[BUG] Default create path with no config or schema does not populate default ef in schema (#5726)

## Description of changes

_Summarize the changes made by this PR._

- Improvements & Bug fixes
- There was a bug in the create collection path, where if the user
provides no configuration and no schema at create time, the default
schema (which has no ef) gets written to sysdb. this got hidden in the
tests since on deserialization, schema builds with the default ef, so
the test thought it correctly was assigned the default ef. the fix for
this is to check if both config and schema are default during
reconciliation, and in that case use the config to build the schema.
- New functionality
  - ...

## Test plan

updated e2e test to catch this bug. validated the test caught the bug,
then fixed it

_How are these changes tested?_

- [ x] 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: jairad26

chromadb/test/api/test_schema_e2e.py

@@ -1458,6 +1458,12 @@ def test_default_embedding_function_when_no_schema_provided(
     # Verify it's the DefaultEmbeddingFunction, not legacy
     assert ef.name() == "default"
 
+    config = collection.configuration
+    assert config is not None
+    config_ef = config.get("embedding_function")
+    assert config_ef is not None
+    assert config_ef.name() == "default"
+
     # Serialize the schema to JSON and verify the embedding function type
     json_data = schema.serialize_to_json()
     embedding_vector = json_data["keys"]["#embedding"]["float_list"]["vector_index"]

rust/types/src/collection_schema.rs

@@ -1241,8 +1241,17 @@ impl Schema {
     ) -> Result<Schema, SchemaError> {
         // 1. Check if collection config is default
         if collection_config.is_default() {
-            // Collection config is default → schema is source of truth
-            return Ok(schema.clone());
+            if schema.is_default() {
+                // if both are default, use collection config to create schema
+                // this handles the case where user did not provide schema or config.
+                // since default schema doesnt have an ef, we need to use the coll config to create
+                // a schema with the ef.
+                let new_schema = Self::convert_collection_config_to_schema(collection_config)?;
+                return Ok(new_schema);
+            } else {
+                // Collection config is default and schema is non-default → schema is source of truth
+                return Ok(schema.clone());
+            }
         }
 
         // 2. Collection config is non-default, schema must be default (already validated earlier)
@@ -3346,8 +3355,8 @@ mod tests {
     #[test]
     fn test_reconcile_with_collection_config_default_config() {
         // Test that when collection config is default, schema is returned as-is
-        let schema = Schema::new_default(KnnIndex::Hnsw);
         let collection_config = InternalCollectionConfiguration::default_hnsw();
+        let schema = Schema::convert_collection_config_to_schema(&collection_config).unwrap();
 
         let result = Schema::reconcile_with_collection_config(&schema, &collection_config).unwrap();
         assert_eq!(result, schema);