gate: pass on macOS: tests use /tmp, gatewayd finds its uid without /proc

M5a task 16. The work is Ornith's, from the stopped run; the design
model checked it against the task file and committed it once the
memoryd lint that stopped the gate was fixed (44bdcbd).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

crates/toolkit/tests/shell.rs

@@ -42,10 +42,12 @@ fn a_command_killed_by_a_signal_says_so() {
 fn the_command_runs_in_cwd_or_in_tmp() {
     let dir = TempDir::new("cwd");
     let here = dir.path().to_str().unwrap();
+    // `pwd` prints the path with symbolic links resolved: on macOS, /tmp is /private/tmp.
+    let real = |path: &str| std::fs::canonicalize(path).unwrap().display().to_string();
     let ran = sh("pwd", Some(here));
-    assert_eq!(ran.stdout, format!("{here}\n\n[exit 0]"));
+    assert_eq!(ran.stdout, format!("{}\n\n[exit 0]", real(here)));
     let ran = sh("pwd", None);
-    assert_eq!(ran.stdout, "/tmp\n\n[exit 0]");
+    assert_eq!(ran.stdout, format!("{}\n\n[exit 0]", real("/tmp")));
 }
 
 #[test]