diff --git a/cmd/hclexp/hclexp.go b/cmd/hclexp/hclexp.go
index 36fd019..1371cc2 100644
--- a/cmd/hclexp/hclexp.go
+++ b/cmd/hclexp/hclexp.go
@@ -252,7 +252,15 @@ func clusterSetFromRoles(cs *hclload.ClusterSet, clusters []manifestClusterBlock
 				dbs = append(dbs, s.Databases...)
 			}
 		}
-		cs.Add(cl.Name, dbs)
+		// No member role composes this cluster in the selected env: it is
+		// modeled elsewhere (env-varying / external), so treat it as absent —
+		// proxies into it are satisfied rather than failing against an empty
+		// schema.
+		if len(dbs) == 0 {
+			cs.AddAbsent(cl.Name)
+		} else {
+			cs.Add(cl.Name, dbs)
+		}
 		for _, alias := range cl.Aliases {
 			cs.AddAlias(alias, cl.Name)
 		}
diff --git a/cmd/hclexp/hclexp_test.go b/cmd/hclexp/hclexp_test.go
index 3ee3f13..e8e3268 100644
--- a/cmd/hclexp/hclexp_test.go
+++ b/cmd/hclexp/hclexp_test.go
@@ -815,6 +815,128 @@ cluster "posthog" { roles = ["data"] }`)
 	require.Len(t, byRole["data"], 2, "exactly the two real problems, nothing more")
 }
 
+// #127: a cluster whose member roles have no composition in the selected env
+// should resolve @absent (proxies satisfied), not register empty-but-mapped
+// (proxies falsely erroring "not declared in that cluster's schema").
+func TestValidateManifest_UncomposedClusterIsAbsent(t *testing.T) {
+	root := t.TempDir()
+	// data role composes the posthog cluster, but only for env "local".
+	writeLayer(t, root, "layers/data/data.hcl", `
+database "posthog" {
+  table "sharded_events" {
+    order_by = ["id"]
+    column "id" { type = "UInt64" }
+    engine "merge_tree" {}
+  }
+}`)
+	// ingestion role is deployed in prod-us and proxies into the posthog cluster.
+	writeLayer(t, root, "layers/ingestion/ing.hcl", `
+database "posthog" {
+  table "events" {
+    engine "distributed" {
+      cluster_name    = "posthog"
+      remote_database = "posthog"
+      remote_table    = "sharded_events"
+    }
+    column "id" { type = "UInt64" }
+  }
+}`)
+	manifest := writeTemp(t, "roles.hcl", `
+role "data" {
+  env "local" { layers = ["layers/data"] }
+}
+role "ingestion" {
+  env "prod-us" { layers = ["layers/ingestion"] }
+}
+cluster "posthog" { roles = ["data"] }`)
+
+	// -env prod-us: data has no prod-us composition, so posthog is uncomposed.
+	results, err := validateManifest(manifest, "prod-us", root, hclload.ParseSkipSet(""), hclload.ValidateOptions{}, nil)
+	require.NoError(t, err)
+	byRole := map[string][]hclload.ValidationError{}
+	for _, r := range results {
+		byRole[r.Role] = r.Errs
+	}
+	require.Empty(t, byRole["ingestion"],
+		"proxy into an uncomposed cluster should be satisfied (@absent), not errored")
+}
+
+// The same cluster, in an env where its member role IS composed, validates the
+// proxy against its real schema.
+func TestValidateManifest_ComposedClusterValidates(t *testing.T) {
+	root := t.TempDir()
+	writeLayer(t, root, "layers/data/data.hcl", `
+database "posthog" {
+  table "sharded_events" {
+    order_by = ["id"]
+    column "id" { type = "UInt64" }
+    engine "merge_tree" {}
+  }
+  table "events" {
+    engine "distributed" {
+      cluster_name    = "posthog"
+      remote_database = "posthog"
+      remote_table    = "sharded_events"
+    }
+    column "id" { type = "UInt64" }
+  }
+}`)
+	manifest := writeTemp(t, "roles.hcl", `
+role "data" {
+  env "local" { layers = ["layers/data"] }
+}
+cluster "posthog" { roles = ["data"] }`)
+
+	results, err := validateManifest(manifest, "local", root, hclload.ParseSkipSet(""), hclload.ValidateOptions{}, nil)
+	require.NoError(t, err)
+	require.Len(t, results, 1)
+	require.Empty(t, results[0].Errs, "composed cluster: the proxy resolves against its real schema")
+}
+
+// #127 corollary: -cluster X=@absent must override a manifest-declared X.
+func TestValidateManifest_AbsentFlagOverridesManifestCluster(t *testing.T) {
+	root := t.TempDir()
+	// posthog is composed (data deployed in prod-us) but declares only 'other',
+	// so a proxy to sharded_events would error unless posthog is forced @absent.
+	writeLayer(t, root, "layers/data/data.hcl", `
+database "posthog" {
+  table "other" {
+    order_by = ["id"]
+    column "id" { type = "UInt64" }
+    engine "merge_tree" {}
+  }
+}`)
+	writeLayer(t, root, "layers/ingestion/ing.hcl", `
+database "posthog" {
+  table "events" {
+    engine "distributed" {
+      cluster_name    = "posthog"
+      remote_database = "posthog"
+      remote_table    = "sharded_events"
+    }
+    column "id" { type = "UInt64" }
+  }
+}`)
+	manifest := writeTemp(t, "roles.hcl", `
+role "data" {
+  env "prod-us" { layers = ["layers/data"] }
+}
+role "ingestion" {
+  env "prod-us" { layers = ["layers/ingestion"] }
+}
+cluster "posthog" { roles = ["data"] }`)
+
+	flags := []clusterEntry{{name: "posthog", stack: absentStack}}
+	results, err := validateManifest(manifest, "prod-us", root, hclload.ParseSkipSet(""), hclload.ValidateOptions{}, flags)
+	require.NoError(t, err)
+	byRole := map[string][]hclload.ValidationError{}
+	for _, r := range results {
+		byRole[r.Role] = r.Errs
+	}
+	require.Empty(t, byRole["ingestion"],
+		"-cluster posthog=@absent should override the manifest-declared posthog and satisfy the proxy")
+}
+
 // writeLayer writes content to root/rel, creating parent dirs.
 func writeLayer(t *testing.T, root, rel, content string) {
 	t.Helper()
diff --git a/internal/loader/hcl/clusterset.go b/internal/loader/hcl/clusterset.go
index ed3cfd4..0cbac92 100644
--- a/internal/loader/hcl/clusterset.go
+++ b/internal/loader/hcl/clusterset.go
@@ -36,6 +36,10 @@ func (cs *ClusterSet) Add(name string, dbs []DatabaseSpec) {
 	}
 	cs.declared[name] = declaredObjects(dbs)
 	cs.resolver[name] = NewSchemaResolver(dbs)
+	// A name is in exactly one category; the latest writer wins so a -cluster
+	// flag reliably overrides a manifest-derived mapping.
+	delete(cs.absent, name)
+	delete(cs.alias, name)
 }
 
