[BUG] TS vector config source key should accept Key (#5840)

## Description of changes

_Summarize the changes made by this PR._

- Improvements & Bug fixes
  - #5830
- New functionality
  - N/A

## Test plan

_How are these changes tested?_

- [ ] Tests pass locally with `pytest` for python, `yarn test` for js, `cargo test` for rust

## Migration plan

_Are there any migrations, or any forwards/backwards compatibility changes needed in order to make sure this change deploys reliably?_

## Observability plan

_What is the plan to instrument and monitor this change?_

## Documentation Changes

_Are all docstrings for user-facing APIs updated if required? Do we need to make documentation changes in the [docs section](https://github.com/chroma-core/chroma/tree/main/docs/docs.trychroma.com)?_

Author: Sicheng-Pan

clients/new-js/packages/chromadb/src/schema.ts

@@ -13,6 +13,7 @@ import {
   getEmbeddingFunction,
   getSparseEmbeddingFunction,
 } from "./embedding-function";
+import { Key } from "./execution";
 
 export const DOCUMENT_KEY = "#document";
 export const EMBEDDING_KEY = "#embedding";
@@ -55,7 +56,7 @@ export class BoolInvertedIndexConfig {
 export interface VectorIndexConfigOptions {
   space?: Space | null;
   embeddingFunction?: EmbeddingFunction | null;
-  sourceKey?: string | null;
+  sourceKey?: string | Key | null;
   hnsw?: ApiHnswIndexConfig | null;
   spann?: ApiSpannIndexConfig | null;
 }
@@ -71,15 +72,15 @@ export class VectorIndexConfig {
   constructor(options: VectorIndexConfigOptions = {}) {
     this.space = options.space ?? null;
     this.embeddingFunction = options.embeddingFunction;
-    this.sourceKey = options.sourceKey ?? null;
+    this.sourceKey = options.sourceKey instanceof Key ? options.sourceKey.name : options.sourceKey ?? null;
     this.hnsw = options.hnsw ?? null;
     this.spann = options.spann ?? null;
   }
 }
 
 export interface SparseVectorIndexConfigOptions {
   embeddingFunction?: SparseEmbeddingFunction | null;
-  sourceKey?: string | null;
+  sourceKey?: string | Key | null;
   bm25?: boolean | null;
 }
 
@@ -91,7 +92,7 @@ export class SparseVectorIndexConfig {
 
   constructor(options: SparseVectorIndexConfigOptions = {}) {
     this.embeddingFunction = options.embeddingFunction;
-    this.sourceKey = options.sourceKey ?? null;
+    this.sourceKey = options.sourceKey instanceof Key ? options.sourceKey.name : options.sourceKey ?? null;
     this.bm25 = options.bm25 ?? null;
   }
 }

clients/new-js/packages/chromadb/test/schema.test.ts

@@ -1709,4 +1709,60 @@ describe("Schema", () => {
     expect(capturedRecords.metadatas[2]).not.toHaveProperty("field_sparse");
     expect(capturedRecords.metadatas[3]).toBeNull();
   });
+
+  it("accepts Key instance for VectorIndexConfig sourceKey", () => {
+    const { K } = require("../src/execution");
+    const schema = new Schema();
+    const vectorConfig = new VectorIndexConfig({
+      sourceKey: K.DOCUMENT,
+    });
+
+    expect(vectorConfig.sourceKey).toBe("#document");
+
+    // Also test with custom key
+    const customKey = K("myfield");
+    const vectorConfig2 = new VectorIndexConfig({
+      sourceKey: customKey,
+    });
+
+    expect(vectorConfig2.sourceKey).toBe("myfield");
+  });
+
+  it("accepts Key instance for SparseVectorIndexConfig sourceKey", () => {
+    const { K } = require("../src/execution");
+    const schema = new Schema();
+    const sparseConfig = new SparseVectorIndexConfig({
+      sourceKey: K.DOCUMENT,
+    });
+
+    expect(sparseConfig.sourceKey).toBe("#document");
+
+    // Also test with custom key
+    const customKey = K("myfield");
+    const sparseConfig2 = new SparseVectorIndexConfig({
+      sourceKey: customKey,
+    });
+
+    expect(sparseConfig2.sourceKey).toBe("myfield");
+  });
+
+  it("serializes Key sourceKey correctly", async () => {
+    const { K } = require("../src/execution");
+    const schema = new Schema();
+    const sparseEf = new MockSparseEmbedding("key_test");
+    
+    schema.createIndex(
+      new SparseVectorIndexConfig({
+        embeddingFunction: sparseEf,
+        sourceKey: K.DOCUMENT,
+      }),
+      "sparse_field"
+    );
+
+    const json = schema.serializeToJSON();
+    expect(json.keys["sparse_field"]?.["sparse_vector"]?.["sparse_vector_index"]?.config?.source_key).toBe("#document");
+
+    const deserialized = await Schema.deserializeFromJSON(json);
+    expect(deserialized?.keys["sparse_field"].sparseVector?.sparseVectorIndex?.config.sourceKey).toBe("#document");
+  });
 });