From 9c6966acff3ac4e8d17b6c59a3b195dd39b9919d Mon Sep 17 00:00:00 2001
From: Joe <joe.melsha@live.com>
Date: Tue, 17 Feb 2026 07:52:29 -0600
Subject: [PATCH] Add default properties caching and update matching logic

- Implemented a caching mechanism for default properties per class in `rbx_dom_lua/init.lua`, allowing for efficient retrieval of encoded default values, including inherited defaults.
- Updated the matching logic in `Reconciler/matching.lua` to account for properties present only on the Studio side, ensuring accurate comparisons against default values during reconciliation.
- Added new test cases to validate the handling of default-omitted properties, enhancing the robustness of the reconciliation process.

These changes improve the efficiency and accuracy of property matching, addressing issues related to default values in the reconciliation workflow.
---
 plugin/rbx_dom_lua/init.lua                   |  38 ++
 plugin/src/Reconciler/matching.lua            |  42 ++
 .../Icon/UIAspectRatioConstraint.model.json5  |   3 +
 .../BillboardGui/Frame/Icon/init.meta.json5   |  46 ++
 .../Frame/Info/UIGradient.model.json5         |  36 ++
 .../Frame/Info/UIStroke.model.json5           |   6 +
 .../BillboardGui/Frame/Info/init.meta.json5   |  60 +++
 .../Hitbox/BillboardGui/Frame/init.meta.json5 |  45 ++
 .../Hitbox/BillboardGui/init.meta.json5       |  26 +
 .../expected/Hitbox/Water.model.json5         |  16 +
 .../expected/Hitbox/init.meta.json5           |  29 ++
 .../expected/TsunamiWave/Texture.model.json5  |  15 +
 .../TsunamiWave/Texture~1.model.json5         |  16 +
 .../TsunamiWave/Texture~10.model.json5        |  16 +
 .../TsunamiWave/Texture~11.model.json5        |  16 +
 .../TsunamiWave/Texture~2.model.json5         |  16 +
 .../TsunamiWave/Texture~3.model.json5         |  15 +
 .../TsunamiWave/Texture~4.model.json5         |  16 +
 .../TsunamiWave/Texture~5.model.json5         |  16 +
 .../TsunamiWave/Texture~6.model.json5         |  16 +
 .../TsunamiWave/Texture~7.model.json5         |  16 +
 .../TsunamiWave/Texture~8.model.json5         |  15 +
 .../TsunamiWave/Texture~9.model.json5         |  16 +
 .../expected/TsunamiWave/glow.model.json5     | 185 ++++++++
 .../expected/TsunamiWave/glow~1.model.json5   | 186 ++++++++
 .../expected/TsunamiWave/glow~2.model.json5   | 186 ++++++++
 .../expected/TsunamiWave/init.meta.json5      |  60 +++
 .../UFOWave_matching/expected/init.meta.json5 |  52 ++
 .../UFOWave_matching/input.rbxm               | Bin 0 -> 21586 bytes
 src/snapshot/matching.rs                      | 443 ++++++++++++++++++
 30 files changed, 1648 insertions(+)
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Icon/UIAspectRatioConstraint.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Icon/init.meta.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Info/UIGradient.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Info/UIStroke.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Info/init.meta.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/init.meta.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/init.meta.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/Water.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/init.meta.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~1.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~10.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~11.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~2.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~3.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~4.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~5.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~6.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~7.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~8.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~9.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/glow.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/glow~1.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/glow~2.model.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/init.meta.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/expected/init.meta.json5
 create mode 100644 rojo-test/syncback-tests/UFOWave_matching/input.rbxm

diff --git a/plugin/rbx_dom_lua/init.lua b/plugin/rbx_dom_lua/init.lua
index e26e3c2a..ed6ab91d 100644
--- a/plugin/rbx_dom_lua/init.lua
+++ b/plugin/rbx_dom_lua/init.lua
@@ -6,6 +6,43 @@ local PropertyDescriptor = require(script.PropertyDescriptor)
 -- Returns nil if the class doesn't exist in the database
 -- The properties table maps property names to metadata (scriptability, serialization status)
 -- To get a full PropertyDescriptor for encoding, use findCanonicalPropertyDescriptor
+-- Cache for default properties per class (includes inherited defaults).
+local defaultPropertiesCache: { [string]: { [string]: any } } = {}
+
+-- Returns a table mapping property names to their encoded default values
+-- for a given class, including inherited defaults from parent classes.
+-- Subclass overrides take precedence. Results are cached per class.
