Nested signal handlers: assertion failure

While debugging a separate issue, we ran into an assertion failure

hello[FATAL src/RecordTask.cc:1840:pop_event()] 
 (task 136189 (rec:136189) at time 254)
 -> Assertion `pending_events.back().type() == expected_type' failed to hold. 

Test case:

#include <signal.h>
#include <stdlib.h>
#include <unistd.h>


static void SEGV_handler(__attribute__((unused)) int sig,
                         __attribute__((unused)) siginfo_t* si,
                         __attribute__((unused)) void* context) {
    alarm(1);
    pause();
}

static void alarm_handler(__attribute__((unused)) int sig,
                         __attribute__((unused)) siginfo_t* si,
                         __attribute__((unused)) void* context) {
    write(1, "hello", 5);
}

int main() {
    int size = 8 * 0x4000;
    void * stk_c = malloc(size);
    stack_t stk = {stk_c, 0, size};
    sigaltstack(&stk, 0);

    struct sigaction sa1, sa2;
    sa1.sa_sigaction = SEGV_handler;
    sa1.sa_flags = SA_SIGINFO | SA_ONSTACK;
    sigemptyset(&sa1.sa_mask);
    sigaction(SIGSEGV, &sa1, NULL);

    sa2.sa_sigaction = alarm_handler;
    sa2.sa_flags = SA_SIGINFO | SA_ONSTACK;
    sigemptyset(&sa2.sa_mask);
    sigaction(SIGALRM, &sa2, NULL);

    raise(SIGSEGV);
}

Use the supplied C reproducer with nested SIGSEGV and SIGALRM handlers, then inspect src/RecordTask.cc around pop_event() at line 1840. Trace how nested signal events are recorded and consumed, and determine what behavior should replace the assertion. Done means the reproducer no longer triggers the reported assertion without regressing signal handling.