fix: use single context var

Author: hanchchch

src/isolate/connections/grpc/agent.py

@@ -44,22 +44,23 @@
 from isolate.connections.grpc.interface import from_grpc
 
 IDLE_TIMEOUT_SECONDS = int(os.getenv("ISOLATE_AGENT_IDLE_TIMEOUT_SECONDS", "0"))
+CONTEXT_VAR_NAME_LOG = os.getenv("ISOLATE_CONTEXT_VAR_NAME_LOG", "")
 
 
 def get_log_context() -> dict[str, Any]:
-    """Extract all contextvars that start with LOG_ prefix."""
-    result = {}
-    for var in contextvars.copy_context():
-        if var.name.startswith("LOG_"):
-            key = var.name[4:].lower()
-            try:
-                value = var.get()
-                # Ellipsis is a placeholder to indicate it's not set
-                if value is not Ellipsis:
-                    result[key] = var.get()
-            except LookupError:
-                pass
-    return result
+    """Extract the contextvar that is set to the ISOLATE_CONTEXT_VAR_NAME_LOG."""
+    if not CONTEXT_VAR_NAME_LOG:
+        return {}
+
+    log_context = next(
+        contextvars.ContextVar(CONTEXT_VAR_NAME_LOG).get(),
+        None,
+    )
+
+    if not isinstance(log_context, dict):
+        return {}
+
+    return log_context
 
 
 class JsonStdoutProxy: