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, 4 deletions

diff --git a/crates/mozart-vcs/src/process.rs b/crates/mozart-vcs/src/process.rs
index 91741a8..8ccc11d 100644
--- a/crates/mozart-vcs/src/process.rs
+++ b/crates/mozart-vcs/src/process.rs
@@ -1,4 +1,4 @@
-use std::collections::HashMap;
+use indexmap::IndexMap;
 use std::path::Path;
 use std::process::Command;
 use std::time::{Duration, Instant};
@@ -18,7 +18,7 @@ pub struct ProcessOutput {
 /// Corresponds to Composer's `ProcessExecutor`.
 pub struct ProcessExecutor {
     timeout: Option<Duration>,
-    env_overrides: HashMap<String, Option<String>>,
+    env_overrides: IndexMap<String, Option<String>>,
 }
 
 impl Default for ProcessExecutor {
@@ -31,14 +31,14 @@ impl ProcessExecutor {
     pub fn new() -> Self {
         Self {
             timeout: None,
-            env_overrides: HashMap::new(),
+            env_overrides: IndexMap::new(),
         }
     }
 
     pub fn with_timeout(secs: u64) -> Self {
         Self {
             timeout: Some(Duration::from_secs(secs)),
-            env_overrides: HashMap::new(),
+            env_overrides: IndexMap::new(),
         }
     }