perf: build lower layer squashes only when a scan reads them

The image source provider now reads images with `image.WithLazyLayerSquashes`: the image squash is built during the read, and each lower layer's squash only when something reads it. A squashed scan never does, so it skips a full file tree copy per layer.

- squashed scans: faster, much less memory on images with many layers
- `scan`/`attest` with all-layers or deep-squashed stay eager (an internal ctx flag), since eager squashing overlaps with fetching and indexing and is faster when every layer gets read
- library callers going through `syft.GetSource` get lazy for every scope, since the scope isn't known when the image is read. All-layers is still correct, just slower
- no public API change

Signed-off-by: Alex Goodman <wagoodman@users.noreply.github.com>

cmd/syft/internal/commands/scan.go

@@ -260,6 +260,11 @@ func getSource(ctx context.Context, opts *options.Catalog, userInput string, sou
 		cfg = cfg.WithDigestAlgorithms(hashers...)
 	}
 
+	if source.ParseScope(opts.Scope) != source.SquashedScope {
+		// every other scope reads each layer's squash, which is cheaper to build while the image is read
+		ctx = internal.WithEagerLayerSquashes(ctx)
+	}
+
 	src, err := syft.GetSource(ctx, userInput, cfg)
 	if err != nil {
 		return nil, fmt.Errorf("could not determine source: %w", err)

go.mod

@@ -22,7 +22,7 @@ require (
 	github.com/anchore/go-sync v0.1.2
 	github.com/anchore/go-version v1.2.2-0.20200701162849-18adb9c92b9b
 	github.com/anchore/packageurl-go v0.2.0
-	github.com/anchore/stereoscope v0.3.4
+	github.com/anchore/stereoscope v0.3.5-0.20261030023738-43c8f7e4fc46
 	github.com/anmitsu/go-shlex v0.0.0-20200514113438-38f4b401e2be
 	github.com/aquasecurity/go-pep440-version v0.0.1
 	github.com/bitnami/go-version v0.0.0-20250131085805-b1f57a8634ef
@@ -156,7 +156,6 @@ require (
 	github.com/aws/smithy-go v1.28.1 // indirect
 	github.com/aymanbagabas/go-osc52/v2 v2.0.1 // indirect
 	github.com/bahlo/generic-list-go v0.2.0 // indirect
-	github.com/becheran/wildmatch-go v1.0.0 // indirect
 	github.com/bgentry/go-netrc v0.0.0-20140422174119-9fd32a8b3d3d // indirect
 	github.com/bodgit/plumbing v1.3.0 // indirect
 	github.com/bodgit/sevenzip v1.6.1 // indirect
@@ -173,7 +172,7 @@ require (
 	github.com/cncf/xds/go v0.0.0-20260202195803-dba9d589def2 // indirect
 	github.com/containerd/cgroups/v3 v3.1.3 // indirect
 	github.com/containerd/containerd/api v1.12.0 // indirect
-	github.com/containerd/containerd/v2 v2.4.1 // indirect
+	github.com/containerd/containerd/v2 v2.4.2 // indirect
 	github.com/containerd/continuity v0.5.0 // indirect
 	github.com/containerd/errdefs v1.0.0 // indirect
 	github.com/containerd/errdefs/pkg v0.3.0 // indirect
@@ -189,9 +188,9 @@ require (
 	github.com/containers/ocicrypt v1.3.2 // indirect
 	github.com/cyberphone/json-canonicalization v0.0.0-20241213102144-19d51d7fe467 // indirect
 	github.com/cyphar/filepath-securejoin v0.7.0 // indirect
-	github.com/docker/cli v29.8.2+incompatible // indirect
+	github.com/docker/cli v29.9.1+incompatible // indirect
 	github.com/docker/docker-credential-helpers v0.9.8 // indirect
-	github.com/docker/go-connections v0.8.1 // indirect
+	github.com/docker/go-connections v0.8.2 // indirect
 	github.com/docker/go-units v0.5.0 // indirect
 	github.com/dsnet/compress v0.0.2-0.20230904184137-39efe44ab707 // indirect
 	github.com/emirpasic/gods v1.18.1 // indirect
@@ -205,7 +204,7 @@ require (
 	github.com/gabriel-vasile/mimetype v1.4.15 // indirect
 	github.com/gkampitakis/ciinfo v0.3.4 // indirect
 	github.com/go-git/gcfg v1.5.1-0.20230307220236-3a3c6141e376 // indirect
-	github.com/go-jose/go-jose/v4 v4.1.5 // indirect
+	github.com/go-jose/go-jose/v4 v4.1.6 // indirect
 	github.com/go-logr/logr v1.4.4 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-restruct/restruct v1.2.0-alpha // indirect
@@ -246,8 +245,8 @@ require (
 	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/moby/docker-image-spec v1.3.1 // indirect
 	github.com/moby/locker v1.0.1 // indirect
-	github.com/moby/moby/api v1.56.0 // indirect
-	github.com/moby/moby/client v0.6.0 // indirect
+	github.com/moby/moby/api v1.56.1 // indirect
+	github.com/moby/moby/client v0.6.2 // indirect
 	github.com/moby/sys/capability v0.4.0 // indirect
 	github.com/moby/sys/signal v0.7.1 // indirect
 	github.com/moby/sys/user v0.4.1 // indirect
@@ -328,7 +327,7 @@ require (
 	go.opentelemetry.io/otel/sdk/metric v1.46.0 // indirect
 	go.opentelemetry.io/otel/trace v1.46.0 // indirect
 	go.podman.io/image/v5 v5.41.2 // indirect
-	go.podman.io/storage v1.64.1 // indirect
+	go.podman.io/storage v1.64.2 // indirect
 	go4.org v0.0.0-20230225012048-214862532bf5 // indirect
 	golang.org/x/crypto v0.58.0 // indirect
 	golang.org/x/oauth2 v0.37.0 // indirect

