diff --git a/libraries/fixture-composition/go/README.md b/libraries/fixture-composition/go/README.md
index 1b55cbd..1470414 100644
--- a/libraries/fixture-composition/go/README.md
+++ b/libraries/fixture-composition/go/README.md
@@ -15,9 +15,16 @@ composed module ships next to its code, plus the composition's own
 - `Merge` reads each `Source` with `Decode` (an error names the source) and
   combines them. Every statement has exactly one source: a role's grant on one
   kind, one installation, one stand-in module. A second source stating one is
-  `ErrConflict`, naming both sources, even when they agree. Sources are merged
-  in the order of their names, so the result does not depend on the order they
-  were found in.
+  `ErrConflict`, naming both sources, even when they agree; so is a second
+  statement of it **within one document**, which `Decode` refuses, since the
+  grants of a kind are a union and a file stating one twice widens it exactly
+  as two files would. Sources are merged in the order of their names, so the
+  result does not depend on the order they were found in.
+- A statement is keyed by organisation, role and kind — never by which module
+  ships the fragment — so the merge does not enforce that a module grants only
+  at its own kinds, and a composition's fragment deliberately grants at a
+  module's (its seeded collection). See the local service's README, "What the
+  merge does not enforce: ownership".
 - `Encode` writes YAML that `Decode` reads back unchanged.
 
 `go test -race ./...` covers the merge of two module fragments and a
diff --git a/libraries/fixture-composition/go/fixturecomposition.go b/libraries/fixture-composition/go/fixturecomposition.go
index a8f63f8..2ff172a 100644
--- a/libraries/fixture-composition/go/fixturecomposition.go
+++ b/libraries/fixture-composition/go/fixturecomposition.go
@@ -48,9 +48,10 @@ var (
 	actionGrammar = regexp.MustCompile(`^[a-z][a-z0-9_-]*$`)
 )
 
-// ErrConflict is two sources stating the same thing: the same role's grant on
-// one kind, the same installation, or the same stand-in module.
-var ErrConflict = errors.New("fixture-composition: two sources state the same grant")
+// ErrConflict is the same thing stated twice — the same role's grant on one
+// kind, the same installation, the same stand-in module — whether by two
+// sources (Merge) or twice within one document (Decode).
+var ErrConflict = errors.New("fixture-composition: one statement, stated twice")
 
 // Document is one fixture-composition document.
 type Document struct {
@@ -150,7 +151,19 @@ func Decode(data []byte) (Document, error) {
 	return doc, doc.validate()
 }
 
