Install ONE `tracing` subscriber in both build profiles via
`otel::init_tracing()` (previously release-only, so spans were a no-op in
dev). Behaviour is now environment-driven, not build-profile-driven:
- OTLP span export happens only when `OTLP_OTLS_ENDPOINT` is set
(release / staging). Unset -> spans are still created with valid
contexts (so outgoing `traceparent` injection keeps working) but export
nowhere; the console `fmt` layer is what shows them.
- `tracing_subscriber::registry()` + `EnvFilter` (RUST_LOG) +
`OpenTelemetryLayer` + console `fmt` layer, installed in both builds.
- Set the global W3C `TraceContextPropagator`: required by the
`tracing-actix-web` request middleware (#139) and by the outgoing
traceparent helpers, both of which read the *global* propagator.
- `tracing-log` bridge stays OFF (`default-features = false`) so the console
fmt layer prints tracing spans only; `log` records keep their existing
path (env_logger in debug, OTel logs in release) without double-printing.
Deps: + tracing, tracing-subscriber (env-filter/fmt/ansi), tracing-opentelemetry
0.32 (pins opentelemetry 0.31 + otel_sdk 0.31, no version bump); opentelemetry_sdk
gains the `testing` feature.
Add `tests/otel_propagation.rs`: the regression matrix from spike #133, pinning
the invariant the whole migration rests on -- an OTel context does NOT cross a
bare `tokio::spawn` on a multi-thread runtime (S2/S4 orphan onto a fresh trace)
but DOES with an explicit parent carry across the spawn (S6 `.instrument()`,
S7 `span.enter()`). This is why every spawn in the codebase must carry the parent.
clippy --all-targets clean; 690 lib + 775 integration + regression + 4 doc-tests pass.