go.sum

@@ -150,8 +150,8 @@ github.com/anchore/go-version v1.2.2-0.20200701162849-18adb9c92b9b h1:e1bmaoJfZV
 github.com/anchore/go-version v1.2.2-0.20200701162849-18adb9c92b9b/go.mod h1:Bkc+JYWjMCF8OyZ340IMSIi2Ebf3uwByOk6ho4wne1E=
 github.com/anchore/packageurl-go v0.2.0 h1:CkrM4RMUwrEGAiE1OVlxaZNzWj0TuHRey7o4T/EAErk=
 github.com/anchore/packageurl-go v0.2.0/go.mod h1:2JCgOQMIsqZ7TmliXG4PnUthPJAKE3mWQbsW2XHjAOE=
-github.com/anchore/stereoscope v0.3.4 h1:dT5AfjCTXUJowMiRIc+VBQVwvwnIEwnxxwA1GwAkMxw=
-github.com/anchore/stereoscope v0.3.4/go.mod h1:+HxqHTt7dvH8mea0mf3ulqkf084VvHiT1grpAQf5uEs=
+github.com/anchore/stereoscope v0.3.5-0.20261030023738-43c8f7e4fc46 h1:0ZL8d1vjsJKNUu480/F8x41O701vbQvYgZFmoiKho7o=
+github.com/anchore/stereoscope v0.3.5-0.20261030023738-43c8f7e4fc46/go.mod h1:sfJpowN3ZfLVtx0QTc+3/kdM7ub37Hpi9aBVmdANqz4=
 github.com/andreyvit/diff v0.0.0-20170406064948-c7f18ee00883/go.mod h1:rCTlJbsFo29Kk6CurOXKm700vrz8f0KW0JNfpkRJY/8=
 github.com/andybalholm/brotli v1.2.0 h1:ukwgCxwYrmACq68yiUqwIWnGY0cTPox/M94sVwToPjQ=
 github.com/andybalholm/brotli v1.2.0/go.mod h1:rzTDkvFWvIrjDXZHkuS16NPggd91W3kUSvPlQ1pLaKY=
@@ -217,8 +217,6 @@ github.com/aymanbagabas/go-udiff v0.3.1 h1:LV+qyBQ2pqe0u42ZsUEtPiCaUoqgA9gYRDs3v
 github.com/aymanbagabas/go-udiff v0.3.1/go.mod h1:G0fsKmG+P6ylD0r6N/KgQD/nWzgfnl8ZBcNLgcbrw8E=
 github.com/bahlo/generic-list-go v0.2.0 h1:5sz/EEAK+ls5wF+NeqDpk5+iNdMDXrh3z3nPnH1Wvgk=
 github.com/bahlo/generic-list-go v0.2.0/go.mod h1:2KvAjgMlE5NNynlg/5iLrrCCZ2+5xWbdbCW3pNTGyYg=
-github.com/becheran/wildmatch-go v1.0.0 h1:mE3dGGkTmpKtT4Z+88t8RStG40yN9T+kFEGj2PZFSzA=
-github.com/becheran/wildmatch-go v1.0.0/go.mod h1:gbMvj0NtVdJ15Mg/mH9uxk2R1QCistMyU7d9KFzroX4=
 github.com/beorn7/perks v0.0.0-20180321164747-3a771d992973/go.mod h1:Dwedo/Wpr24TaqPxmxbtue+5NUziq4I4S80YR8gNf3Q=
 github.com/beorn7/perks v1.0.0/go.mod h1:KWe93zE9D1o94FZ5RNwFwVgaQK1VOXiVxmqh+CedLV8=
 github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
@@ -300,8 +298,8 @@ github.com/containerd/cgroups/v3 v3.1.3 h1:eUNflyMddm18+yrDmZPn3jI7C5hJ9ahABE5q6
