docs: Add tracing tutorial with Jaeger

examples/all-signals/Cargo.toml

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+[package]
+name = "all-signals"
+version = "0.1.0"
+edition = "2021"
+license = "Apache-2.0"
+rust-version = "1.75.0"
+publish = false
+
+[[bin]]
+name = "all-signals"
+path = "src/main.rs"
+bench = false
+
+[dependencies]
+opentelemetry = { path = "../../opentelemetry" }
+opentelemetry_sdk = { path = "../../opentelemetry-sdk" }
+opentelemetry-otlp = { workspace = true, features = ["grpc-tonic"] }
+tokio = { workspace = true, features = ["full"] }
+

examples/all-signals/README.md

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+# Getting Started with OpenTelemetry Tracing in Rust
+
+This tutorial demonstrates how to instrument a Rust application with
+OpenTelemetry tracing and visualize the traces using
+[Jaeger](https://www.jaegertracing.io/).
+
+## Running the example
+
+### Prerequisites
+
+- **Docker**: Install from [docker.com](https://docs.docker.com/get-docker/) for
+  running Jaeger locally
+
+### Step 1: Start Jaeger
+
+Start Jaeger using Docker:
+
+```shell
+docker run --rm -d --name jaeger \
+  -p 16686:16686 \
+  -p 4317:4317 \
+  cr.jaegertracing.io/jaegertracing/jaeger:2.8.0
+```
+
+This exposes:
+
+- Port `16686`: Jaeger web UI
+- Port `4317`: OTLP endpoint for receiving traces
+
+Verify it's running at <http://localhost:16686/>
+
+![Jaeger UI](jaeger-start.png)
+
+### Step 2: Run the application
+
+```shell
+cargo run
+```
+
+This will:
+
+1. Initialize OpenTelemetry with OTLP exporter pointing to `localhost:4317`
+2. Create a parent span (`Main operation`) and child span (`Sub operation`)
+3. Send the trace data to Jaeger
+
+### Step 3: View traces in Jaeger
+
+1. Open [http://localhost:16686](http://localhost:16686) and refresh
+2. Select `DemoApp` from the **Service** dropdown
+3. Click **Find Traces**
+
+![Jaeger trace list](jaeger-traces.png)
+
+Click on a trace to open Trace Details view, which shows the span hierarchy and timing:
+
+![Jaeger trace details](jaeger-trace-details.png)
+
+You'll see the `Main operation` span containing the `Sub operation` span, along
+with their timing information and any attributes or events.
+
+## Data flow
+
+```mermaid
+graph LR
+    A[Rust App] -->|OTLP| B[Jaeger]
+    B --> C[Web UI]
+```
+
+### Cleanup
+
+```shell
+docker stop jaeger
+```
+
+## Next steps (TODO)
+
+- Add metrics and logs instrumentation
+- Add sampling and context propagation
+- Add distributed tracing across multiple services

examples/all-signals/src/main.rs

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+use opentelemetry::global;
+use opentelemetry::trace::{TraceContextExt, Tracer};
+use opentelemetry::KeyValue;
+use opentelemetry_otlp::SpanExporter;
+use opentelemetry_sdk::trace::SdkTracerProvider;
+use opentelemetry_sdk::Resource;
+use std::sync::OnceLock;
+use std::time::Duration;
+
+fn get_resource() -> Resource {
+    static RESOURCE: OnceLock<Resource> = OnceLock::new();
+    RESOURCE
+        .get_or_init(|| Resource::builder().with_service_name("DemoApp").build())
+        .clone()
+}
+
+fn init_traces() -> SdkTracerProvider {
+    let exporter = SpanExporter::builder()
+        .with_tonic()
+        .build()
+        .expect("Failed to create span exporter");
+    SdkTracerProvider::builder()
+        .with_resource(get_resource())
+        .with_batch_exporter(exporter)
+        .build()
+}
+
+#[tokio::main]
+async fn main() {
+    let tracer_provider = init_traces();
+    global::set_tracer_provider(tracer_provider.clone());
+    let tracer = global::tracer("my-application");
+
+    tracer.in_span("Main operation", |cx| {
+        let span = cx.span();
+        span.set_attribute(KeyValue::new("operation.name", "demo"));
+
+        // Simulate some work
+        std::thread::sleep(Duration::from_millis(200));
+
+        tracer.in_span("Sub operation", |cx| {
+            let span = cx.span();
+            span.set_attribute(KeyValue::new("operation.type", "processing"));
+
+            // Simulate sub-operation work
+            std::thread::sleep(Duration::from_millis(50));
+
+            span.add_event("Processing completed", vec![]);
+        });
+    });
+
+    tracer_provider
+        .shutdown()
+        .expect("Failed to shutdown tracer provider");
+}