test: deepen and complete project-wide test coverage (#297)

* test: deepen coverage for health doctor provider and tunnels

* test: add broad trait and module re-export coverage

src/doctor/mod.rs

@@ -114,3 +114,89 @@ fn parse_rfc3339(raw: &str) -> Option<DateTime<Utc>> {
         .ok()
         .map(|dt| dt.with_timezone(&Utc))
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::config::Config;
+    use serde_json::json;
+    use tempfile::TempDir;
+
+    fn test_config(tmp: &TempDir) -> Config {
+        let mut config = Config::default();
+        config.workspace_dir = tmp.path().join("workspace");
+        config.config_path = tmp.path().join("config.toml");
+        config
+    }
+
+    #[test]
+    fn parse_rfc3339_accepts_valid_timestamp() {
+        let parsed = parse_rfc3339("2025-01-02T03:04:05Z");
+        assert!(parsed.is_some());
+    }
+
+    #[test]
+    fn parse_rfc3339_rejects_invalid_timestamp() {
+        let parsed = parse_rfc3339("not-a-timestamp");
+        assert!(parsed.is_none());
+    }
+
+    #[test]
+    fn run_returns_ok_when_state_file_missing() {
+        let tmp = TempDir::new().unwrap();
+        let config = test_config(&tmp);
+
+        let result = run(&config);
+
+        assert!(result.is_ok());
+    }
+
+    #[test]
+    fn run_returns_error_for_invalid_json_state_file() {
+        let tmp = TempDir::new().unwrap();
+        let config = test_config(&tmp);
+        let state_file = crate::daemon::state_file_path(&config);
+
+        std::fs::write(&state_file, "not-json").unwrap();
+
+        let result = run(&config);
+
+        assert!(result.is_err());
+        let error_text = result.unwrap_err().to_string();
+        assert!(error_text.contains("Failed to parse"));
+    }
+
+    #[test]
+    fn run_accepts_well_formed_state_snapshot() {
+        let tmp = TempDir::new().unwrap();
+        let config = test_config(&tmp);
+        let state_file = crate::daemon::state_file_path(&config);
+
+        let now = Utc::now().to_rfc3339();
+        let snapshot = json!({
+            "updated_at": now,
+            "components": {
+                "scheduler": {
+                    "status": "ok",
+                    "last_ok": now,
+                    "last_error": null,
+                    "updated_at": now,
+                    "restart_count": 0
+                },
+                "channel:discord": {
+                    "status": "ok",
+                    "last_ok": now,
+                    "last_error": null,
+                    "updated_at": now,
+                    "restart_count": 0
+                }
+            }
+        });
+
+        std::fs::write(&state_file, serde_json::to_vec_pretty(&snapshot).unwrap()).unwrap();
+
+        let result = run(&config);
+
+        assert!(result.is_ok());
+    }
+}