feat: Add from_resumption_token classmethod to LDAIConfigTracker

Move the resumption token decoding logic from LDAIClient.create_tracker
into a classmethod on LDAIConfigTracker per spec 1.1.20.2. The client
method now delegates to LDAIConfigTracker.from_resumption_token.

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

Author: jsonbailey

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

@@ -1,5 +1,3 @@
-import base64
-import json
 import uuid
 from typing import Any, Callable, Dict, List, Optional, Tuple
 
@@ -68,9 +66,7 @@ def create_tracker(self, token: str, context: Context) -> LDAIConfigTracker:
         """
         Reconstruct a tracker from a resumption token.
 
-        This is used for cross-process scenarios such as deferred feedback,
-        where a different service needs to associate tracking events with the
-        original execution's ``runId``.
+        Delegates to :meth:`LDAIConfigTracker.from_resumption_token`.
 
         :param token: A URL-safe Base64-encoded resumption token obtained from
             :attr:`LDAIConfigTracker.resumption_token`.
@@ -79,29 +75,7 @@ def create_tracker(self, token: str, context: Context) -> LDAIConfigTracker:
             ``runId`` from the token.
         :raises ValueError: If the token is invalid or missing required fields.
         """
-        try:
-            # Add padding back before decoding
-            padded = token + "=" * (-len(token) % 4)
-            payload = json.loads(
-                base64.urlsafe_b64decode(padded.encode("utf-8")).decode("utf-8")
-            )
-        except (json.JSONDecodeError, Exception) as e:
-            raise ValueError(f"Invalid resumption token: {e}") from e
-
-        for field in ("runId", "configKey", "version"):
-            if field not in payload:
-                raise ValueError(f"Invalid resumption token: missing required field '{field}'")
-
-        return LDAIConfigTracker(
-            ld_client=self._client,
-            run_id=payload["runId"],
-            config_key=payload["configKey"],
-            variation_key=payload.get("variationKey") or "",
-            version=payload["version"],
-            context=context,
-            model_name="",
-            provider_name="",
-        )
+        return LDAIConfigTracker.from_resumption_token(token, self._client, context)
 
     def _completion_config(
         self,

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

@@ -130,6 +130,48 @@ def resumption_token(self) -> str:
         payload = json.dumps(data)
         return base64.urlsafe_b64encode(payload.encode("utf-8")).rstrip(b"=").decode("utf-8")
 
+    @classmethod
+    def from_resumption_token(cls, token: str, ld_client: LDClient, context: Context) -> 'LDAIConfigTracker':
+        """
+        Reconstruct a tracker from a resumption token.
+
+        This is used for cross-process scenarios such as deferred feedback,
+        where a different service needs to associate tracking events with the
+        original execution's ``runId``.
+
+        :param token: A URL-safe Base64-encoded resumption token obtained from
+            :attr:`resumption_token`.
+        :param ld_client: LaunchDarkly client instance.
+        :param context: The context to use for track events.
+        :return: A new :class:`LDAIConfigTracker` bound to the original
+            ``runId`` from the token.
+        :raises ValueError: If the token is invalid or missing required fields.
+        """
+        try:
+            padded = token + "=" * (-len(token) % 4)
+            payload = json.loads(
+                base64.urlsafe_b64decode(padded.encode("utf-8")).decode("utf-8")
+            )
+        except (json.JSONDecodeError, Exception) as e:
+            raise ValueError(f"Invalid resumption token: {e}") from e
+
+        for field in ("runId", "configKey", "version"):
+            if field not in payload:
+                raise ValueError(
+                    f"Invalid resumption token: missing required field '{field}'"
+                )
+
+        return cls(
+            ld_client=ld_client,
+            run_id=payload["runId"],
+            config_key=payload["configKey"],
+            variation_key=payload.get("variationKey") or "",
+            version=payload["version"],
+            context=context,
+            model_name="",
+            provider_name="",
+        )
+
     def __get_track_data(self) -> dict:
         """
         Get tracking data for events.