refactor: Move context before model/provider params, fix resumption token

Reorder LDAIConfigTracker.__init__ to match updated spec: context now
comes before model_name and provider_name.

Also fix resumption_token to omit variationKey from the JSON when it is
empty, and handle the absent key when reconstructing from a token.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jsonbailey

packages/sdk/server-ai/src/ldai/client.py

@@ -96,11 +96,11 @@ def create_tracker(self, token: str, context: Context) -> LDAIConfigTracker:
             ld_client=self._client,
             run_id=payload["runId"],
             config_key=payload["configKey"],
-            variation_key=payload.get("variationKey", ""),
+            variation_key=payload.get("variationKey") or "",
             version=payload["version"],
+            context=context,
             model_name="",
             provider_name="",
-            context=context,
         )
 
     def _completion_config(
@@ -864,9 +864,9 @@ def tracker_factory() -> LDAIConfigTracker:
                 config_key=key,
                 variation_key=variation_key,
                 version=version,
+                context=context,
                 model_name=model_name,
                 provider_name=provider_name,
-                context=context,
                 graph_key=graph_key,
             )
 

packages/sdk/server-ai/src/ldai/tracker.py

@@ -80,9 +80,9 @@ def __init__(
         config_key: str,
         variation_key: str,
         version: int,
+        context: Context,
         model_name: str,
         provider_name: str,
-        context: Context,
         graph_key: Optional[str] = None,
     ):
         """
@@ -93,9 +93,9 @@ def __init__(
         :param config_key: Configuration key for tracking.
         :param variation_key: Variation key for tracking.
         :param version: Version of the variation.
+        :param context: Context for evaluation.
         :param model_name: Name of the model used.
         :param provider_name: Name of the provider used.
-        :param context: Context for evaluation.
         :param graph_key: When set, include ``graphKey`` in all event payloads
             (e.g. config-level metrics inside a graph).
         """
@@ -116,15 +116,18 @@ def resumption_token(self) -> str:
         A URL-safe Base64-encoded JSON string that can be used to reconstruct
         a tracker in a different process (e.g. for deferred feedback).
 
-        The token contains ``runId``, ``configKey``, ``variationKey``, and
-        ``version``.  ``modelName`` and ``providerName`` are **not** included.
+        The token contains ``runId``, ``configKey``, ``version``, and
+        optionally ``variationKey`` (omitted when empty).
+        ``modelName`` and ``providerName`` are **not** included.
         """
-        payload = json.dumps({
+        data: dict = {
             "runId": self._run_id,
             "configKey": self._config_key,
-            "variationKey": self._variation_key,
-            "version": self._version,
-        })
+        }
+        if self._variation_key:
+            data["variationKey"] = self._variation_key
+        data["version"] = self._version
+        payload = json.dumps(data)
         return base64.urlsafe_b64encode(payload.encode("utf-8")).rstrip(b"=").decode("utf-8")
 
     def __get_track_data(self) -> dict:

packages/sdk/server-ai/tests/test_tracker.py

@@ -716,6 +716,27 @@ def test_resumption_token_is_url_safe_base64(client: LDClient):
     base64.urlsafe_b64decode(padded.encode("utf-8"))
 
 
+def test_resumption_token_omits_variation_key_when_empty(client: LDClient):
+    import base64
+    import json
+
+    context = Context.create("user-key")
+    tracker = LDAIConfigTracker(
+        ld_client=client, run_id="test-run-id", config_key="cfg-key",
+        variation_key="", version=1, context=context,
+        model_name="model", provider_name="provider",
+    )
+
+    token = tracker.resumption_token
+    padded = token + "=" * (-len(token) % 4)
+    decoded = json.loads(base64.urlsafe_b64decode(padded.encode("utf-8")).decode("utf-8"))
+
+    assert "variationKey" not in decoded
+    assert decoded["runId"] == "test-run-id"
+    assert decoded["configKey"] == "cfg-key"
+    assert decoded["version"] == 1
+
+
 def test_tracker_with_explicit_run_id(client: LDClient):
     context = Context.create("user-key")
     tracker = LDAIConfigTracker(