diff --git a/README.md b/README.md
index 2c42fa8..5726e04 100644
--- a/README.md
+++ b/README.md
@@ -110,7 +110,7 @@ go install github.com/mhiro2/seedling/cmd/seedling-gen@latest
    seedling-gen sql --explain schema.sql
    ```
 
-   This generates struct types, `RegisterBlueprints()`, deterministic `Defaults` for common scalar fields, relations, and Insert stubs. Fill in the `// TODO` callbacks with your DB logic:
+   This generates struct types, `NewRegistry()`, `RegisterBlueprints(reg)`, deterministic `Defaults` for common scalar fields, relations, and Insert stubs. Fill in the `// TODO` callbacks with your DB logic:
 
    ```go
    Insert: func(ctx context.Context, db seedling.DBTX, v Company) (Company, error) {
@@ -127,10 +127,9 @@ go install github.com/mhiro2/seedling/cmd/seedling-gen@latest
 
    ```go
    func TestUser(t *testing.T) {
-       seedling.ResetRegistry()
-       testutil.RegisterBlueprints()
+       reg := testutil.NewRegistry()
 
-       result := seedling.InsertOne[testutil.User](t, db)
+       result := seedling.NewSession[testutil.User](reg).InsertOne(t, db)
        user := result.Root()
 
        if user.ID == 0 {
@@ -146,12 +145,11 @@ go install github.com/mhiro2/seedling/cmd/seedling-gen@latest
 
    ```go
    func TestNamedUser(t *testing.T) {
-       seedling.ResetRegistry()
-       testutil.RegisterBlueprints()
+       reg := testutil.NewRegistry()
 
-       company := seedling.InsertOne[testutil.Company](t, db).Root()
+       company := seedling.NewSession[testutil.Company](reg).InsertOne(t, db).Root()
 
-       result := seedling.InsertOne[testutil.User](t, db,
+       result := seedling.NewSession[testutil.User](reg).InsertOne(t, db,
            seedling.Set("Name", "alice"),
            seedling.Use("company", company),
        )
@@ -161,12 +159,11 @@ go install github.com/mhiro2/seedling/cmd/seedling-gen@latest
    }
 
    func TestTaskProject(t *testing.T) {
-       seedling.ResetRegistry()
-       testutil.RegisterBlueprints()
+       reg := testutil.NewRegistry()
 
        // Only("project") inserts task + project subtree only,
        // skipping the assignee relation entirely.
-       result := seedling.InsertOne[testutil.Task](t, db,
+       result := seedling.NewSession[testutil.Task](reg).InsertOne(t, db,
            seedling.Only("project"),
        )
        _ = result
@@ -191,7 +188,7 @@ go install github.com/mhiro2/seedling/cmd/seedling-gen@latest
 ## 📂 Examples
 
 - [basic](./examples/basic): register blueprints and insert rows with automatic parent creation
-- [quickstart](./examples/quickstart): generated-style `RegisterBlueprints()` flow that matches the README Quick Start
+- [quickstart](./examples/quickstart): generated-style `NewRegistry()` / `RegisterBlueprints(reg)` flow that matches the README Quick Start
 - [custom-defaults](./examples/custom-defaults): customize values with `Set`, `With`, and `Generate`
 - [reuse-parent](./examples/reuse-parent): reuse existing rows with `Use`
 - [batch-insert](./examples/batch-insert): batch inserts with shared `Ref` dependencies and per-row `SeqRef` overrides
diff --git a/cmd/seedling-gen/main_test.go b/cmd/seedling-gen/main_test.go
index 20ce036..b2d72f0 100644
--- a/cmd/seedling-gen/main_test.go
+++ b/cmd/seedling-gen/main_test.go
@@ -235,6 +235,9 @@ func TestGenerate_OutputIncludesExpectedSections(t *testing.T) {
 		{name: "context import", substr: `"context"`, message: "output should import context"},
 		{name: "time import", substr: `"time"`, message: "output should import time"},
 		{name: "seedling import", substr: `"github.com/mhiro2/seedling"`, message: "output should import seedling"},
+		{name: "new registry helper", substr: "func NewRegistry() *seedling.Registry", message: "output should contain local registry helper"},
+		{name: "registry argument", substr: "func RegisterBlueprints(reg *seedling.Registry)", message: "output should accept a registry argument"},
+		{name: "register to registry", substr: "seedling.MustRegisterTo(reg", message: "output should register into the provided registry"},
 		{name: "company struct", substr: "type Company struct", message: "output should contain Company struct"},
 		{name: "user struct", substr: "type User struct", message: "output should contain User struct"},
 		{name: "company blueprint", substr: `Name:    "company"`, message: "output should register company blueprint"},
@@ -315,7 +318,10 @@ func TestGenerate_EmptyInput(t *testing.T) {
 	if !strings.Contains(output, "package empty") {
 		t.Fatalf("expected package declaration, got:\n%s", output)
 	}
-	if !strings.Contains(output, "func RegisterBlueprints()") {
+	if !strings.Contains(output, "func NewRegistry() *seedling.Registry") {
+		t.Fatalf("expected NewRegistry function, got:\n%s", output)
+	}
+	if !strings.Contains(output, "func RegisterBlueprints(reg *seedling.Registry)") {
 		t.Fatalf("expected RegisterBlueprints function, got:\n%s", output)
 	}
 }
diff --git a/cmd/seedling-gen/normalized_ir.go b/cmd/seedling-gen/normalized_ir.go
index cc7bb37..b1e0e47 100644
--- a/cmd/seedling-gen/normalized_ir.go
+++ b/cmd/seedling-gen/normalized_ir.go
@@ -53,11 +53,17 @@ type {{.StructName}} struct {
 `
 
