diff --git a/crates/forge_config/src/reader.rs b/crates/forge_config/src/reader.rs
index cc1342aaf1..3e82ecdcbc 100644
--- a/crates/forge_config/src/reader.rs
+++ b/crates/forge_config/src/reader.rs
@@ -30,6 +30,9 @@ static LOAD_DOT_ENV: LazyLock<()> = LazyLock::new(|| {
     }
 });
 
+/// Caches base-path resolution for the process lifetime.
+static BASE_PATH: LazyLock<PathBuf> = LazyLock::new(ConfigReader::resolve_base_path);
+
 /// Merges [`ForgeConfig`] from layered sources using a builder pattern.
 #[derive(Default)]
 pub struct ConfigReader {
@@ -58,6 +61,10 @@ impl ConfigReader {
     ///    existing directory without disruption.
     /// 3. `~/.forge` as the default path.
     pub fn base_path() -> PathBuf {
+        BASE_PATH.clone()
+    }
+
+    fn resolve_base_path() -> PathBuf {
         if let Ok(path) = std::env::var("FORGE_CONFIG") {
             return PathBuf::from(path);
         }
@@ -199,7 +206,7 @@ mod tests {
     #[test]
     fn test_base_path_uses_forge_config_env_var() {
         let _guard = EnvGuard::set(&[("FORGE_CONFIG", "/custom/forge/dir")]);
-        let actual = ConfigReader::base_path();
+        let actual = ConfigReader::resolve_base_path();
         let expected = PathBuf::from("/custom/forge/dir");
         assert_eq!(actual, expected);
     }
@@ -210,7 +217,7 @@ mod tests {
         // cannot race with test_base_path_uses_forge_config_env_var.
         let _guard = EnvGuard::set_and_remove(&[], &["FORGE_CONFIG"]);
 
-        let actual = ConfigReader::base_path();
+        let actual = ConfigReader::resolve_base_path();
         // Without FORGE_CONFIG set the path must be either "forge" (legacy,
         // preferred when ~/forge exists) or ".forge" (default new path).
         let name = actual.file_name().unwrap();
diff --git a/crates/forge_infra/src/env.rs b/crates/forge_infra/src/env.rs
index d281eabd52..7a42705e51 100644
--- a/crates/forge_infra/src/env.rs
+++ b/crates/forge_infra/src/env.rs
@@ -158,43 +158,12 @@ impl EnvironmentInfra for ForgeEnvironmentInfra {
 #[cfg(test)]
 mod tests {
     use std::path::PathBuf;
-    use std::sync::{Mutex, MutexGuard};
 
     use forge_config::ForgeConfig;
     use pretty_assertions::assert_eq;
 
     use super::*;
 
-    /// Serializes tests that mutate environment variables to prevent races.
-    static ENV_MUTEX: Mutex<()> = Mutex::new(());
-
-    /// Holds env vars set for a test's duration and removes them on drop,
-    /// while holding [`ENV_MUTEX`].
-    struct EnvGuard {
-        keys: Vec<&'static str>,
-        _lock: MutexGuard<'static, ()>,
-    }
-
-    impl EnvGuard {
-        #[must_use]
-        fn set(pairs: &[(&'static str, &str)]) -> Self {
-            let lock = ENV_MUTEX.lock().unwrap_or_else(|e| e.into_inner());
-            let keys = pairs.iter().map(|(k, _)| *k).collect();
-            for (key, value) in pairs {
-                unsafe { std::env::set_var(key, value) };
-            }
-            Self { keys, _lock: lock }
-        }
-    }
-
-    impl Drop for EnvGuard {
-        fn drop(&mut self) {
-            for key in &self.keys {
-                unsafe { std::env::remove_var(key) };
-            }
-        }
-    }
-
     #[test]
     fn test_to_environment_sets_cwd() {
         let fixture_cwd = PathBuf::from("/test/cwd");
@@ -203,11 +172,22 @@ mod tests {
     }
 
     #[test]
-    fn test_to_environment_uses_forge_config_env_var() {
-        let _guard = EnvGuard::set(&[("FORGE_CONFIG", "/custom/config/dir")]);
-        let actual = to_environment(PathBuf::from("/any/cwd"));
-        let expected = PathBuf::from("/custom/config/dir");
-        assert_eq!(actual.base_path, expected);
+    fn test_to_environment_base_path_is_stable_after_env_var_change() {
+        let fixture_cwd = PathBuf::from("/any/cwd");
+        let expected = to_environment(fixture_cwd.clone()).base_path;
+
+        let previous = std::env::var("FORGE_CONFIG").ok();
+        unsafe { std::env::set_var("FORGE_CONFIG", "/custom/config/dir") };
+
+        let actual = to_environment(fixture_cwd).base_path;
+
+        if let Some(value) = previous {
+            unsafe { std::env::set_var("FORGE_CONFIG", value) };
+        } else {
+            unsafe { std::env::remove_var("FORGE_CONFIG") };
+        }
+
+        assert_eq!(actual, expected);
     }
 
     #[test]