Make tests that wait for concurrent work wait on the event or a condition with a long deadline (issue 1814)

A test that slept a fixed time and then asserted what a goroutine, process or
watcher did failed under the checker's load. Each now waits for its positive
evidence (a started baseline, a call counted, a state reached) within 30 s, and
the concurrency-limit tests meet at a barrier instead of overlapping by sleep.

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

modules/mesh-mail-notifier/cmd/mesh-mail-notifier/run_test.go

@@ -38,7 +38,7 @@ func TestRunStartsTheWatcherEvenWhenStdinIsAtEOF(t *testing.T) {
 
 	select {
 	case <-started:
-	case <-time.After(time.Second):
+	case <-time.After(30 * time.Second):
 		t.Fatal("the watcher was not started before stdio.Serve returned")
 	}
 
@@ -47,7 +47,7 @@ func TestRunStartsTheWatcherEvenWhenStdinIsAtEOF(t *testing.T) {
 		if err != nil {
 			t.Fatalf("run over stdin at EOF: %v", err)
 		}
-	case <-time.After(time.Second):
+	case <-time.After(30 * time.Second):
 		t.Fatal("run did not return once stdin reached EOF, as systemd gives a process nobody talks to")
 	}
 
@@ -55,12 +55,12 @@ func TestRunStartsTheWatcherEvenWhenStdinIsAtEOF(t *testing.T) {
 	// not yet torn down. A watcher that stopped when run returned would never take this ping.
 	select {
 	case ping <- struct{}{}:
-	case <-time.After(time.Second):
+	case <-time.After(30 * time.Second):
 		t.Fatal("the watcher is no longer running once run returned: it must not stop just because stdio.Serve did")
 	}
 	select {
 	case <-pong:
-	case <-time.After(time.Second):
+	case <-time.After(30 * time.Second):
 		t.Fatal("the watcher did not answer once run returned")
 	}
 	close(ping)
@@ -98,13 +98,13 @@ func TestWatchRetriesASubscribeRefusalWithBackoffAndNeverExits(t *testing.T) {
 		if err != nil {
 			t.Fatalf("run over stdin at EOF: %v", err)
 		}
-	case <-time.After(time.Second):
+	case <-time.After(30 * time.Second):
 		t.Fatal("run did not return once stdin reached EOF: a subscribe refusal must not hold up or kill the process")
 	}
 
 	select {
 	case <-subscribed:
-	case <-time.After(time.Second):
+	case <-time.After(30 * time.Second):
 		t.Fatal("the watcher never subscribed after its first two refusals")
 	}