diff --git a/src/context-engine/context-engine.test.ts b/src/context-engine/context-engine.test.ts
index 770ab643fd1..0bfb890aed2 100644
--- a/src/context-engine/context-engine.test.ts
+++ b/src/context-engine/context-engine.test.ts
@@ -360,7 +360,7 @@ describe("Engine contract tests", () => {
     const resolved = getContextEngineFactory("mock");
     expect(resolved).toBe(factory);
 
-    const engine = await resolved!();
+    const engine = await resolved!({});
     expect(engine).toBeInstanceOf(MockContextEngine);
     expect(engine.info.id).toBe("mock");
   });
@@ -706,7 +706,7 @@ describe("Factory context passing", () => {
     const engineId = `factory-ctx-${Date.now().toString(36)}`;
     let receivedCtx: ContextEngineFactoryContext | undefined;
 
-    const factory: ContextEngineFactory = (ctx?: ContextEngineFactoryContext) => {
+    const factory: ContextEngineFactory = (ctx: ContextEngineFactoryContext) => {
       receivedCtx = ctx;
       return {
         info: { id: engineId, name: "Ctx Engine" },
@@ -771,7 +771,7 @@ describe("Factory context passing", () => {
     // Override the default "legacy" engine to intercept the no-config path
     registerContextEngineForOwner(
       "legacy",
-      (ctx?: ContextEngineFactoryContext) => {
+      (ctx: ContextEngineFactoryContext) => {
         receivedCtx = ctx;
         return {
           info: { id: "legacy", name: "NoConfig Engine", version: "1" },
diff --git a/src/context-engine/registry.ts b/src/context-engine/registry.ts
index e257a8e67b5..3ebd1023df4 100644
--- a/src/context-engine/registry.ts
+++ b/src/context-engine/registry.ts
@@ -19,12 +19,13 @@ export type ContextEngineFactoryContext = {
  * A factory that creates a ContextEngine instance.
  * Supports async creation for engines that need DB connections etc.
  *
- * Factories may accept an optional {@link ContextEngineFactoryContext} parameter
- * for runtime context. No-arg factories remain supported for backward compatibility
- * since the parameter is optional.
+ * The factory receives a {@link ContextEngineFactoryContext} with runtime
+ * environment context (config, paths). Existing no-arg factories remain
+ * backward compatible because TypeScript permits assigning functions with
+ * fewer parameters to wider signatures.
  */
 export type ContextEngineFactory = (
-  ctx?: ContextEngineFactoryContext,
+  ctx: ContextEngineFactoryContext,
 ) => ContextEngine | Promise<ContextEngine>;
 export type ContextEngineRegistrationResult = { ok: true } | { ok: false; existingOwner: string };