 // AddAbsent declares a cluster that has no composition available in this env.
@@ -46,6 +50,11 @@ func (cs *ClusterSet) AddAbsent(name string) {
 		*cs = NewClusterSet()
 	}
 	cs.absent[name] = true
+	// Clear any prior mapping/alias so `-cluster NAME=@absent` overrides a
+	// manifest-declared cluster (mapped is checked before absent otherwise).
+	delete(cs.declared, name)
+	delete(cs.resolver, name)
+	delete(cs.alias, name)
 }
 
 // AddAlias records that alias resolves to base: a Distributed remote on the
@@ -56,6 +65,9 @@ func (cs *ClusterSet) AddAlias(alias, base string) {
 		*cs = NewClusterSet()
 	}
 	cs.alias[alias] = base
+	delete(cs.declared, alias)
+	delete(cs.resolver, alias)
+	delete(cs.absent, alias)
 }
 
 // resolveCluster follows alias links to the terminal (base) cluster name. A
diff --git a/internal/loader/hcl/validate_test.go b/internal/loader/hcl/validate_test.go
index 276bc28..63dcf64 100644
--- a/internal/loader/hcl/validate_test.go
+++ b/internal/loader/hcl/validate_test.go
@@ -550,6 +550,32 @@ func TestValidate_ProxyColumns_AbsentRemoteNoColumnCheck(t *testing.T) {
 		"@absent remote has no schema, so no column check fires")
 }
 
+// A name is in exactly one category: a later AddAbsent overrides a prior Add
+// (so `-cluster NAME=@absent` overrides a manifest-declared cluster).
+func TestValidate_ClusterSet_AbsentOverridesMapped(t *testing.T) {
+	cs := NewClusterSet()
+	cs.Add("aux", []DatabaseSpec{mkDBMixed("posthog",
+		[]TableSpec{mkTable("sharded", EngineMergeTree{})}, nil)})
+	cs.AddAbsent("aux") // override → absent
+	dbs := []DatabaseSpec{mkDBMixed("posthog",
+		[]TableSpec{mkDistTableOn("p", "aux", "posthog", "gone")}, nil)}
+	assert.Empty(t, Validate(dbs, ParseSkipSet(""), cs),
+		"AddAbsent overrides a prior Add; the proxy is satisfied")
+}
+
+// Conversely, a later Add overrides a prior AddAbsent (a real mapping wins over
+// an earlier absent marker).
+func TestValidate_ClusterSet_MappedOverridesAbsent(t *testing.T) {
+	cs := NewClusterSet()
+	cs.AddAbsent("aux")
+	cs.Add("aux", []DatabaseSpec{mkDBMixed("posthog",
+		[]TableSpec{mkTable("sharded", EngineMergeTree{})}, nil)}) // override → mapped
+	dbs := []DatabaseSpec{mkDBMixed("posthog",
+		[]TableSpec{mkDistTableOn("p", "aux", "posthog", "gone")}, nil)}
+	assert.Len(t, Validate(dbs, ParseSkipSet(""), cs), 1,
+		"Add overrides a prior AddAbsent; the proxy is validated and the missing remote errors")
+}
+
 // A cluster marked @absent has no local composition; references into it are
 // structurally unresolvable and count as satisfied.
 func TestValidate_DistributedRemote_AbsentCluster(t *testing.T) {