diff --git a/compiler/semantic/checker.go b/compiler/semantic/checker.go
index e3c9a0c883..e34cde370f 100644
--- a/compiler/semantic/checker.go
+++ b/compiler/semantic/checker.go
@@ -9,7 +9,6 @@ import (
 	"github.com/brimdata/super"
 	"github.com/brimdata/super/compiler/ast"
 	"github.com/brimdata/super/compiler/semantic/sem"
-	"github.com/brimdata/super/runtime/sam/expr/agg"
 	"github.com/brimdata/super/sup"
 )
 
@@ -1155,11 +1154,11 @@ func (c *checker) error(loc ast.Node, err error) {
 func (c *checker) newFuser() *fuser {
 	//XXX "complete" option will be true when we have dual support for fusion
 	// and static types
-	return &fuser{agg.NewFuser(c.t.sctx, false), c.unknown}
+	return &fuser{super.NewFuser(c.t.sctx, false), c.unknown}
 }
 
 type fuser struct {
-	fuser   *agg.Fuser
+	fuser   *super.Fuser
 	unknown super.Type
 }
 
diff --git a/csup/fusedtype.go b/csup/fusedtype.go
index d6fbd43d14..0487eb3913 100644
--- a/csup/fusedtype.go
+++ b/csup/fusedtype.go
@@ -6,7 +6,6 @@ import (
 	"math"
 
 	"github.com/brimdata/super"
-	"github.com/brimdata/super/runtime/sam/expr/agg"
 )
 
 func FusedType(sctx *super.Context, r io.ReaderAt) (super.Type, error) {
@@ -21,7 +20,7 @@ func FusedType(sctx *super.Context, r io.ReaderAt) (super.Type, error) {
 	if _, err := s.Seek(0, io.SeekStart); err != nil {
 		return nil, err
 	}
-	fuser := agg.NewFuser(super.NewContext(), false)
+	fuser := super.NewFuser(super.NewContext(), false)
 	for size > 0 {
 		typ, n, err := readPart(sctx, r, size)
 		if err != nil {
diff --git a/csup/writer.go b/csup/writer.go
index 6c65e4a558..512e5762f0 100644
--- a/csup/writer.go
+++ b/csup/writer.go
@@ -6,7 +6,6 @@ import (
 	"io"
 
 	"github.com/brimdata/super"
-	"github.com/brimdata/super/runtime/sam/expr/agg"
 	"github.com/brimdata/super/sio"
 	"github.com/brimdata/super/sio/bsupio"
 	"github.com/brimdata/super/sup"
@@ -22,7 +21,7 @@ var maxObjectSize uint32 = 120_000
 type Serializer struct {
 	writer    io.WriteCloser
 	dynamic   *vbuild.DynamicBuilder
-	fuser     *agg.Fuser
+	fuser     *super.Fuser
 	fuserSctx *super.Context
 	size      uint64
 }
@@ -118,7 +117,7 @@ func (w *Serializer) finalizeObject() error {
 func (w *Serializer) fuse(dynamic *vector.Dynamic) {
 	if w.fuser == nil {
 		w.fuserSctx = super.NewContext()
-		w.fuser = agg.NewFuser(w.fuserSctx, false)
+		w.fuser = super.NewFuser(w.fuserSctx, false)
 	}
 	for _, vec := range dynamic.Values {
 		typ, err := w.fuserSctx.TranslateType(vec.Type())
diff --git a/runtime/sam/expr/agg/fuser.go b/fuser.go
similarity index 64%
rename from runtime/sam/expr/agg/fuser.go
rename to fuser.go
index d0297500c0..fcee11e3ee 100644
--- a/runtime/sam/expr/agg/fuser.go
+++ b/fuser.go
@@ -1,28 +1,25 @@
-package agg
+package super
 
 import (
 	"fmt"
 	"slices"
-
-	"github.com/brimdata/super"
-	"github.com/brimdata/super/sup"
 )
 
 // Fuser constructs a fused supertype for all the types passed to Fuse.
 type Fuser struct {
-	sctx     *super.Context
+	sctx     *Context
 	complete bool
 
-	typ   super.Type
-	types map[super.Type]struct{}
+	typ   Type
+	types map[Type]struct{}
 }
 
