feat: scaffold cortex workspace

Rust reverse-proxy for multi-node mistral.rs inference clusters.
Includes crate structure (cortex-core, cortex-gateway, cortex-agent,
cortex-cli), config loading, OpenAI/Anthropic translation stubs,
model routing, eviction, polling, and streaming proxy scaffolding.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/cortex-gateway/src/metrics.rs

@@ -0,0 +1,55 @@
+//! Prometheus metrics exporter.
+//!
+//! Runs on a separate port from the main API, exposing `/metrics`
+//! in Prometheus text format.
+
+use anyhow::Result;
+use metrics_exporter_prometheus::PrometheusBuilder;
+use std::net::SocketAddr;
+
+/// Install the Prometheus metrics recorder and return a handle.
+/// The `/metrics` endpoint is served by the exporter's built-in HTTP server.
+pub fn install(listen: &str) -> Result<()> {
+    let addr: SocketAddr = listen.parse()?;
+
+    PrometheusBuilder::new()
+        .with_http_listener(addr)
+        .install()
+        .map_err(|e| anyhow::anyhow!("failed to install Prometheus exporter: {e}"))?;
+
+    tracing::info!("prometheus metrics exporter on {addr}");
+
+    // Register histograms and counters used by the proxy layer.
+    // The `metrics` crate lazily creates metrics on first use, but
+    // describing them up front gives Prometheus proper HELP/TYPE lines.
+    metrics::describe_histogram!(
+        "cortex_request_duration_seconds",
+        "Total request latency in seconds"
+    );
+    metrics::describe_histogram!(
+        "cortex_time_to_first_token_seconds",
+        "Time to first token in seconds"
+    );
+    metrics::describe_histogram!(
+        "cortex_tokens_per_second",
+        "Generation throughput in tokens per second"
+    );
+    metrics::describe_counter!(
+        "cortex_requests_total",
+        "Total number of proxied requests"
+    );
+    metrics::describe_counter!(
+        "cortex_request_errors_total",
+        "Total number of failed proxy requests"
+    );
+    metrics::describe_counter!(
+        "cortex_evictions_total",
+        "Total number of model evictions"
+    );
+    metrics::describe_counter!(
+        "cortex_cold_starts_total",
+        "Total number of cold-start model loads"
+    );
+
+    Ok(())
+}