Plain POSIX files: remove commit on close (fs.rs)

Staging every write until close broke tempfile, git, and SQLite, which
expect normal files. Actors that need an atomic publish write a temporary
file and rename it; the SDK has write_atomic for that.

cli/src/world.rs

@@ -19,7 +19,8 @@ use std::path::{Component, Path, PathBuf};
 use anyhow::{Context, Result, bail};
 use serde::{Deserialize, Serialize};
 
-use crate::fs::TMP_PREFIX;
+/// Name prefix of the host's temporary files and folders. Copies skip them.
+pub const TMP_PREFIX: &str = ".sausage-tmp-";
 
 /// IDs of the actors that the host implements natively.
 pub const NATIVE: &[&str] = &["broker", "console", "cargo"];