fix(global): add ~/.composer fallback, XDG auto-detection, and no-arg handling

Rewrite composer_home() with Composer-compatible resolution: detect XDG
environment (any XDG_* var or /etc/xdg), prefer existing directories,
and fall back to ~/.composer for legacy systems. Consolidate duplicate
composer_home_dir() from global.rs into shared config_helpers. Accept
no subcommand gracefully with a helpful error instead of a parse error.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/crates/mozart/src/commands/config.rs b/crates/mozart/src/commands/config.rs
index 5105fd6..92f9b59 100644
--- a/crates/mozart/src/commands/config.rs
+++ b/crates/mozart/src/commands/config.rs
@@ -147,7 +147,7 @@ impl ComposerConfig {
             .unwrap_or("vendor")
             .to_string();
 
-        let home = composer_home();
+        let home = composer_home().to_string_lossy().into_owned();
 
         let cache_dir = self
             .values
@@ -466,7 +466,7 @@ fn resolve_config_file_path(args: &ConfigArgs, cli: &super::Cli) -> anyhow::Resu
         anyhow::bail!("Cannot combine --global and --file");
     }
     if args.global {
-        return Ok(PathBuf::from(composer_home()).join("config.json"));
+        return Ok(composer_home().join("config.json"));
     }
     if let Some(ref file) = args.file {
         return Ok(PathBuf::from(file));
@@ -900,7 +900,7 @@ fn execute_read(
     let mut config = ComposerConfig::defaults();
 
     if args.global {
-        let global_config_path = PathBuf::from(composer_home()).join("config.json");
+        let global_config_path = composer_home().join("config.json");
         let overrides = load_config_section(&global_config_path)?;
         config.merge(&overrides);
     } else {