+local function findDefaultProperties(className: string): { [string]: any }
+	local cached = defaultPropertiesCache[className]
+	if cached then
+		return cached
+	end
+
+	local defaults: { [string]: any } = {}
+	local currentClassName: string? = className
+
+	repeat
+		local currentClass = database.Classes[currentClassName]
+		if currentClass == nil then
+			break
+		end
+
+		local classDefaults = currentClass.DefaultProperties
+		if classDefaults then
+			for propName, encodedValue in classDefaults do
+				if defaults[propName] == nil then
+					defaults[propName] = encodedValue
+				end
+			end
+		end
+
+		currentClassName = currentClass.Superclass
+	until currentClassName == nil
+
+	defaultPropertiesCache[className] = defaults
+	return defaults
+end
+
 local function findClassDescriptor(className)
 	local classData = database.Classes[className]
 	if classData == nil then
@@ -111,6 +148,7 @@ return {
 	writeProperty = writeProperty,
 	findCanonicalPropertyDescriptor = findCanonicalPropertyDescriptor,
 	findClassDescriptor = findClassDescriptor,
+	findDefaultProperties = findDefaultProperties,
 	Error = Error,
 	EncodedValue = require(script.EncodedValue),
 }
diff --git a/plugin/src/Reconciler/matching.lua b/plugin/src/Reconciler/matching.lua
index 9eb7c0dd..45d8823f 100644
--- a/plugin/src/Reconciler/matching.lua
+++ b/plugin/src/Reconciler/matching.lua
@@ -330,6 +330,48 @@ function Matching._countOwnDiffs(vInst: any, studioInstance: Instance): number
 		end
 	end
 
+	-- Properties present only on the Studio side (not in virtual).
+	-- Syncback strips default-valued properties from model files, so virtual
+	-- instances may omit properties that Studio has at non-default values.
+	-- Without this check, a virtual instance missing e.g. Face scores equally
+	-- against all Studio instances in the group, causing wrong pairings.
+	local defaults = RbxDom.findDefaultProperties(vInst.ClassName)
+	if defaults then
+		for propName, encodedDefault in defaults do
+			if propName == "Tags" or propName == "Attributes" then
+				continue
+			end
+
+			-- Skip properties already compared from the virtual side
+			if vProps and vProps[propName] ~= nil then
+				continue
+			end
+
+			-- Skip Ref/UniqueId types (not comparable during hydration)
+			local ty = next(encodedDefault)
+			if ty == "Ref" or ty == "UniqueId" then
+				continue
+			end
+
+			-- pcall guards against unsupported types (e.g. SharedString)
+			local pcallOk, decodeOk, defaultValue = pcall(RbxDom.EncodedValue.decode, encodedDefault)
+			if not pcallOk or not decodeOk then
+				continue
+			end
+
+			local readOk, studioValue = pcall(function()
+				return (studioInstance :: any)[propName]
+			end)
+			if not readOk then
+				continue
+			end
+
+			if not trueEquals(defaultValue, studioValue) then
+				cost += 1
+			end
+		end
+	end
+
 	-- Tags: count individual adds/removes
 	local vTags = vInst.Properties and vInst.Properties.Tags
 	if vTags then
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Icon/UIAspectRatioConstraint.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Icon/UIAspectRatioConstraint.model.json5
new file mode 100644
index 00000000..cace7a97
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Icon/UIAspectRatioConstraint.model.json5
@@ -0,0 +1,3 @@
+{
+  className: "UIAspectRatioConstraint"
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Icon/init.meta.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Icon/init.meta.json5
new file mode 100644
index 00000000..f121b2cc
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Icon/init.meta.json5
@@ -0,0 +1,46 @@
+{
+  className: "ImageLabel",
+  properties: {
+    AnchorPoint: [
+      0.5,
+      0
+    ],
+    BackgroundColor3: [
+      1,
+      1,
+      1
+    ],
+    BackgroundTransparency: 1,
+    BorderColor3: [
+      0,
+      0,
+      0
+    ],
+    BorderSizePixel: 0,
+    ImageContent: "rbxassetid://131974996946194",
+    Position: {
+      UDim2: [
+        [
+          0.5,
+          0
+        ],
+        [
+          0.5,
+          0
+        ]
+      ]
+    },
+    Size: {
+      UDim2: [
+        [
+          0.699999988079071,
+          0
+        ],
+        [
+          0.699999988079071,
+          0
+        ]
+      ]
+    }
+  }
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Info/UIGradient.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Info/UIGradient.model.json5
new file mode 100644
index 00000000..197d4910
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Info/UIGradient.model.json5
@@ -0,0 +1,36 @@
+{
+  className: "UIGradient",
+  properties: {
+    Color: {
+      ColorSequence: {
+        keypoints: [
+          {
+            color: [
+              0.1882352977991104,
+              0.11372549086809158,
+              1
+            ],
+            time: 0
+          },
+          {
+            color: [
+              0.5490196347236633,
+              0,
+              1
+            ],
+            time: 0.608996570110321
+          },
+          {
+            color: [
+              0.501960813999176,
+              0,
+              0.9176470637321472
+            ],
+            time: 1
+          }
+        ]
+      }
+    },
+    Rotation: -90
+  }
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Info/UIStroke.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Info/UIStroke.model.json5
new file mode 100644
index 00000000..2afd1ec6
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Info/UIStroke.model.json5
@@ -0,0 +1,6 @@
+{
+  className: "UIStroke",
+  properties: {
+    Thickness: 2
+  }
