Stop the peek-activity test blaming the pty's own delivery on the peek

TestPeekDoesNotCountAsActivityInTheSession took its baseline the moment the
echo became findable in the ring, which can be one chunk of several. Every
chunk read back from the pty moves LastActive, so the pump finishing its
delivery a millisecond later looked exactly like a peek that had touched the
stamp — a race that never fired locally and fired on CI's first run.

The property is unchanged and worth keeping; the measurement now waits for
the session to actually go quiet before it starts. 40 runs under -race.

Author: karngyan

internal/daemon/peek_test.go

@@ -100,13 +100,39 @@ func TestPeekMintsNoRefAndLeavesNoSubscriber(t *testing.T) {
 	})
 }
 
+// quiet waits until a session's LastActive stops moving, and answers with it.
+//
+// Without this the case below measures the wrong thing. The stamp moves on
+// every chunk read back from the pty, and a pty round trip is the kernel's
+// business: peekTarget returns as soon as the echo is *findable* in the ring,
+// which can be one chunk of several. A baseline taken there and compared a
+// millisecond later catches the pump finishing its delivery and blames the
+// peek for it — which is exactly how this failed in CI and never once
+// locally.
+func quiet(t *testing.T, s *session.Session) time.Time {
+	t.Helper()
+	deadline := time.Now().Add(5 * time.Second)
+	last := s.Info().LastActive
+	for {
+		time.Sleep(20 * time.Millisecond)
+		now := s.Info().LastActive
+		if now.Equal(last) {
+			return now
+		}
+		if time.Now().After(deadline) {
+			t.Fatal("the session never stopped producing output")
+		}
+		last = now
+	}
+}
+
 func TestPeekDoesNotCountAsActivityInTheSession(t *testing.T) {
 	// The sessions list orders by LastActive by default, so a preview that
 	// touched the stamp would sort the row under the pointer to the top of the
 	// list the pointer is resting on.
 	ts, reg := newTestServer(t)
 	s := peekTarget(t, reg, "quiet")
-	before := s.Info().LastActive
+	before := quiet(t, s)
 
 	c := dial(t, ts)
 	writeControl(t, c, wire.Hello{Ver: "test"})