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, 4 insertions, 3 deletions

diff --git a/crates/mozart-vcs/src/driver/hg.rs b/crates/mozart-vcs/src/driver/hg.rs
index f884c50..0782775 100644
--- a/crates/mozart-vcs/src/driver/hg.rs
+++ b/crates/mozart-vcs/src/driver/hg.rs
@@ -1,4 +1,5 @@
-use std::collections::{BTreeMap, HashMap};
+use indexmap::IndexMap;
+use std::collections::BTreeMap;
 use std::path::PathBuf;
 
 use anyhow::Result;
@@ -17,7 +18,7 @@ pub struct HgDriver {
     root_identifier: Option<String>,
     tags: Option<BTreeMap<String, String>>,
     branches: Option<BTreeMap<String, String>>,
-    info_cache: HashMap<String, Option<serde_json::Value>>,
+    info_cache: IndexMap<String, Option<serde_json::Value>>,
     hg_util: HgUtil,
     config: DriverConfig,
 }
@@ -31,7 +32,7 @@ impl HgDriver {
             root_identifier: None,
             tags: None,
             branches: None,
-            info_cache: HashMap::new(),
+            info_cache: IndexMap::new(),
             hg_util: HgUtil::new(process),
             config,
         }