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Info/init.meta.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Info/init.meta.json5
new file mode 100644
index 00000000..bb5f1ca4
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/Info/init.meta.json5
@@ -0,0 +1,60 @@
+{
+  className: "TextLabel",
+  properties: {
+    AnchorPoint: [
+      0.5,
+      0
+    ],
+    BackgroundColor3: [
+      1,
+      1,
+      1
+    ],
+    BackgroundTransparency: 1,
+    BorderColor3: [
+      0,
+      0,
+      0
+    ],
+    BorderSizePixel: 0,
+    FontFace: {
+      cachedFaceId: null,
+      family: "rbxasset://fonts/families/LuckiestGuy.json",
+      style: "Normal",
+      weight: "Regular"
+    },
+    Position: {
+      UDim2: [
+        [
+          0.5,
+          0
+        ],
+        [
+          0,
+          0
+        ]
+      ]
+    },
+    Size: {
+      UDim2: [
+        [
+          1,
+          0
+        ],
+        [
+          0.5,
+          0
+        ]
+      ]
+    },
+    Text: "UFO",
+    TextColor3: [
+      1,
+      1,
+      1
+    ],
+    TextScaled: true,
+    TextSize: 14,
+    TextWrapped: true
+  }
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/init.meta.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/init.meta.json5
new file mode 100644
index 00000000..00b3efd0
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/Frame/init.meta.json5
@@ -0,0 +1,45 @@
+{
+  className: "Frame",
+  properties: {
+    AnchorPoint: [
+      0.5,
+      0.5
+    ],
+    BackgroundColor3: [
+      1,
+      1,
+      1
+    ],
+    BackgroundTransparency: 1,
+    BorderColor3: [
+      0,
+      0,
+      0
+    ],
+    BorderSizePixel: 0,
+    Position: {
+      UDim2: [
+        [
+          0.5,
+          0
+        ],
+        [
+          0.5,
+          0
+        ]
+      ]
+    },
+    Size: {
+      UDim2: [
+        [
+          1,
+          0
+        ],
+        [
+          1,
+          0
+        ]
+      ]
+    }
+  }
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/init.meta.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/init.meta.json5
new file mode 100644
index 00000000..7262f7a0
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/BillboardGui/init.meta.json5
@@ -0,0 +1,26 @@
+{
+  className: "BillboardGui",
+  properties: {
+    Active: true,
+    LightInfluence: 1,
+    ResetOnSpawn: false,
+    Size: {
+      UDim2: [
+        [
+          60,
+          0
+        ],
+        [
+          40,
+          0
+        ]
+      ]
+    },
+    StudsOffset: [
+      0,
+      75,
+      0
+    ],
+    ZIndexBehavior: "Sibling"
+  }
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/Water.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/Water.model.json5
new file mode 100644
index 00000000..696e6de6
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/Water.model.json5
@@ -0,0 +1,16 @@
+{
+  attributes: {
+    Rojo_Ref_SoundGroup: "ServerStorage/__server_muted.model.json5"
+  },
+  className: "Sound",
+  properties: {
+    AudioContent: "rbxassetid://9120549564",
+    Looped: true,
+    Playing: true,
+    SourceAssetId: 9120549564,
+    Tags: [
+      "SoundGroupEffects"
+    ],
+    Volume: 3
+  }
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/init.meta.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/init.meta.json5
new file mode 100644
index 00000000..afc3c11f
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/Hitbox/init.meta.json5
@@ -0,0 +1,29 @@
+{
+  className: "Part",
+  properties: {
+    Anchored: true,
+    BottomSurface: "Smooth",
+    CFrame: [
+      789.7578125,
+      37.375,
+      0.00000762939453125,
+      1,
+      0,
+      0,
+      0,
+      1,
+      0,
+      0,
+      0,
+      1
+    ],
+    CanCollide: false,
+    Size: [
+      25.515625,
+      70.75,
+      260
+    ],
+    TopSurface: "Smooth",
+    Transparency: 1
+  }
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture.model.json5
new file mode 100644
index 00000000..5e975d2a
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture.model.json5
@@ -0,0 +1,15 @@
+{
+  className: "Texture",
+  properties: {
+    Color3: [
+      0.41568630933761597,
+      0,
+      1
+    ],
+    Face: "Top",
+    StudsPerTileU: 200,
+    StudsPerTileV: 200,
+    TextureContent: "rbxassetid://10025668350",
+    Transparency: 0.6000000238418579
+  }
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~1.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~1.model.json5
new file mode 100644
index 00000000..11e28cd8
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~1.model.json5
@@ -0,0 +1,16 @@
+{
+  className: "Texture",
+  name: "Texture",
+  properties: {
+    Color3: [
+      0.41568630933761597,
+      0,
+      1
+    ],
+    Face: "Right",
+    StudsPerTileU: 200,
+    StudsPerTileV: 200,
+    TextureContent: "rbxassetid://10025668350",
+    Transparency: 0.6000000238418579
+  }
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~10.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~10.model.json5
new file mode 100644
index 00000000..dc4b910d
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~10.model.json5
@@ -0,0 +1,16 @@
+{
+  className: "Texture",
+  name: "Texture",
+  properties: {
+    Color3: [
+      0.40000003576278687,
+      0,
+      1
+    ],
+    Face: "Right",
+    StudsPerTileU: 200,
+    StudsPerTileV: 200,
+    TextureContent: "rbxassetid://10023635072",
+    Transparency: 0.6499999761581421
+  }
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~11.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~11.model.json5
