feat: extend alarmdefault and argecho

user/argecho.c

@@ -0,0 +1,24 @@
+#include "ulib.h"
+
+/*
+ * Real ring-3 proof that shell.c's `$NAME`/`$?` expansion (shellExpandArgv,
+ * shellExpandToken) genuinely reaches a SPAWNED program's own argv, not
+ * just a shell builtin's -- every earlier consumer of expansion (export,
+ * env, echo) is a builtin, and shell.c's doEcho never calls shellExpandArgv
+ * at all (only runProgram/runPipelineStages do, for a real spawned
+ * process), so nothing in this kernel's live-demo chain had ever actually
+ * typed a `$` at the real shell before this program existed. Prints each
+ * argv[1..argc) on its own line, prefixed like globcat.c's own
+ * "globcat: " diagnostic style -- a generic argv printer, not tied to any
+ * one variable, so a future demo can reuse it for any other `$NAME`/`$?`
+ * case without needing yet another single-purpose binary.
+ */
+int main(int argc, char** argv)
+{
+    for (int i = 1; i < argc; i++) {
+        print("argecho: ");
+        print(argv[i]);
+        print("\n");
+    }
+    return 0;
+}