feat: text gate protected mode — standalone text node (backend)

protected=True makes run() emit stored_text and ignore upstream with no pause;
IS_CHANGED caches on stored_text when protected (NaN otherwise). text input is
now optional so the node can run standalone.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_textgate.py

@@ -16,3 +16,31 @@ def test_textgate_io_shape():
 def test_textgate_is_changed_nan():
     v = textgate.TextGate.IS_CHANGED(text="hi", unique_id="1")
     assert math.isnan(v)
+
+
+def test_textgate_text_input_is_optional():
+    it = textgate.TextGate.INPUT_TYPES()
+    assert "text" in it["optional"]
+    assert "protected" in it["optional"]
+    assert "stored_text" in it["optional"]
+
+
+def test_textgate_protected_returns_stored_text_without_pause():
+    # protected mode must return the stored text directly — no GateBus, no comfy
+    out = textgate.TextGate().run(
+        unique_id="1", text="from upstream", signal="sig",
+        protected=True, stored_text="my authored text",
+    )
+    assert out == ("my authored text", "sig")
+
+
+def test_textgate_is_changed_protected_returns_stored_text():
+    v = textgate.TextGate.IS_CHANGED(
+        unique_id="1", protected=True, stored_text="frozen")
+    assert v == "frozen"
+
+
+def test_textgate_is_changed_not_protected_is_nan():
+    v = textgate.TextGate.IS_CHANGED(
+        unique_id="1", protected=False, stored_text="ignored")
+    assert math.isnan(v)