new file mode 100644
index 00000000..df4f761f
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~11.model.json5
@@ -0,0 +1,16 @@
+{
+  className: "Texture",
+  name: "Texture",
+  properties: {
+    Color3: [
+      0.40000003576278687,
+      0,
+      1
+    ],
+    Face: "Top",
+    StudsPerTileU: 200,
+    StudsPerTileV: 200,
+    TextureContent: "rbxassetid://10023635072",
+    Transparency: 0.6499999761581421
+  }
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~2.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~2.model.json5
new file mode 100644
index 00000000..9f5fd1c3
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~2.model.json5
@@ -0,0 +1,16 @@
+{
+  className: "Texture",
+  name: "Texture",
+  properties: {
+    Color3: [
+      0.41568630933761597,
+      0,
+      1
+    ],
+    Face: "Left",
+    StudsPerTileU: 200,
+    StudsPerTileV: 200,
+    TextureContent: "rbxassetid://10025668350",
+    Transparency: 0.6000000238418579
+  }
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~3.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~3.model.json5
new file mode 100644
index 00000000..cc60c294
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~3.model.json5
@@ -0,0 +1,15 @@
+{
+  className: "Texture",
+  name: "Texture",
+  properties: {
+    Color3: [
+      0.41568630933761597,
+      0,
+      1
+    ],
+    StudsPerTileU: 200,
+    StudsPerTileV: 200,
+    TextureContent: "rbxassetid://10025668350",
+    Transparency: 0.6000000238418579
+  }
+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~4.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~4.model.json5
new file mode 100644
index 00000000..cec50fee
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~4.model.json5
@@ -0,0 +1,16 @@
+{
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diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~5.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~5.model.json5
new file mode 100644
index 00000000..30761828
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~5.model.json5
@@ -0,0 +1,16 @@
+{
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+  name: "Texture",
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+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~6.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~6.model.json5
new file mode 100644
index 00000000..015bfdce
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~6.model.json5
@@ -0,0 +1,16 @@
+{
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diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~7.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~7.model.json5
new file mode 100644
index 00000000..c9f537bd
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~7.model.json5
@@ -0,0 +1,16 @@
+{
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diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~8.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~8.model.json5
new file mode 100644
index 00000000..869ecc79
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~8.model.json5
@@ -0,0 +1,15 @@
+{
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diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~9.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~9.model.json5
new file mode 100644
index 00000000..470357ae
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/Texture~9.model.json5
@@ -0,0 +1,16 @@
+{
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diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/glow.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/glow.model.json5
new file mode 100644
index 00000000..f62c6a95
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/glow.model.json5
@@ -0,0 +1,185 @@
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diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/glow~1.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/glow~1.model.json5
new file mode 100644
index 00000000..943be0f1
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/glow~1.model.json5
@@ -0,0 +1,186 @@
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diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/glow~2.model.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/glow~2.model.json5
new file mode 100644
index 00000000..25ec3941
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/glow~2.model.json5
@@ -0,0 +1,186 @@
+{
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diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/init.meta.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/init.meta.json5
new file mode 100644
index 00000000..017fe065
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/TsunamiWave/init.meta.json5
@@ -0,0 +1,60 @@
+{
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diff --git a/rojo-test/syncback-tests/UFOWave_matching/expected/init.meta.json5 b/rojo-test/syncback-tests/UFOWave_matching/expected/init.meta.json5
new file mode 100644
index 00000000..36ad4609
--- /dev/null
+++ b/rojo-test/syncback-tests/UFOWave_matching/expected/init.meta.json5
@@ -0,0 +1,52 @@
+{
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+}
diff --git a/rojo-test/syncback-tests/UFOWave_matching/input.rbxm b/rojo-test/syncback-tests/UFOWave_matching/input.rbxm
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diff --git a/src/snapshot/matching.rs b/src/snapshot/matching.rs
index 4fba9b39..42f36918 100644
--- a/src/snapshot/matching.rs
+++ b/src/snapshot/matching.rs
@@ -739,6 +739,449 @@ mod tests {
         }
     }
 
+    /// Helper: builds a RojoTree from child snapshots (with properties).
