Merge branch 'feature/init-name-resolution'

Two bugs:

1. Meta stem fallback used raw instance name (unslugged), so names with
   forbidden chars like '/' would create bogus directory components in
   the meta path. Fix: fallback now slugifies + init-prefixes, matching
   name_for_inst.

2. AdjacentMetadata name check used split('.').next() to extract the
   filesystem stem, breaking dotted names like "Name.new" (stem became
   "Name", mismatched the instance name, wrote an unnecessary name
   property). Fix: check the conditions that cause name_for_inst to
   diverge (invalid chars or init-prefix) directly instead of comparing
   path stems.

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

CHANGELOG.md

@@ -33,6 +33,7 @@ Making a new release? Simply add the new header with the version and date undern
 
 * `inf` and `nan` values in properties are now synced ([#1176])
 * Fixed a bug caused by having reference properties (such as `ObjectValue.Value`) that point to an Instance not included in syncback. ([#1179])
+* Implemented support for the "name" property in meta/model JSON files. ([#1187])
 * Fixed instance replacement fallback failing when too many instances needed to be replaced. ([#1192])
 * Added actors and bindable/remote event/function variants to be synced back as JSON files. ([#1199])
 * Fixed a bug where MacOS paths weren't being handled correctly. ([#1201])
@@ -42,6 +43,7 @@ Making a new release? Simply add the new header with the version and date undern
 
 [#1176]: https://github.com/rojo-rbx/rojo/pull/1176
 [#1179]: https://github.com/rojo-rbx/rojo/pull/1179
+[#1187]: https://github.com/rojo-rbx/rojo/pull/1187
 [#1192]: https://github.com/rojo-rbx/rojo/pull/1192
 [#1199]: https://github.com/rojo-rbx/rojo/pull/1199
 [#1201]: https://github.com/rojo-rbx/rojo/pull/1201

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
 

rojo-test/build-test-snapshots/end_to_end__tests__build__json_model_legacy_name.snap

@@ -1,16 +0,0 @@
----
-source: tests/tests/build.rs
-expression: contents
----
-<roblox version="4">
-  <Item class="Folder" referent="0">
-    <Properties>
-      <string name="Name">json_model_legacy_name</string>
-    </Properties>
-    <Item class="Folder" referent="1">
-      <Properties>
-        <string name="Name">Expected Name</string>
-      </Properties>
-    </Item>
-  </Item>
-</roblox>

rojo-test/build-test-snapshots/end_to_end__tests__build__model_json_name_input.snap

@@ -0,0 +1,23 @@
+---
+source: tests/tests/build.rs
+assertion_line: 109
+expression: contents
+---
+<roblox version="4">
+  <Item class="DataModel" referent="0">
+    <Properties>
+      <string name="Name">model_json_name_input</string>
+    </Properties>
+    <Item class="Workspace" referent="1">
+      <Properties>
+        <string name="Name">Workspace</string>
+        <bool name="NeedsPivotMigration">false</bool>
+      </Properties>
+      <Item class="StringValue" referent="2">
+        <Properties>
+          <string name="Name">/Bar</string>
+        </Properties>
+      </Item>
+    </Item>
+  </Item>
+</roblox>

rojo-test/build-test-snapshots/end_to_end__tests__build__slugified_name_roundtrip.snap

@@ -0,0 +1,20 @@
+---
+source: tests/tests/build.rs
+assertion_line: 108
+expression: contents
+---
+<roblox version="4">
+  <Item class="Folder" referent="0">
+    <Properties>
+      <string name="Name">slugified_name_roundtrip</string>
+    </Properties>
+    <Item class="Script" referent="1">
+      <Properties>
+        <string name="Name">/Script</string>
+        <token name="RunContext">0</token>
+        <string name="Source"><![CDATA[print("Hello world!")
+]]></string>
+      </Properties>
+    </Item>
+  </Item>
+</roblox>

rojo-test/build-tests/json_model_legacy_name/default.project.json

@@ -1,6 +0,0 @@
-{
-  "name": "json_model_legacy_name",
-  "tree": {
-    "$path": "folder"
-  }
-}

