Carry trace context across the Redis Stream by hand

Redis Streams have no headers, so the gateway injects traceparent into
the message fields inside a PRODUCER span. The notifier and audit
consumers extract it and open one CONSUMER span per message, so their
DB and XACK spans join the transaction's trace. The idle XREADGROUP poll
runs under suppress_instrumentation (it was a ~2s root trace every loop),
and audit strips the trace fields so its stored payload is unchanged.

The gateway also stops tracing its frontend's /api/health/ polling.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

services/gateway/app.py

@@ -24,7 +24,7 @@ app = FastAPI(title=SERVICE_NAME)
 
 FastAPIInstrumentor.instrument_app(
     app,
-    excluded_urls="/healthz",
+    excluded_urls="/healthz,/api/health/",
     exclude_spans=["receive", "send"],
 )
 

services/gateway/orchestrator.py

@@ -3,6 +3,8 @@ import time
 import uuid
 
 import httpx
+from opentelemetry import propagate, trace
+from opentelemetry.trace import SpanKind
 
 from common.http import downstream_client
 from common.redis_client import redis_client
@@ -11,6 +13,7 @@ from common.settings import settings
 from . import chaos
 
 logger = logging.getLogger("gateway")
+tracer = trace.get_tracer(__name__)
 
 REJECT_THRESHOLD = 0.8
 
@@ -129,17 +132,29 @@ async def create_transaction(payload: dict, request_id: str) -> dict:
         settled = settle_resp.json()
 
         try:
-            await redis_client.xadd(
-                settings.stream_name,
-                {
-                    "transaction_id": tx_id,
-                    "account_id": created["account_id"],
-                    "kind": created["kind"],
-                    "amount_minor": str(created["amount_minor"]),
-                    "status": settled["status"],
-                    "risk_score": str(risk_score),
+            fields = {
+                "transaction_id": tx_id,
+                "account_id": created["account_id"],
+                "kind": created["kind"],
+                "amount_minor": str(created["amount_minor"]),
+                "status": settled["status"],
+                "risk_score": str(risk_score),
+            }
+            with tracer.start_as_current_span(
+                f"send {settings.stream_name}",
+                kind=SpanKind.PRODUCER,
+                attributes={
+                    "messaging.system": "redis",
+                    "messaging.destination.name": settings.stream_name,
+                    "messaging.operation.type": "send",
                 },
-            )
+            ) as span:
+                # Redis Streams carry no trace context, so it travels in the
+                # message itself. Injected inside the PRODUCER span, so the
+                # consumers' parent is this span.
+                propagate.inject(fields)
+                msg_id = await redis_client.xadd(settings.stream_name, fields)
+                span.set_attribute("messaging.message.id", msg_id)
         except Exception:
             logger.exception(f"failed to publish transaction {tx_id} to the stream")