sausage core: modules per topic, journal writer thread with WAL and batches, hash cache by metadata, 49 tests per rule

Blank stdout lines give no warning. core.exit requests the exit in its
own handler.

cli/src/world.rs

@@ -2,10 +2,13 @@
 use anyhow::{Result, bail};
 use std::path::{Path, PathBuf};
 #[derive(Clone)]
+/// The absolute host folder shared by all processes.
 pub struct World {
+    /// The absolute path of the world on the host.
     pub root: PathBuf,
 }
 impl World {
+    /// Validate reserved root names and resolve the world path.
     pub fn open(path: &Path) -> Result<Self> {
         for name in ["proc", "run", "self"] {
             if path.join(name).symlink_metadata().is_ok() {
@@ -16,6 +19,7 @@ impl World {
             root: path.canonicalize()?,
         })
     }
+    /// Create the folders and empty boot configuration of a new world.
     pub fn create(path: &Path) -> Result<Self> {
         if path.exists() {
             bail!("world already exists: {}", path.display());
@@ -26,13 +30,16 @@ impl World {
         std::fs::write(path.join("config/boot.json"), "[]\n")?;
         Self::open(path)
     }
+    /// Return the folder that contains a plugin component.
     pub fn plugin_dir(&self, name: &str) -> PathBuf {
         self.root.join("plugins").join(name)
     }
+    /// Return the persistent state folder of a plugin.
     pub fn state_dir(&self, name: &str) -> PathBuf {
         self.root.join("state").join(name)
     }
 }
+/// Write a temporary sibling and rename it over the destination.
 pub fn write_atomic(path: &Path, bytes: &[u8]) -> Result<()> {
     std::fs::create_dir_all(path.parent().unwrap())?;
     let tmp = path.with_extension("tmp");
@@ -40,6 +47,7 @@ pub fn write_atomic(path: &Path, bytes: &[u8]) -> Result<()> {
     std::fs::rename(tmp, path)?;
     Ok(())
 }
+/// Replace a build copy with a source tree, without target folders.
 pub fn replace_source(from: &Path, to: &Path) -> Result<()> {
     if to.exists() {
         std::fs::remove_dir_all(to)?;