diff --git a/packages/1-framework/1-core/framework-components/src/shared/resolve-codec.ts b/packages/1-framework/1-core/framework-components/src/shared/resolve-codec.ts
index 200f26a65bd5..68fb58d3f8c2 100644
--- a/packages/1-framework/1-core/framework-components/src/shared/resolve-codec.ts
+++ b/packages/1-framework/1-core/framework-components/src/shared/resolve-codec.ts
@@ -66,12 +66,9 @@ export function validateCodecTypeParams(descriptor: AnyCodecDescriptor, ref: Cod
 
 /**
  * Resolves a `Codec` instance: validates `ref.typeParams` via
- * {@link validateCodecTypeParams} then calls `descriptor.factory(validated)(ctx)`.
- *
- * The descriptor's `factory` is typed against its own `P`; the registry erases
- * `P` to `any`, so the factory is narrowed to `(params: unknown) => (ctx) => Codec`
- * at the call boundary. The `paramsSchema` validates the input above before we
- * forward it, so the narrowing is safe by construction.
+ * {@link validateCodecTypeParams} then calls `descriptor.factory(validated)(ctx)`
+ * as a method on `descriptor`, preserving `this` for factories that build
+ * their returned codec from the descriptor instance (e.g. `new XCodec(this)`).
  */
 export function materializeCodec(
   descriptor: AnyCodecDescriptor,
@@ -79,8 +76,5 @@ export function materializeCodec(
   ctx: CodecInstanceContext,
 ): Codec {
   const validated = validateCodecTypeParams(descriptor, ref);
-  return blindCast<
-    (params: unknown) => (ctx: CodecInstanceContext) => Codec,
-    'registry erases P to any; paramsSchema validates input before forwarding'
-  >(descriptor.factory)(validated)(ctx);
+  return descriptor.factory(validated)(ctx);
 }
diff --git a/packages/1-framework/1-core/framework-components/test/materialize-codec.test.ts b/packages/1-framework/1-core/framework-components/test/materialize-codec.test.ts
new file mode 100644
index 000000000000..f57fefef9e06
--- /dev/null
+++ b/packages/1-framework/1-core/framework-components/test/materialize-codec.test.ts
@@ -0,0 +1,125 @@
+import type { JsonValue } from '@internal/contract/types';
+import type { StandardSchemaV1 } from '@standard-schema/spec';
+import { test } from 'vitest';
+import {
+  type AnyCodecDescriptor,
+  type CodecCallContext,
+  type CodecDescriptor,
+  CodecDescriptorImpl,
+  CodecImpl,
+  type CodecInstanceContext,
+  type CodecRef,
+  type CodecTrait,
+  materializeCodec,
+  voidParamsSchema,
+} from '../src/exports/codec';
+
+class Int4FixtureCodec extends CodecImpl<'demo/int4@1', readonly ['equality'], number, number> {
+  async encode(value: number, _ctx: CodecCallContext): Promise<number> {
+    return value;
+  }
+  async decode(wire: number, _ctx: CodecCallContext): Promise<number> {
+    return wire;
+  }
+  encodeJson(value: number): JsonValue {
+    return value;
+  }
+  decodeJson(json: JsonValue): number {
+    return json as number;
+  }
+}
+
+class Int4FixtureDescriptor extends CodecDescriptorImpl<void> {
+  override readonly codecId = 'demo/int4@1' as const;
+  override readonly traits: readonly CodecTrait[] = ['equality'];
+  override readonly targetTypes: readonly string[] = ['int4'];
+  override readonly paramsSchema: StandardSchemaV1<void> = voidParamsSchema;
+  override factory(): (ctx: CodecInstanceContext) => Int4FixtureCodec {
+    return () => new Int4FixtureCodec(this);
+  }
+}
+
+const int4FixtureDescriptor = new Int4FixtureDescriptor();
+
+type VectorParams = { readonly length: number };
+const vectorFixtureParamsSchema: StandardSchemaV1<VectorParams> = {
+  '~standard': {
+    version: 1,
+    vendor: 'demo',
+    validate: (input) => ({ value: input as VectorParams }),
+  },
+};
+
+class VectorFixtureCodec<N extends number> extends CodecImpl<
+  'demo/vector@1',
+  readonly ['equality'],
+  string,
+  number[]
+> {
+  constructor(
+    descriptor: CodecDescriptor<VectorParams>,
+    public readonly dimension: N,
+  ) {
+    super(descriptor);
+  }
+  async encode(value: number[], _ctx: CodecCallContext): Promise<string> {
+    return `[${value.join(',')}]`;
+  }
+  async decode(wire: string, _ctx: CodecCallContext): Promise<number[]> {
+    return wire.slice(1, -1).split(',').map(Number);
+  }
+  encodeJson(value: number[]): JsonValue {
+    return value;
+  }
+  decodeJson(json: JsonValue): number[] {
+    return json as number[];
+  }
+}
+
+class VectorFixtureDescriptor extends CodecDescriptorImpl<VectorParams> {
+  override readonly codecId = 'demo/vector@1' as const;
+  override readonly traits: readonly CodecTrait[] = ['equality'];
+  override readonly targetTypes: readonly string[] = ['vector'];
+  override readonly paramsSchema = vectorFixtureParamsSchema;
+  override factory<N extends number>(params: {
+    readonly length: N;
+  }): (ctx: CodecInstanceContext) => VectorFixtureCodec<N> {
+    return () => new VectorFixtureCodec<N>(this, params.length);
+  }
+}
+
+const vectorFixtureDescriptor = new VectorFixtureDescriptor();
+
+const stubCtx = {} as CodecInstanceContext;
+
+function descriptorFor(ref: CodecRef): AnyCodecDescriptor {
+  if (ref.codecId === int4FixtureDescriptor.codecId) return int4FixtureDescriptor;
+  if (ref.codecId === vectorFixtureDescriptor.codecId) return vectorFixtureDescriptor;
+  throw new Error(`no fixture descriptor for ${ref.codecId}`);
+}
+
+test('materializeCodec resolves a non-parameterized codec whose id reads the descriptor codecId', ({
+  expect,
+}) => {
+  const ref: CodecRef = { codecId: 'demo/int4@1' };
+  const codec = materializeCodec(descriptorFor(ref), ref, stubCtx);
+  expect(codec.id).toBe('demo/int4@1');
+});
+
+test('materializeCodec resolves a parameterized codec whose id reads the descriptor codecId', ({
+  expect,
+}) => {
+  const ref: CodecRef = { codecId: 'demo/vector@1', typeParams: { length: 1536 } };
+  const codec = materializeCodec(descriptorFor(ref), ref, stubCtx);
+  expect(codec.id).toBe('demo/vector@1');
+});
+
+test('materializeCodec produces a codec whose encode/decode still run through the descriptor-bound factory', async ({
+  expect,
+}) => {
+  const ref: CodecRef = { codecId: 'demo/vector@1', typeParams: { length: 3 } };
+  const codec = materializeCodec(descriptorFor(ref), ref, stubCtx);
+  const wire = await codec.encode([1, 2, 3], {});
+  expect(wire).toBe('[1,2,3]');
+  expect(await codec.decode(wire, {})).toEqual([1, 2, 3]);
+});