rojo-test/build-tests/json_model_legacy_name/folder/Expected Name.model.json

@@ -1,4 +0,0 @@
-{
-  "Name": "Overridden Name",
-  "ClassName": "Folder"
-}

rojo-test/build-tests/model_json_name_input/default.project.json

@@ -0,0 +1,11 @@
+{
+  "name": "model_json_name_input",
+  "tree": {
+    "$className": "DataModel",
+    "Workspace": {
+      "$className": "Workspace",
+      "$path": "src"
+    }
+  }
+}
+

rojo-test/build-tests/model_json_name_input/src/Bar.model.json

@@ -0,0 +1,5 @@
+{
+  "name": "/Bar",
+  "className": "StringValue"
+}
+

rojo-test/build-tests/slugified_name_roundtrip/_Script/init.meta.json

@@ -0,0 +1,4 @@
+{
+  "name": "/Script"
+}
+

rojo-test/build-tests/slugified_name_roundtrip/_Script/init.server.luau

@@ -0,0 +1,2 @@
+print("Hello world!")
+

rojo-test/build-tests/slugified_name_roundtrip/default.project.json

@@ -0,0 +1,6 @@
+{
+  "name": "slugified_name_roundtrip",
+  "tree": {
+    "$path": "src"
+  }
+}

rojo-test/build-tests/slugified_name_roundtrip/src/_Script/init.meta.json

@@ -0,0 +1,3 @@
+{
+  "name": "/Script"
+}

rojo-test/build-tests/slugified_name_roundtrip/src/_Script/init.server.luau

@@ -0,0 +1 @@
+print("Hello world!")

rojo-test/syncback-test-snapshots/end_to_end__rojo_test__syncback_util__model_json_name-stdout.snap

@@ -0,0 +1,6 @@
+---
+source: tests/rojo_test/syncback_util.rs
+assertion_line: 101
+expression: "String::from_utf8_lossy(&output.stdout)"
+---
+

rojo-test/syncback-test-snapshots/end_to_end__rojo_test__syncback_util__slugified_name-stdout.snap

@@ -0,0 +1,13 @@
+---
+source: tests/rojo_test/syncback_util.rs
+assertion_line: 101
+expression: "String::from_utf8_lossy(&output.stdout)"
+---
+Writing default.project.json
+Writing src/Camera.rbxm
+Writing src/Terrain.rbxm
+Writing src/_Folder/init.meta.json
+Writing src/_Script.meta.json
+Writing src/_Script.server.luau
+Writing src
+Writing src/_Folder

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__model_json_name-src__foo.model.json.snap

@@ -0,0 +1,9 @@
+---
+source: tests/tests/syncback.rs
+assertion_line: 31
+expression: src/foo.model.json
+---
+{
+  "name": "/Bar",
+  "className": "StringValue"
+}

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__slugified_name-src___Folder.model.json.snap

@@ -0,0 +1,8 @@
+---
+source: tests/tests/syncback.rs
+assertion_line: 31
+expression: src/_Folder.model.json
+---
+{
+  "className": "Folder"
+}

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__slugified_name-src___Folder__init.meta.json.snap

@@ -0,0 +1,8 @@
+---
+source: tests/tests/syncback.rs
+assertion_line: 31
+expression: src/_Folder/init.meta.json
+---
+{
+  "name": "/Folder"
+}

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__slugified_name-src___Script.meta.json.snap

@@ -0,0 +1,8 @@
+---
+source: tests/tests/syncback.rs
+assertion_line: 31
+expression: src/_Script.meta.json
+---
+{
+  "name": "/Script"
+}

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__slugified_name-src___Script.server.luau.snap

@@ -0,0 +1,6 @@
+---
+source: tests/tests/syncback.rs
+assertion_line: 31
+expression: src/_Script.server.luau
+---
+print("Hello world!")

