Fix Gemma4 ignoring thinking=false

PR #14304 started priming an empty, already-closed thought block
(<|channel>thought\n<channel|>) on the model turn when thinking is off.
Google's canonical Gemma 4 chat template never does this: <|think|> in the
system turn is the only thought channel switch, and the generation prompt
ends at <|turn>model\n. Priming a closed block instead cues the model into
reasoning, which then leaks into the answer untagged.

The rendered template now matches google/gemma-4-e4b-it chat_template.jinja
byte for byte for thinking on and off.

comfy/text_encoders/gemma4.py

@@ -1310,7 +1310,9 @@ class Gemma4_Tokenizer():
             if llama_template is not None:
                 llama_text = llama_template.format(text)
             else:
-                # Build template from modalities present
+                # Build template from modalities present.
+                # <|think|> in the system turn is the only thought channel switch. Priming a closed
+                # thought block on the model turn does not disable it, the model reasons inline instead.
                 system = "<|turn>system\n<|think|>\n<turn|>\n" if thinking else ""
                 media = ""
                 if len(images) > 0:
@@ -1333,9 +1335,7 @@ class Gemma4_Tokenizer():
                     num_samples = int(waveform.shape[-1] * 16000 / sample_rate) if sample_rate != 16000 else waveform.shape[-1]
                     n_audio_tokens = self._audio_token_count(num_samples)
                     media += "<|audio>" + "<|audio|>" * n_audio_tokens + "<audio|>"
-                # Non-thinking mode primes an empty thought channel so the model answers directly.
-                model_open = "" if thinking else "<|channel>thought\n<channel|>"
-                llama_text = f"{system}<|turn>user\n{text}{media}<turn|>\n<|turn>model\n{model_open}"
+                llama_text = f"{system}<|turn>user\n{text}{media}<turn|>\n<|turn>model\n"
 
         text_tokens = super().tokenize_with_weights(llama_text, return_word_ids)
 

tests-unit/comfy_test/gemma4_template_test.py

@@ -0,0 +1,41 @@
+from comfy.cli_args import args
+
+args.cpu = True  # importing comfy.model_management probes the torch device at import time
+
+from comfy.text_encoders.gemma4 import Gemma4_Tokenizer
+
+PROMPT = "describe a cute anime girl with fennec ears"
+
+
+class _CaptureTemplate:
+    """Stands in for SDTokenizer.tokenize_with_weights so the built template is checked without model files."""
+    def tokenize_with_weights(self, text, return_word_ids=False, **kwargs):
+        self.llama_text = text
+        return {}
+
+
+class _Gemma4TemplateProbe(Gemma4_Tokenizer, _CaptureTemplate):
+    pass
+
+
+def build_template(**kwargs):
+    probe = _Gemma4TemplateProbe()
+    probe.tokenize_with_weights(PROMPT, **kwargs)
+    return probe.llama_text
+
+
+def test_thinking_disabled_does_not_prime_a_thought_channel():
+    template = build_template(skip_template=False, thinking=False)
+    assert template == f"<|turn>user\n{PROMPT}<turn|>\n<|turn>model\n"
+    assert "channel" not in template
+    assert "<|think|>" not in template
+
+
+def test_thinking_enabled_asks_for_the_thought_channel():
+    template = build_template(skip_template=False, thinking=True)
+    assert template == f"<|turn>system\n<|think|>\n<turn|>\n<|turn>user\n{PROMPT}<turn|>\n<|turn>model\n"
+
+
+def test_skip_template_passes_text_through_unchanged():
+    assert build_template(skip_template=True, thinking=False) == PROMPT
+    assert build_template(skip_template=True, thinking=True) == PROMPT