Add initial work from Codex

backend/microservices/common/__init__.py

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+"""Shared helpers for microservices."""

backend/microservices/common/http.py

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+from __future__ import annotations
+
+from opentelemetry import trace
+
+
+def current_trace_headers() -> dict[str, str]:
+    span_context = trace.get_current_span().get_span_context()
+    if not span_context.is_valid:
+        return {}
+    return {
+        "x-trace-id": f"{span_context.trace_id:032x}",
+        "x-span-id": f"{span_context.span_id:016x}",
+    }
+
+
+def with_internal_service_token(headers: dict[str, str], token: str) -> dict[str, str]:
+    merged = dict(headers)
+    merged["x-internal-service-token"] = token
+    return merged