diff --git a/internal/modules/chunk/dnd/scenes/scriptorium_assets.go b/internal/modules/chunk/dnd/scenes/scriptorium_assets.go
index ec03ef5..284cde9 100644
--- a/internal/modules/chunk/dnd/scenes/scriptorium_assets.go
+++ b/internal/modules/chunk/dnd/scenes/scriptorium_assets.go
@@ -18,7 +18,7 @@ func RegisterPromptAssets(registry *llm.AssetRegistry) error {
 		{Name: "dnd.scenes.yaml", Path: "assets/prompts/dnd.scenes.yaml"},
 		{Name: "task.md", Path: "assets/prompts/task.md"},
 		{Name: "instructions.md", Path: "assets/prompts/instructions.md"},
-	})
+	}, sharedassets.SharedPromptFiles()...)
 	if err != nil {
 		return fmt.Errorf("prepare scene prompt assets: %w", err)
 	}
diff --git a/internal/modules/extract/dnd/spells/scriptorium_assets.go b/internal/modules/extract/dnd/spells/scriptorium_assets.go
index 47949d6..f661f89 100644
--- a/internal/modules/extract/dnd/spells/scriptorium_assets.go
+++ b/internal/modules/extract/dnd/spells/scriptorium_assets.go
@@ -18,7 +18,7 @@ func RegisterPromptAssets(registry *llm.AssetRegistry) error {
 		{Name: "dnd.spells.yaml", Path: "assets/prompts/dnd.spells.yaml"},
 		{Name: "task.md", Path: "assets/prompts/task.md"},
 		{Name: "instructions.md", Path: "assets/prompts/instructions.md"},
-	})
+	}, sharedassets.SharedPromptFiles()...)
 	if err != nil {
 		return fmt.Errorf("prepare spell prompt assets: %w", err)
 	}
diff --git a/internal/modules/sharedassets/assets.go b/internal/modules/sharedassets/assets.go
index a5c818b..be3a323 100644
--- a/internal/modules/sharedassets/assets.go
+++ b/internal/modules/sharedassets/assets.go
@@ -9,10 +9,28 @@ import (
 //go:embed assets/prompts/*.md
 var embeddedAssets embed.FS
 
+var commonDNDPromptFiles = []string{
+	"common-dnd-system.md",
+	"common-dnd-transcript.md",
+	"common-dnd-references.md",
+}
+
 func Register(registry *llm.AssetRegistry) error {
 	return registry.RegisterPromptFS(embeddedAssets, "assets/prompts")
 }
 
+func SharedPromptFiles() []SharedPromptFile {
+	files := make([]SharedPromptFile, 0, len(commonDNDPromptFiles))
+	for _, name := range commonDNDPromptFiles {
+		files = append(files, SharedPromptFile{
+			Name: name,
+			FS:   embeddedAssets,
+			Path: "assets/prompts/" + name,
+		})
+	}
+	return files
+}
+
 func CommonHashParts() []llm.AssetHashPart {
 	return []llm.AssetHashPart{
 		{FS: embeddedAssets, Path: "assets/prompts/common-dnd-system.md"},
diff --git a/internal/modules/sharedassets/prompt_fs.go b/internal/modules/sharedassets/prompt_fs.go
index a998539..5ba030f 100644
--- a/internal/modules/sharedassets/prompt_fs.go
+++ b/internal/modules/sharedassets/prompt_fs.go
@@ -18,14 +18,18 @@ type ModulePromptFile struct {
 	Path string
 }
 
-// ModulePromptFS builds a prompt filesystem for a module directory from
-// module-owned prompt files plus common D&D shared prompt files under the
-// module's sharedassets subdirectory.
-func ModulePromptFS(moduleDir string, moduleFS fs.FS, files []ModulePromptFile) (fs.FS, error) {
-	return modulePromptFS(moduleDir, moduleFS, files, embeddedAssets)
+// SharedPromptFile maps a caller-owned shared prompt file into a module's
+// Scriptorium-visible sharedassets prompt subdirectory.
+type SharedPromptFile struct {
+	Name string
+	FS   fs.FS
+	Path string
 }
 
