Fix the global otel trace tracking

sample.env

@@ -32,8 +32,11 @@ LANGFUSE_HOST="https://cloud.langfuse.com"
 
 # Trace context file for distributed tracing (optional)
 # Used for linking traces between fastomop and omcp across processes
-# Default: Uses system temp directory (e.g., /tmp/ on Unix, %TEMP% on Windows)
+# Default behavior (cross-platform):
+#   - Windows: Uses %TEMP%\.fastomop_langfuse_trace_context.json
+#   - macOS/Linux: Uses /tmp/.fastomop_langfuse_trace_context.json
 # Only set this if you need a custom location or for cross-service coordination
+# IMPORTANT: fastomop and omcp must use the same file path for trace propagation to work
 #LANGFUSE_TRACE_CONTEXT_FILE=/tmp/.fastomop_langfuse_trace_context.json
 
 # ============================================================================

src/omcp/config.py

@@ -4,9 +4,15 @@
 from dotenv import load_dotenv
 from langfuse import Langfuse
 from langfuse import observe
+from opentelemetry.propagate import set_global_textmap
+from opentelemetry.trace.propagation.tracecontext import TraceContextTextMapPropagator
 
 load_dotenv()
 
+# Configure OpenTelemetry W3C Trace Context propagator
+# This is required for cross-process trace propagation with Langfuse V3
+set_global_textmap(TraceContextTextMapPropagator())
+
 # Global configuration variables
 ENABLE_LOGGING = os.environ.get("ENABLE_LOGGING", "true").lower() == "true"
 ENABLE_LANGFUSE = os.environ.get("ENABLE_LANGFUSE", "true").lower() == "true"

src/omcp/trace_context.py

@@ -9,14 +9,22 @@
 """
 
 import os
-import tempfile
 import json
+import platform
+import tempfile
 from pathlib import Path
 from typing import Optional, Dict
 
 
 # Shared trace context file path (same as fastomop)
-default_path = Path(tempfile.gettempdir()) / ".fastomop_langfuse_trace_context.json"
+# Use platform-specific temp directory for cross-platform compatibility
+if platform.system() == "Windows":
+    default_path = Path(tempfile.gettempdir()) / ".fastomop_langfuse_trace_context.json"
+else:
+    # On Unix-like systems (macOS/Linux), use /tmp for consistency across processes
+    # tempfile.gettempdir() can return different paths in different contexts on macOS
+    default_path = Path("/tmp") / ".fastomop_langfuse_trace_context.json"
+
 TRACE_CONTEXT_FILE = Path(
     os.environ.get("LANGFUSE_TRACE_CONTEXT_FILE", str(default_path))
 )
@@ -44,10 +52,16 @@ def read_trace_context() -> Dict[str, Optional[str]]:
                     # Backward compatibility: also read old trace_id format
                     "trace_id": context.get("trace_id"),
                 }
-    except Exception:
+    except Exception as e:
         # Non-critical error, return empty context
-        # Don't log here to avoid noise, caller can decide how to handle None values
-        pass
+        # Only log if file exists but can't be read (actual error)
+        if TRACE_CONTEXT_FILE.exists():
+            import logging
+
+            logger = logging.getLogger("omcp")
+            logger.warning(
+                f"Failed to read trace context from {TRACE_CONTEXT_FILE}: {e}"
+            )
 
     return {
         "traceparent": None,