+    fn make_tree_from_snapshots(children: Vec<InstanceSnapshot>) -> (RojoTree, Vec<Ref>) {
+        let root_snap = InstanceSnapshot {
+            snapshot_id: Ref::none(),
+            metadata: InstanceMetadata::default(),
+            name: Cow::Borrowed("DataModel"),
+            class_name: ustr("DataModel"),
+            properties: Default::default(),
+            children,
+        };
+        let tree = RojoTree::new(root_snap);
+        let root_id = tree.get_root_id();
+        let child_ids: Vec<Ref> = tree.get_instance(root_id).unwrap().children().to_vec();
+        (tree, child_ids)
+    }
+
+    // ================================================================
+    // Default-omission matching tests
+    //
+    // These reproduce the scenario where syncback strips default-valued
+    // properties from model files, creating an asymmetry between the
+    // snapshot (sparse) and tree (full properties from Studio).
+    //
+    // The matching must still pair instances correctly despite some
+    // snapshots missing properties that the tree has at their defaults.
+    // ================================================================
+
+    #[test]
+    fn reflection_database_has_expected_defaults() {
+        // Validates the reflection database has the defaults we rely on.
+        use rbx_dom_weak::types::Variant;
+
+        let db = rbx_reflection_database::get().expect("reflection database should load");
+        let texture = db.classes.get("Texture").expect("Texture class should exist");
+        let face_default = texture
+            .default_properties
+            .get("Face")
+            .expect("Texture should have Face default");
+        match face_default {
+            Variant::Enum(e) => assert_eq!(e.to_u32(), 5, "Face default should be Front (5)"),
+            other => panic!("Face default should be Enum, got {:?}", other),
+        }
+
+        let part = db.classes.get("Part").expect("Part class should exist");
+        let anchored_default = part
+            .default_properties
+            .get("Anchored")
+            .expect("Part should have Anchored default");
+        assert_eq!(
+            anchored_default,
+            &Variant::Bool(false),
+            "Anchored default should be false"
+        );
+    }
+
+    #[test]
+    fn texture_face_six_instances_default_omitted() {
+        // Exact reproduction of the Texture Face bug:
+        // 6 Textures all named "Texture", each with a different Face.
+        // Snapshot side: 5 have explicit Face, 1 omits Face (Front=default).
+        // Tree side: all 6 have explicit Face (populated from Studio).
+        //
+        // Without the default-aware fix, the snapshot without Face scores
+        // equally against all tree instances, steals one by iteration order,
+        // and displaces the correct match.