-func modulePromptFS(moduleDir string, moduleFS fs.FS, files []ModulePromptFile, sharedFS fs.FS) (fs.FS, error) {
+// ModulePromptFS builds a prompt filesystem for a module directory from
+// module-owned prompt files plus caller-provided shared prompt files under the
+// module's sharedassets subdirectory.
+func ModulePromptFS(moduleDir string, moduleFS fs.FS, files []ModulePromptFile, sharedFiles ...SharedPromptFile) (fs.FS, error) {
 	cleanModuleDir, err := cleanPromptPath(moduleDir)
 	if err != nil {
 		return nil, fmt.Errorf("module prompt directory: %w", err)
@@ -33,10 +37,7 @@ func modulePromptFS(moduleDir string, moduleFS fs.FS, files []ModulePromptFile,
 	if moduleFS == nil {
 		return nil, fmt.Errorf("module prompt filesystem must not be nil")
 	}
-	if sharedFS == nil {
-		return nil, fmt.Errorf("shared prompt filesystem must not be nil")
-	}
-	assets := make(promptMapFS, len(files)+len(commonDNDPromptFiles))
+	assets := make(promptMapFS, len(files)+len(sharedFiles))
 	for _, file := range files {
 		name, err := cleanPromptPath(file.Name)
 		if err != nil {
@@ -56,22 +57,30 @@ func modulePromptFS(moduleDir string, moduleFS fs.FS, files []ModulePromptFile,
 		assets["assets/prompts/"+cleanModuleDir+"/"+name] = append([]byte(nil), data...)
 	}
 
-	for _, name := range commonDNDPromptFiles {
-		data, err := fs.ReadFile(sharedFS, "assets/prompts/"+name)
+	for _, file := range sharedFiles {
+		name, err := cleanPromptPath(file.Name)
 		if err != nil {
-			return nil, fmt.Errorf("read shared prompt asset %s: %w", name, err)
+			return nil, fmt.Errorf("shared prompt file name %q: %w", file.Name, err)
+		}
+		if strings.Contains(name, "/") {
+			return nil, fmt.Errorf("shared prompt file name %q must not contain path separators", file.Name)
+		}
+		if file.FS == nil {
+			return nil, fmt.Errorf("shared prompt file %q filesystem must not be nil", file.Name)
+		}
+		filePath, err := cleanPromptPath(file.Path)
+		if err != nil {
+			return nil, fmt.Errorf("shared prompt file path %q: %w", file.Path, err)
+		}
+		data, err := fs.ReadFile(file.FS, filePath)
+		if err != nil {
+			return nil, fmt.Errorf("read shared prompt asset %s: %w", filePath, err)
 		}
 		assets["assets/prompts/"+cleanModuleDir+"/sharedassets/"+name] = append([]byte(nil), data...)
 	}
 	return assets, nil
 }
 
-var commonDNDPromptFiles = []string{
-	"common-dnd-system.md",
-	"common-dnd-transcript.md",
-	"common-dnd-references.md",
-}
-
 type promptMapFS map[string][]byte
 
 func (m promptMapFS) Open(name string) (fs.File, error) {
diff --git a/internal/modules/sharedassets/prompt_fs_test.go b/internal/modules/sharedassets/prompt_fs_test.go
index 896da05..6605f0d 100644
--- a/internal/modules/sharedassets/prompt_fs_test.go
+++ b/internal/modules/sharedassets/prompt_fs_test.go
@@ -8,34 +8,40 @@ import (
 )
 
