feat(html): restore context translator swapping

Co-Authored-By: Virgil <virgil@lethean.io>

context.go

@@ -16,7 +16,7 @@ type translatorCloner interface {
 
 // context.go: Context carries rendering state through the node tree.
 // Example: NewContext("en-GB") initialises locale-specific rendering state.
-// Locale and translator selection happen at construction time.
+// Locale and translator selection are managed through dedicated setters.
 type Context struct {
 	Identity     string
 	Locale       string
@@ -110,6 +110,20 @@ func NewContextWithService(svc Translator, locale ...string) *Context {
 	return ctx
 }
 
+// SetService swaps the translator used by the context and reapplies the
+// current locale to it.
+// Example: ctx.SetService(svc).
+func (ctx *Context) SetService(svc Translator) *Context {
+	if ctx == nil {
+		return nil
+	}
+
+	ensureContextDefaults(ctx)
+	ctx.service = svc
+	applyLocaleToService(ctx.service, ctx.Locale)
+	return ctx
+}
+
 // SetEntitlements updates the feature gate callback used by Entitled nodes and
 // returns the same context.
 // Example: ctx.SetEntitlements(func(feature string) bool { return feature == "premium" }).
@@ -181,6 +195,17 @@ func (ctx *Context) WithLocale(locale string) *Context {
 	return clone
 }
 
+// WithService returns a cloned context with a different translator.
+// Example: next := ctx.WithService(svc).
+func (ctx *Context) WithService(svc Translator) *Context {
+	clone := ctx.Clone()
+	if clone == nil {
+		return nil
+	}
+	clone.SetService(svc)
+	return clone
+}
+
 // WithEntitlements returns a cloned context with a different feature gate callback.
 // Example: next := ctx.WithEntitlements(func(feature string) bool { return feature == "premium" }).
 func (ctx *Context) WithEntitlements(entitlements func(feature string) bool) *Context {

context_test.go

@@ -88,6 +88,24 @@ func TestContext_SetLocale_ReappliesToTranslator(t *testing.T) {
 	}
 }
 
+func TestContext_SetService_ReappliesCurrentLocale(t *testing.T) {
+	ctx := NewContext("fr-FR")
+	svc := &localeTranslator{}
+
+	if got := ctx.SetService(svc); got != ctx {
+		t.Fatalf("SetService should return the same context")
+	}
+	if ctx.service != svc {
+		t.Fatalf("SetService should replace the active translator")
+	}
+	if svc.language != "fr" {
+		t.Fatalf("SetService should apply the existing locale to the new translator, got %q", svc.language)
+	}
+	if got := Text("prompt.yes").Render(ctx); got != "o" {
+		t.Fatalf("SetService translation = %q, want %q", got, "o")
+	}
+}
+
 func TestContext_SetEntitlements_UpdatesFeatureGate(t *testing.T) {
 	ctx := NewContext()
 
@@ -282,6 +300,34 @@ func TestContext_WithLocaleReturnsClonedContext(t *testing.T) {
 	}
 }
 
+func TestContext_WithServiceReturnsClonedContext(t *testing.T) {
+	ctx := NewContext("fr-FR")
+	ctx.SetIdentity("user-001")
+	ctx.SetData("theme", "dark")
+
+	svc := &localeTranslator{}
+	next := ctx.WithService(svc)
+
+	if next == ctx {
+		t.Fatal("WithService should return a cloned context")
+	}
+	if got := ctx.service; got == svc {
+		t.Fatal("WithService should not mutate the original context service")
+	}
+	if got := next.service; got != svc {
+		t.Fatalf("WithService should set the requested service on the clone, got %v", got)
+	}
+	if svc.language != "fr" {
+		t.Fatalf("WithService should apply the existing locale to the new translator, got %q", svc.language)
+	}
+	if got := next.Data["theme"]; got != "dark" {
+		t.Fatalf("WithService should preserve existing data on the clone, got %v", got)
+	}
+	if got := next.Locale; got != "fr-FR" {
+		t.Fatalf("WithService should preserve the locale on the clone, got %q", got)
+	}
+}
+
 func TestContext_WithEntitlementsReturnsClonedContext(t *testing.T) {
 	ctx := NewContext()
 	ctx.SetIdentity("user-001")
@@ -328,12 +374,18 @@ func TestContext_Setters_NilReceiver(t *testing.T) {
 	if got := ctx.SetLocale("en-GB"); got != nil {
 		t.Fatalf("nil Context.SetLocale should return nil, got %v", got)
 	}
+	if got := ctx.SetService(&localeTranslator{}); got != nil {
+		t.Fatalf("nil Context.SetService should return nil, got %v", got)
+	}
 	if got := ctx.SetEntitlements(func(string) bool { return true }); got != nil {
 		t.Fatalf("nil Context.SetEntitlements should return nil, got %v", got)
 	}
 	if got := ctx.WithLocale("en-GB"); got != nil {
 		t.Fatalf("nil Context.WithLocale should return nil, got %v", got)
 	}
+	if got := ctx.WithService(&localeTranslator{}); got != nil {
+		t.Fatalf("nil Context.WithService should return nil, got %v", got)
+	}
 	if got := ctx.WithEntitlements(func(string) bool { return true }); got != nil {
 		t.Fatalf("nil Context.WithEntitlements should return nil, got %v", got)
 	}

docs/architecture.md

@@ -101,7 +101,7 @@ Two constructors are provided:
 - `NewContext()` creates a context with sensible defaults and an empty `Data` map.
 - `NewContextWithService(svc)` creates a context backed by a specific `i18n.Service` instance.
 
-The `service` field is intentionally unexported. When nil, `Text` nodes fall back to the global `i18n.T()` default. This prevents callers from setting the service inconsistently after construction.
+The `service` field is intentionally unexported. When nil, `Text` nodes fall back to the global `i18n.T()` default. Callers can replace the active translator with `SetService()` or `WithService()`, which reapply the current locale to the new service.
 
 ## HLCRF Layout
 

docs/history.md

@@ -101,7 +101,7 @@ These are not regressions; they are design choices or deferred work recorded for
 
 3. **Responsive accepts only Layout.** `Responsive.Variant()` takes `*Layout` rather than `Node`. The rationale is that `CompareVariants` in the pipeline needs access to the slot structure. Accepting `Node` would require a different approach to variant analysis.
 
-4. **Context.service is private and immutable.** The i18n service is selected at construction time via `NewContext()` or `NewContextWithService()` and cannot be swapped afterwards. This keeps rendering state stable and avoids accidental cross-request mutation.
+4. **Context.service is private, but swappable through setters.** The i18n service remains unexported, but `SetService()` and `WithService()` let callers replace it while keeping the current locale applied.
 
 5. **TypeScript definitions are generated.** `codegen.GenerateTypeDefinitions()` produces a `.d.ts` companion for the generated Web Components.