 // XXX this is used by type checker but I think we can use the other one
-func NewFuser(sctx *super.Context, complete bool) *Fuser {
-	return &Fuser{sctx: sctx, complete: complete, types: make(map[super.Type]struct{})}
+func NewFuser(sctx *Context, complete bool) *Fuser {
+	return &Fuser{sctx: sctx, complete: complete, types: make(map[Type]struct{})}
 }
 
-func (f *Fuser) Fuse(t super.Type) {
+func (f *Fuser) Fuse(t Type) {
 	if _, ok := f.types[t]; ok {
 		return
 	}
@@ -36,26 +33,26 @@ func (f *Fuser) Fuse(t super.Type) {
 }
 
 // Type returns the computed supertype.
-func (f *Fuser) Type() super.Type {
+func (f *Fuser) Type() Type {
 	return f.typ
 }
 
-func (f *Fuser) fuse(a, b super.Type) super.Type {
+func (f *Fuser) fuse(a, b Type) Type {
 	if a == b {
 		return a
 	}
-	if typ, ok := a.(*super.TypeFusion); ok {
+	if typ, ok := a.(*TypeFusion); ok {
 		return f.fusion(f.fuse(typ.Type, b))
 	}
-	if typ, ok := b.(*super.TypeFusion); ok {
+	if typ, ok := b.(*TypeFusion); ok {
 		return f.fusion(f.fuse(a, typ.Type))
 	}
 	if isAll(a) || isAll(b) {
-		return super.TypeAll
+		return TypeAll
 	}
 	switch a := a.(type) {
-	case *super.TypeRecord:
-		if b, ok := b.(*super.TypeRecord); ok {
+	case *TypeRecord:
+		if b, ok := b.(*TypeRecord); ok {
 			fields := slices.Clone(a.Fields)
 			// First change all fields to optional that are in "a" but not in "b".
 			for k, field := range fields {
@@ -71,7 +68,7 @@ func (f *Fuser) fuse(a, b super.Type) super.Type {
 					fields[i].Type = f.fuse(fields[i].Type, field.Type)
 				} else {
 					typ := f.makeOption(field.Type)
-					fields = append(fields, super.NewField(field.Name, typ))
+					fields = append(fields, NewField(field.Name, typ))
 				}
 			}
 			fusedRec := f.sctx.MustLookupTypeRecord(fields)
@@ -80,30 +77,30 @@ func (f *Fuser) fuse(a, b super.Type) super.Type {
 			}
 			return fusedRec
 		}
-	case *super.TypeArray:
-		if b, ok := b.(*super.TypeArray); ok {
+	case *TypeArray:
+		if b, ok := b.(*TypeArray); ok {
 			return f.fusion(f.sctx.LookupTypeArray(f.fuse(a.Type, b.Type)))
 		}
-	case *super.TypeSet:
-		if b, ok := b.(*super.TypeSet); ok {
+	case *TypeSet:
+		if b, ok := b.(*TypeSet); ok {
 			return f.fusion(f.sctx.LookupTypeSet(f.fuse(a.Type, b.Type)))
 		}
-	case *super.TypeMap:
-		if b, ok := b.(*super.TypeMap); ok {
+	case *TypeMap:
+		if b, ok := b.(*TypeMap); ok {
 			keyType := f.fuse(a.KeyType, b.KeyType)
 			valType := f.fuse(a.ValType, b.ValType)
 			return f.fusion(f.sctx.LookupTypeMap(keyType, valType))
 		}
-	case *super.TypeUnion:
+	case *TypeUnion:
 		types := f.fuseIntoUnionTypes(nil, a)
 		types = f.fuseIntoUnionTypes(types, b)
 		if len(types) == 1 {
 			return types[0]
 		}
-		union := f.sctx.MustLookupTypeUnion(super.Flatten(types))
+		union := f.sctx.MustLookupTypeUnion(Flatten(types))
 		return f.fusion(union)
-	case *super.TypeEnum:
-		if b, ok := b.(*super.TypeEnum); ok {
+	case *TypeEnum:
+		if b, ok := b.(*TypeEnum); ok {
 			var newSymbols []string
 			for _, s := range b.Symbols {
 				if !slices.Contains(a.Symbols, s) {
@@ -116,12 +113,12 @@ func (f *Fuser) fuse(a, b super.Type) super.Type {
 			symbols := append(slices.Clone(a.Symbols), newSymbols...)
 			return f.fusion(f.sctx.LookupTypeEnum(symbols))
 		}
-	case *super.TypeError:
-		if b, ok := b.(*super.TypeError); ok {
+	case *TypeError:
+		if b, ok := b.(*TypeError); ok {
 			return f.fusion(f.sctx.LookupTypeError(f.fuse(a.Type, b.Type)))
 		}
-	case *super.TypeNamed:
-		if b, ok := b.(*super.TypeNamed); ok && a.Name == b.Name {
+	case *TypeNamed:
+		if b, ok := b.(*TypeNamed); ok && a.Name == b.Name {
 			// if we got here without match a=b above, then there are
 			// two different types with the same name, which the type
 			// context shouldn't allow.
@@ -131,61 +128,61 @@ func (f *Fuser) fuse(a, b super.Type) super.Type {
 		// a barrier to type fusion.  Instead we fall through here and ,
 		// fuse the named type with the other type.
 	}
-	if _, ok := b.(*super.TypeUnion); ok {
+	if _, ok := b.(*TypeUnion); ok {
 		return f.fuse(b, a)
 	}
 	// Neither a nor b can be an anonymous union at this point.
-	return f.fusion(f.sctx.MustLookupTypeUnion([]super.Type{a, b}))
+	return f.fusion(f.sctx.MustLookupTypeUnion([]Type{a, b}))
 }
 
