feat: cargo config writer for automatic hot tier routing

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

claw-store/src/cargo_init.rs

@@ -0,0 +1,76 @@
+use anyhow::{Context, Result};
+use std::path::Path;
+
+/// Write .cargo/config.toml in the project's warm directory pointing
+/// CARGO_TARGET_DIR at the hot NVMe path. Safe to re-run (idempotent).
+pub fn write_cargo_config(warm_path: &Path, hot_target_path: &Path) -> Result<()> {
+    let cargo_dir = warm_path.join(".cargo");
+    std::fs::create_dir_all(&cargo_dir)
+        .with_context(|| format!("creating .cargo dir at {}", cargo_dir.display()))?;
+
+    let target = hot_target_path.to_str()
+        .context("hot_target_path is not valid UTF-8")?;
+
+    let content = format!(
+        "# claw-store managed — do not edit manually\n\
+         [build]\n\
+         target-dir = \"{}\"\n",
+        target
+    );
+
+    let config_path = cargo_dir.join("config.toml");
+    std::fs::write(&config_path, content)
+        .with_context(|| format!("writing {}", config_path.display()))
+}
+
+/// Returns true if .cargo/config.toml exists and points to the expected hot path.
+pub fn verify_cargo_config(warm_path: &Path, hot_target_path: &Path) -> Result<bool> {
+    let config_path = warm_path.join(".cargo/config.toml");
+    if !config_path.exists() { return Ok(false); }
+    let content = std::fs::read_to_string(&config_path)?;
+    let target = hot_target_path.to_str().unwrap_or("");
+    Ok(content.contains(target))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use tempfile::TempDir;
+
+    #[test]
+    fn test_write_cargo_config() {
+        let dir = TempDir::new().unwrap();
+        let warm = dir.path().join("my-project");
+        std::fs::create_dir_all(&warm).unwrap();
+        let hot_target: std::path::PathBuf = "/hot/targets/my-project".into();
+
+        write_cargo_config(&warm, &hot_target).unwrap();
+
+        let cargo_dir = warm.join(".cargo");
+        let config_file = cargo_dir.join("config.toml");
+        assert!(config_file.exists());
+
+        let content = std::fs::read_to_string(&config_file).unwrap();
+        assert!(content.contains("[build]"));
+        assert!(content.contains("/hot/targets/my-project"));
+    }
+
+    #[test]
+    fn test_verify_cargo_config_detects_correct() {
+        let dir = TempDir::new().unwrap();
+        let warm = dir.path().join("proj");
+        std::fs::create_dir_all(&warm).unwrap();
+        let hot: std::path::PathBuf = "/hot/targets/proj".into();
+        write_cargo_config(&warm, &hot).unwrap();
+        assert!(verify_cargo_config(&warm, &hot).unwrap());
+    }
+
+    #[test]
+    fn test_verify_cargo_config_detects_missing() {
+        let dir = TempDir::new().unwrap();
+        let warm = dir.path().join("no-config-proj");
+        std::fs::create_dir_all(&warm).unwrap();
+        let hot: std::path::PathBuf = "/hot/targets/no-config-proj".into();
+        assert!(!verify_cargo_config(&warm, &hot).unwrap());
+    }
+}