+// validate holds one document — a single fragment, or a merged one — to the
+// rules that do not depend on the fixture, the one-statement-one-source rule
+// included: the same (organisation, role, kind), the same installation and the
+// same stand-in module are each stated once in a document, as they are stated
+// by one source across documents (Merge).
+//
+// Within one document that rule is what the cross-source rule exists for. The
+// grants of a kind are a UNION — a role holding `documents.collection:read` on
+// `{id: seeded}` and again on `{all: true}` reads every collection, the exact
+// widening the rule refuses between two fragments — and whoever reads the
+// first statement has no reason to look for a second further down the file.
 func (d Document) validate() error {
+	grants := map[string]bool{}
 	for _, r := range d.Roles {
 		key := r.Key()
 		switch {
@@ -163,24 +176,42 @@ func (d Document) validate() error {
 			if err := CheckScope(sc.Kind, sc.Actions); err != nil {
 				return fmt.Errorf("%s: %w", key, err)
 			}
-			grants := make([]resources.Grant, 0, len(sc.Resources))
+			if grants[key+" "+sc.Kind] {
+				return fmt.Errorf("%w: %s's grant on %s is stated twice in one document; state it once, with every action and resource it covers",
+					ErrConflict, key, sc.Kind)
+			}
+			grants[key+" "+sc.Kind] = true
+			compiled := make([]resources.Grant, 0, len(sc.Resources))
 			for _, m := range sc.Resources {
-				grants = append(grants, m.Grant())
+				compiled = append(compiled, m.Grant())
 			}
-			if _, err := resources.Compile(grants); err != nil {
+			if _, err := resources.Compile(compiled); err != nil {
 				return fmt.Errorf("%s scope %s: %w", key, sc.Kind, err)
 			}
 		}
 	}
+	installations := map[string]bool{}
 	for _, i := range d.Installations {
 		if i.Target == "" || i.Role == "" {
 			return errors.New("an installation names no target or no role")
 		}
+		key := i.Organization + "/" + i.Target
+		if installations[key] {
+			return fmt.Errorf("%w: the installation of %s at %s is stated twice in one document; state it once",
+				ErrConflict, i.Target, i.Organization)
+		}
+		installations[key] = true
 	}
+	modules := map[string]bool{}
 	for _, m := range d.Modules {
 		if !kindGrammar.MatchString(m.Module) || len(m.Kinds) == 0 {
 			return fmt.Errorf("stand-in module %q names no valid module or no kind", m.Module)
 		}
+		if modules[m.Module] {
+			return fmt.Errorf("%w: stand-in module %s is stated twice in one document; state it once, with every kind it serves",
+				ErrConflict, m.Module)
+		}
+		modules[m.Module] = true
 		for _, k := range m.Kinds {
 			if err := CheckScope(k.Kind, k.Actions); err != nil {
 				return fmt.Errorf("stand-in module %s: %w", m.Module, err)
@@ -230,7 +261,9 @@ type Source struct {
 // owns it is the one a reader goes to: a composition narrowing a module's grant
 // to a seeded resource must not be silently widened by the module's, and a
 // module's grant copied into a composition is the drift this exists to end.
-// Within one source the document reads as it does alone.
+// Within ONE source the same rule holds, and for the same reason — the grants
+// of a kind are a union, so a fragment stating one twice widens it exactly as
+// two fragments would — which Decode refuses (validate).
 //
 // The result does not depend on the order the sources are given in: they are
 // merged in the order of their names, and two sources of one name are refused.
diff --git a/libraries/fixture-composition/go/fixturecomposition_test.go b/libraries/fixture-composition/go/fixturecomposition_test.go
index 42798e5..79bfad6 100644
--- a/libraries/fixture-composition/go/fixturecomposition_test.go
+++ b/libraries/fixture-composition/go/fixturecomposition_test.go
@@ -167,3 +167,59 @@ func TestMergeOfNothingIsTheSchemaAlone(t *testing.T) {
 		t.Fatalf("%q %v", encoded, err)
 	}
 }
+
+// The one-statement-one-source rule holds inside a fragment too: the grants of
+// a kind are a union, so a fragment stating the same (organisation, role, kind)
+// twice widens it exactly as two fragments would — `{id: seeded}` and again
+// `{all: true}` reads every resource of the kind, the failure the rule exists
+// to stop. The same holds for an installation and a stand-in module.
+func TestADocumentStatingOneThingTwiceIsRefused(t *testing.T) {
+	for name, tc := range map[string]struct{ doc, reason string }{
+		"widening grant": {`roles:
+  - organization: acme
+    name: viewer
+    scopes:
+      - {kind: documents.collection, actions: [read], resources: [{id: seeded}]}
+      - {kind: documents.collection, actions: [read], resources: [{all: true}]}`,
+			"acme/viewer's grant on documents.collection is stated twice in one document"},
+		"two role entries": {`roles:
+  - organization: acme
+    name: viewer
+    scopes: [{kind: documents, actions: [read]}]
+  - organization: acme
+    name: viewer
+    scopes: [{kind: documents, actions: [write]}]`,
+			"acme/viewer's grant on documents is stated twice"},
+		"installation": {`installations:
+  - {organization: acme, target: atlas, role: viewer, owner: alex}
+  - {organization: acme, target: atlas, role: editor, owner: alex}`,
+			"the installation of atlas at acme is stated twice"},
+		"stand-in": {`modules:
+  - {module: oracle, kinds: [{kind: oracle.answers, actions: [read]}]}
+  - {module: oracle, kinds: [{kind: oracle.answers, actions: [write]}]}`,
+			"stand-in module oracle is stated twice"},
+	} {
+		t.Run(name, func(t *testing.T) {
+			_, err := fixturecomposition.Decode([]byte(head + tc.doc + "\n"))
+			if !errors.Is(err, fixturecomposition.ErrConflict) || !strings.Contains(err.Error(), tc.reason) {
+				t.Fatalf("got %v, want a conflict naming %q", err, tc.reason)
+			}
+			// The merge names the fragment it came from.
+			_, err = fixturecomposition.Merge([]fixturecomposition.Source{{Name: "module ledger", Data: []byte(head + tc.doc + "\n")}})
+			if !errors.Is(err, fixturecomposition.ErrConflict) || !strings.HasPrefix(err.Error(), "module ledger: ") {
+				t.Fatalf("got %v, want the conflict named against module ledger", err)
+			}
+		})
+	}
+	// One role stating two different kinds, and two roles stating one kind,
+	// are not duplicates.
+	for _, doc := range []string{
+		`roles: [{organization: acme, name: viewer, scopes: [{kind: documents, actions: [read]}, {kind: robin.conversations, actions: [read]}]}]`,
+		`roles: [{organization: acme, name: viewer, scopes: [{kind: documents, actions: [read]}]}, {organization: acme, name: editor, scopes: [{kind: documents, actions: [read]}]}]`,
+		`installations: [{organization: acme, target: atlas, role: viewer, owner: alex}, {organization: globex, target: atlas, role: viewer, owner: zoe}]`,
+	} {
+		if _, err := fixturecomposition.Decode([]byte(head + doc + "\n")); err != nil {
+			t.Errorf("%s: %v", doc, err)
+		}
+	}
+}
diff --git a/modules/authority/services/local/README.md b/modules/authority/services/local/README.md
index dec7e17..7eae879 100644
--- a/modules/authority/services/local/README.md
+++ b/modules/authority/services/local/README.md
@@ -130,9 +130,27 @@ the one parser of the document:
   refused naming both, even when they agree, so a composition narrowing a
   module's grant to its seeded collection is never silently widened by the
   module's, and a module's grant copied into a playground is refused rather
-  than left to drift;
+  than left to drift. One **fragment** stating the same one twice is refused
+  too, and for the same reason: the grants of a kind are a union, so a file
+  granting `{id: seeded}` and again `{all: true}` widens exactly as two files
+  would;
 - the result does not depend on the order fragments are found in.
 