-func (f *Fuser) makeOption(t super.Type) super.Type {
-	if fusion, ok := t.(*super.TypeFusion); ok {
+func (f *Fuser) makeOption(t Type) Type {
+	if fusion, ok := t.(*TypeFusion); ok {
 		return f.sctx.LookupTypeFusion(f.makeOption(fusion.Type))
 	}
 	return f.sctx.Option(t)
 }
 
-func isAll(t super.Type) bool {
-	_, ok := t.(*super.TypeOfAll)
+func isAll(t Type) bool {
+	_, ok := t.(*TypeOfAll)
 	return ok
 }
 
-func (f *Fuser) redefPanic(named *super.TypeNamed) {
+func (f *Fuser) redefPanic(named *TypeNamed) {
 	previous := f.sctx.LookupByName(named.Name)
-	panic(fmt.Sprintf("type %s redefined: %s to %s", named.Name, sup.String(previous), sup.String(named.Type)))
+	panic(fmt.Sprintf("type %s redefined: %#v to %#v", named.Name, previous, named.Type))
 }
 
-func (f *Fuser) fuseInternal(typ super.Type) super.Type {
-	if typ, ok := typ.(*super.TypeFusion); ok {
+func (f *Fuser) fuseInternal(typ Type) Type {
+	if typ, ok := typ.(*TypeFusion); ok {
 		return f.fusion(f.fuseInternal(typ.Type))
 	}
-	var out super.Type
+	var out Type
 	switch typ := typ.(type) {
-	case *super.TypeRecord:
+	case *TypeRecord:
 		fields := slices.Clone(typ.Fields)
 		for i, field := range fields {
 			fields[i].Type = f.fuseInternal(field.Type)
 		}
 		out = f.sctx.MustLookupTypeRecord(fields)
-	case *super.TypeArray:
+	case *TypeArray:
 		out = f.sctx.LookupTypeArray(f.fuseInternal(typ.Type))
-	case *super.TypeSet:
+	case *TypeSet:
 		out = f.sctx.LookupTypeSet(f.fuseInternal(typ.Type))
-	case *super.TypeMap:
+	case *TypeMap:
 		out = f.sctx.LookupTypeMap(f.fuseInternal(typ.KeyType), f.fuseInternal(typ.ValType))
-	case *super.TypeUnion:
-		var types []super.Type
+	case *TypeUnion:
+		var types []Type
 		for _, t := range typ.Types {
 			types = f.fuseIntoUnionTypes(types, f.fuseInternal(t))
 		}
 		if len(types) == 1 {
 			out = types[0]
 		} else {
-			out = f.sctx.MustLookupTypeUnion(super.Flatten(types))
+			out = f.sctx.MustLookupTypeUnion(Flatten(types))
 		}
-	case *super.TypeEnum:
+	case *TypeEnum:
 		return typ
-	case *super.TypeError:
+	case *TypeError:
 		out = f.sctx.LookupTypeError(f.fuseInternal(typ.Type))
 	default:
 		out = typ
@@ -198,16 +195,16 @@ func (f *Fuser) fuseInternal(typ super.Type) super.Type {
 