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__slugified_name-src___Script__init.meta.json.snap

@@ -0,0 +1,8 @@
+---
+source: tests/tests/syncback.rs
+assertion_line: 31
+expression: src/_Script/init.meta.json
+---
+{
+  "name": "/Script"
+}

rojo-test/syncback-test-snapshots/end_to_end__tests__syncback__slugified_name-src___Script__init.server.luau.snap

@@ -0,0 +1,6 @@
+---
+source: tests/tests/syncback.rs
+assertion_line: 31
+expression: src/_Script/init.server.luau
+---
+print("Hello world!")

rojo-test/syncback-tests/model_json_name/input-project/default.project.json

@@ -0,0 +1,11 @@
+{
+  "name": "model_json_name",
+  "tree": {
+    "$className": "DataModel",
+    "Workspace": {
+      "$className": "Workspace",
+      "$path": "src"
+    }
+  }
+}
+

rojo-test/syncback-tests/model_json_name/input-project/src/foo.model.json

@@ -0,0 +1,5 @@
+{
+  "name": "/Bar",
+  "className": "StringValue"
+}
+

rojo-test/syncback-tests/slugified_name/input-project/default.project.json

@@ -0,0 +1,10 @@
+{
+  "name": "slugified_name",
+  "tree": {
+    "$className": "DataModel",
+    "Workspace": {
+      "$className": "Workspace",
+      "$path": "src"
+    }
+  }
+}

src/change_processor.rs

@@ -9,6 +9,7 @@ use std::{
 };
 
 use crate::{
+    git::SharedGitFilter,
     message_queue::MessageQueue,
     snapshot::{
         apply_patch_set, compute_patch_set, AppliedPatchSet, InstigatingSource, PatchSet, RojoTree,
@@ -46,11 +47,15 @@ pub struct ChangeProcessor {
 impl ChangeProcessor {
     /// Spin up the ChangeProcessor, connecting it to the given tree, VFS, and
     /// outbound message queue.
+    ///
+    /// If `git_filter` is provided, it will be refreshed on every VFS event
+    /// to ensure newly changed files are acknowledged.
     pub fn start(
         tree: Arc<Mutex<RojoTree>>,
         vfs: Arc<Vfs>,
         message_queue: Arc<MessageQueue<AppliedPatchSet>>,
         tree_mutation_receiver: Receiver<PatchSet>,
+        git_filter: Option<SharedGitFilter>,
     ) -> Self {
         let (shutdown_sender, shutdown_receiver) = crossbeam_channel::bounded(1);
         let vfs_receiver = vfs.event_receiver();
@@ -58,6 +63,7 @@ impl ChangeProcessor {
             tree,
             vfs,
             message_queue,
+            git_filter,
         };
 
         let job_thread = jod_thread::Builder::new()
@@ -111,6 +117,10 @@ struct JobThreadContext {
     /// Whenever changes are applied to the DOM, we should push those changes
     /// into this message queue to inform any connected clients.
     message_queue: Arc<MessageQueue<AppliedPatchSet>>,
+
+    /// Optional Git filter for --git-since mode. When set, will be refreshed
+    /// on every VFS event to ensure newly changed files are acknowledged.
+    git_filter: Option<SharedGitFilter>,
 }
 
 impl JobThreadContext {
@@ -160,6 +170,14 @@ impl JobThreadContext {
     fn handle_vfs_event(&self, event: VfsEvent) {
         log::trace!("Vfs event: {:?}", event);
 
+        // If we have a git filter, refresh it to pick up any new changes.
+        // This ensures that files modified during the session will be acknowledged.
+        if let Some(ref git_filter) = self.git_filter {
+            if let Err(err) = git_filter.refresh() {
+                log::warn!("Failed to refresh git filter: {:?}", err);
+            }
+        }
+
         // Update the VFS immediately with the event.
         self.vfs
             .commit_event(&event)

src/cli/build.rs

@@ -81,7 +81,7 @@ impl BuildCommand {
         let vfs = Vfs::new_default();
         vfs.set_watch_enabled(self.watch);
 
