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-registry/src/downloader.rs b/crates/mozart-registry/src/downloader.rs
index 8c1f0b0..c13ebdc 100644
--- a/crates/mozart-registry/src/downloader.rs
+++ b/crates/mozart-registry/src/downloader.rs
@@ -1,6 +1,6 @@
 use crate::cache::Cache;
+use indexmap::IndexSet;
 use sha1::{Digest, Sha1};
-use std::collections::HashSet;
 use std::fs;
 use std::io::{Cursor, Read, Write};
 use std::path::Path;
@@ -168,7 +168,7 @@ fn find_top_level_dir(entries: &[String]) -> Option<String> {
         return None;
     }
 
-    let mut prefixes: HashSet<String> = HashSet::new();
+    let mut prefixes: IndexSet<String> = IndexSet::new();
     for entry in entries {
         let slash_pos = entry.find('/')?;
         prefixes.insert(entry[..slash_pos + 1].to_string());