feat: add timestamp to output filenames for cache-busting

Add get_timestamp() and format_output_filename() utilities to folder_paths.py
that generate unique filenames with UTC timestamps. This eliminates the need
for client-side cache-busting query parameters.

New filename format: prefix_00001_20260131-220945-123456_.ext

Updated all save nodes to use the new format:
- nodes.py (SaveImage, SaveLatent, SaveImageWebsocket)
- comfy_api/latest/_ui.py (UILatent)
- comfy_extras/nodes_video.py (SaveWEBM, SaveAnimatedPNG, SaveAnimatedWEBP)
- comfy_extras/nodes_images.py (SaveSVG)
- comfy_extras/nodes_hunyuan3d.py (Save3D)
- comfy_extras/nodes_model_merging.py (SaveCheckpointSimple)
- comfy_extras/nodes_lora_extract.py (LoraSave)
- comfy_extras/nodes_train.py (SaveEmbedding)

Amp-Thread-ID: https://ampcode.com/threads/T-019c17e5-1c0a-736f-970d-e411aae222fc

tests-unit/folder_paths_test/output_filename_test.py

@@ -0,0 +1,106 @@
+"""Tests for folder_paths.format_output_filename and get_timestamp functions."""
+
+import re
+import sys
+import os
+
+# Add the ComfyUI root to the path for imports
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__)))))
+
+import folder_paths
+
+
+class TestGetTimestamp:
+    """Tests for get_timestamp function."""
+
+    def test_returns_string(self):
+        """Should return a string."""
+        result = folder_paths.get_timestamp()
+        assert isinstance(result, str)
+
+    def test_format_matches_expected_pattern(self):
+        """Should return format YYYYMMDD-HHMMSS-ffffff."""
+        result = folder_paths.get_timestamp()
+        # Pattern: 8 digits, hyphen, 6 digits, hyphen, 6 digits
+        pattern = r"^\d{8}-\d{6}-\d{6}$"
+        assert re.match(pattern, result), f"Timestamp '{result}' does not match expected pattern"
+
+    def test_is_filesystem_safe(self):
+        """Should not contain characters that are unsafe for filenames."""
+        result = folder_paths.get_timestamp()
+        unsafe_chars = ['/', '\\', ':', '*', '?', '"', '<', '>', '|', ' ']
+        for char in unsafe_chars:
+            assert char not in result, f"Timestamp contains unsafe character: {char}"
+
+
+class TestFormatOutputFilename:
+    """Tests for format_output_filename function."""
+
+    def test_basic_format(self):
+        """Should format filename with counter and timestamp."""
+        result = folder_paths.format_output_filename("test", 1, "png")
+        # Pattern: test_00001_YYYYMMDD-HHMMSS-ffffff_.png
+        pattern = r"^test_00001_\d{8}-\d{6}-\d{6}_\.png$"
+        assert re.match(pattern, result), f"Filename '{result}' does not match expected pattern"
+
+    def test_counter_padding(self):
+        """Should pad counter to 5 digits."""
+        result = folder_paths.format_output_filename("test", 42, "png")
+        assert "_00042_" in result
+
+    def test_extension_with_leading_dot(self):
+        """Should handle extension with leading dot."""
+        result = folder_paths.format_output_filename("test", 1, ".png")
+        assert result.endswith("_.png")
+        assert "..png" not in result
+
+    def test_extension_without_leading_dot(self):
+        """Should handle extension without leading dot."""
+        result = folder_paths.format_output_filename("test", 1, "webm")
+        assert result.endswith("_.webm")
+
+    def test_batch_num_replacement(self):
+        """Should replace %batch_num% placeholder."""
+        result = folder_paths.format_output_filename("test_%batch_num%", 1, "png", batch_num="3")
+        assert "test_3_" in result
+        assert "%batch_num%" not in result
+
+    def test_custom_timestamp(self):
+        """Should use provided timestamp instead of generating one."""
+        custom_ts = "20260101-120000-000000"
+        result = folder_paths.format_output_filename("test", 1, "png", timestamp=custom_ts)
+        assert custom_ts in result
+
+    def test_different_extensions(self):
+        """Should work with various extensions."""
+        extensions = ["png", "webp", "webm", "svg", "glb", "safetensors", "latent"]
+        for ext in extensions:
+            result = folder_paths.format_output_filename("test", 1, ext)
+            assert result.endswith(f"_.{ext}")
+
+
+if __name__ == "__main__":
+    # Simple test runner
+    import traceback
+
+    test_classes = [TestGetTimestamp, TestFormatOutputFilename]
+    passed = 0
+    failed = 0
+
+    for test_class in test_classes:
+        instance = test_class()
+        for method_name in dir(instance):
+            if method_name.startswith("test_"):
+                try:
+                    getattr(instance, method_name)()
+                    print(f"✓ {test_class.__name__}.{method_name}")
+                    passed += 1
+                except AssertionError as e:
+                    print(f"✗ {test_class.__name__}.{method_name}: {e}")
+                    failed += 1
+                except Exception as e:
+                    print(f"✗ {test_class.__name__}.{method_name}: {traceback.format_exc()}")
+                    failed += 1
+
+    print(f"\n{passed} passed, {failed} failed")
+    sys.exit(0 if failed == 0 else 1)