diff --git a/NEXT_STEPS.md b/NEXT_STEPS.md
index 91b66a2..be81050 100644
--- a/NEXT_STEPS.md
+++ b/NEXT_STEPS.md
@@ -36,6 +36,7 @@ Estado al cierre:
   - `libs/cach/engine.ts` delega lectura `get()` en `runtime-get.ts`.
   - `libs/cach/engine.ts` delega escritura `set()` en `runtime-set.ts`.
   - `libs/cach/engine.ts` delega `query()` en `runtime-query.ts`; conserva composition root para context/io/delete/invalidate/mutate/explain.
+  - `arts/sium/engine-sium.ts` delega resolucion Lang/fallback e issues en `engine-resolver.ts`.
   - `arts/conn/connection.ts` delega decode/routing de frames entrantes en `connection-message-router.ts`.
   - `arts/conn/connection.ts` delega el intento open/auth/flush/join en `connection-connect.ts`.
   - `arts/conn/connection.ts` delega current transport, attach/detach y close en `connection-transport-runtime.ts`.
diff --git a/src/arts/sium/engine-resolver.ts b/src/arts/sium/engine-resolver.ts
new file mode 100644
index 0000000..3ac187f
--- /dev/null
+++ b/src/arts/sium/engine-resolver.ts
@@ -0,0 +1,61 @@
+import type { EngineLang, LangParams, SupportedLocale } from '$lang';
+import { ID_FALLBACK_SEPARATOR, parseLangRef } from '$lang';
+import { SIUM_DIAGNOSTIC_EVENTS } from './consts';
+import { emitSiumDiagnostic, type SiumDiagnostics } from './diagnostics';
+import { resolve as resolveFallbackTemplate } from './langs';
+import type { Issue } from './core';
+
+export interface SiumResolver {
+	readonly resolve: (message: string, params?: LangParams, locale?: SupportedLocale) => string;
+	readonly resolveIssue: (issue: Issue, locale?: SupportedLocale) => string;
+	readonly resolveIssues: (issues: ReadonlyArray<Issue>, locale?: SupportedLocale) => string[];
+}
+
+interface SiumResolverOptions {
+	readonly lang?: EngineLang;
+	readonly defaultLocale: SupportedLocale;
+	readonly diagnostics: SiumDiagnostics;
+}
+
+function composeLangPath(message: string): string | undefined {
+	const parsed = parseLangRef(message);
+	if (parsed === null) return undefined;
+	if (parsed.fallback === undefined) return parsed.path;
+	return `${parsed.path}${ID_FALLBACK_SEPARATOR}${parsed.fallback}`;
+}
+
+function fallbackMessage(message: string, params?: LangParams): string {
+	const parsed = parseLangRef(message);
+	return resolveFallbackTemplate(parsed?.fallback ?? parsed?.path ?? message, params);
+}
+
+export function createSiumResolver(options: SiumResolverOptions): SiumResolver {
+	const { lang, defaultLocale, diagnostics } = options;
+
+	const resolve: SiumResolver['resolve'] = (message, params, locale = defaultLocale) => {
+		const langPath = composeLangPath(message);
+		if (lang === undefined || langPath === undefined) {
+			return fallbackMessage(message, params);
+		}
+
+		try {
+			return lang.t(langPath, params, locale);
+		} catch (error) {
+			emitSiumDiagnostic(diagnostics, SIUM_DIAGNOSTIC_EVENTS.RESOLVE_FALLBACK, {
+				message,
+				error
+			});
+			return fallbackMessage(message, params);
+		}
+	};
+
+	const resolveIssue: SiumResolver['resolveIssue'] = (entry, locale) => {
+		return resolve(entry.message, entry.params, locale);
+	};
+
+	const resolveIssues: SiumResolver['resolveIssues'] = (issues, locale) => {
+		return issues.map((entry) => resolveIssue(entry, locale));
+	};
+
+	return { resolve, resolveIssue, resolveIssues };
+}
diff --git a/src/arts/sium/engine-sium.ts b/src/arts/sium/engine-sium.ts
index 300d687..d21bed6 100644
--- a/src/arts/sium/engine-sium.ts
+++ b/src/arts/sium/engine-sium.ts
@@ -1,8 +1,8 @@
 import type { EngineLang, LangParams, SupportedLocale } from '$lang';
-import { ID_FALLBACK_SEPARATOR, parseLangRef } from '$lang';
 import type { Logger } from '$libs/logr';
 import { SIUM_DIAGNOSTIC_EVENTS } from './consts';
 import { createSiumDiagnostics, emitSiumDiagnostic, issueDiagnosticMeta } from './diagnostics';
+import { createSiumResolver } from './engine-resolver';
 import {
 	array,
 	boolean,
@@ -59,7 +59,7 @@ import {
 	timeValue,
 	year
 } from './types';
-import { ISSUE_CODES, resolve as resolveFallbackTemplate, siumLangs } from './langs';
+import { ISSUE_CODES, siumLangs } from './langs';
 
 export interface EngineSiumOptions {
 	lang?: EngineLang;
@@ -134,18 +134,6 @@ export interface EngineSium {
 	) => Result<O>;
 }
 
-function composeLangPath(message: string): string | undefined {
-	const parsed = parseLangRef(message);
-	if (parsed === null) return undefined;
-	if (parsed.fallback === undefined) return parsed.path;
-	return `${parsed.path}${ID_FALLBACK_SEPARATOR}${parsed.fallback}`;
-}
-
-function fallbackMessage(message: string, params?: LangParams): string {
-	const parsed = parseLangRef(message);
-	return resolveFallbackTemplate(parsed?.fallback ?? parsed?.path ?? message, params);
-}
-
 /**
  * Public Sium facade.
  *
@@ -156,31 +144,7 @@ export function createEngineSium(options: EngineSiumOptions = {}): EngineSium {
 	const { lang, logger } = options;
 	const diagnostics = createSiumDiagnostics(logger);
 	const defaultLocale = options.locale ?? lang?.getDefaultLocale() ?? 'es';
-
-	const resolveMessage: EngineSium['resolve'] = (message, params, locale = defaultLocale) => {
-		const langPath = composeLangPath(message);
-		if (lang === undefined || langPath === undefined) {
-			return fallbackMessage(message, params);
-		}
-
-		try {
-			return lang.t(langPath, params, locale);
-		} catch (error) {
-			emitSiumDiagnostic(diagnostics, SIUM_DIAGNOSTIC_EVENTS.RESOLVE_FALLBACK, {
-				message,
-				error
-			});
-			return fallbackMessage(message, params);
-		}
-	};
-
-	const resolveIssue: EngineSium['resolveIssue'] = (entry, locale) => {
-		return resolveMessage(entry.message, entry.params, locale);
-	};
-
-	const resolveIssues: EngineSium['resolveIssues'] = (issues, locale) => {
-		return issues.map((entry) => resolveIssue(entry, locale));
-	};
+	const resolver = createSiumResolver({ lang, defaultLocale, diagnostics });
 
 	const validate: EngineSium['validate'] = async (schema, input, ctx) => {
 		const result = await schema.validate(input, ctx);
@@ -258,9 +222,9 @@ export function createEngineSium(options: EngineSiumOptions = {}): EngineSium {
 		alpha,
 		issueCodes: ISSUE_CODES,
 		langSchema: siumLangs,
-		resolve: resolveMessage,
-		resolveIssue,
-		resolveIssues,
+		resolve: resolver.resolve,
+		resolveIssue: resolver.resolveIssue,
+		resolveIssues: resolver.resolveIssues,
 		validate,
 		validateSync
 	};