feat(core): add Composer struct mirroring requireComposer/tryComposer

Introduce mozart_core::composer::Composer with require()/try_load()
constructors and a config() accessor, modelled on PHP Composer's
BaseCommand::requireComposer / tryComposer. ComposerConfig and
composer_home move into mozart-core so Composer::load can resolve
placeholders consistently.

Migrate dump-autoload, archive, exec and run-script away from ad-hoc
composer.json reads. exec and run-script now fail when composer.json
is missing instead of silently falling back to "vendor/bin",
matching the upstream requireComposer contract.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

1 files changed, 3 insertions, 14 deletions

diff --git a/crates/mozart/src/commands/dump_autoload.rs b/crates/mozart/src/commands/dump_autoload.rs
index c35690b..ec25b54 100644
--- a/crates/mozart/src/commands/dump_autoload.rs
+++ b/crates/mozart/src/commands/dump_autoload.rs
@@ -66,20 +66,9 @@ pub async fn execute(
     let vendor_dir = working_dir.join("vendor");
     let dev_mode = !args.no_dev;
 
-    // B: Read config-driven defaults from composer.json
-    let composer_json_path = working_dir.join("composer.json");
-    let mut composer_config = super::config::ComposerConfig::defaults();
-    if composer_json_path.exists()
-        && let Ok(content) = std::fs::read_to_string(&composer_json_path)
-        && let Ok(value) = serde_json::from_str::<serde_json::Value>(&content)
-        && let Some(cfg_obj) = value.get("config").and_then(|v| v.as_object())
-    {
-        let overrides: std::collections::BTreeMap<String, serde_json::Value> = cfg_obj
-            .iter()
-            .map(|(k, v)| (k.clone(), v.clone()))
-            .collect();
-        composer_config.merge(&overrides);
-    }
+    // B: Load Composer state (composer.json is required for dump-autoload)
+    let composer = mozart_core::composer::Composer::require(&working_dir)?;
+    let composer_config = composer.config();
 
     let optimize = args.optimize
         || composer_config