Merge branch 'fix/git-since-live-sync'

The VFS only sets up file watches via read() and read_dir(), not
metadata(). When git filtering caused snapshot_from_vfs to return
early for $path directories, read_dir was never called, so no file
watch was established. This meant file modifications never generated
VFS events and were silently ignored until the server was restarted.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugin/src/Reconciler/reify.lua

@@ -41,14 +41,41 @@ function reifyInstanceInner(unappliedPatch, deferredRefs, instanceMap, virtualIn
 		invariant("Cannot reify an instance not present in virtualInstances\nID: {}", id)
 	end
 
-	-- Instance.new can fail if we're passing in something that can't be
-	-- created, like a service, something enabled with a feature flag, or
-	-- something that requires higher security than we have.
-	local createSuccess, instance = pcall(Instance.new, virtualInstance.ClassName)
+	-- Before creating a new instance, check if the parent already has an
+	-- untracked child with the same Name and ClassName. This enables "late
+	-- adoption" of instances that exist in Studio but weren't in the initial
+	-- Rojo tree (e.g., when using --git-since filtering). Without this,
+	-- newly acknowledged files would create duplicate instances.
+	local adoptedExisting = false
+	local instance = nil
 
-	if not createSuccess then
-		addAllToPatch(unappliedPatch, virtualInstances, id)
-		return
+	for _, child in ipairs(parentInstance:GetChildren()) do
+		local accessSuccess, name, className = pcall(function()
+			return child.Name, child.ClassName
+		end)
+
+		if accessSuccess
+			and name == virtualInstance.Name
+			and className == virtualInstance.ClassName
+			and instanceMap.fromInstances[child] == nil
+		then
+			instance = child
+			adoptedExisting = true
+			break
+		end
+	end
+
+	if not adoptedExisting then
+		-- Instance.new can fail if we're passing in something that can't be
+		-- created, like a service, something enabled with a feature flag, or
+		-- something that requires higher security than we have.
+		local createSuccess
+		createSuccess, instance = pcall(Instance.new, virtualInstance.ClassName)
+
+		if not createSuccess then
+			addAllToPatch(unappliedPatch, virtualInstances, id)
+			return
+		end
 	end
 
 	-- TODO: Can this fail? Previous versions of Rojo guarded against this, but
@@ -96,7 +123,9 @@ function reifyInstanceInner(unappliedPatch, deferredRefs, instanceMap, virtualIn
 		reifyInstanceInner(unappliedPatch, deferredRefs, instanceMap, virtualInstances, childId, instance)
 	end
 
-	instance.Parent = parentInstance
+	if not adoptedExisting then
+		instance.Parent = parentInstance
+	end
 	instanceMap:insert(id, instance)
 end
 

src/cli/syncback.rs

@@ -54,6 +54,11 @@ pub struct SyncbackCommand {
     /// If provided, the prompt for writing to the file system is skipped.
     #[clap(long, short = 'y')]
     pub non_interactive: bool,
+
+    /// If provided, forces syncback to use JSON model files instead of binary
+    /// .rbxm files for instances that would otherwise serialize as binary.
+    #[clap(long)]
+    pub dangerously_force_json: bool,
 }
 
 impl SyncbackCommand {
@@ -104,6 +109,7 @@ impl SyncbackCommand {
             &mut dom_old,
             dom_new,
             session_old.root_project(),
+            self.dangerously_force_json,
         )?;
         log::debug!(
             "Syncback finished in {:.02}s!",

src/snapshot_middleware/project.rs

@@ -83,6 +83,19 @@ pub fn snapshot_project(
             // file being updated.
             snapshot.metadata.relevant_paths.push(path.to_path_buf());
 
+            // When git filter is active, also register the project folder as a
+            // relevant path. This serves as a catch-all so that file changes
+            // not under any specific $path node can still walk up the directory
+            // tree and trigger a re-snapshot of the entire project.
+            if context.has_git_filter() {
+                if let Some(folder) = path.parent() {
+                    let normalized = vfs
+                        .canonicalize(folder)
+                        .unwrap_or_else(|_| folder.to_path_buf());
+                    snapshot.metadata.relevant_paths.push(normalized);
+                }
+            }
+
             Ok(Some(snapshot))
         }
         None => Ok(None),
@@ -137,6 +150,26 @@ pub fn snapshot_project_node(
             // Take the snapshot's metadata as-is, which will be mutated later
             // on.
             metadata = snapshot.metadata;
+        } else if context.has_git_filter() {
+            // When the git filter is active and the $path was filtered out
+            // (no acknowledged files yet), we still need to register the path
+            // in relevant_paths. This allows the change processor to map file
+            // changes in this directory back to this project node instance,
+            // triggering a re-snapshot that will pick up newly modified files.
+            let normalized = vfs
+                .canonicalize(full_path.as_ref())
+                .unwrap_or_else(|_| full_path.to_path_buf());
+            metadata.relevant_paths.push(normalized);
+
+            // The VFS only sets up file watches via read() and read_dir(),
+            // not via metadata(). Since the git filter caused snapshot_from_vfs
+            // to return early (before read_dir was called), the VFS is not
+            // watching this path. We must read the directory here to ensure
+            // the VFS sets up a recursive watch, otherwise file change events
+            // will never fire and live sync won't detect modifications.
+            if full_path.is_dir() {
+                let _ = vfs.read_dir(&full_path);
+            }
         }
     }
 

