Adopt rustfmt and clean up clippy warnings

Formats the whole backend to rustfmt defaults and fixes all 23
outstanding clippy warnings (collapsible ifs, clone-to-slice-ref,
type-complexity, single-arm match, unnecessary is_none check), then
wires cargo fmt --check and -D warnings into make lint so both stay
enforced going forward.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TeyhRfMYjMditek6geDRoQ

src/engine/ingest.rs

@@ -2,8 +2,8 @@ use std::collections::BTreeMap;
 use std::path::{Path, PathBuf};
 
 use crate::consts::{METRICS_POLL_INTERVAL, STDIN_POLL_INTERVAL as POLL_INTERVAL};
-use crate::engine::{EngineHandle, EngineMessage, IngestedLine, MetricSample};
 use crate::engine::timestamp::Timestamp;
+use crate::engine::{EngineHandle, EngineMessage, IngestedLine, MetricSample};
 use tokio::fs::File;
 use tokio::io::{AsyncBufReadExt, BufReader};
 
@@ -67,15 +67,12 @@ pub async fn run_file(engine: EngineHandle, path: PathBuf) {
             let mut chunk = String::new();
             match reader.read_line(&mut chunk).await {
                 Ok(0) => {
-                    match tokio::fs::metadata(&path).await {
-                        Ok(meta) => {
-                            let new_id = file_id(&meta);
-                            if new_id != id || meta.len() < offset {
-                                continue 'reopen;
-                            }
-                            id = new_id;
+                    if let Ok(meta) = tokio::fs::metadata(&path).await {
+                        let new_id = file_id(&meta);
+                        if new_id != id || meta.len() < offset {
+                            continue 'reopen;
                         }
-                        Err(_) => {}
+                        id = new_id;
                     }
                     tokio::time::sleep(POLL_INTERVAL).await;
                 }
@@ -83,9 +80,7 @@ pub async fn run_file(engine: EngineHandle, path: PathBuf) {
                     offset += n as u64;
                     pending.push_str(&chunk);
                     if pending.ends_with('\n') {
-                        let text = pending
-                            .trim_end_matches(['\n', '\r'])
-                            .to_string();
+                        let text = pending.trim_end_matches(['\n', '\r']).to_string();
                         pending.clear();
 
                         let line = IngestedLine {
@@ -128,7 +123,12 @@ pub async fn run_metrics_poll(engine: EngineHandle, url: String) {
             Ok(body) => {
                 let now = Timestamp::now();
                 for sample in parse_openmetrics(&body, now) {
-                    if engine.tx.send(EngineMessage::IngestMetricSample(sample)).await.is_err() {
+                    if engine
+                        .tx
+                        .send(EngineMessage::IngestMetricSample(sample))
+                        .await
+                        .is_err()
+                    {
                         return;
                     }
                 }
@@ -140,7 +140,9 @@ pub async fn run_metrics_poll(engine: EngineHandle, url: String) {
 }
 
 fn parse_openmetrics(body: &str, now: Timestamp) -> Vec<MetricSample> {
-    body.lines().filter_map(|line| parse_openmetrics_line(line, now)).collect()
+    body.lines()
+        .filter_map(|line| parse_openmetrics_line(line, now))
+        .collect()
 }
 
 fn parse_openmetrics_line(line: &str, now: Timestamp) -> Option<MetricSample> {
@@ -161,7 +163,10 @@ fn parse_openmetrics_line(line: &str, now: Timestamp) -> Option<MetricSample> {
     let (metric_name, labels) = match name_and_labels.find('{') {
         Some(open) => {
             let close = name_and_labels.rfind('}')?;
-            (name_and_labels[..open].to_string(), parse_openmetrics_labels(&name_and_labels[open + 1..close]))
+            (
+                name_and_labels[..open].to_string(),
+                parse_openmetrics_labels(&name_and_labels[open + 1..close]),
+            )
         }
         None => (name_and_labels.to_string(), BTreeMap::new()),
     };
@@ -169,13 +174,23 @@ fn parse_openmetrics_line(line: &str, now: Timestamp) -> Option<MetricSample> {
         return None;
     }
 
-    Some(MetricSample { metric_name, labels, value, timestamp })
+    Some(MetricSample {
+        metric_name,
+        labels,
+        value,
+        timestamp,
+    })
 }
 
 fn parse_openmetrics_labels(raw: &str) -> BTreeMap<String, String> {
     raw.split(',')
         .filter_map(|pair| pair.split_once('='))
-        .map(|(name, value)| (name.trim().to_string(), value.trim().trim_matches('"').to_string()))
+        .map(|(name, value)| {
+            (
+                name.trim().to_string(),
+                value.trim().trim_matches('"').to_string(),
+            )
+        })
         .collect()
 }
 
@@ -197,10 +212,8 @@ mod openmetrics_tests {
     #[test]
     fn parses_labels_and_explicit_timestamp() {
         let now = Timestamp::from_millis(1000);
-        let samples = parse_openmetrics(
-            r#"http_requests_total{method="GET",path="/a"} 7 5000"#,
-            now,
-        );
+        let samples =
+            parse_openmetrics(r#"http_requests_total{method="GET",path="/a"} 7 5000"#, now);
         assert_eq!(samples.len(), 1);
         let sample = &samples[0];
         assert_eq!(sample.metric_name, "http_requests_total");
@@ -223,9 +236,9 @@ mod openmetrics_tests {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use std::time::Duration;
-    use std::io::Write;
     use crate::engine::test_handle;
+    use std::io::Write;
+    use std::time::Duration;
     use tokio::sync::mpsc;
 
     async fn recv_text(rx: &mut mpsc::Receiver<EngineMessage>) -> String {
@@ -250,7 +263,10 @@ mod tests {
 
         assert_eq!(recv_text(&mut rx).await, "first");
 
-        let mut f = std::fs::OpenOptions::new().append(true).open(&path).unwrap();
+        let mut f = std::fs::OpenOptions::new()
+            .append(true)
+            .open(&path)
+            .unwrap();
         writeln!(f, "second").unwrap();
         assert_eq!(recv_text(&mut rx).await, "second");
     }