Address fourth review round: observability, docs accuracy, dep hygiene, tests

- Warn when no timing data was found at all (empty --times-dir previously
  produced empty CSVs without any hint) — best_cars empty + non-empty car
  list now logs a warning in parse_all_times
- Remove the inaccurate "known gap" doc from write_trash_csv: category 1
  (not best on any track) already covers non-final cars, so the
  documented gap never existed
- Gate env_logger behind the bin-logging feature (default-on) and mark
  the records binary as requiring it, so downstream lib consumers do not
  pull env_logger transitively; lib builds clean with --no-default-features
- Switch fetch_car progress output from println! to log::info! so
  RUST_LOG controls it
- atomic_write takes &Path instead of &PathBuf
- Add direct unit tests for is_final_build (sum-8 finals, maxed builds,
  sub-8 non-finals, malformed inputs) and a parsing test covering
  missing/null/non-numeric "t" fields (warn + skip, valid entries still
  parsed)

src/output/mod.rs

@@ -6,7 +6,7 @@
 use std::collections::{HashMap, HashSet};
 use std::fs;
 use std::io::Write;
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 
 use top_drives::{
     compare_cars, escape_csv_field, is_final_build, AnalysisContext, AppError, BestCarRecord, Car,
@@ -55,7 +55,7 @@ pub fn compare_records(a: &BestCarRecord, b: &BestCarRecord) -> std::cmp::Orderi
 /// If the write callback returns an error, the temporary file is cleaned up
 /// and no partial file is left at the target path.
 fn atomic_write(
-    path: &PathBuf,
+    path: &Path,
     write_fn: impl FnOnce(&mut fs::File) -> Result<(), AppError>,
 ) -> Result<(), AppError> {
     let tmp_path = PathBuf::from(format!("{}.tmp", path.display()));
@@ -179,11 +179,6 @@ pub fn write_very_best_csv(
 /// Non-final builds are excluded from category 2 because they
 /// belong in `improve.csv` instead. Prize cars and RQ ≥ 80 are always excluded.
 ///
-/// **Known gap:** an owned non-final car that is not best on any track in *any*
-/// config appears in neither trash.csv (not final yet) nor improve.csv (no best
-/// config to suggest as a target). Such cars stay under the radar until they
-/// either reach a final build or are manually reviewed.
-///
 /// Format: RQ,Brand,Model,Year,Config
 pub fn write_trash_csv(
     output_dir: &str,

src/parsing/mod.rs

@@ -336,6 +336,15 @@ pub async fn parse_all_times(
         });
     }
 
+    // Missing timing files are silent (expected for most cars), so a wrong or
+    // empty --times-dir would otherwise produce empty CSVs without any hint.
+    if ctx.best_cars.is_empty() && !car_list.is_empty() {
+        log::warn!(
+            "no timing data found in {times_dir} for {} car(s) — all output CSVs will be empty",
+            car_list.len()
+        );
+    }
+
     Ok(car_list)
 }
 
@@ -394,7 +403,7 @@ async fn fetch_car(rid: &str, times_dir: &str) -> Result<(), AppError> {
     let file_name = rid.to_owned() + ".json";
     let url = format!("{CAR_TIMING_API_BASE}{rid}");
     let local_file_path = format!("{times_dir}/{file_name}");
-    println!("Fetching {url}.");
+    log::info!("Fetching {url}.");
     top_drives::get_file(&url, &local_file_path).await
 }
 
@@ -544,6 +553,55 @@ mod tests {
         assert!(ctx.best_cars.contains_key(&("Monaco Streets".to_string(), 85, "Wet".to_string())));
     }
 
+    #[test]
+    fn test_parse_car_times_skips_missing_or_non_numeric_time() {
+        let ctx = AnalysisContext::new();
+        let car = Car {
+            rid: "TestCar_2020".to_string(),
+            brand: "TestBrand".to_string(),
+            only_name: "TestModel".to_string(),
+            year: 2020,
+            rq: 85,
+            prize: false,
+            guid: "guid_test".to_string(),
+        };
+
+        let dir = tempfile::tempdir().unwrap();
+        let times_dir = dir.path().to_str().unwrap();
+        let file_path = dir.path().join("TestCar_2020.json");
+
+        // "t" missing entirely, null, and a string — all must be skipped
+        // without panicking or inserting a record.
+        let json_content = r#"{
+            "data": {
+                "111": {
+                    "times": {
+                        "laguna_a00": { "u": "Player1" },
+                        "mnCity_a01": { "t": null, "u": "Player2" },
+                        "testBowl_a02": { "t": "112.45", "u": "Player3" },
+                        "butte_a01": { "t": 50.0, "u": "Player4" }
+                    }
+                }
+            }
+        }"#;
+        fs::write(&file_path, json_content).unwrap();
+
+        let my_cars: HashSet<String> = HashSet::new();
+        parse_car_times(car, &my_cars, &ctx.best_cars, times_dir).unwrap();
+
+        // Only the valid butte entry survives.
+        assert!(!ctx.best_cars.contains_key(&("Laguna Seca".to_string(), 85, "Dry".to_string())));
+        assert!(!ctx.best_cars.contains_key(&(
+            "Monaco Streets".to_string(),
+            85,
+            "Wet".to_string()
+        )));
+        assert!(
+            ctx.best_cars.contains_key(&("Butte".to_string(), 85, "Wet".to_string())),
+            "valid time entry should still be parsed"
+        );
+    }
+
     #[test]
     fn test_parse_car_times_filters_downvoted() {
         let ctx = AnalysisContext::new();

src/types.rs

@@ -164,3 +164,43 @@ pub fn is_final_build(config: &str) -> bool {
     }
     bytes.iter().map(|&b| b - b'0').sum::<u8>() >= 8
 }
+
+#[cfg(test)]
+mod tests {
+    use super::is_final_build;
+
+    #[test]
+    fn final_builds_have_digit_sum_eight() {
+        assert!(is_final_build("323"));
+        assert!(is_final_build("332"));
+        assert!(is_final_build("233"));
+        assert!(is_final_build("521"));
+        assert!(is_final_build("800"));
+    }
+
+    #[test]
+    fn maxed_builds_beyond_eight_are_final() {
+        assert!(is_final_build("879"));
+        assert!(is_final_build("999"));
+        assert!(is_final_build("990"));
+    }
+
+    #[test]
+    fn unfinished_builds_below_eight_are_not_final() {
+        assert!(!is_final_build("111"));
+        assert!(!is_final_build("221"));
+        assert!(!is_final_build("610"));
+        assert!(!is_final_build("070"));
+    }
+
+    #[test]
+    fn malformed_configs_are_not_final() {
+        assert!(!is_final_build(""));
+        assert!(!is_final_build("12"));
+        assert!(!is_final_build("1234"));
+        assert!(!is_final_build("abc"));
+        assert!(!is_final_build("3a3"));
+        assert!(!is_final_build(" 33"));
+        assert!(!is_final_build("33 "));
+    }
+}