fix(task): preserve essential env vars under deny_env on Linux

e2e/sandbox/test_sandbox_task

@@ -6,9 +6,17 @@ cat >mise.toml <<'TOML'
 [tasks.env_test]
 run = "echo ${SANDBOX_TASK_SECRET:-empty}"
 deny_env = true
+
+[tasks.path_test]
+run = 'echo "PATH=${PATH:-unset} HOME=${HOME:-unset}"'
+deny_env = true
 TOML
 
 export SANDBOX_TASK_SECRET="should_not_see"
 
 # Task with deny_env should not see the var
 assert "mise run env_test" "empty"
+
+# deny_env should still let essential vars (PATH, HOME, ...) through
+assert_not_contains "mise run path_test" "PATH=unset"
+assert_not_contains "mise run path_test" "HOME=unset"

src/cmd.rs

@@ -622,9 +622,18 @@ impl<'a> CmdLineRunner<'a> {
 
         #[cfg(target_os = "linux")]
         {
-            // On Linux, clear inherited env before pre_exec so child only sees filtered vars
+            // On Linux, clear inherited env before pre_exec so child only sees filtered vars.
+            // env_clear() also wipes envs explicitly set via .envs(), so save and restore them.
             if sandbox.effective_deny_env() {
+                let saved: Vec<(std::ffi::OsString, std::ffi::OsString)> = self
+                    .cmd
+                    .get_envs()
+                    .filter_map(|(k, v)| v.map(|v| (k.to_os_string(), v.to_os_string())))
+                    .collect();
                 self.cmd.env_clear();
+                for (k, v) in saved {
+                    self.cmd.env(k, v);
+                }
             }
             // Use pre_exec to apply Landlock/seccomp in the child process
             // before it execs the target program. This avoids restricting the mise process.