+        use rbx_dom_weak::types::{Enum, Variant};
+
+        let faces = [
+            ("Top", Enum::from_u32(1)),
+            ("Right", Enum::from_u32(0)),
+            ("Left", Enum::from_u32(3)),
+            ("Bottom", Enum::from_u32(4)),
+            ("Back", Enum::from_u32(2)),
+        ];
+        let face_front = Enum::from_u32(5);
+
+        let shared_props = vec![("Transparency", Variant::Float32(0.65))];
+
+        // Snapshots: 5 with explicit Face + 1 without (Front default)
+        let mut snaps: Vec<InstanceSnapshot> = faces
+            .iter()
+            .map(|(_, face_enum)| {
+                let mut props = shared_props.clone();
+                props.push(("Face", Variant::Enum(face_enum.clone())));
+                make_snapshot_with_props("Texture", "Texture", props)
+            })
+            .collect();
+        // The Front one: NO Face property (default omitted by syncback)
+        snaps.push(make_snapshot_with_props(
+            "Texture",
+            "Texture",
+            shared_props.clone(),
+        ));
+
+        // Tree: all 6 with explicit Face (Studio always has all properties)
+        let mut tree_children: Vec<InstanceSnapshot> = faces
+            .iter()
+            .map(|(_, face_enum)| {
+                let mut props = shared_props.clone();
+                props.push(("Face", Variant::Enum(face_enum.clone())));
+                make_snapshot_with_props("Texture", "Texture", props)
+            })
+            .collect();
+        tree_children.push(make_snapshot_with_props(
+            "Texture",
+            "Texture",
+            {
+                let mut props = shared_props.clone();
+                props.push(("Face", Variant::Enum(face_front.clone())));
+                props
+            },
+        ));
+
+        let (tree, tree_refs) = make_tree_from_snapshots(tree_children);
+        let result = match_forward(snaps, &tree_refs, &tree);
+
+        assert_eq!(result.matched.len(), 6);
+        assert!(result.unmatched_snapshot.is_empty());
+        assert!(result.unmatched_tree.is_empty());
+
+        // Verify each pair has matching Face values.
+        for (snap, tree_ref) in &result.matched {
+            let inst = tree.get_instance(*tree_ref).unwrap();
+            let snap_face = snap.properties.get(&ustr("Face"));
+            let tree_face = inst.properties().get(&ustr("Face")).unwrap();
+
+            match snap_face {
+                Some(sv) => {
+                    assert!(
+                        variant_eq(sv, tree_face),
+                        "Face mismatch: snap={:?}, tree={:?}",
+                        sv,
+                        tree_face
+                    );
+                }
+                None => {
+                    // Snapshot omitted Face = must match tree Face=Front (5)
+                    assert!(
+                        variant_eq(tree_face, &Variant::Enum(face_front.clone())),
+                        "Snapshot without Face should match Front, got {:?}",
+                        tree_face
+                    );
+                }
+            }
+        }
+    }
+
+    #[test]
+    fn texture_face_twelve_instances_two_groups() {
+        // Exact reproduction of the user's real scenario:
+        // 12 Textures split into two groups of 6 by TextureContent.
+        // Each group covers all 6 faces, with Front omitted (default).
+        // Tree has all 12 with explicit Face.
+        use rbx_dom_weak::types::{Enum, Variant};
+
+        let face_values: Vec<Enum> = vec![
+            Enum::from_u32(1), // Top
+            Enum::from_u32(0), // Right
+            Enum::from_u32(3), // Left
+            Enum::from_u32(4), // Bottom
+            Enum::from_u32(2), // Back
+        ];
+        let face_front = Enum::from_u32(5);
+
+        let mut snaps = Vec::new();
+        let mut tree_children = Vec::new();
+
+        for group_transparency in [0.6_f32, 0.65_f32] {
+            // 5 with explicit Face
+            for face in &face_values {
+                snaps.push(make_snapshot_with_props(
+                    "Texture",
+                    "Texture",
+                    vec![
+                        ("Transparency", Variant::Float32(group_transparency)),
+                        ("Face", Variant::Enum(face.clone())),
+                    ],
+                ));
+                tree_children.push(make_snapshot_with_props(
+                    "Texture",
+                    "Texture",
+                    vec![
+                        ("Transparency", Variant::Float32(group_transparency)),
+                        ("Face", Variant::Enum(face.clone())),
+                    ],
+                ));
+            }
+            // 1 without Face (Front default)
+            snaps.push(make_snapshot_with_props(
+                "Texture",
+                "Texture",
+                vec![("Transparency", Variant::Float32(group_transparency))],
+            ));
+            tree_children.push(make_snapshot_with_props(
+                "Texture",
+                "Texture",
+                vec![
+                    ("Transparency", Variant::Float32(group_transparency)),
+                    ("Face", Variant::Enum(face_front.clone())),
+                ],
+            ));
+        }
+
+        // Reverse tree order to make it harder
+        tree_children.reverse();
+
+        let (tree, tree_refs) = make_tree_from_snapshots(tree_children);
+        let result = match_forward(snaps, &tree_refs, &tree);
+
+        assert_eq!(result.matched.len(), 12);
+        assert!(result.unmatched_snapshot.is_empty());
+        assert!(result.unmatched_tree.is_empty());
+
+        for (snap, tree_ref) in &result.matched {
+            let inst = tree.get_instance(*tree_ref).unwrap();
+            let snap_face = snap.properties.get(&ustr("Face"));
+            let tree_face = inst.properties().get(&ustr("Face")).unwrap();
+
+            // Transparency must match (distinguishes the two groups)
+            let snap_t = snap.properties.get(&ustr("Transparency")).unwrap();
+            let tree_t = inst.properties().get(&ustr("Transparency")).unwrap();
+            assert!(
+                variant_eq(snap_t, tree_t),
+                "Group mismatch: snap Transparency={:?}, tree={:?}",
+                snap_t,
+                tree_t
+            );
+
+            match snap_face {
+                Some(sv) => assert!(
+                    variant_eq(sv, tree_face),
+                    "Face mismatch: snap={:?}, tree={:?}",
+                    sv,
+                    tree_face
+                ),
+                None => assert!(
+                    variant_eq(tree_face, &Variant::Enum(face_front.clone())),
+                    "Omitted Face should match Front, got {:?}",
+                    tree_face
+                ),
+            }
+        }
+    }
+
+    #[test]
+    fn part_anchored_default_omitted() {
+        // 4 Parts named "Block": 3 have Anchored=true (explicit),
+        // 1 omits Anchored (false is the default). Tree has all 4.