-        let session = ServeSession::new(vfs, project_path)?;
+        let session = ServeSession::new(vfs, project_path, None)?;
         let mut cursor = session.message_queue().cursor();
 
         write_model(&session, &output_path, output_kind)?;

src/cli/plugin.rs

@@ -54,7 +54,7 @@ fn initialize_plugin() -> anyhow::Result<ServeSession> {
     in_memory_fs.load_snapshot("/plugin", plugin_snapshot)?;
 
     let vfs = Vfs::new(in_memory_fs);
-    Ok(ServeSession::new(vfs, "/plugin")?)
+    Ok(ServeSession::new(vfs, "/plugin", None)?)
 }
 
 fn install_plugin() -> anyhow::Result<()> {

src/cli/serve.rs

@@ -9,7 +9,7 @@ use clap::Parser;
 use memofs::Vfs;
 use termcolor::{BufferWriter, Color, ColorChoice, ColorSpec, WriteColor};
 
-use crate::{serve_session::ServeSession, web::LiveServer};
+use crate::{git::GitFilter, serve_session::ServeSession, web::LiveServer};
 
 use super::{resolve_path, GlobalOptions};
 
@@ -31,6 +31,19 @@ pub struct ServeCommand {
     /// it has none.
     #[clap(long)]
     pub port: Option<u16>,
+
+    /// Only sync files that have changed since the given Git reference.
+    ///
+    /// When this option is set, Rojo will only include files that have been
+    /// modified, added, or are untracked since the specified Git reference
+    /// (e.g., "HEAD", "main", a commit hash). This is useful for working with
+    /// large projects where you only want to sync your local changes.
+    ///
+    /// Scripts that have not changed will still be acknowledged if modified
+    /// during the session, and all synced instances will have
+    /// ignoreUnknownInstances set to true to preserve descendants in Studio.
+    #[clap(long, value_name = "REF")]
+    pub git_since: Option<String>,
 }
 
 impl ServeCommand {
@@ -39,7 +52,19 @@ impl ServeCommand {
 
         let vfs = Vfs::new_default();
 
-        let session = Arc::new(ServeSession::new(vfs, project_path)?);
+        // Set up Git filter if --git-since was specified
+        let git_filter = if let Some(ref base_ref) = self.git_since {
+            let repo_root = GitFilter::find_repo_root(&project_path)?;
+            log::info!(
+                "Git filter enabled: only syncing files changed since '{}'",
+                base_ref
+            );
+            Some(Arc::new(GitFilter::new(repo_root, base_ref.clone(), &project_path)?))
+        } else {
+            None
+        };
+
+        let session = Arc::new(ServeSession::new(vfs, project_path, git_filter)?);
 
         let ip = self
             .address
@@ -53,17 +78,25 @@ impl ServeCommand {
 
         let server = LiveServer::new(session);
 
-        let _ = show_start_message(ip, port, global.color.into());
+        let _ = show_start_message(ip, port, self.git_since.as_deref(), global.color.into());
         server.start((ip, port).into());
 
         Ok(())
     }
 }
 
-fn show_start_message(bind_address: IpAddr, port: u16, color: ColorChoice) -> io::Result<()> {
+fn show_start_message(
+    bind_address: IpAddr,
+    port: u16,
+    git_since: Option<&str>,
+    color: ColorChoice,
+) -> io::Result<()> {
     let mut green = ColorSpec::new();
     green.set_fg(Some(Color::Green)).set_bold(true);
 
+    let mut yellow = ColorSpec::new();
+    yellow.set_fg(Some(Color::Yellow)).set_bold(true);
+
     let writer = BufferWriter::stdout(color);
     let mut buffer = writer.buffer();
 
@@ -84,6 +117,13 @@ fn show_start_message(bind_address: IpAddr, port: u16, color: ColorChoice) -> io
     buffer.set_color(&green)?;
     writeln!(&mut buffer, "{}", port)?;
 