 const normalizedBlueprintTemplate = `
-func RegisterBlueprints() {
+func NewRegistry() *seedling.Registry {
+	reg := seedling.NewRegistry()
+	RegisterBlueprints(reg)
+	return reg
+}
+
+func RegisterBlueprints(reg *seedling.Registry) {
 {{- range $i, $model := .}}
 {{- if $i}}
 {{ end }}
-	seedling.MustRegister(seedling.Blueprint[{{$model.TypeExpr}}]{
+	seedling.MustRegisterTo(reg, seedling.Blueprint[{{$model.TypeExpr}}]{
 		Name:  "{{$model.BlueprintID}}",
 		Table: "{{$model.TableName}}",
 {{- if isCompositePK $model}}
diff --git a/doc.go b/doc.go
index 3ab60af..d377f15 100644
--- a/doc.go
+++ b/doc.go
@@ -52,32 +52,34 @@
 //
 // Register a [Blueprint] for each model that seedling should create:
 //
-//	seedling.MustRegister(seedling.Blueprint[Company]{
-//	    Name:    "company",
-//	    Table:   "companies",
-//	    PKField: "ID",
-//	    Defaults: func() Company {
-//	        return Company{Name: "test-company"}
-//	    },
-//	    Insert: func(ctx context.Context, db seedling.DBTX, v Company) (Company, error) {
-//	        return insertCompany(ctx, db, v)
-//	    },
-//	})
-//
-//	seedling.MustRegister(seedling.Blueprint[User]{
-//	    Name:    "user",
-//	    Table:   "users",
-//	    PKField: "ID",
-//	    Defaults: func() User {
-//	        return User{Name: "test-user"}
-//	    },
-//	    Relations: []seedling.Relation{
-//	        {Name: "company", Kind: seedling.BelongsTo, LocalField: "CompanyID", RefBlueprint: "company"},
-//	    },
-//	    Insert: func(ctx context.Context, db seedling.DBTX, v User) (User, error) {
-//	        return insertUser(ctx, db, v)
-//	    },
-//	})
+//	func registerBlueprints(reg *seedling.Registry) {
+//	    seedling.MustRegisterTo(reg, seedling.Blueprint[Company]{
+//	        Name:    "company",
+//	        Table:   "companies",
+//	        PKField: "ID",
+//	        Defaults: func() Company {
+//	            return Company{Name: "test-company"}
+//	        },
+//	        Insert: func(ctx context.Context, db seedling.DBTX, v Company) (Company, error) {
+//	            return insertCompany(ctx, db, v)
+//	        },
+//	    })
+//
+//	    seedling.MustRegisterTo(reg, seedling.Blueprint[User]{
+//	        Name:    "user",
+//	        Table:   "users",
+//	        PKField: "ID",
+//	        Defaults: func() User {
+//	            return User{Name: "test-user"}
+//	        },
+//	        Relations: []seedling.Relation{
+//	            {Name: "company", Kind: seedling.BelongsTo, LocalField: "CompanyID", RefBlueprint: "company"},
+//	        },
+//	        Insert: func(ctx context.Context, db seedling.DBTX, v User) (User, error) {
+//	            return insertUser(ctx, db, v)
+//	        },
+//	    })
+//	}
 //
 // DBTX is intentionally opaque. Your insert callback and your call sites must
 // agree on the concrete handle type passed as db.
@@ -85,7 +87,10 @@
 // Then create rows directly in your tests:
 //
 //	func TestUser(t *testing.T) {
-//	    result := seedling.InsertOne[User](t, db)
+//	    reg := seedling.NewRegistry()
+//	    registerBlueprints(reg)
+//
+//	    result := seedling.NewSession[User](reg).InsertOne(t, db)
 //	    user := result.Root()
 //	    // user.ID and user.CompanyID are populated.
 //	}
diff --git a/docs/guide.md b/docs/guide.md
index f49319f..e8bed7d 100644
--- a/docs/guide.md
+++ b/docs/guide.md
@@ -258,7 +258,7 @@ Supported locales: `en` (default), `ja`, `zh`, `ko`, `de`, `fr`.
 ## Examples
 
