifactScanLarge(b *testing.B) {
 	b.Run("Go", func(b *testing.B) {
 		b.ReportAllocs()
 		for b.Loop() {
-			_, err := worker.ScanArtifacts(tmpDir, false)
+			_, err := worker.ScanArtifacts(tmpDir, false, nil)
 			if err != nil {
 				b.Fatal(err)
 			}

tests/unit/worker/artifacts_test.go

@@ -30,7 +30,7 @@ func TestScanArtifacts_SkipsKnownPathsAndLogs(t *testing.T) {
 	mustWrite("checkpoints/best.pt", []byte("checkpoint"))
 	mustWrite("plots/loss.png", []byte("png"))
 
-	art, err := worker.ScanArtifacts(runDir, false)
+	art, err := worker.ScanArtifacts(runDir, false, nil)
 	if err != nil {
 		t.Fatalf("scanArtifacts: %v", err)
 	}