+**What the merge does not enforce: ownership.** A statement is keyed by
+organisation, role and kind alone, never by which module ships the fragment, so
+a module's fragment *can* grant at another module's kinds — and a composition's
+fragment does, by design: the robin playground grants its viewer
+`documents.collection` on the collection its own seed writes, a kind the
+document store owns. "One definition per module" is therefore a convention
+about where a grant is written, enforced only in that two fragments cannot
+state the same grant; it is not a check that a module grants on its own kinds.
+Nothing is lost by that: these fragments reach the development fixture alone,
+never a host, and a grant at a kind no composed module serves resolves to
+nothing (the authority intersects every capability with the delivered
+manifests), so the failure mode is a refusal, not a widening. A composition
+that wanted ownership enforced would have to name each kind's owning module in
+the document, which v1 does not.
+
 The authority module's own fragment
 (`modules/authority/configurations/local/fixture-composition.yaml`) is the
 schema line alone, so a composition of the authority and nothing else boots
diff --git a/modules/authority/services/local/code/pkg/business/state/composition.go b/modules/authority/services/local/code/pkg/business/state/composition.go
index 40be0d2..a9e5148 100644
--- a/modules/authority/services/local/code/pkg/business/state/composition.go
+++ b/modules/authority/services/local/code/pkg/business/state/composition.go
@@ -32,7 +32,9 @@ const CompositionSchema = fixturecomposition.Schema
 // until its own delivery replaces it. The document is read by the library's
 // one parser, which holds every rule that does not depend on the fixture;
 // this checks it against the fixture. Nothing is applied unless the whole
-// document is valid. It returns one line per effect, for the boot log.
+// document is valid, and the one applying step that can fail runs before the
+// one that cannot, so a refused installation leaves every role as it was. It
+// returns one line per effect, for the boot log.
 func (s *State) ApplyComposition(ctx context.Context, data []byte) ([]string, error) {
 	doc, err := fixturecomposition.Decode(data)
 	if err != nil {
@@ -46,12 +48,13 @@ func (s *State) ApplyComposition(ctx context.Context, data []byte) ([]string, er
 	if err != nil {
 		return nil, fmt.Errorf("%s: %w", CompositionDocument, err)
 	}
-	s.mu.Lock()
-	for key, role := range roles {
-		s.roles[key] = role
-	}
-	s.refreshRolesLocked()
-	s.mu.Unlock()
+	// The installations and stand-in modules go first, and the role grants
+	// after: everything above was validation, which changed nothing, and of the
+	// two applying steps only this one can fail. Granting first meant a
+	// composition whose installation was then refused had already widened the
+	// fixture's roles — the document was part-applied, against what this says.
+	// (LoadFixture's own internal steps are not individually reversible; a
+	// failure inside it still leaves what it applied before failing.)
 	if len(doc.Installations) > 0 || len(doc.Modules) > 0 {
 		setup, err := yaml.Marshal(fixtureFile{Installations: doc.Installations, Modules: doc.Modules})
 		if err != nil {
@@ -61,6 +64,12 @@ func (s *State) ApplyComposition(ctx context.Context, data []byte) ([]string, er
 			return nil, fmt.Errorf("%s: %w", CompositionDocument, err)
 		}
 	}
+	s.mu.Lock()
+	for key, role := range roles {
+		s.roles[key] = role
+	}
+	s.refreshRolesLocked()
+	s.mu.Unlock()
 	return append(lines, more...), nil
 }
 
