fix(observability): use platform-correct log directories and atomic writes

.config/bito.yaml

@@ -0,0 +1,36 @@
+# .bito.yaml — generated by building-in-the-open plugin
+# Edit freely. Re-run plugin setup to regenerate from defaults.
+
+dialect: en-us
+max_grade: 12.0
+passive_max_percent: 15.0
+tokenizer: claude
+
+rules:
+  - paths: [".handoffs/*.md"]
+    checks:
+      completeness:
+        template: handoff
+      tokens:
+        budget: 2000
+
+  - paths: ["record/decisions/*.md"]
+    checks:
+      completeness:
+        template: adr
+      readability:
+        max_grade: 12.0
+
+  - paths: ["record/designs/*.md"]
+    checks:
+      completeness:
+        template: design-doc
+      readability:
+        max_grade: 12.0
+
+  - paths: ["docs/**/*.md", "README.md"]
+    checks:
+      readability:
+        max_grade: 12.0
+      grammar:
+        passive_max: 15.0

.config/scrat.toml

@@ -0,0 +1,8 @@
+[project]
+type = "rust"
+
+[commands]
+test = "just test"
+
+[ship]
+no_publish = true

.repo.yml

@@ -1,5 +1,5 @@
 # Changes here will be overwritten by Copier
-_commit: v1.2.0
+_commit: v1.3.0
 _src_path: gh:claylo/claylo-rs
 categories:
 - command-line-utilities

crates/bito-core/src/observability.rs

@@ -29,9 +29,9 @@ pub struct ObservabilityConfig {
 
 impl ObservabilityConfig {
     /// Create config from environment variables with optional overrides.
-    pub fn from_env_with_overrides(log_dir: Option<PathBuf>) -> Self {
+    pub fn from_env_with_overrides(service: &str, log_dir: Option<PathBuf>) -> Self {
         Self {
-            service: env!("CARGO_PKG_NAME").to_string(),
+            service: service.to_string(),
             log_dir,
         }
     }
@@ -193,9 +193,12 @@ where
         event.record(&mut visitor);
         map.extend(visitor.values);
 
-        let mut writer = self.writer.make_writer();
-        if serde_json::to_writer(&mut writer, &Value::Object(map)).is_ok() {
-            let _ = writer.write_all(b"\n");
+        // Buffer the entire line so it's written in a single write() syscall,
+        // which is atomic with O_APPEND for lines under PIPE_BUF (typically 4096).
+        if let Ok(mut buf) = serde_json::to_vec(&Value::Object(map)) {
+            buf.push(b'\n');
+            let mut writer = self.writer.make_writer();
+            let _ = writer.write_all(&buf);
         }
     }
 }
@@ -354,9 +357,9 @@ fn resolve_log_target_with(
         candidates.push(PathBuf::from(DEFAULT_LOG_DIR_UNIX));
     }
 
-    // Use XDG-compliant data directory for log storage
-    if let Some(proj_dirs) = directories::ProjectDirs::from("", "", service) {
-        candidates.push(proj_dirs.data_local_dir().join("logs"));
+    // Platform-appropriate log directory
+    if let Some(log_dir) = platform_log_dir(service) {
+        candidates.push(log_dir);
     }
 
     if let Ok(dir) = std::env::current_dir() {
@@ -413,6 +416,26 @@ fn ensure_writable(dir: &Path, file_name: &str) -> Result<(), String> {
     Ok(())
 }
 
+/// Resolve the platform-appropriate log directory for a service.
+///
+/// - macOS: `~/Library/Logs/{service}/`
+/// - Linux/BSD: `$XDG_STATE_HOME/{service}/logs/` (default `~/.local/state/{service}/logs/`)
+/// - Windows: `{LocalAppData}/{service}/logs/` (via `directories` crate)
+fn platform_log_dir(service: &str) -> Option<PathBuf> {
+    if cfg!(target_os = "macos") {
+        std::env::var_os("HOME").map(|home| PathBuf::from(home).join("Library/Logs").join(service))
+    } else if cfg!(unix) {
+        let state_base = std::env::var_os("XDG_STATE_HOME")
+            .map(PathBuf::from)
+            .or_else(|| {
+                std::env::var_os("HOME").map(|home| PathBuf::from(home).join(".local/state"))
+            })?;
+        Some(state_base.join(service).join("logs"))
+    } else {
+        directories::ProjectDirs::from("", "", service).map(|p| p.data_local_dir().join("logs"))
+    }
+}
+
 // ============================================================================
 // Tests
 // ============================================================================
@@ -496,6 +519,27 @@ mod tests {
         assert_eq!(&ts[10..11], "T", "date-time separator");
     }
 
+    #[test]
+    fn platform_log_dir_contains_service_name() {
+        let dir = platform_log_dir("test-svc").expect("platform_log_dir should return Some");
+        let path = dir.to_str().expect("path should be valid UTF-8");
+        assert!(
+            path.contains("test-svc"),
+            "log dir should contain service name: {path}"
+        );
+    }
+
+    #[test]
+    #[cfg(target_os = "macos")]
+    fn platform_log_dir_uses_library_logs_on_macos() {
+        let dir = platform_log_dir("test-svc").unwrap();
+        let path = dir.to_str().unwrap();
+        assert!(
+            path.contains("Library/Logs"),
+            "macOS log dir should use ~/Library/Logs/: {path}"
+        );
+    }
+
     #[test]
     fn days_to_ymd_known_dates() {
         // 1970-01-01 = day 0

crates/bito/src/main.rs

@@ -51,6 +51,7 @@ async fn main() -> anyhow::Result<()> {
     let (config, config_sources) = loader.load().context("failed to load configuration")?;
 
     let obs_config = observability::ObservabilityConfig::from_env_with_overrides(
+        env!("CARGO_PKG_NAME"),
         config
             .log_dir
             .as_ref()

crates/bito/tests/cli.rs

@@ -12,7 +12,12 @@ use predicates::prelude::*;
 /// cargo build directories, but works correctly for standard project layouts.
 #[allow(deprecated)]
 fn cmd() -> Command {
-    Command::cargo_bin(env!("CARGO_PKG_NAME")).unwrap()
+    let mut cmd = Command::cargo_bin(env!("CARGO_PKG_NAME")).unwrap();
+    // Route log output to a temp directory so tests don't write to production paths
+    let prefix = env!("CARGO_PKG_NAME").to_uppercase().replace('-', "_");
+    let test_log_dir = std::env::temp_dir().join(format!("{}-test-logs", env!("CARGO_PKG_NAME")));
+    cmd.env(format!("{prefix}_LOG_DIR"), test_log_dir);
+    cmd
 }
 
 // =============================================================================

crates/bito/tests/config_integration.rs

@@ -13,7 +13,12 @@ use tempfile::TempDir;
 /// Returns a Command configured to run our binary.
 #[allow(deprecated)]
 fn cmd() -> Command {
-    Command::cargo_bin(env!("CARGO_PKG_NAME")).unwrap()
+    let mut cmd = Command::cargo_bin(env!("CARGO_PKG_NAME")).unwrap();
+    // Route log output to a temp directory so tests don't write to production paths
+    let prefix = env!("CARGO_PKG_NAME").to_uppercase().replace('-', "_");
+    let test_log_dir = std::env::temp_dir().join(format!("{}-test-logs", env!("CARGO_PKG_NAME")));
+    cmd.env(format!("{prefix}_LOG_DIR"), test_log_dir);
+    cmd
 }
 
 /// Run `info --json` from a directory and parse the JSON output.