 func TestModulePromptFSCombinesModuleAndSharedPrompts(t *testing.T) {
-	fsys, err := ModulePromptFS("dnd.test", fstest.MapFS{
-		"assets/prompts/dnd.test.yaml": {Data: []byte("id: dnd.test")},
-		"assets/prompts/task.md":       {Data: []byte("task")},
+	sharedFS := fstest.MapFS{
+		"shared/system.md":     {Data: []byte("system")},
+		"shared/reference.md":  {Data: []byte("reference")},
+		"nested/transcript.md": {Data: []byte("transcript")},
+	}
+	fsys, err := ModulePromptFS("module.test", fstest.MapFS{
+		"assets/prompts/module.test.yaml": {Data: []byte("id: module.test")},
+		"assets/prompts/task.md":          {Data: []byte("task")},
 	}, []ModulePromptFile{
-		{Name: "dnd.test.yaml", Path: "assets/prompts/dnd.test.yaml"},
+		{Name: "module.test.yaml", Path: "assets/prompts/module.test.yaml"},
 		{Name: "task.md", Path: "assets/prompts/task.md"},
-	})
+	},
+		SharedPromptFile{Name: "system.md", FS: sharedFS, Path: "shared/system.md"},
+		SharedPromptFile{Name: "reference.md", FS: sharedFS, Path: "shared/reference.md"},
+		SharedPromptFile{Name: "transcript.md", FS: sharedFS, Path: "nested/transcript.md"},
+	)
 	if err != nil {
 		t.Fatalf("ModulePromptFS() error = %v, want nil", err)
 	}
 
 	tests := map[string]string{
-		"assets/prompts/dnd.test/dnd.test.yaml":                         "id: dnd.test",
-		"assets/prompts/dnd.test/task.md":                               "task",
-		"assets/prompts/dnd.test/sharedassets/common-dnd-system.md":     "",
-		"assets/prompts/dnd.test/sharedassets/common-dnd-transcript.md": "",
-		"assets/prompts/dnd.test/sharedassets/common-dnd-references.md": "",
+		"assets/prompts/module.test/module.test.yaml":           "id: module.test",
+		"assets/prompts/module.test/task.md":                    "task",
+		"assets/prompts/module.test/sharedassets/system.md":     "system",
+		"assets/prompts/module.test/sharedassets/reference.md":  "reference",
+		"assets/prompts/module.test/sharedassets/transcript.md": "transcript",
 	}
 	for path, want := range tests {
 		data, err := fs.ReadFile(fsys, path)
 		if err != nil {
 			t.Fatalf("ReadFile(%q) error = %v, want nil", path, err)
 		}
-		if len(data) == 0 {
-			t.Fatalf("ReadFile(%q) returned empty content", path)
-		}
-		if want != "" && !strings.Contains(string(data), want) {
-			t.Fatalf("ReadFile(%q) = %q, want substring %q", path, data, want)
+		if string(data) != want {
+			t.Fatalf("ReadFile(%q) = %q, want %q", path, data, want)
 		}
 	}
 
@@ -46,10 +52,17 @@ func TestModulePromptFSCombinesModuleAndSharedPrompts(t *testing.T) {
 	if len(entries) != 1 || entries[0].Name() != "assets" || !entries[0].IsDir() {
 		t.Fatalf("ReadDir(.) = %#v, want assets directory", entries)
 	}
+	entries, err = fs.ReadDir(fsys, "assets/prompts/module.test/sharedassets")
+	if err != nil {
+		t.Fatalf("ReadDir(sharedassets) error = %v, want nil", err)
+	}
+	if len(entries) != 3 || entries[0].Name() != "reference.md" || entries[1].Name() != "system.md" || entries[2].Name() != "transcript.md" {
+		t.Fatalf("ReadDir(sharedassets) = %#v, want sorted shared prompt entries", entries)
+	}
 }
 