 // fuseIntoUnionTypes fuses typ into types while maintaining the invariant that
 // types contains at most one type of each complex kind but no unions.
-func (f *Fuser) fuseIntoUnionTypes(types []super.Type, typ super.Type) []super.Type {
+func (f *Fuser) fuseIntoUnionTypes(types []Type, typ Type) []Type {
 	switch typ := typ.(type) {
-	case *super.TypeNamed:
+	case *TypeNamed:
 		return f.addNamed(types, typ)
-	case *super.TypeUnion:
+	case *TypeUnion:
 		for _, t := range typ.Types {
 			types = f.fuseIntoUnionTypes(types, t)
 		}
 		return types
-	case *super.TypeFusion:
+	case *TypeFusion:
 		return f.fuseIntoUnionTypes(types, typ.Type)
 	}
 	typKind := typ.Kind()
@@ -216,7 +213,7 @@ func (f *Fuser) fuseIntoUnionTypes(types []super.Type, typ super.Type) []super.T
 		case t == typ:
 			// This is already in the union.
 			return types
-		case typKind != super.PrimitiveKind && typKind == t.Kind() && !super.IsTypeNamed(t):
+		case typKind != PrimitiveKind && typKind == t.Kind() && !IsTypeNamed(t):
 			types[i] = noFusion(f.fuse(t, typ))
 			return types
 		}
@@ -224,9 +221,9 @@ func (f *Fuser) fuseIntoUnionTypes(types []super.Type, typ super.Type) []super.T
 	return append(types, noFusion(typ))
 }
 
-func (f *Fuser) addNamed(types []super.Type, named *super.TypeNamed) []super.Type {
+func (f *Fuser) addNamed(types []Type, named *TypeNamed) []Type {
 	for _, t := range types {
-		if existingNamed, ok := t.(*super.TypeNamed); ok && existingNamed.Name == named.Name {
+		if existingNamed, ok := t.(*TypeNamed); ok && existingNamed.Name == named.Name {
 			if existingNamed.Type != named.Type {
 				f.redefPanic(named)
 			}
@@ -236,24 +233,24 @@ func (f *Fuser) addNamed(types []super.Type, named *super.TypeNamed) []super.Typ
 	return append(types, named)
 }
 
-func noFusion(typ super.Type) super.Type {
-	if s, ok := typ.(*super.TypeFusion); ok {
+func noFusion(typ Type) Type {
+	if s, ok := typ.(*TypeFusion); ok {
 		return s.Type
 	}
 	return typ
 }
 
-func (f *Fuser) fusion(typ super.Type) super.Type {
+func (f *Fuser) fusion(typ Type) Type {
 	if !f.complete {
 		return typ
 	}
-	if typ, ok := typ.(*super.TypeFusion); ok {
+	if typ, ok := typ.(*TypeFusion); ok {
 		return typ
 	}
 	return f.sctx.LookupTypeFusion(typ)
 }
 
-func indexOfField(fields []super.Field, name string) (int, bool) {
+func indexOfField(fields []Field, name string) (int, bool) {
 	for i, f := range fields {
 		if f.Name == name {
 			return i, true
@@ -267,13 +264,13 @@ func indexOfField(fields []super.Field, name string) (int, bool) {
 // As long as all the fields names and optionality are the same, then
 // any type differences in the fused type of the child fields will be
 // captured by a fusion wrapper somewhere in the descendent type.
-func recChanged(a, b *super.TypeRecord) bool {
+func recChanged(a, b *TypeRecord) bool {
 	if len(a.Fields) != len(b.Fields) {
 		return true
 	}
 	for k, af := range a.Fields {
 		bf := b.Fields[k]
-		if af.Name != bf.Name || super.IsOptionType(af.Type) != super.IsOptionType(bf.Type) {
+		if af.Name != bf.Name || IsOptionType(af.Type) != IsOptionType(bf.Type) {
 			return true
 		}
 	}
diff --git a/runtime/sam/expr/agg/fuser_test.go b/fuser_test.go
similarity index 82%
rename from runtime/sam/expr/agg/fuser_test.go
rename to fuser_test.go
index d210d49831..82cc3baa54 100644
--- a/runtime/sam/expr/agg/fuser_test.go
+++ b/fuser_test.go
@@ -1,4 +1,4 @@
-package agg
+package super_test
 