diff --git a/modules/authority/services/local/code/pkg/business/state/composition_test.go b/modules/authority/services/local/code/pkg/business/state/composition_test.go
index bb3447f..47c9a32 100644
--- a/modules/authority/services/local/code/pkg/business/state/composition_test.go
+++ b/modules/authority/services/local/code/pkg/business/state/composition_test.go
@@ -130,7 +130,12 @@ modules:
 // A composition grants concrete permissions to roles the fixture defines, and
 // a refused document changes nothing.
 func TestCompositionRefusesByName(t *testing.T) {
-	valid := `{organization: acme, name: editor, scopes: [{kind: ledger.entry, actions: [read]}]}`
+	// A valid entry prepended to every roles case below, so a refused later
+	// entry cannot leave it applied. Its kind differs from the cases' own:
+	// one document states each (organisation, role, kind) once, so reusing
+	// ledger.entry here would make every case a duplicate and hide what it
+	// is actually testing.
+	valid := `{organization: acme, name: editor, scopes: [{kind: ledger.audit, actions: [read]}]}`
 	for name, tc := range map[string]struct{ doc, reason string }{
 		"empty":             {"", "the document is empty"},
 		"null":              {"null", "not a mapping"},
@@ -185,3 +190,38 @@ func TestTheShippedDefaultAddsNothing(t *testing.T) {
 		t.Fatalf("%v %v", lines, err)
 	}
 }
+
+// A document the fixture validates but that fails while being APPLIED leaves
+// every role as it was: the applying step that can fail runs before the one
+// that cannot.
+//
+// The document has to fail INSIDE LoadFixture to exercise that, which is the
+// whole point of the ordering. A refused installation does not: an owner the
+// fixture does not define is caught by checkComposedSetup, pure validation
+// that runs before either applying step in both orderings, so such a document
+// never reaches the code the ordering moves. A stand-in module named after a
+// fixture person does: checkComposedSetup only checks its kinds and logs a
+// line, and the core refuses it when the manifest is applied ("names a
+// person; a module's principal is its own"). With the role writes first, that
+// left the editor holding the grant from a document that was refused.
+func TestADocumentRefusedWhileApplyingLeavesTheRolesAlone(t *testing.T) {
+	k := fixtureOnly(t)
+	before := k.State.RoleScopes("acme", "editor")
+	lines, err := k.State.ApplyComposition(context.Background(), []byte(head+`
+roles:
+  - organization: acme
+    name: editor
+    scopes:
+      - {kind: ledger.entry, actions: [approve]}
+modules:
+  - module: maya
+    kinds: [{kind: maya.things, actions: [read]}]
+`))
+	if err == nil || !strings.Contains(err.Error(), "names a person") {
+		t.Fatalf("got %v (%v), want the stand-in module refused while applying", err, lines)
+	}
+	after := k.State.RoleScopes("acme", "editor")
+	if !state.Attenuates(before, after) || !state.Attenuates(after, before) {
+		t.Fatalf("a refused document granted the editor anyway: %v → %v", before, after)
+	}
+}
diff --git a/modules/authority/services/local/code/pkg/business/state/state.go b/modules/authority/services/local/code/pkg/business/state/state.go
index 007d1d4..ffc500f 100644
--- a/modules/authority/services/local/code/pkg/business/state/state.go
+++ b/modules/authority/services/local/code/pkg/business/state/state.go
@@ -7,7 +7,6 @@
 package state
 
 import (
-	fixturecomposition "github.com/codefly-dev/authority/libraries/fixture-composition/go"
 	"context"
 	"crypto/ed25519"
 	"errors"
@@ -20,6 +19,7 @@ import (
 	"github.com/codefly-dev/authority/libraries/authority-core/go/domain"
 	"github.com/codefly-dev/authority/libraries/authority-core/go/memstore"
 	"github.com/codefly-dev/authority/libraries/authority-core/go/scope"
+	fixturecomposition "github.com/codefly-dev/authority/libraries/fixture-composition/go"
 	resources "github.com/codefly-dev/authority/libraries/resources/go"
 	basev0 "github.com/codefly-dev/core/generated/go/codefly/base/v0"
 	"github.com/codefly-dev/core/workloadidentity"