Add Tempo-gated e2e test for OTel tracing

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

docs/testing.md

@@ -92,8 +92,38 @@ compiles only under `-tags=e2e`, manages its own kind cluster
 (`make test-e2e` / `make cleanup-test-e2e`), and has been kept compiling
 (`go vet -tags=e2e ./...` is part of the routine) but is **not part of
 `make test` and was not used for the release verification** — the manual
-kind run below covers strictly more. Treat it as scaffold to grow into if
-CI wants an automated cluster smoke test.
+kind run below covers strictly more.
+
+### The OTel tracing spec (Tempo-gated)
+
+`test/e2e/tracing_test.go` proves the full tracing pipeline against a
+**real Tempo**: deploy in kind with tracing enabled, create two
+kubernetes-provider proxies, delete them, and assert in Tempo that the
+traces exist with the documented span topology (`Reconcile Proxy` →
+`reconcile.managed` / `provider.create` / `status.patch`, and
+`reconcile.delete` / `provider.delete` on the way out).
+
+It **skips unless both env vars are set** (so the rest of the suite runs
+anywhere). Homelab invocation:
+
+```bash
+TEMPO_URL=http://192.168.0.30:3200 \
+OTLP_ENDPOINT=http://192.168.0.30:4318 \
+make test-e2e
+```
+
+Worth knowing:
+
+- Every span of a run carries the resource attribute
+  `test.run.id=e2e-<nanos>` (injected via `OTEL_RESOURCE_ATTRIBUTES`, no
+  code involved); the run ID is printed in the test log, and
+  `{resource.test.run.id="<id>"}` in Grafana shows exactly that run.
+- The spec preflights the OTLP endpoint **from inside the cluster** with a
+  curl pod and fails fast with a clear message if it's unreachable —
+  export failures are otherwise only visible at `-zap-log-level=1`.
+- Proxy CRs are created in `default`, not the operator namespace: the
+  squid pods carry no securityContext and the operator namespace enforces
+  restricted PSS.
 
 ## The kind verification run (the real end-to-end)