fix(catshare): echo PTT state so JTDX doesn't drop transmit

JTDX polls get_ptt DURING transmit to confirm the rig is keyed (WSJT-X does not,
which is why it worked and JTDX cut after ~2 s). We answered a blanket "0" (RX),
so JTDX concluded PTT had failed and dropped the over. get_ptt now echoes the
last PTT state commanded via set_ptt — always consistent with the client's own
command. Trace showed T 1 → three t→"0" polls → T 0.

internal/rigctld/rigctld_test.go

@@ -138,6 +138,28 @@ func TestHandleReportsBackendFailure(t *testing.T) {
 	}
 }
 
+// get_ptt must echo the last commanded PTT state. WSJT-X/JTDX poll get_ptt while
+// transmitting to confirm the rig is keyed; a blanket "0" made them decide PTT
+// had failed and abort the over after a second or two.
+func TestGetPTTEchoesSetPTT(t *testing.T) {
+	s := New(0, &fakeRig{}, nil)
+	if got, _ := s.handle("t"); got != "0\n" {
+		t.Fatalf("initial get_ptt = %q, want 0", got)
+	}
+	if got, _ := s.handle("T 1"); got != "RPRT 0\n" {
+		t.Fatalf("set_ptt 1 = %q, want RPRT 0", got)
+	}
+	if got, _ := s.handle("t"); got != "1\n" {
+		t.Fatalf("get_ptt after T 1 = %q, want 1 — client would abort TX", got)
+	}
+	if got, _ := s.handle("T 0"); got != "RPRT 0\n" {
+		t.Fatalf("set_ptt 0 = %q, want RPRT 0", got)
+	}
+	if got, _ := s.handle("t"); got != "0\n" {
+		t.Fatalf("get_ptt after T 0 = %q, want 0", got)
+	}
+}
+
 // dump_state is parsed POSITIONALLY by Hamlib clients: WSJT-X reads the first
 // line as the protocol version and refuses to continue if the block is short or
 // misshapen. Pinning its shape is what stops a well-meaning edit from silently