fix(depends): prefer installed packages over lockfile and add platform support

Without --locked, prefer vendor/composer/installed.json over composer.lock
to match Composer's data source priority. Add platform packages (php, ext-*,
lib-*) from detect_platform() so queries like `depends php` work. Show a
specific error message when a platform package is not found.

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

2 files changed, 31 insertions, 2 deletions

diff --git a/crates/mozart/src/commands/dependency.rs b/crates/mozart/src/commands/dependency.rs
index 5073be0..f2856d9 100644
--- a/crates/mozart/src/commands/dependency.rs
+++ b/crates/mozart/src/commands/dependency.rs
@@ -59,12 +59,35 @@ pub fn load_packages(working_dir: &Path, locked: bool) -> Result<Vec<PackageInfo
     let composer_json_path = working_dir.join("composer.json");
 
     // Load locked / installed packages
-    let mut packages: Vec<PackageInfo> = if locked || lock_path.exists() {
+    let mut packages: Vec<PackageInfo> = if locked {
         load_from_lockfile(&lock_path)?
     } else {
-        load_from_installed(working_dir)?
+        let installed = load_from_installed(working_dir);
+        match installed {
+            Ok(pkgs) if !pkgs.is_empty() => pkgs,
+            _ => {
+                if lock_path.exists() {
+                    load_from_lockfile(&lock_path)?
+                } else {
+                    vec![]
+                }
+            }
+        }
     };
 
+    // Add platform packages (php, ext-*, lib-*, composer-*-api)
+    let platform = mozart_core::platform::detect_platform();
+    for pp in &platform {
+        packages.push(PackageInfo {
+            name: pp.name.clone(),
+            version: pp.version.clone(),
+            require: BTreeMap::new(),
+            require_dev: BTreeMap::new(),
+            conflict: BTreeMap::new(),
+            is_root: false,
+        });
+    }
+
     // Add the root package (composer.json) as a synthetic entry
     if composer_json_path.exists()
         && let Ok(root) = mozart_core::package::read_from_file(&composer_json_path)
diff --git a/crates/mozart/src/commands/depends.rs b/crates/mozart/src/commands/depends.rs
index 673fd35..c65f775 100644
--- a/crates/mozart/src/commands/depends.rs
+++ b/crates/mozart/src/commands/depends.rs
@@ -44,6 +44,12 @@ pub async fn execute(
 
     // Verify the target package is known
     let target_known = packages.iter().any(|p| p.name.to_lowercase() == target);
+    if !target_known && mozart_core::platform::is_platform_package(&target) {
+        anyhow::bail!(
+            "Could not find platform package \"{}\". Is PHP available?",
+            args.package
+        );
+    }
     if !target_known {
         anyhow::bail!(
             "Could not find package \"{}\" in your project",