 - [basic](../examples/basic) -- register blueprints and insert rows with automatic parent creation
-- [quickstart](../examples/quickstart) -- generated-style `RegisterBlueprints()` flow that matches the README Quick Start
+- [quickstart](../examples/quickstart) -- generated-style `NewRegistry()` / `RegisterBlueprints(reg)` flow that matches the README Quick Start
 - [custom-defaults](../examples/custom-defaults) -- customize values with `Set`, `With`, and `Generate`
 - [reuse-parent](../examples/reuse-parent) -- reuse existing rows with `Use`
 - [batch-insert](../examples/batch-insert) -- batch inserts with shared `Ref` dependencies and per-row `SeqRef` overrides
diff --git a/examples/basic/basic_test.go b/examples/basic/basic_test.go
index ec41ba9..b2ff492 100644
--- a/examples/basic/basic_test.go
+++ b/examples/basic/basic_test.go
@@ -7,16 +7,17 @@ import (
 	"github.com/mhiro2/seedling/examples/basic"
 )
 
-func setup(t *testing.T) {
+func setup(t *testing.T) *seedling.Registry {
 	t.Helper()
-	seedling.ResetRegistry()
-	basic.RegisterBlueprints()
+	reg := seedling.NewRegistry()
+	basic.RegisterBlueprints(reg)
+	return reg
 }
 
 func TestInsertOne_Company(t *testing.T) {
-	setup(t)
+	reg := setup(t)
 
-	company := seedling.InsertOne[basic.Company](t, nil)
+	company := seedling.NewSession[basic.Company](reg).InsertOne(t, nil)
 
 	if company.Root().ID == 0 {
 		t.Fatal("expected company ID to be set")
@@ -27,10 +28,10 @@ func TestInsertOne_Company(t *testing.T) {
 }
 
 func TestInsertOne_User(t *testing.T) {
-	setup(t)
+	reg := setup(t)
 
 	// InsertOne[User] automatically creates a parent Company.
-	user := seedling.InsertOne[basic.User](t, nil)
+	user := seedling.NewSession[basic.User](reg).InsertOne(t, nil)
 
 	if user.Root().ID == 0 {
 		t.Fatal("expected user ID to be set")
@@ -44,9 +45,9 @@ func TestInsertOne_User(t *testing.T) {
 }
 
 func TestInsertOne_UserWithSet(t *testing.T) {
-	setup(t)
+	reg := setup(t)
 
-	user := seedling.InsertOne[basic.User](t, nil,
+	user := seedling.NewSession[basic.User](reg).InsertOne(t, nil,
 		seedling.Set("Name", "alice"),
 		seedling.Set("Email", "alice@example.com"),
 	)
diff --git a/examples/basic/blueprints.go b/examples/basic/blueprints.go
index 828b495..4f88ee4 100644
--- a/examples/basic/blueprints.go
+++ b/examples/basic/blueprints.go
@@ -13,10 +13,9 @@ func nextID() int {
 	return int(idSeq.Add(1))
 }
 
-// RegisterBlueprints registers the Company and User blueprints.
-// Call seedling.ResetRegistry() before this in tests to start fresh.
-func RegisterBlueprints() {
-	seedling.MustRegister(seedling.Blueprint[Company]{
+// RegisterBlueprints registers the Company and User blueprints in reg.
+func RegisterBlueprints(reg *seedling.Registry) {
+	seedling.MustRegisterTo(reg, seedling.Blueprint[Company]{
 		Name:    "company",
 		Table:   "companies",
 		PKField: "ID",
@@ -29,7 +28,7 @@ func RegisterBlueprints() {
 		},
 	})
 