 github.com/containerd/cgroups/v3 v3.1.3/go.mod h1:PKZ2AcWmSBsY/tJUVhtS/rluX0b1uq1GmPO1ElCmbOw=
 github.com/containerd/containerd/api v1.12.0 h1:kuQm82SbDrCuO4n7hf2L8zsBtZLuympyq5X/VotfX2A=
 github.com/containerd/containerd/api v1.12.0/go.mod h1:EBcSzoi9Vl18cdODaXUCskf3D2NT8lsSXeZJnU5jIUc=
-github.com/containerd/containerd/v2 v2.4.1 h1:DUx/ZJN7cEu0WuzHClDB+68H/bqMEH5pWoEjf0ae4hc=
-github.com/containerd/containerd/v2 v2.4.1/go.mod h1:vgLdtvl3prFk1d3ZVqQcsDD5Q9IKM+vAIdU54U85w+I=
+github.com/containerd/containerd/v2 v2.4.2 h1:p6Qg+xbEz8lvwdhHDx0U469xENvp4LgGBx+E7djXkGw=
+github.com/containerd/containerd/v2 v2.4.2/go.mod h1:vgLdtvl3prFk1d3ZVqQcsDD5Q9IKM+vAIdU54U85w+I=
 github.com/containerd/continuity v0.5.0 h1:7a85HZpCSs+1Zps0Ee3DPSuAWY+0SJM1JNM51nlEVDg=
 github.com/containerd/continuity v0.5.0/go.mod h1:/lNJvtJKUQStBzpVQ1+rasXO1LAWtUQssk28EZvJ3nE=
 github.com/containerd/errdefs v1.0.0 h1:tg5yIfIlQIrxYtu9ajqY42W3lpS19XqdxRQeEwYG8PI=
@@ -353,14 +351,14 @@ github.com/distribution/reference v0.6.0 h1:0IXCQ5g4/QMHHkarYzh5l+u8T3t73zM5Qvfr
 github.com/distribution/reference v0.6.0/go.mod h1:BbU0aIcezP1/5jX/8MP0YiH4SdvB5Y4f/wlDRiLyi3E=
 github.com/djherbis/times v1.6.0 h1:w2ctJ92J8fBvWPxugmXIv7Nz7Q3iDMKNx9v5ocVH20c=
 github.com/djherbis/times v1.6.0/go.mod h1:gOHeRAz2h+VJNZ5Gmc/o7iD9k4wW7NMVqieYCY99oc0=
-github.com/docker/cli v29.8.2+incompatible h1:2zgdFuoFst2T80oS42vhKGxkd0JRo305eIEKTsxR7pQ=
-github.com/docker/cli v29.8.2+incompatible/go.mod h1:JLrzqnKDaYBop7H2jaqPtU4hHvMKP+vjCwu2uszcLI8=
+github.com/docker/cli v29.9.1+incompatible h1:E4YGy7TMkPk7mFsXTVUyjHxVeJdjTDfIS0X4Q0+ioQ0=
+github.com/docker/cli v29.9.1+incompatible/go.mod h1:JLrzqnKDaYBop7H2jaqPtU4hHvMKP+vjCwu2uszcLI8=
 github.com/docker/distribution v2.8.3+incompatible h1:AtKxIZ36LoNK51+Z6RpzLpddBirtxJnzDrHLEKxTAYk=
 github.com/docker/distribution v2.8.3+incompatible/go.mod h1:J2gT2udsDAN96Uj4KfcMRqY0/ypR+oyYUYmja8H+y+w=
 github.com/docker/docker-credential-helpers v0.9.8 h1:bIREROb7So6PRlq6KTtdS9MPEjC29OQRkFNlvK2OX8Q=