 func TestModulePromptFSRejectsMissingModuleFile(t *testing.T) {
-	_, err := ModulePromptFS("dnd.test", fstest.MapFS{}, []ModulePromptFile{
+	_, err := ModulePromptFS("module.test", fstest.MapFS{}, []ModulePromptFile{
 		{Name: "task.md", Path: "assets/prompts/task.md"},
 	})
 	if err == nil || !strings.Contains(err.Error(), "read module prompt asset assets/prompts/task.md") {
@@ -58,18 +71,18 @@ func TestModulePromptFSRejectsMissingModuleFile(t *testing.T) {
 }
 
 func TestModulePromptFSRejectsMissingSharedFile(t *testing.T) {
-	_, err := modulePromptFS("dnd.test", fstest.MapFS{
+	_, err := ModulePromptFS("module.test", fstest.MapFS{
 		"assets/prompts/task.md": {Data: []byte("task")},
 	}, []ModulePromptFile{
 		{Name: "task.md", Path: "assets/prompts/task.md"},
-	}, fstest.MapFS{})
-	if err == nil || !strings.Contains(err.Error(), "read shared prompt asset common-dnd-system.md") {
-		t.Fatalf("modulePromptFS() error = %v, want missing shared asset context", err)
+	}, SharedPromptFile{Name: "system.md", FS: fstest.MapFS{}, Path: "shared/system.md"})
+	if err == nil || !strings.Contains(err.Error(), "read shared prompt asset shared/system.md") {
+		t.Fatalf("ModulePromptFS() error = %v, want missing shared asset context", err)
 	}
 }
 
 func TestModulePromptFSRejectsNestedVirtualFileName(t *testing.T) {
-	_, err := ModulePromptFS("dnd.test", fstest.MapFS{
+	_, err := ModulePromptFS("module.test", fstest.MapFS{
 		"assets/prompts/task.md": {Data: []byte("task")},
 	}, []ModulePromptFile{
 		{Name: "nested/task.md", Path: "assets/prompts/task.md"},
@@ -78,3 +91,33 @@ func TestModulePromptFSRejectsNestedVirtualFileName(t *testing.T) {
 		t.Fatalf("ModulePromptFS() error = %v, want nested file name error", err)
 	}
 }
+
+func TestModulePromptFSRejectsNestedSharedFileName(t *testing.T) {
+	_, err := ModulePromptFS("module.test", fstest.MapFS{
+		"assets/prompts/task.md": {Data: []byte("task")},
+	}, []ModulePromptFile{
+		{Name: "task.md", Path: "assets/prompts/task.md"},
+	}, SharedPromptFile{Name: "nested/system.md", FS: fstest.MapFS{}, Path: "shared/system.md"})
+	if err == nil || !strings.Contains(err.Error(), "shared prompt file name") || !strings.Contains(err.Error(), "must not contain path separators") {
+		t.Fatalf("ModulePromptFS() error = %v, want nested shared file name error", err)
+	}
+}
+
+func TestModulePromptFSRejectsInvalidModuleDir(t *testing.T) {
+	_, err := ModulePromptFS(".", fstest.MapFS{}, nil)
+	if err == nil || !strings.Contains(err.Error(), "module prompt directory") {
+		t.Fatalf("ModulePromptFS() error = %v, want module directory context", err)
+	}
+}
+
+func TestModulePromptFSRejectsNilFilesystems(t *testing.T) {
+	_, err := ModulePromptFS("module.test", nil, nil)
+	if err == nil || !strings.Contains(err.Error(), "module prompt filesystem must not be nil") {
+		t.Fatalf("ModulePromptFS() error = %v, want nil module filesystem error", err)
+	}
+
+	_, err = ModulePromptFS("module.test", fstest.MapFS{}, nil, SharedPromptFile{Name: "system.md", Path: "shared/system.md"})
+	if err == nil || !strings.Contains(err.Error(), "shared prompt file \"system.md\" filesystem must not be nil") {
+		t.Fatalf("ModulePromptFS() error = %v, want nil shared filesystem error", err)
+	}
+}