+        use rbx_dom_weak::types::Variant;
+
+        let mut snaps = Vec::new();
+        let mut tree_children = Vec::new();
+
+        for i in 0..3 {
+            let props = vec![
+                ("Transparency", Variant::Float32(i as f32 * 0.1)),
+                ("Anchored", Variant::Bool(true)),
+            ];
+            snaps.push(make_snapshot_with_props("Block", "Part", props.clone()));
+            tree_children.push(make_snapshot_with_props("Block", "Part", props));
+        }
+        // The one with default Anchored=false: snapshot omits it
+        snaps.push(make_snapshot_with_props(
+            "Block",
+            "Part",
+            vec![("Transparency", Variant::Float32(0.3))],
+        ));
+        tree_children.push(make_snapshot_with_props(
+            "Block",
+            "Part",
+            vec![
+                ("Transparency", Variant::Float32(0.3)),
+                ("Anchored", Variant::Bool(false)),
+            ],
+        ));
+
+        tree_children.reverse();
+
+        let (tree, tree_refs) = make_tree_from_snapshots(tree_children);
+        let result = match_forward(snaps, &tree_refs, &tree);
+
+        assert_eq!(result.matched.len(), 4);
+
+        for (snap, tree_ref) in &result.matched {
+            let inst = tree.get_instance(*tree_ref).unwrap();
+            let snap_t = snap.properties.get(&ustr("Transparency")).unwrap();
+            let tree_t = inst.properties().get(&ustr("Transparency")).unwrap();
+            assert!(
+                variant_eq(snap_t, tree_t),
+                "Transparency mismatch: snap={:?}, tree={:?}",
+                snap_t,
+                tree_t
+            );
+        }
+    }
+
+    #[test]
+    fn multiple_defaults_omitted_all_at_once() {
+        // Tree instances have MANY extra properties all at their class defaults.
+        // Snapshots omit all of them. The match should not be thrown off.
+        use rbx_dom_weak::types::Variant;
+
+        // Two sparse snapshots differing only by Transparency
+        let snap_a = make_snapshot_with_props(
+            "Wall",
+            "Part",
+            vec![("Transparency", Variant::Float32(0.0))],
+        );
+        let snap_b = make_snapshot_with_props(
+            "Wall",
+            "Part",
+            vec![("Transparency", Variant::Float32(1.0))],
+        );
+
+        // Tree has Transparency + many known Part defaults from Studio.
+        // These are all at their default values, so count_own_diffs should
+        // skip them (not inflate match cost).
