refactor(stats): take stats_url as a StatsFlusher::new parameter

StatsFlusher derived its intake URL internally via
trace_stats_url(&config.site), which hardcodes
https://trace.agent.{site}/api/v0.2/stats. Lift the URL to the caller:
main.rs now computes trace_stats_url at the call site and passes it in.

Mirrors how TraceFlusher already works (URL comes from outside via
SendData's embedded Endpoint) and unblocks redirecting StatsFlusher to
alternate endpoints such as in-process test harnesses.

Retry-loop debug logs now report endpoint.url so they match the URL
actually contacted.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: lucaspimentel

bottlecap/src/bin/bottlecap/main.rs

@@ -1131,6 +1131,7 @@ fn start_trace_agent(
         stats_aggregator.clone(),
         Arc::clone(config),
         trace_http_client.clone(),
+        libdd_trace_utils::config_utils::trace_stats_url(&config.site),
     ));
 
     let stats_processor = Arc::new(stats_processor::ServerlessStatsProcessor {});

bottlecap/src/traces/stats_flusher.rs

@@ -14,13 +14,14 @@ use crate::traces::stats_aggregator::StatsAggregator;
 use dogstatsd::api_key::ApiKeyFactory;
 use libdd_common::Endpoint;
 use libdd_trace_protobuf::pb;
-use libdd_trace_utils::{config_utils::trace_stats_url, stats_utils};
+use libdd_trace_utils::stats_utils;
 use tracing::{debug, error};
 
 pub struct StatsFlusher {
     aggregator: Arc<Mutex<StatsAggregator>>,
     config: Arc<config::Config>,
     api_key_factory: Arc<ApiKeyFactory>,
+    stats_url: String,
     endpoint: OnceCell<Endpoint>,
     http_client: HttpClient,
 }
@@ -32,11 +33,13 @@ impl StatsFlusher {
         aggregator: Arc<Mutex<StatsAggregator>>,
         config: Arc<config::Config>,
         http_client: HttpClient,
+        stats_url: String,
     ) -> Self {
         StatsFlusher {
             aggregator,
             config,
             api_key_factory,
+            stats_url,
             endpoint: OnceCell::new(),
             http_client,
         }
@@ -64,9 +67,8 @@ impl StatsFlusher {
             .endpoint
             .get_or_init({
                 move || async move {
-                    let stats_url = trace_stats_url(&self.config.site);
                     Endpoint {
-                        url: hyper::Uri::from_str(&stats_url)
+                        url: hyper::Uri::from_str(&self.stats_url)
                             .expect("can't make URI from stats url, exiting"),
                         api_key: Some(api_key_clone.into()),
                         timeout_ms: self.config.flush_timeout * S_TO_MS,
@@ -92,8 +94,6 @@ impl StatsFlusher {
             }
         };
 
-        let stats_url = trace_stats_url(&self.config.site);
-
         for attempt in 1..=FLUSH_RETRY_COUNT {
             let start = std::time::Instant::now();
             let resp = stats_utils::send_stats_payload_with_client(
@@ -108,14 +108,16 @@ impl StatsFlusher {
             match resp {
                 Ok(()) => {
                     debug!(
-                        "STATS | Successfully flushed stats to {stats_url} in {} ms (attempt {attempt}/{FLUSH_RETRY_COUNT})",
+                        "STATS | Successfully flushed stats to {} in {} ms (attempt {attempt}/{FLUSH_RETRY_COUNT})",
+                        endpoint.url,
                         elapsed.as_millis()
                     );
                     return None;
                 }
                 Err(e) => {
                     debug!(
-                        "STATS | Failed to send stats to {stats_url} in {} ms (attempt {attempt}/{FLUSH_RETRY_COUNT}): {e:?}",
+                        "STATS | Failed to send stats to {} in {} ms (attempt {attempt}/{FLUSH_RETRY_COUNT}): {e:?}",
+                        endpoint.url,
                         elapsed.as_millis()
                     );
                 }