fix(openviking): guard empty tool_id in batch skip set; reuse env_var_enabled

Two follow-up fixes on top of the cherry-picked structured-sync work:

- _messages_to_openviking_batch only added a recall tool result's id to
  skipped_tool_ids when the id was non-empty. An empty tool_call_id (which
  the canonical transcript can carry; agent_runtime_helpers defaults it to
  "") poisoned the skip set with "", silently dropping any *other* tool
  result that also lacked an id. Move the recall-skip add inside the
  existing `if tool_id:` guard. Adds a regression test (mutation-checked:
  fails on pre-fix code, passes after).

- _sync_trace_enabled() open-coded the canonical truthy-env check; reuse
  utils.env_var_enabled (byte-identical {1,true,yes,on} semantics).

plugins/memory/openviking/__init__.py

@@ -49,7 +49,7 @@ from agent.message_content import flatten_message_text
 from agent.memory_provider import MemoryProvider
 from agent.skill_commands import extract_user_instruction_from_skill_message
 from tools.registry import tool_error
-from utils import atomic_json_write
+from utils import atomic_json_write, env_var_enabled
 
 logger = logging.getLogger(__name__)
 
@@ -160,7 +160,7 @@ def _derive_openviking_user_text(content: Any) -> str:
 
 
 def _sync_trace_enabled() -> bool:
-    return os.environ.get(_SYNC_TRACE_ENV, "").strip().lower() in {"1", "true", "yes", "on"}
+    return env_var_enabled(_SYNC_TRACE_ENV)
 
 
 def _preview(value: Any, limit: int = 160) -> str:
@@ -2461,8 +2461,8 @@ class OpenVikingMemoryProvider(MemoryProvider):
                 tool_id = str(message.get("tool_call_id") or message.get("id") or "")
                 if tool_id:
                     completed_tool_ids.add(tool_id)
-                if cls._is_openviking_recall_tool_name(message.get("name")):
-                    skipped_tool_ids.add(tool_id)
+                    if cls._is_openviking_recall_tool_name(message.get("name")):
+                        skipped_tool_ids.add(tool_id)
                 continue
             if message.get("role") != "assistant":
                 continue