swarm-queue-client: add an authenticated HttpClient for OTLP exporters (otel-auth feature)

swarm-queue-client/Cargo.toml

@@ -30,6 +30,18 @@ kv = ["async-nats/kv"]
 # `cargo check -p swarm-nats-auth` — no `kv` anywhere in that build —
 # surfaced it as `cannot find jetstream in async_nats`).
 notices = ["async-nats/jetstream"]
+# OFF by default, same reasoning as `kv`/`notices` above: only a caller
+# wiring an OTLP exporter's `HttpClient` seam to this crate's identity
+# (today, `swarm-controller`'s `vcs_metrics`/`hive_jobq_metrics`) needs
+# `opentelemetry_http`/`async-trait`/`bytes`/`http` pulled in — a plain
+# queue-connect-only consumer (the auth-callout responder, a hive
+# publishing its status) has no reason to carry them.
+otel-auth = [
+  "dep:opentelemetry-http",
+  "dep:async-trait",
+  "dep:bytes",
+  "dep:http",
+]
 
 [dependencies]
 # Bare (no `kv`/`jetstream`) unless a consumer opts into the `kv` feature
@@ -45,6 +57,12 @@ async-nats.workspace = true
 # feature's comment above), and `cargo check -p swarm-queue-client` alone
 # must not depend on what else is in the build.
 reqwest = { workspace = true, features = ["blocking"] }
+# All four `optional = true`, gated behind the `otel-auth` feature above —
+# see that feature's own comment for why.
+opentelemetry-http = { workspace = true, optional = true }
+async-trait = { workspace = true, optional = true }
+bytes = { workspace = true, optional = true }
+http = { workspace = true, optional = true }
 serde.workspace = true
 serde_json.workspace = true
 # A library, so its errors are a matchable enum rather than an opaque