-	seedling.MustRegister(seedling.Blueprint[User]{
+	seedling.MustRegisterTo(reg, seedling.Blueprint[User]{
 		Name:    "user",
 		Table:   "users",
 		PKField: "ID",
diff --git a/examples/batch-insert/batch_insert_test.go b/examples/batch-insert/batch_insert_test.go
index 6b15083..6148737 100644
--- a/examples/batch-insert/batch_insert_test.go
+++ b/examples/batch-insert/batch_insert_test.go
@@ -9,19 +9,20 @@ import (
 	batchinsert "github.com/mhiro2/seedling/examples/batch-insert"
 )
 
-func setup(t *testing.T) {
+func setup(t *testing.T) *seedling.Registry {
 	t.Helper()
-	seedling.ResetRegistry()
 	batchinsert.ResetIDs()
-	batchinsert.RegisterBlueprints()
+	reg := seedling.NewRegistry()
+	batchinsert.RegisterBlueprints(reg)
+	return reg
 }
 
 func TestInsertManyE_SharedProject(t *testing.T) {
 	// Arrange
-	setup(t)
+	reg := setup(t)
 
 	// Act
-	result, err := seedling.InsertManyE[batchinsert.Task](context.Background(), nil, 2,
+	result, err := seedling.NewSession[batchinsert.Task](reg).InsertManyE(context.Background(), nil, 2,
 		seedling.Ref("project", seedling.Set("Name", "shared-project")),
 	)
 	if err != nil {
@@ -60,10 +61,10 @@ func TestInsertManyE_SharedProject(t *testing.T) {
 
 func TestInsertManyE_SeqRefCreatesDistinctProjects(t *testing.T) {
 	// Arrange
-	setup(t)
+	reg := setup(t)
 
 	// Act
-	result, err := seedling.InsertManyE[batchinsert.Task](context.Background(), nil, 2,
+	result, err := seedling.NewSession[batchinsert.Task](reg).InsertManyE(context.Background(), nil, 2,
 		seedling.SeqRef("project", func(i int) []seedling.Option {
 			return []seedling.Option{seedling.Set("Name", fmt.Sprintf("project-%d", i))}
 		}),
diff --git a/examples/batch-insert/blueprints.go b/examples/batch-insert/blueprints.go
index 446908e..a173703 100644
--- a/examples/batch-insert/blueprints.go
+++ b/examples/batch-insert/blueprints.go
@@ -13,9 +13,9 @@ func nextID() int {
 	return int(idSeq.Add(1))
 }
 
-// RegisterBlueprints registers Company, Project, and Task blueprints.
-func RegisterBlueprints() {
-	seedling.MustRegister(seedling.Blueprint[Company]{
+// RegisterBlueprints registers Company, Project, and Task blueprints in reg.
+func RegisterBlueprints(reg *seedling.Registry) {
+	seedling.MustRegisterTo(reg, seedling.Blueprint[Company]{
 		Name:    "company",
 		Table:   "companies",
 		PKField: "ID",
@@ -28,7 +28,7 @@ func RegisterBlueprints() {
 		},
 	})
 
-	seedling.MustRegister(seedling.Blueprint[Project]{
+	seedling.MustRegisterTo(reg, seedling.Blueprint[Project]{
 		Name:    "project",
 		Table:   "projects",
 		PKField: "ID",
@@ -44,7 +44,7 @@ func RegisterBlueprints() {
 		},
 	})
 
-	seedling.MustRegister(seedling.Blueprint[Task]{
+	seedling.MustRegisterTo(reg, seedling.Blueprint[Task]{
 		Name:    "task",
 		Table:   "tasks",
 		PKField: "ID",
diff --git a/examples/custom-defaults/blueprints.go b/examples/custom-defaults/blueprints.go
index 7952283..040de53 100644
--- a/examples/custom-defaults/blueprints.go
+++ b/examples/custom-defaults/blueprints.go
@@ -13,9 +13,9 @@ func nextID() int {
 	return int(idSeq.Add(1))
 }
 
-// RegisterBlueprints registers the User blueprint with sensible defaults.
-func RegisterBlueprints() {
-	seedling.MustRegister(seedling.Blueprint[User]{
+// RegisterBlueprints registers the User blueprint with sensible defaults in reg.
+func RegisterBlueprints(reg *seedling.Registry) {
+	seedling.MustRegisterTo(reg, seedling.Blueprint[User]{
 		Name:    "user",
 		Table:   "users",
 		PKField: "ID",
diff --git a/examples/custom-defaults/custom_defaults_test.go b/examples/custom-defaults/custom_defaults_test.go
index 397fcba..5248e45 100644
--- a/examples/custom-defaults/custom_defaults_test.go
+++ b/examples/custom-defaults/custom_defaults_test.go
@@ -7,16 +7,17 @@ import (
 	customdefaults "github.com/mhiro2/seedling/examples/custom-defaults"
 )
 
