test: add automated state verification to integration tests

Co-authored-by: aider (deepseek/deepseek-reasoner) <aider@aider.chat>

src/main.c

@@ -2,6 +2,7 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <string.h>
+#include <signal.h>
 #include <jack/jack.h>
 #include <jack/midiport.h>
 
@@ -101,6 +102,12 @@ static void jack_shutdown(void *arg)
     exit(0);
 }
 
+static void sigusr1_handler(int signo) {
+    (void)signo;
+    int code = (int)current_state + 1;
+    _exit(code);
+}
+
 int main(int argc, char *argv[])
 {
     (void)argc;
@@ -151,6 +158,9 @@ int main(int argc, char *argv[])
 
     fprintf(stderr, "looper running (client name '%s')\n", client_name);
 
+    /* allow SIGUSR1 to report state and exit */
+    signal(SIGUSR1, sigusr1_handler);
+
     while (1) {
         sleep(1);
     }