 import (
 	"testing"
@@ -8,7 +8,7 @@ import (
 )
 
 func TestFuserSamePrimitiveTypeTwice(t *testing.T) {
-	s := NewFuser(super.NewContext(), false)
+	s := super.NewFuser(super.NewContext(), false)
 	typ := super.TypeInt64
 	s.Fuse(typ)
 	s.Fuse(typ)
diff --git a/runtime/sam/expr/agg/fuse.go b/runtime/sam/expr/agg/fuse.go
index b6494d120d..0cabc8a2f0 100644
--- a/runtime/sam/expr/agg/fuse.go
+++ b/runtime/sam/expr/agg/fuse.go
@@ -31,7 +31,7 @@ func (f *fuse) Result(sctx *super.Context) super.Value {
 	if len(f.shapes)+len(f.partials) == 0 {
 		return super.Null
 	}
-	fuser := NewFuser(sctx, f.complete)
+	fuser := super.NewFuser(sctx, f.complete)
 	for _, p := range f.partials {
 		typ, err := sctx.LookupByValue(p.Bytes())
 		if err != nil {
diff --git a/runtime/vam/expr/agg/fuse.go b/runtime/vam/expr/agg/fuse.go
index ee4f65c2a0..e655c4998f 100644
--- a/runtime/vam/expr/agg/fuse.go
+++ b/runtime/vam/expr/agg/fuse.go
@@ -4,7 +4,6 @@ import (
 	"fmt"
 
 	"github.com/brimdata/super"
-	samagg "github.com/brimdata/super/runtime/sam/expr/agg"
 	"github.com/brimdata/super/vector"
 )
 
@@ -54,7 +53,7 @@ func (f *fuse) Result(sctx *super.Context) vector.Any {
 	if len(f.types)+len(f.partials) == 0 {
 		return vector.NewNull(1)
 	}
-	fuser := samagg.NewFuser(sctx, f.complete)
+	fuser := super.NewFuser(sctx, f.complete)
 	for _, p := range f.partials {
 		typ, err := sctx.LookupByValue(p.Bytes())
 		if err != nil {
diff --git a/runtime/vam/op/fuse.go b/runtime/vam/op/fuse.go
index e9cdaad6ce..0989f77dbb 100644
--- a/runtime/vam/op/fuse.go
+++ b/runtime/vam/op/fuse.go
@@ -2,7 +2,6 @@ package op
 
 import (
 	"github.com/brimdata/super"
-	samagg "github.com/brimdata/super/runtime/sam/expr/agg"
 	"github.com/brimdata/super/runtime/vam/expr"
 	"github.com/brimdata/super/runtime/vam/expr/function"
 	"github.com/brimdata/super/sup"
@@ -15,7 +14,7 @@ type Fuse struct {
 	parent   vio.Puller
 	complete bool
 
-	fuser    *samagg.Fuser
+	fuser    *super.Fuser
 	vecs     []vector.Any
 	upcaster *function.Upcast
 	defuser  *expr.Defuse
@@ -38,7 +37,7 @@ func (f *Fuse) Pull(done bool) (vector.Any, error) {
 		return f.parent.Pull(done)
 	}
 	if f.fuser == nil {
-		f.fuser = samagg.NewFuser(f.sctx, f.complete)
+		f.fuser = super.NewFuser(f.sctx, f.complete)
 		for {
 			vec, err := f.parent.Pull(false)
 			if err != nil {
diff --git a/sio/anyio/file.go b/sio/anyio/file.go
index d664cc962a..1edffa577c 100644
--- a/sio/anyio/file.go
+++ b/sio/anyio/file.go
@@ -7,7 +7,6 @@ import (
 
 	"github.com/brimdata/super"
 	"github.com/brimdata/super/pkg/storage"
-	"github.com/brimdata/super/runtime/sam/expr/agg"
 	"github.com/brimdata/super/sbuf"
 	"github.com/brimdata/super/sio"
 )
@@ -94,7 +93,7 @@ func FileType(ctx context.Context, sctx *super.Context, engine storage.Engine, p
 	}
 	// XXX this should pass super true when type checker can handle it
 	rr := sbuf.PullerReader(sbuf.NewMaterializer(f))
-	fuser := agg.NewFuser(sctx, false)
+	fuser := super.NewFuser(sctx, false)
 	for range sampleSize {
 		val, err := rr.Read()
 		if val == nil || err != nil {