fix(lock): disambiguate idiomatic lock target

e2e/lockfile/test_lockfile_idiomatic_version_file

@@ -48,6 +48,29 @@ idiomatic_version_file_enable_tools = ["dummy"]
 lockfile = true
 EOF
 
+# Keep mise.toml and .mise/config.toml together to verify that an idiomatic
+# .dummy-version maps to .mise/mise.lock instead of the root mise.lock.
+mkdir -p .mise
+cat <<'EOF' >.mise/config.toml
+[settings]
+idiomatic_version_file_enable_tools = ["dummy"]
+lockfile = true
+EOF
+
+echo "1" >.dummy-version
+
+output=$(mise lock --dry-run --platform "$PLATFORM" 2>&1)
+assert_contains "echo '$output'" ".mise/mise.lock"
+assert_not_contains "echo '$output'" "for ~/workdir/mise.lock"
+
+rm -rf mise.toml .mise .dummy-version
+
+cat <<'EOF' >mise.toml
+[settings]
+idiomatic_version_file_enable_tools = ["dummy"]
+lockfile = true
+EOF
+
 echo "1" >.dummy-version
 touch mise.lock
 

src/lockfile.rs

@@ -898,6 +898,9 @@ pub fn lockfile_path_for_config(config_path: &Path) -> (PathBuf, bool) {
 ///
 /// Idiomatic version files are not config files themselves, so their lock entries
 /// belong to the nearest active mise config root that contains the version file.
+/// If multiple base configs share that root, the later entry in config_files wins
+/// so colocated configs have a deterministic lockfile target, such as
+/// .mise/config.toml mapping .dummy-version to .mise/mise.lock instead of mise.lock.
 pub fn lockfile_path_for_tool_source(
     config: &Config,
     source: &ToolSource,
@@ -907,21 +910,24 @@ pub fn lockfile_path_for_tool_source(
         ToolSource::IdiomaticVersionFile(path) => config
             .config_files
             .iter()
-            .filter(|(_, cf)| cf.source().is_mise_toml())
-            .filter_map(|(config_path, cf)| {
+            .enumerate()
+            .filter(|(_, (_, cf))| cf.source().is_mise_toml())
+            .filter_map(|(idx, (config_path, cf))| {
                 let root = cf.project_root().unwrap_or_else(|| cf.config_root());
                 let is_base = !is_local_config(config_path)
                     && extract_env_from_config_path(config_path).is_none();
                 path.starts_with(&root).then(|| {
                     (
                         root.components().count(),
                         is_base,
+                        // Tie-break same-root base configs by config_files order.
+                        idx,
                         lockfile_path_for_config(config_path),
                     )
                 })
             })
-            .max_by_key(|(root_depth, is_base, _)| (*root_depth, *is_base))
-            .map(|(_, _, lockfile)| lockfile),
+            .max_by_key(|(root_depth, is_base, idx, _)| (*root_depth, *is_base, *idx))
+            .map(|(_, _, _, lockfile)| lockfile),
         _ => None,
     }
 }