 github.com/docker/docker-credential-helpers v0.9.8/go.mod h1:v1S+hepowrQXITkEfw6o4+BMbGot02wiKpzWhGUZK6c=
-github.com/docker/go-connections v0.8.1 h1:JibmG5hULs5qXSr/cp/w3Pw5fZuStt4MOHMUExb29/M=
-github.com/docker/go-connections v0.8.1/go.mod h1:no1qkHdjq7kLMGUXYAduOhYPSJxxvgWBh7ogVvptn3Q=
+github.com/docker/go-connections v0.8.2 h1:9d9DEokx5W7qlr0shkFXIxEA7+TTD+llwzcykSlxMNc=
+github.com/docker/go-connections v0.8.2/go.mod h1:no1qkHdjq7kLMGUXYAduOhYPSJxxvgWBh7ogVvptn3Q=
 github.com/docker/go-units v0.5.0 h1:69rxXcBk27SvSaaxTtLh/8llcHD8vYHT7WSdRZ/jvr4=
 github.com/docker/go-units v0.5.0/go.mod h1:fgPhTUdO+D/Jk86RDLlptpiXQzgHJF7gydDDbaIK4Dk=
 github.com/dsnet/compress v0.0.2-0.20230904184137-39efe44ab707 h1:2tV76y6Q9BB+NEBasnqvs7e49aEBFI8ejC89PSnWH+4=
@@ -443,8 +441,8 @@ github.com/go-git/go-git/v5 v5.19.3/go.mod h1:Ye4C8dVigkqrv9UsB4NMdSLV4yAIkLiIhW
 github.com/go-gl/glfw v0.0.0-20190409004039-e6da0acd62b1/go.mod h1:vR7hzQXu2zJy9AVAgeJqvqgH9Q5CA+iKCZ2gyEVpxRU=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20191125211704-12ad95a8df72/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=
 github.com/go-gl/glfw/v3.3/glfw v0.0.0-20200222043503-6f7a984d4dc4/go.mod h1:tQ2UAYgL5IevRw8kRxooKSPJfGvJ9fJQFa0TUsXzTg8=
-github.com/go-jose/go-jose/v4 v4.1.5 h1:RjgjO2LOtWOJKUC5wpwY9LR3B3vwVAz6JS2YHfYU6eA=
-github.com/go-jose/go-jose/v4 v4.1.5/go.mod h1:x4oUasVrzR7071A4TnHLGSPpNOm2a21K9Kf04k1rs08=
+github.com/go-jose/go-jose/v4 v4.1.6 h1:sNRkftxFJxwsILiQukqp5z83QBSmntVwmgRY7AqBDO4=
+github.com/go-jose/go-jose/v4 v4.1.6/go.mod h1:x4oUasVrzR7071A4TnHLGSPpNOm2a21K9Kf04k1rs08=
 github.com/go-kit/kit v0.8.0/go.mod h1:xBxKIO96dXMWWy0MnWVtmwkA9/13aqxPnvrjFYMA2as=
 github.com/go-kit/kit v0.9.0/go.mod h1:xBxKIO96dXMWWy0MnWVtmwkA9/13aqxPnvrjFYMA2as=
 github.com/go-logfmt/logfmt v0.3.0/go.mod h1:Qt1PoO58o5twSAckw1HlFXLmHsOX5/0LbT9GBnD5lWE=
@@ -748,10 +746,10 @@ github.com/moby/docker-image-spec v1.3.1 h1:jMKff3w6PgbfSa69GfNg+zN/XLhfXJGnEx3N
 github.com/moby/docker-image-spec v1.3.1/go.mod h1:eKmb5VW8vQEh/BAr2yvVNvuiJuY6UIocYsFu/DxxRpo=