-func setup(t *testing.T) {
+func setup(t *testing.T) *seedling.Registry {
 	t.Helper()
-	seedling.ResetRegistry()
-	customdefaults.RegisterBlueprints()
+	reg := seedling.NewRegistry()
+	customdefaults.RegisterBlueprints(reg)
+	return reg
 }
 
 func TestDefaultUser(t *testing.T) {
-	setup(t)
+	reg := setup(t)
 
-	user := seedling.InsertOne[customdefaults.User](t, nil)
+	user := seedling.NewSession[customdefaults.User](reg).InsertOne(t, nil)
 
 	if user.Root().Role != "member" {
 		t.Fatalf("expected Role = %q, got %q", "member", user.Root().Role)
@@ -27,10 +28,10 @@ func TestDefaultUser(t *testing.T) {
 }
 
 func TestAdminUser(t *testing.T) {
-	setup(t)
+	reg := setup(t)
 
 	// Use the AdminUser() helper for type-safe default customization.
-	admin := seedling.InsertOne[customdefaults.User](t, nil,
+	admin := seedling.NewSession[customdefaults.User](reg).InsertOne(t, nil,
 		customdefaults.AdminUser(),
 	)
 
@@ -47,9 +48,9 @@ func TestAdminUser(t *testing.T) {
 }
 
 func TestInactiveUser(t *testing.T) {
-	setup(t)
+	reg := setup(t)
 
-	user := seedling.InsertOne[customdefaults.User](t, nil,
+	user := seedling.NewSession[customdefaults.User](reg).InsertOne(t, nil,
 		customdefaults.InactiveUser(),
 	)
 
@@ -63,10 +64,10 @@ func TestInactiveUser(t *testing.T) {
 }
 
 func TestCombineWithOptions(t *testing.T) {
-	setup(t)
+	reg := setup(t)
 
 	// Multiple With options can be combined.
-	user := seedling.InsertOne[customdefaults.User](t, nil,
+	user := seedling.NewSession[customdefaults.User](reg).InsertOne(t, nil,
 		customdefaults.AdminUser(),
 		customdefaults.InactiveUser(),
 	)
@@ -80,10 +81,10 @@ func TestCombineWithOptions(t *testing.T) {
 }
 
 func TestWithInline(t *testing.T) {
-	setup(t)
+	reg := setup(t)
 
 	// With() can also be used inline for one-off customizations.
-	user := seedling.InsertOne[customdefaults.User](t, nil,
+	user := seedling.NewSession[customdefaults.User](reg).InsertOne(t, nil,
 		seedling.With(func(u *customdefaults.User) {
 			u.Name = "custom-name"
 			u.Role = "viewer"
diff --git a/examples/quickstart/blueprints.go b/examples/quickstart/blueprints.go
index 42b2161..cb20e31 100644
--- a/examples/quickstart/blueprints.go
+++ b/examples/quickstart/blueprints.go
@@ -13,9 +13,16 @@ func nextID() int {
 	return int(idSeq.Add(1))
 }
 
-// RegisterBlueprints registers the generated-style Company and User blueprints.
-func RegisterBlueprints() {
-	seedling.MustRegister(seedling.Blueprint[Company]{
+// NewRegistry returns a local registry populated with this example's blueprints.
+func NewRegistry() *seedling.Registry {
+	reg := seedling.NewRegistry()
+	RegisterBlueprints(reg)
+	return reg
+}
+
+// RegisterBlueprints registers the generated-style Company and User blueprints in reg.
+func RegisterBlueprints(reg *seedling.Registry) {
+	seedling.MustRegisterTo(reg, seedling.Blueprint[Company]{
 		Name:    "company",
 		Table:   "companies",
 		PKField: "ID",
@@ -28,7 +35,7 @@ func RegisterBlueprints() {
 		},
 	})
 
-	seedling.MustRegister(seedling.Blueprint[User]{
+	seedling.MustRegisterTo(reg, seedling.Blueprint[User]{
 		Name:    "user",
 		Table:   "users",
 		PKField: "ID",
diff --git a/examples/quickstart/quickstart_test.go b/examples/quickstart/quickstart_test.go
index 444d258..85e4dfe 100644
--- a/examples/quickstart/quickstart_test.go
+++ b/examples/quickstart/quickstart_test.go
@@ -7,19 +7,18 @@ import (
 	"github.com/mhiro2/seedling/examples/quickstart"
 )
 
