Show the resolved default settings path in --help; add Prometheus/OpenMetrics polling

--settings-path's help text now names the actual resolved default path
(computed once via LazyLock) instead of only describing where to look for
one. Also adds an optional --metrics-url flag that polls a Prometheus/
OpenMetrics-compatible endpoint on an interval, pushing samples straight
into a metric's bucket (bypassing log-line regex matching) so they're
queryable via PromQL/dashboards alongside log-derived metrics.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o

src/main.rs

@@ -14,7 +14,7 @@ mod settings;
 mod timestamp;
 
 use std::path::PathBuf;
-use std::sync::{Arc, Mutex};
+use std::sync::{Arc, LazyLock, Mutex};
 
 use clap::Parser;
 use tokio::net::TcpListener;
@@ -23,6 +23,17 @@ use tokio::sync::mpsc;
 use profile::ProfileStore;
 use settings::Settings;
 
+/// The resolved default settings path, rendered into `--help` so `--settings-path`'s help text
+/// names a real, concrete location instead of only describing where to look for one.
+static SETTINGS_PATH_HELP: LazyLock<String> = LazyLock::new(|| {
+    format!(
+        "Path to the settings file. Defaults to {}.",
+        settings::default_settings_path()
+            .map(|path| path.display().to_string())
+            .unwrap_or_else(|| "a per-OS config location".to_string())
+    )
+});
+
 /// Observability dashboard from terminal output.
 #[derive(Parser, Debug)]
 struct Args {
@@ -31,13 +42,16 @@ struct Args {
     #[arg(long, default_value_t = 0)]
     port: u16,
 
-    /// Path to the settings file. Defaults to a per-OS config location.
-    #[arg(long)]
+    #[arg(long, help = SETTINGS_PATH_HELP.as_str())]
     settings_path: Option<PathBuf>,
 
     /// File to tail for log lines, instead of reading from stdin. Behaves like `tail -f`.
     #[arg(long)]
     file: Option<PathBuf>,
+
+    /// URL of a Prometheus/OpenMetrics-compatible endpoint to poll for metrics, in addition to log ingestion.
+    #[arg(long)]
+    metrics_url: Option<String>,
 }
 
 #[tokio::main]
@@ -94,6 +108,10 @@ async fn main() {
         }
     }
 
+    if let Some(metrics_url) = args.metrics_url.clone() {
+        tokio::spawn(ingest::run_metrics_poll(engine_tx.clone(), metrics_url));
+    }
+
     let app = api::router(engine_tx, settings, settings_path);
     let listener = TcpListener::bind(("0.0.0.0", args.port))
         .await