 github.com/moby/locker v1.0.1 h1:fOXqR41zeveg4fFODix+1Ch4mj/gT0NE1XJbp/epuBg=
 github.com/moby/locker v1.0.1/go.mod h1:S7SDdo5zpBK84bzzVlKr2V0hz+7x9hWbYC/kq7oQppc=
-github.com/moby/moby/api v1.56.0 h1:GQzua3NA599ASSIICx0iFgiJeO9YkdDARvQsm23ZZuQ=
-github.com/moby/moby/api v1.56.0/go.mod h1:sZ+THbVWkjOmBPPfbnzdD/G1LuIexWhqlSHHPTDQ1Uk=
-github.com/moby/moby/client v0.6.0 h1:AJjEB21QPbXSXjDsZorFBoDZPhMrfbpaPLgSMAW9Bgs=
-github.com/moby/moby/client v0.6.0/go.mod h1:OCo00wNRyA3m4lmJ228W3JbyCN4ZNNYjpOXiJydBdcQ=
+github.com/moby/moby/api v1.56.1 h1:PpWkvVPB7Fr/No8w+TfyJ/I6rWZ2YPZhT3JorIg+06c=
+github.com/moby/moby/api v1.56.1/go.mod h1:sZ+THbVWkjOmBPPfbnzdD/G1LuIexWhqlSHHPTDQ1Uk=
+github.com/moby/moby/client v0.6.2 h1:ekSPlMccrZGcw6Scb8T9D39qE0mB+XupU/yS0zNw9N4=
+github.com/moby/moby/client v0.6.2/go.mod h1:DGcnO7qmPJrqobx/ggQgQ/AUk+2wgVdQv7uxB0/mEsc=
 github.com/moby/sys/capability v0.4.0 h1:4D4mI6KlNtWMCM1Z/K0i7RV1FkX+DBDHKVJpCndZoHk=
 github.com/moby/sys/capability v0.4.0/go.mod h1:4g9IK291rVkms3LKCDOoYlnV8xKwoDTpIrNEE35Wq0I=
 github.com/moby/sys/mountinfo v0.7.2 h1:1shs6aH5s4o5H2zQLn796ADW1wMrIwHsyJ2v9KouLrg=
@@ -1074,8 +1072,8 @@ go.opentelemetry.io/otel/trace v1.46.0/go.mod h1:J7GAXweO77XSFkB/rmAqk9D6ihszhFj
 go.opentelemetry.io/proto/otlp v0.7.0/go.mod h1:PqfVotwruBrMGOCsRd/89rSnXhoiJIqeYNgFYFoEGnI=
 go.podman.io/image/v5 v5.41.2 h1:YnVaFrGLPWSBmipKfNvlOsGcBtk5bUxlPxQ+A6CS/uo=
 go.podman.io/image/v5 v5.41.2/go.mod h1:T/bzxEFpdpAzyHabPmcq5K+my3wBsht22sFkFjJSKT4=
-go.podman.io/storage v1.64.1 h1:DqbG8scW/bD3xHiSRzV7O5fzn46qVC+SwmUN6C6Fr5w=
-go.podman.io/storage v1.64.1/go.mod h1:ft0DzCRMZs1yn0rszmLYXEEwgd7IIc66JRwSRPUDwwc=
+go.podman.io/storage v1.64.2 h1:sIBU2vsdGo2gghTF17oxw4G4gojEZkPmt0LKiZWIwqc=
+go.podman.io/storage v1.64.2/go.mod h1:ft0DzCRMZs1yn0rszmLYXEEwgd7IIc66JRwSRPUDwwc=
 go.uber.org/atomic v1.7.0/go.mod h1:fEN4uk6kAWBTFdckzkM89CLk9XfWZrxpCo0nPH17wJc=
 go.uber.org/goleak v1.3.0 h1:2K3zAYmnTNqV73imy9J1T3WC+gmCePx2hEGkimedGto=
 go.uber.org/goleak v1.3.0/go.mod h1:CoHD4mav9JJNrW/WLlf7HGZPjdw8EucARQHekz1X6bE=