-func setup(t *testing.T) {
+func setup(t *testing.T) *seedling.Registry {
 	t.Helper()
-	seedling.ResetRegistry()
 	quickstart.ResetIDs()
-	quickstart.RegisterBlueprints()
+	return quickstart.NewRegistry()
 }
 
 func TestQuickStart_InsertOneUser(t *testing.T) {
 	// Arrange
-	setup(t)
+	reg := setup(t)
 
 	// Act
-	user := seedling.InsertOne[quickstart.User](t, nil).Root()
+	user := seedling.NewSession[quickstart.User](reg).InsertOne(t, nil).Root()
 
 	// Assert
 	if user.ID == 0 {
@@ -35,13 +34,13 @@ func TestQuickStart_InsertOneUser(t *testing.T) {
 
 func TestQuickStart_ReuseCompanyWithUse(t *testing.T) {
 	// Arrange
-	setup(t)
-	company := seedling.InsertOne[quickstart.Company](t, nil,
+	reg := setup(t)
+	company := seedling.NewSession[quickstart.Company](reg).InsertOne(t, nil,
 		seedling.Set("Name", "shared-company"),
 	).Root()
 
 	// Act
-	user := seedling.InsertOne[quickstart.User](t, nil,
+	user := seedling.NewSession[quickstart.User](reg).InsertOne(t, nil,
 		seedling.Set("Name", "alice"),
 		seedling.Use("company", company),
 	).Root()
diff --git a/examples/reuse-parent/blueprints.go b/examples/reuse-parent/blueprints.go
index 2f62350..d8529e0 100644
--- a/examples/reuse-parent/blueprints.go
+++ b/examples/reuse-parent/blueprints.go
@@ -13,9 +13,9 @@ func nextID() int {
 	return int(idSeq.Add(1))
 }
 
-// RegisterBlueprints registers Company, Project, and Task blueprints.
-func RegisterBlueprints() {
-	seedling.MustRegister(seedling.Blueprint[Company]{
+// RegisterBlueprints registers Company, Project, and Task blueprints in reg.
+func RegisterBlueprints(reg *seedling.Registry) {
+	seedling.MustRegisterTo(reg, seedling.Blueprint[Company]{
 		Name:    "company",
 		Table:   "companies",
 		PKField: "ID",
@@ -28,7 +28,7 @@ func RegisterBlueprints() {
 		},
 	})
 
-	seedling.MustRegister(seedling.Blueprint[Project]{
+	seedling.MustRegisterTo(reg, seedling.Blueprint[Project]{
 		Name:    "project",
 		Table:   "projects",
 		PKField: "ID",
@@ -49,7 +49,7 @@ func RegisterBlueprints() {
 		},
 	})
 
-	seedling.MustRegister(seedling.Blueprint[Task]{
+	seedling.MustRegisterTo(reg, seedling.Blueprint[Task]{
 		Name:    "task",
 		Table:   "tasks",
 		PKField: "ID",
diff --git a/examples/reuse-parent/reuse_parent_test.go b/examples/reuse-parent/reuse_parent_test.go
index 3c4aa9a..9eaca72 100644
--- a/examples/reuse-parent/reuse_parent_test.go
+++ b/examples/reuse-parent/reuse_parent_test.go
@@ -7,26 +7,27 @@ import (
 	reuseparent "github.com/mhiro2/seedling/examples/reuse-parent"
 )
 
-func setup(t *testing.T) {
+func setup(t *testing.T) *seedling.Registry {
 	t.Helper()
-	seedling.ResetRegistry()
-	reuseparent.RegisterBlueprints()
+	reg := seedling.NewRegistry()
+	reuseparent.RegisterBlueprints(reg)
+	return reg
 }
 
 func TestUse_ShareParentCompany(t *testing.T) {
-	setup(t)
+	reg := setup(t)
 
 	// First, create a shared Company.
-	company := seedling.InsertOne[reuseparent.Company](t, nil,
+	company := seedling.NewSession[reuseparent.Company](reg).InsertOne(t, nil,
 		seedling.Set("Name", "Shared Corp"),
 	)
 
 	// Create two Projects under the same Company using Use().
-	projectA := seedling.InsertOne[reuseparent.Project](t, nil,
+	projectA := seedling.NewSession[reuseparent.Project](reg).InsertOne(t, nil,
 		seedling.Set("Name", "Project Alpha"),
 		seedling.Use("company", company.Root()),
 	)
-	projectB := seedling.InsertOne[reuseparent.Project](t, nil,
+	projectB := seedling.NewSession[reuseparent.Project](reg).InsertOne(t, nil,
 		seedling.Set("Name", "Project Beta"),
 		seedling.Use("company", company.Root()),
 	)
@@ -47,23 +48,23 @@ func TestUse_ShareParentCompany(t *testing.T) {
 }
 
 func TestUse_ShareParentProject(t *testing.T) {
-	setup(t)
+	reg := setup(t)
 
