Merge branch 'pratik/otel-phase4-consensus-tracing' into pratik/otel-phase5-docs-deployment

CMakeLists.txt

@@ -141,11 +141,13 @@ if(rocksdb)
 endif()
 
 # OpenTelemetry distributed tracing (optional).
-# When ON, links against opentelemetry-cpp and defines XRPL_ENABLE_TELEMETRY
+# When on, links against opentelemetry-cpp and defines XRPL_ENABLE_TELEMETRY
 # so that SpanGuard factory methods produce real OTel spans.
-# When OFF (default), all tracing code compiles to no-ops with zero overhead.
-# Enable via: conan install -o telemetry=True, or cmake -Dtelemetry=ON.
-option(telemetry "Enable OpenTelemetry tracing" ON)
+# When off, all tracing code compiles to no-ops with zero overhead.
+#
+# There is no CMake option. The one switch is `conan install -o telemetry=`,
+# which decides whether opentelemetry-cpp is fetched and sets the variable read
+# below through the generated toolchain.
 if(telemetry)
     find_package(opentelemetry-cpp CONFIG REQUIRED)
     add_compile_definitions(XRPL_ENABLE_TELEMETRY)

docs/build/telemetry.md

@@ -29,9 +29,9 @@ When enabled, it instruments RPC requests with trace spans that are exported via
 OTLP/HTTP to an OpenTelemetry Collector, which forwards them to a tracing backend
 such as Grafana Tempo.
 
-Telemetry is **off by default** at both compile time and runtime:
+Telemetry is gated twice — once at compile time and once at runtime:
 
-- **Compile time**: The Conan option `telemetry` and CMake option `telemetry` must be set to `True`/`ON`.
+- **Compile time**: The Conan option `telemetry` must be `True`. It is the only switch: there is no CMake option, because `conan install` writes the value into the generated toolchain and CMake reads it from there.
   When disabled, all `SpanGuard` calls compile to inline no-ops (defined in `SpanGuard.h`)
   with zero overhead — no OTel SDK dependency required.
 - **Runtime**: The `[telemetry]` config section must set `enabled=1`.