src/syncback/mod.rs

@@ -52,6 +52,7 @@ pub fn syncback_loop(
     old_tree: &mut RojoTree,
     mut new_tree: WeakDom,
     project: &Project,
+    force_json: bool,
 ) -> anyhow::Result<FsSnapshot> {
     let ignore_patterns = project
         .syncback_rules
@@ -153,6 +154,7 @@ pub fn syncback_loop(
         old_tree,
         new_tree: &new_tree,
         project,
+        force_json,
     };
 
     let mut snapshots = vec![SyncbackSnapshot {
@@ -197,7 +199,7 @@ pub fn syncback_loop(
             }
         }
 
-        let middleware = get_best_middleware(&snapshot);
+        let middleware = get_best_middleware(&snapshot, force_json);
 
         log::trace!(
             "Middleware for {inst_path} is {:?} (path is {})",
@@ -213,10 +215,14 @@ pub fn syncback_loop(
         let syncback = match middleware.syncback(&snapshot) {
             Ok(syncback) => syncback,
             Err(err) if middleware == Middleware::Dir => {
-                let new_middleware = match env::var(DEBUG_MODEL_FORMAT_VAR) {
-                    Ok(value) if value == "1" => Middleware::Rbxmx,
-                    Ok(value) if value == "2" => Middleware::JsonModel,
-                    _ => Middleware::Rbxm,
+                let new_middleware = if force_json {
+                    Middleware::JsonModel
+                } else {
+                    match env::var(DEBUG_MODEL_FORMAT_VAR) {
+                        Ok(value) if value == "1" => Middleware::Rbxmx,
+                        Ok(value) if value == "2" => Middleware::JsonModel,
+                        _ => Middleware::Rbxm,
+                    }
                 };
                 let file_name = snapshot
                     .path
@@ -295,7 +301,7 @@ pub struct SyncbackReturn<'sync> {
     pub removed_children: Vec<InstanceWithMeta<'sync>>,
 }
 
-pub fn get_best_middleware(snapshot: &SyncbackSnapshot) -> Middleware {
+pub fn get_best_middleware(snapshot: &SyncbackSnapshot, force_json: bool) -> Middleware {
     // At some point, we're better off using an O(1) method for checking
     // equality for classes like this.
     static JSON_MODEL_CLASSES: OnceLock<HashSet<&str>> = OnceLock::new();
@@ -367,10 +373,18 @@ pub fn get_best_middleware(snapshot: &SyncbackSnapshot) -> Middleware {
     }
 
     if middleware == Middleware::Rbxm {
-        middleware = match env::var(DEBUG_MODEL_FORMAT_VAR) {
-            Ok(value) if value == "1" => Middleware::Rbxmx,
-            Ok(value) if value == "2" => Middleware::JsonModel,
-            _ => Middleware::Rbxm,
+        middleware = if force_json {
+            if !inst.children().is_empty() {
+                Middleware::Dir
+            } else {
+                Middleware::JsonModel
+            }
+        } else {
+            match env::var(DEBUG_MODEL_FORMAT_VAR) {
+                Ok(value) if value == "1" => Middleware::Rbxmx,
+                Ok(value) if value == "2" => Middleware::JsonModel,
+                _ => Middleware::Rbxm,
+            }
         }
     }
 

src/syncback/snapshot.rs

@@ -20,6 +20,7 @@ pub struct SyncbackData<'sync> {
     pub(super) old_tree: &'sync RojoTree,
     pub(super) new_tree: &'sync WeakDom,
     pub(super) project: &'sync Project,
+    pub(super) force_json: bool,
 }
 
 pub struct SyncbackSnapshot<'sync> {
@@ -43,7 +44,7 @@ impl<'sync> SyncbackSnapshot<'sync> {
             path: PathBuf::new(),
             middleware: None,
         };
-        let middleware = get_best_middleware(&snapshot);
+        let middleware = get_best_middleware(&snapshot, self.data.force_json);
         let name = name_for_inst(middleware, snapshot.new_inst(), snapshot.old_inst())?;
         snapshot.path = self.path.join(name.as_ref());
 
@@ -69,7 +70,7 @@ impl<'sync> SyncbackSnapshot<'sync> {
             path: PathBuf::new(),
             middleware: None,
         };
-        let middleware = get_best_middleware(&snapshot);
+        let middleware = get_best_middleware(&snapshot, self.data.force_json);
         let name = name_for_inst(middleware, snapshot.new_inst(), snapshot.old_inst())?;
         snapshot.path = base_path.join(name.as_ref());