 	// Create a shared Project (which auto-creates a Company).
-	project := seedling.InsertOne[reuseparent.Project](t, nil,
+	project := seedling.NewSession[reuseparent.Project](reg).InsertOne(t, nil,
 		seedling.Set("Name", "Shared Project"),
 	)
 
 	// Create multiple Tasks under the same Project using Use().
-	task1 := seedling.InsertOne[reuseparent.Task](t, nil,
+	task1 := seedling.NewSession[reuseparent.Task](reg).InsertOne(t, nil,
 		seedling.Set("Title", "Task 1"),
 		seedling.Use("project", project.Root()),
 	)
-	task2 := seedling.InsertOne[reuseparent.Task](t, nil,
+	task2 := seedling.NewSession[reuseparent.Task](reg).InsertOne(t, nil,
 		seedling.Set("Title", "Task 2"),
 		seedling.Use("project", project.Root()),
 	)
-	task3 := seedling.InsertOne[reuseparent.Task](t, nil,
+	task3 := seedling.NewSession[reuseparent.Task](reg).InsertOne(t, nil,
 		seedling.Set("Title", "Task 3"),
 		seedling.Use("project", project.Root()),
 	)
diff --git a/examples/sqlc/blueprints.go b/examples/sqlc/blueprints.go
index 0483b53..e5e3d3b 100644
--- a/examples/sqlc/blueprints.go
+++ b/examples/sqlc/blueprints.go
@@ -14,7 +14,7 @@ func nextID() int64 {
 	return idSeq.Add(1)
 }
 
-// RegisterBlueprints registers Organization and Member blueprints.
+// RegisterBlueprints registers Organization and Member blueprints in reg.
 //
 // In a real project, the Insert functions would call sqlc-generated query methods:
 //
@@ -23,8 +23,8 @@ func nextID() int64 {
 //	}
 //
 // Here we use mock inserts that assign incrementing IDs.
-func RegisterBlueprints() {
-	seedling.MustRegister(seedling.Blueprint[Organization]{
+func RegisterBlueprints(reg *seedling.Registry) {
+	seedling.MustRegisterTo(reg, seedling.Blueprint[Organization]{
 		Name:    "organization",
 		Table:   "organizations",
 		PKField: "ID",
@@ -38,7 +38,7 @@ func RegisterBlueprints() {
 		},
 	})
 
-	seedling.MustRegister(seedling.Blueprint[Member]{
+	seedling.MustRegisterTo(reg, seedling.Blueprint[Member]{
 		Name:    "member",
 		Table:   "members",
 		PKField: "ID",
diff --git a/examples/sqlc/sqlc_test.go b/examples/sqlc/sqlc_test.go
index 75dc230..5885c58 100644
--- a/examples/sqlc/sqlc_test.go
+++ b/examples/sqlc/sqlc_test.go
@@ -8,17 +8,18 @@ import (
 	example "github.com/mhiro2/seedling/examples/sqlc"
 )
 
-func setup(t *testing.T) {
+func setup(t *testing.T) *seedling.Registry {
 	t.Helper()
-	seedling.ResetRegistry()
-	example.RegisterBlueprints()
+	reg := seedling.NewRegistry()
+	example.RegisterBlueprints(reg)
+	return reg
 }
 
 func TestInsertOne_Member(t *testing.T) {
-	setup(t)
+	reg := setup(t)
 
 	// seedling auto-creates the parent Organization.
-	member := seedling.InsertOne[example.Member](t, nil)
+	member := seedling.NewSession[example.Member](reg).InsertOne(t, nil)
 
 	if member.Root().ID == 0 {
 		t.Fatal("expected member ID to be set")
@@ -32,9 +33,9 @@ func TestInsertOne_Member(t *testing.T) {
 }
 
 func TestInsertOne_Organization(t *testing.T) {
-	setup(t)
+	reg := setup(t)
 
-	org := seedling.InsertOne[example.Organization](t, nil,
+	org := seedling.NewSession[example.Organization](reg).InsertOne(t, nil,
 		seedling.Set("Name", "Acme Corp"),
 	)
 
