Make Gemma 4 channel close markers channel aware

decode() rewrote every <channel|> into </think>, including the close of a
channel that is not the thought channel. Only close a thought channel that was
actually opened in the decoded text; other channel markers are left alone for
the caller to strip.

tests-unit/comfy_test/test_gemma4_tokenizer.py

@@ -0,0 +1,45 @@
+import torch
+
+from comfy.cli_args import args as cli_args
+
+if not torch.cuda.is_available():
+    cli_args.cpu = True
+
+from comfy.text_encoders.gemma4 import Gemma4SDTokenizer  # noqa: E402
+
+
+class _StubTokenizer:
+    """Returns a canned decode so the marker translation can be tested without model files."""
+    def __init__(self, text):
+        self.text = text
+
+    def decode(self, token_ids, skip_special_tokens=False):
+        return self.text
+
+
+def decode(text):
+    tokenizer = Gemma4SDTokenizer.__new__(Gemma4SDTokenizer)
+    tokenizer.tokenizer = _StubTokenizer(text)
+    return tokenizer.decode([])
+
+
+class TestGemma4Decode:
+    def test_thought_channel_becomes_think_tags(self):
+        assert decode("<|channel>thought\nreasoning<channel|>the answer") == "<think>\nreasoning</think>the answer"
+
+    def test_primed_empty_thought_channel(self):
+        assert decode("<|channel>thought\n<channel|>the answer") == "<think>\n</think>the answer"
+
+    def test_unclosed_thought_channel(self):
+        assert decode("<|channel>thought\nreasoning") == "<think>\nreasoning"
+
+    def test_other_channel_close_is_not_reasoning(self):
+        # Non-thinking LTX2 prompt enhancement primes a "final" channel, so only its close is
+        # generated. Turning that into </think> made the whole answer look like reasoning.
+        assert decode("the answer<channel|>") == "the answer<channel|>"
+
+    def test_other_channel_kept_after_a_thought_channel(self):
+        assert decode("<|channel>thought\nreasoning<channel|><|channel>final\nthe answer<channel|>") == "<think>\nreasoning</think><|channel>final\nthe answer<channel|>"
+
+    def test_turn_and_eos_are_stripped(self):
+        assert decode("the answer<turn|><eos>") == "the answer"