fix(resolver): handle virtual packages and deduplicate pool exploration

Virtual/meta packages (e.g. "psr/http-client-implementation") don't
exist on Packagist and caused a fatal error during transitive dependency
exploration. These packages are resolved via provides/replaces from
other packages already in the pool, so 404 errors are now skipped.

Also fix PoolBuilder::next_pending() repeatedly returning the same
virtual package name by tracking explored names in a HashSet, since
virtual packages are never added to inputs and the old check
(inputs.any(name)) never matched them.

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

2 files changed, 23 insertions, 11 deletions

diff --git a/crates/mozart-registry/src/resolver.rs b/crates/mozart-registry/src/resolver.rs
index 66864f7..3e0936f 100644
--- a/crates/mozart-registry/src/resolver.rs
+++ b/crates/mozart-registry/src/resolver.rs
@@ -467,14 +467,18 @@ pub async fn resolve(request: &ResolveRequest) -> Result<Vec<ResolvedPackage>, R
                 continue;
             }
 
-            let versions = handle
-                .block_on(packagist::fetch_package_versions(
-                    &name,
-                    repo_cache.as_ref(),
-                ))
-                .map_err(|e| {
-                    ResolveError::DependencyFetchError(format!("Failed to fetch {}: {}", name, e))
-                })?;
+            let versions = match handle.block_on(packagist::fetch_package_versions(
+                &name,
+                repo_cache.as_ref(),
+            )) {
+                Ok(v) => v,
+                Err(_) => {
+                    // Virtual/meta packages (e.g. "psr/http-client-implementation")
+                    // don't exist on Packagist. They are resolved via provides/replaces
+                    // from other packages already in the pool.
+                    continue;
+                }
+            };
 
             for pv in &versions {
                 let inputs =
diff --git a/crates/mozart-sat-resolver/src/pool_builder.rs b/crates/mozart-sat-resolver/src/pool_builder.rs
index 40977ef..a642fc3 100644
--- a/crates/mozart-sat-resolver/src/pool_builder.rs
+++ b/crates/mozart-sat-resolver/src/pool_builder.rs
@@ -13,6 +13,8 @@ pub struct PoolBuilder {
     added: HashSet<String>,
     /// Queue of package names that need to be explored.
     pending_names: VecDeque<String>,
+    /// Package names that have already been explored (returned by next_pending).
+    explored_names: HashSet<String>,
     /// Platform packages to ignore.
     ignore_platform_reqs: HashSet<String>,
 }
@@ -23,6 +25,7 @@ impl PoolBuilder {
             inputs: Vec::new(),
             added: HashSet::new(),
             pending_names: VecDeque::new(),
+            explored_names: HashSet::new(),
             ignore_platform_reqs: HashSet::new(),
         }
     }
@@ -56,10 +59,15 @@ impl PoolBuilder {
     /// and add them via `add_package`.
     pub fn next_pending(&mut self) -> Option<String> {
         while let Some(name) = self.pending_names.pop_front() {
-            // Check if we already have any versions for this name
-            if !self.inputs.iter().any(|p| p.name == name) {
-                return Some(name);
+            // Skip if already explored or already has versions in inputs
+            if self.explored_names.contains(&name) {
+                continue;
             }
+            if self.inputs.iter().any(|p| p.name == name) {
+                continue;
+            }
+            self.explored_names.insert(name.clone());
+            return Some(name);
         }
         None
     }