@@ -47,9 +48,9 @@ func TestInsertOne_Organization(t *testing.T) {
 }
 
 func TestInsertMany_Members(t *testing.T) {
-	setup(t)
+	reg := setup(t)
 
-	members := seedling.InsertMany[example.Member](t, nil, 3,
+	members := seedling.NewSession[example.Member](reg).InsertMany(t, nil, 3,
 		seedling.Seq("Name", func(i int) string {
 			return fmt.Sprintf("member-%d", i)
 		}),
diff --git a/examples/with-tx/blueprints.go b/examples/with-tx/blueprints.go
index c5f6438..c73ab00 100644
--- a/examples/with-tx/blueprints.go
+++ b/examples/with-tx/blueprints.go
@@ -13,9 +13,9 @@ func nextID() int {
 	return int(idSeq.Add(1))
 }
 
-// RegisterBlueprints registers the Company and User blueprints for SQL transaction examples.
-func RegisterBlueprints() {
-	seedling.MustRegister(seedling.Blueprint[Company]{
+// RegisterBlueprints registers the Company and User blueprints for SQL transaction examples in reg.
+func RegisterBlueprints(reg *seedling.Registry) {
+	seedling.MustRegisterTo(reg, seedling.Blueprint[Company]{
 		Name:    "company",
 		Table:   "companies",
 		PKField: "ID",
@@ -28,7 +28,7 @@ func RegisterBlueprints() {
 		},
 	})
 
-	seedling.MustRegister(seedling.Blueprint[User]{
+	seedling.MustRegisterTo(reg, seedling.Blueprint[User]{
 		Name:    "user",
 		Table:   "users",
 		PKField: "ID",
diff --git a/examples/with-tx/with_tx_test.go b/examples/with-tx/with_tx_test.go
index 358d7ad..1f855da 100644
--- a/examples/with-tx/with_tx_test.go
+++ b/examples/with-tx/with_tx_test.go
@@ -12,21 +12,22 @@ import (
 	withtx "github.com/mhiro2/seedling/examples/with-tx"
 )
 
-func setup(t *testing.T) {
+func setup(t *testing.T) *seedling.Registry {
 	t.Helper()
-	seedling.ResetRegistry()
 	withtx.ResetIDs()
-	withtx.RegisterBlueprints()
+	reg := seedling.NewRegistry()
+	withtx.RegisterBlueprints(reg)
+	return reg
 }
 
 func TestWithTx_InsertOneUser(t *testing.T) {
 	// Arrange
-	setup(t)
+	reg := setup(t)
 	db := openDB(t)
 
 	// Act
 	tx := seedling.WithTx(t, db)
-	user := seedling.InsertOne[withtx.User](t, tx).Root()
+	user := seedling.NewSession[withtx.User](reg).InsertOne(t, tx).Root()
 
 	// Assert
 	if user.ID == 0 {
diff --git a/skills/seedling-gen-cli/SKILL.md b/skills/seedling-gen-cli/SKILL.md
index 5e555d0..66de79e 100644
--- a/skills/seedling-gen-cli/SKILL.md
+++ b/skills/seedling-gen-cli/SKILL.md
@@ -11,7 +11,7 @@ Use this skill when a Go project wants seedling blueprint scaffolding.
 
 - Go model structs for tables or entities
 - deterministic `Defaults` for common scalar fields
-- `RegisterBlueprints()` scaffolding
+- `NewRegistry()` / `RegisterBlueprints(reg)` scaffolding
 - relation definitions such as `seedling.BelongsTo`
 - project-specific `Insert` stubs with `// TODO: implement` markers
 
diff --git a/skills/seedling-test-setup/SKILL.md b/skills/seedling-test-setup/SKILL.md
index 6bb6bf9..3f0b6ba 100644
--- a/skills/seedling-test-setup/SKILL.md
+++ b/skills/seedling-test-setup/SKILL.md
@@ -198,6 +198,6 @@ result := plan.Insert(t, db) // execute the plan
 
 ## Notes
 
-- Always register blueprints before calling `InsertOne` / `InsertMany`. If using the global registry, call `seedling.ResetRegistry()` in test setup to avoid cross-test leaks.
+- Always register blueprints into a test-local registry before calling `InsertOne` / `InsertMany`; prefer `seedling.NewSession[T](reg)` over the global helpers.
 - `InsertOne` / `InsertMany` accept a `testing.TB` and fail the test on error. Use the `E` variants (`InsertOneE`, `InsertManyE`) in non-test contexts or when you need explicit error handling.
 - Prefer transaction rollback over `Cleanup` for test isolation — it is faster and guarantees no leftover data.