telemetry: adopt the end-to-end synthetic convention (UPDATE 4)

Replaces the keyed marker from 1c3b5b0 with the ecosystem convention:
any X-Windy-Synthetic value marks the request synthetic; the flag lives in
a per-request contextvar, labels this request's rows, and is FORWARDED on
downstream calls (Eternitas trust lookup, Gitea API). The canary sends
"1". Rows are still recorded; the label separates, never suppresses.

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

api/app/auth.py

@@ -28,6 +28,7 @@ from api.app.config import Settings
 from api.app.ept import EptInvalid, looks_like_ept, verify_ept
 from api.app.errors import RepairPointer, passport_unresolvable
 from api.app.hub_jwt import HubTokenInvalid, verify_hub_token
+from api.app.telemetry import synthetic_headers
 
 log = logging.getLogger(__name__)
 
@@ -125,7 +126,7 @@ async def resolve_passport(settings: Settings, passport: str) -> tuple[str, tupl
         )
 
     url = f"{settings.eternitas_base_url}/api/v1/trust/{passport}"
-    headers = {"X-API-Key": settings.eternitas_platform_api_key}
+    headers = {"X-API-Key": settings.eternitas_platform_api_key, **synthetic_headers()}
     last_status = 0
     for attempt in range(3):
         async with httpx.AsyncClient(timeout=httpx.Timeout(8.0, connect=3.0)) as client:

api/app/config.py

@@ -71,9 +71,6 @@ class Settings(BaseSettings):
     # root-only /etc/windygit/telemetry.env on Veron, never in the repo.
     windygit_telemetry_token: str = ""
     telemetry_ingest_url: str = "https://admin.windyword.ai/v1/events"
-    # Shared with our canary (Gitea repo secret CANARY_SYNTHETIC_KEY). A request
-    # carrying it in X-Windy-Synthetic is our own tooling -> synthetic:true.
-    windygit_synthetic_key: str = ""
 
     # Internal callers (the Cloud portal calling /internal/*). A first-class
     # caller class, not a bypass: unset means service calls are REFUSED.

api/app/main.py

@@ -27,7 +27,7 @@ from api.app.providers.registry import (
     R2Provider,
 )
 from api.app.routes import health, repos, webhooks
-from api.app.telemetry import Telemetry, caller_class, is_synthetic
+from api.app.telemetry import SYNTHETIC, Telemetry, caller_class, is_synthetic
 
 logging.basicConfig(
     level=logging.INFO,
@@ -139,7 +139,11 @@ app.include_router(webhooks.router)
 async def _count_requests(request: Request, call_next):
     """Heartbeat counts (requests, 4xx/5xx, refusals, p95). Never raises."""
     start = time.perf_counter()
-    response = await call_next(request)
+    marker = SYNTHETIC.set(is_synthetic(request.headers))
+    try:
+        response = await call_next(request)
+    finally:
+        SYNTHETIC.reset(marker)
     tel = getattr(request.app.state, "telemetry", None)
     if tel is not None:
         tel.record_request(
@@ -167,11 +171,7 @@ async def _repair_pointer_handler(request: Request, exc: RepairPointer) -> JSONR
             caller=caller_class(request.headers),
             route=getattr(route, "path", None),
             upstream_status=getattr(exc, "upstream_status", None),
-            synthetic=is_synthetic(
-                request.headers, request.app.state.settings.windygit_synthetic_key
-            )
-            if hasattr(request.app.state, "settings")
-            else False,
+            synthetic=is_synthetic(request.headers),
         )
     return JSONResponse(status_code=exc.status_code, content=exc.detail)
 

api/app/services/gitea_client.py

@@ -20,6 +20,7 @@ import httpx
 
 from api.app.config import Settings
 from api.app.errors import RepairPointer, provider_unconfigured
+from api.app.telemetry import synthetic_headers
 
 _TIMEOUT = httpx.Timeout(20.0, connect=5.0)
 
@@ -36,6 +37,7 @@ class GiteaClient:
         return {
             "Authorization": f"token {self._s.gitea_admin_token}",
             "Content-Type": "application/json",
+            **synthetic_headers(),  # end-to-end synthetic convention (Telemetry UPDATE 4)
         }
 
     async def _request(self, method: str, path: str, **kw: Any) -> httpx.Response:

api/app/telemetry.py

@@ -26,6 +26,7 @@ rows (bounded) and retries on the next tick; it never raises into a request.
 from __future__ import annotations
 
 import asyncio
+import contextvars
 import json
 import logging
 import time
@@ -65,12 +66,21 @@ def _iso(epoch: float) -> str:
     return datetime.fromtimestamp(epoch, UTC).isoformat().replace("+00:00", "Z")
 
 
-def is_synthetic(headers, key: str) -> bool:
-    """Our own tooling proves itself with the shared key; a bare header proves nothing."""
-    import hmac
+# Ecosystem convention (Telemetry UPDATE 4): synthetic traffic travels END TO
+# END. Originators (canaries, probes, journeys) send `X-Windy-Synthetic: 1`;
+# every service marks all of that request's rows synthetic:true AND forwards the
+# header on every downstream call. Absent = real. Never strip it, never set it
+# on real traffic. The label separates rows — it never suppresses them.
+SYNTHETIC: contextvars.ContextVar[bool] = contextvars.ContextVar("windy_synthetic", default=False)
 
-    presented = headers.get("x-windy-synthetic") or ""
-    return bool(key) and bool(presented) and hmac.compare_digest(presented, key)
+
+def is_synthetic(headers) -> bool:
+    return bool((headers.get("x-windy-synthetic") or "").strip())
+
+
+def synthetic_headers() -> dict:
+    """Merge into every downstream request made while serving this one."""
+    return {"X-Windy-Synthetic": "1"} if SYNTHETIC.get() else {}
 
 
 def caller_class(headers) -> str: