Close test-gap noise rows and sync coverage documentation.

Restore P1/P2/fleet/erasure COVERED rows in PROBLEMS.md with refreshed counts; drop fixed poll-duplication and Vitest-noise items. Silence ECONNREFUSED stderr in Vitest setup, alias download mock exports, and expand erasure/Path Tracer test coverage.

server/internal/erasure/codec_test.go

@@ -72,6 +72,31 @@ func TestDecodeInsufficientShards(t *testing.T) {
 	}
 }
 
+func TestEncodeRejectsEmptyPayload(t *testing.T) {
+	if _, _, err := Encode(nil, DefaultParams()); err == nil {
+		t.Fatal("expected error for empty payload")
+	}
+}
+
+func TestParamsNormalizeInvalid(t *testing.T) {
+	if _, err := (Params{DataShards: 0, ParityShards: 0}).Normalize(); err != nil {
+		t.Fatalf("zero values should normalize: %v", err)
+	}
+	if _, err := (Params{DataShards: -1, ParityShards: 1}).Normalize(); err == nil {
+		t.Fatal("expected error for negative data shards")
+	}
+	if _, err := (Params{DataShards: 200, ParityShards: 100}).Normalize(); err == nil {
+		t.Fatal("expected error for too many shards")
+	}
+}
+
+func TestParamsShardCounts(t *testing.T) {
+	p := Params{DataShards: 4, ParityShards: 2}
+	if p.MinShards() != 4 || p.TotalShards() != 6 {
+		t.Fatalf("min=%d total=%d", p.MinShards(), p.TotalShards())
+	}
+}
+
 func TestBuildPlanStoresShards(t *testing.T) {
 	store := NewShardStore()
 	payload := []byte("lane-plan-payload")