internal/layer_squashes.go

@@ -0,0 +1,17 @@
+package internal
+
+import "context"
+
+type eagerLayerSquashesKey struct{}
+
+// WithEagerLayerSquashes has the image source provider build every layer's squashed tree while it reads the
+// image, instead of the first time each one is used. Set it when the scan will read lower layers (any scope but
+// squashed): eager squashing overlaps with fetching and indexing the layers, so those scans finish sooner.
+func WithEagerLayerSquashes(ctx context.Context) context.Context {
+	return context.WithValue(ctx, eagerLayerSquashesKey{}, true)
+}
+
+func EagerLayerSquashes(ctx context.Context) bool {
+	v, _ := ctx.Value(eagerLayerSquashesKey{}).(bool)
+	return v
+}

syft/source/stereoscopesource/image_source_provider.go

@@ -6,6 +6,7 @@ import (
 	"github.com/anchore/go-collections"
 	"github.com/anchore/stereoscope"
 	"github.com/anchore/stereoscope/pkg/image"
+	"github.com/anchore/syft/internal"
 	"github.com/anchore/syft/syft/source"
 )
 
@@ -29,6 +30,10 @@ func (l stereoscopeImageSourceProvider) Name() string {
 }
 
 func (l stereoscopeImageSourceProvider) Provide(ctx context.Context) (source.Source, error) {
+	if !internal.EagerLayerSquashes(ctx) {
+		// lower layer squashes are only built if something reads them, so a squashed scan never pays for them
+		ctx = image.WithLazyLayerSquashes(ctx)
+	}
 	img, err := l.stereoscopeProvider.Provide(ctx)
 	if err != nil {
 		return nil, err

syft/source/stereoscopesource/image_source_provider_test.go

@@ -0,0 +1,76 @@
+package stereoscopesource
+
+import (
+	"context"
+	"path/filepath"
+	"testing"
+
+	"github.com/google/go-containerregistry/pkg/name"
+	"github.com/google/go-containerregistry/pkg/v1/random"
+	"github.com/google/go-containerregistry/pkg/v1/tarball"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/anchore/stereoscope"
+	"github.com/anchore/stereoscope/pkg/filetree"
+	"github.com/anchore/stereoscope/pkg/image"
+	"github.com/anchore/syft/internal"
+	"github.com/anchore/syft/syft/source"
+)
+
+func Test_stereoscopeImageSourceProvider_layerSquashes(t *testing.T) {
+	img, err := random.Image(1024, 3)
+	require.NoError(t, err)
+	tag, err := name.NewTag("localhost/layer-squashes:latest")
+	require.NoError(t, err)
+	archive := filepath.Join(t.TempDir(), "image.tar")
+	require.NoError(t, tarball.WriteToFile(archive, tag, img))
+
+	provide := func(t *testing.T, ctx context.Context) *stereoscopeImageSource {
+		providers := Providers(ProviderConfig{
+			StereoscopeImageProviderConfig: stereoscope.ImageProviderConfig{UserInput: archive},
+		})
+		for _, p := range providers {
+			if p.Value.Name() != image.DockerTarballSource {
+				continue
+			}
+			src, err := p.Value.Provide(ctx)
+			require.NoError(t, err)
+			t.Cleanup(func() { require.NoError(t, src.Close()) })
+			return src.(*stereoscopeImageSource)
+		}
+		t.Fatalf("no %s provider", image.DockerTarballSource)
+		return nil
+	}
+
+	lazy := provide(t, context.Background())
+	eager := provide(t, internal.WithEagerLayerSquashes(context.Background()))
+
+	// lower layers are built on first use unless eager was asked for, the top is the image squash either way
+	require.Len(t, lazy.image.Layers, 3)
+	for idx := range lazy.image.Layers {
+		_, isTree := lazy.image.Layers[idx].SquashedTree.(*filetree.FileTree)
+		assert.Equalf(t, idx == 2, isTree, "lazy layer %d", idx)
+		assert.IsTypef(t, &filetree.FileTree{}, eager.image.Layers[idx].SquashedTree, "eager layer %d", idx)
+	}
+
+	// every scope sees the same files either way
+	for _, scope := range []source.Scope{source.SquashedScope, source.AllLayersScope, source.DeepSquashedScope} {
+		t.Run(string(scope), func(t *testing.T) {
+			files := func(src *stereoscopeImageSource) []string {
+				res, err := src.FileResolver(scope)
+				require.NoError(t, err)
+				locs, err := res.FilesByGlob("**/*")
+				require.NoError(t, err)
+				var out []string
+				for _, l := range locs {
+					out = append(out, l.RealPath+"@"+l.FileSystemID)
+				}
+				return out
+			}
+			want := files(eager)
+			require.NotEmpty(t, want)
+			assert.ElementsMatch(t, want, files(lazy))
+		})
+	}
+}