+        let extra_defaults: Vec<(&str, Variant)> = vec![
+            ("Anchored", Variant::Bool(false)),
+            ("CastShadow", Variant::Bool(true)),
+            ("CanCollide", Variant::Bool(true)),
+            ("CanTouch", Variant::Bool(true)),
+            ("Locked", Variant::Bool(false)),
+            ("Massless", Variant::Bool(false)),
+        ];
+
+        let mut tree_props_a = vec![("Transparency", Variant::Float32(0.0))];
+        tree_props_a.extend(extra_defaults.iter().cloned());
+        let mut tree_props_b = vec![("Transparency", Variant::Float32(1.0))];
+        tree_props_b.extend(extra_defaults.iter().cloned());
+
+        // Tree in reversed order
+        let (tree, tree_refs) = make_tree_from_snapshots(vec![
+            make_snapshot_with_props("Wall", "Part", tree_props_b),
+            make_snapshot_with_props("Wall", "Part", tree_props_a),
+        ]);
+        let result = match_forward(vec![snap_a, snap_b], &tree_refs, &tree);
+
+        assert_eq!(result.matched.len(), 2, "Both should match");
+
+        for (snap, tree_ref) in &result.matched {
+            let inst = tree.get_instance(*tree_ref).unwrap();
+            let snap_t = snap.properties.get(&ustr("Transparency")).unwrap();
+            let tree_t = inst.properties().get(&ustr("Transparency")).unwrap();
+            assert!(
+                variant_eq(snap_t, tree_t),
+                "Part with 6 extra default props mismatched: snap={:?}, tree={:?}",
+                snap_t,
+                tree_t
+            );
+        }
+    }
+
+    #[test]
+    fn ten_ambiguous_textures_stress() {
+        // 10 Textures: 8 with unique Face values (some repeated across
+        // groups), 2 with Front omitted. Two distinguishing groups by
+        // Transparency. The matcher must handle this without mis-pairing.
+        use rbx_dom_weak::types::{Enum, Variant};
+
+        let faces_group_a = [
+            Some(Enum::from_u32(1)), // Top
+            Some(Enum::from_u32(0)), // Right
+            Some(Enum::from_u32(3)), // Left
+            None,                     // Front (default, omitted)
+            Some(Enum::from_u32(4)), // Bottom
+        ];
+        let faces_group_b = [
+            Some(Enum::from_u32(2)), // Back
+            Some(Enum::from_u32(4)), // Bottom
+            None,                     // Front (default, omitted)
+            Some(Enum::from_u32(1)), // Top
+            Some(Enum::from_u32(3)), // Left
+        ];
+        let face_front = Enum::from_u32(5);
+
+        let mut snaps = Vec::new();
+        let mut tree_children = Vec::new();
+
+        for (group_t, faces) in [(0.5_f32, &faces_group_a[..]), (0.8_f32, &faces_group_b[..])] {
+            for face_opt in faces {
+                let mut snap_props = vec![("Transparency", Variant::Float32(group_t))];
+                let mut tree_props = vec![("Transparency", Variant::Float32(group_t))];
+
+                if let Some(face) = face_opt {
+                    snap_props.push(("Face", Variant::Enum(face.clone())));
+                    tree_props.push(("Face", Variant::Enum(face.clone())));
+                } else {
+                    // Snapshot omits Face; tree has Front
+                    tree_props.push(("Face", Variant::Enum(face_front.clone())));
+                }
+
+                snaps.push(make_snapshot_with_props("Texture", "Texture", snap_props));
+                tree_children.push(make_snapshot_with_props(
+                    "Texture",
+                    "Texture",
+                    tree_props,
+                ));
+            }
+        }
+
+        // Shuffle tree order (reverse)
+        tree_children.reverse();
+
+        let (tree, tree_refs) = make_tree_from_snapshots(tree_children);
+        let result = match_forward(snaps, &tree_refs, &tree);
+
+        assert_eq!(result.matched.len(), 10);
+        assert!(result.unmatched_snapshot.is_empty());
+        assert!(result.unmatched_tree.is_empty());
+
+        for (snap, tree_ref) in &result.matched {
+            let inst = tree.get_instance(*tree_ref).unwrap();
+
+            // Transparency must match (group discriminator)
+            let snap_t = snap.properties.get(&ustr("Transparency")).unwrap();
+            let tree_t = inst.properties().get(&ustr("Transparency")).unwrap();
+            assert!(
+                variant_eq(snap_t, tree_t),
+                "Group mismatch: snap={:?}, tree={:?}",
+                snap_t,
+                tree_t
+            );
+
+            // Face must match
+            let snap_face = snap.properties.get(&ustr("Face"));
+            let tree_face = inst.properties().get(&ustr("Face")).unwrap();
+            match snap_face {
+                Some(sv) => assert!(
+                    variant_eq(sv, tree_face),
+                    "Face mismatch: snap={:?}, tree={:?}",
+                    sv,
+                    tree_face
+                ),
+                None => assert!(
+                    variant_eq(tree_face, &Variant::Enum(face_front.clone())),
+                    "Omitted Face should match Front, got {:?}",
+                    tree_face
+                ),
+            }
+        }
+    }
+
     #[test]
     fn depth_limit_completes_quickly() {
         // Deeply nested tree (depth=6) with same-named instances at each level.