fix(scheduler): rotate over connected users only for true fair share

The lead-user rotation rotated the full ListAllUsers set, so a connectionless
orphan identity ate a rotation slot — collapsing onto the next real user and
skewing the lead share (two real users got 2/3 vs 1/3 instead of 50/50). Filter
to connected users BEFORE rotating so the rotation is over exactly the users that
consume the caption budget. A dead identity can no longer skew fairness.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cmd/tapir/scheduler_test.go

@@ -128,6 +128,21 @@ func TestDiscoveryPassRotatesLeadUser(t *testing.T) {
 	require.Equal(t, 3, rc.count("c"))
 }
 
+// A connectionless orphan must not consume a rotation slot: rotation is over the
+// connected users only, so two real users alternate the lead 50/50 even with a
+// dead identity listed between them.
+func TestDiscoveryPassRotationIgnoresConnectionlessUsers(t *testing.T) {
+	lister := fakeLister{users: usersN("a", "orphan", "c"), noConn: map[string]bool{"orphan": true}}
+	rc := newCountingRunUser()
+
+	runDiscoveryPass(context.Background(), 0, lister, rc.run, quietLog())
+	runDiscoveryPass(context.Background(), 1, lister, rc.run, quietLog())
+
+	require.Equal(t, []string{"a", "c", "c", "a"}, rc.runOrder(),
+		"only connected users rotate; the orphan never runs and never holds a slot")
+	require.Equal(t, 0, rc.count("orphan"))
+}
+
 func TestDiscoveryPassSkipsUsersWithoutConnections(t *testing.T) {
 	// b never connected a video source (e.g. a stale Dex-era orphan identity).
 	// It must be skipped silently — not run and logged as a token error every pass.