+    if let Some(base_ref) = git_since {
+        buffer.set_color(&ColorSpec::new())?;
+        write!(&mut buffer, "  Mode:    ")?;
+        buffer.set_color(&yellow)?;
+        writeln!(&mut buffer, "git-since ({})", base_ref)?;
+    }
+
     writeln!(&mut buffer)?;
 
     buffer.set_color(&ColorSpec::new())?;

src/cli/sourcemap.rs

@@ -78,7 +78,7 @@ impl SourcemapCommand {
         vfs.set_watch_enabled(self.watch);
 
         log::trace!("Setting up session for sourcemap generation");
-        let session = ServeSession::new(vfs, project_path)?;
+        let session = ServeSession::new(vfs, project_path, None)?;
         let mut cursor = session.message_queue().cursor();
 
         let filter = if self.include_non_scripts {

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 {
@@ -73,7 +78,7 @@ impl SyncbackCommand {
         vfs.set_watch_enabled(false);
 
         let project_start_timer = Instant::now();
-        let session_old = ServeSession::new(vfs, path_old.clone())?;
+        let session_old = ServeSession::new(vfs, path_old.clone(), None)?;
         log::debug!(
             "Finished opening project in {:0.02}s",
             project_start_timer.elapsed().as_secs_f32()
@@ -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/cli/upload.rs

@@ -42,7 +42,7 @@ impl UploadCommand {
 
         let vfs = Vfs::new_default();
 
-        let session = ServeSession::new(vfs, project_path)?;
+        let session = ServeSession::new(vfs, project_path, None)?;
 
         let tree = session.tree();
         let inner_tree = tree.inner();

src/git.rs

@@ -0,0 +1,380 @@
+//! Git integration for filtering files based on changes since a reference.
+
+use std::{
+    collections::HashSet,
+    path::{Path, PathBuf},
+    process::Command,
+    sync::{Arc, RwLock},
+};
+
+use anyhow::{bail, Context};
+
+/// A filter that tracks which files have been changed since a Git reference.
+///
+/// When active, only files that have been modified, added, or deleted according
+/// to Git will be "acknowledged" and synced to Studio. This allows users to
+/// work with large projects where they only want to sync their local changes.
+///
+/// Once a file is acknowledged (either initially or during the session), it
+/// stays acknowledged for the entire session. This prevents files from being
+/// deleted in Studio if their content is reverted to match the git reference.
+#[derive(Debug)]
+pub struct GitFilter {
+    /// The Git repository root directory.
+    repo_root: PathBuf,
+
+    /// The Git reference to compare against (e.g., "HEAD", "main", a commit hash).
+    base_ref: String,
+
+    /// Cache of paths that are currently different from the base ref according to git.
+    /// This is refreshed on every VFS event.
+    git_changed_paths: RwLock<HashSet<PathBuf>>,
+
+    /// Paths that have been acknowledged at any point during this session.
+    /// Once a path is added here, it stays acknowledged forever (for this session).
+    /// This prevents files from being deleted if their content is reverted.
+    session_acknowledged_paths: RwLock<HashSet<PathBuf>>,
+}
+
+impl GitFilter {
+    /// Creates a new GitFilter for the given repository root and base reference.
+    ///
+    /// The `repo_root` should be the root of the Git repository (where .git is located).
+    /// The `base_ref` is the Git reference to compare against (e.g., "HEAD", "main").
+    /// The `project_path` is the path to the project being served - it will always be
+    /// acknowledged regardless of git status to ensure the project structure exists.
+    pub fn new(repo_root: PathBuf, base_ref: String, project_path: &Path) -> anyhow::Result<Self> {
+        let filter = Self {
+            repo_root,
+            base_ref,
+            git_changed_paths: RwLock::new(HashSet::new()),
+            session_acknowledged_paths: RwLock::new(HashSet::new()),
+        };
+
+        // Always acknowledge the project path and its directory so the project
+        // structure exists even when there are no git changes
+        filter.acknowledge_project_path(project_path);
+
+        // Initial refresh to populate the cache with git changes
+        filter.refresh()?;
+
+        Ok(filter)
+    }
+
+    /// Acknowledges the project path and its containing directory.
+    /// This ensures the project structure always exists regardless of git status.
+    fn acknowledge_project_path(&self, project_path: &Path) {
+        let mut session = self.session_acknowledged_paths.write().unwrap();
+
+        // Acknowledge the project path itself (might be a directory or .project.json file)
+        let canonical = project_path.canonicalize().unwrap_or_else(|_| project_path.to_path_buf());
+        session.insert(canonical.clone());
+
+        // Acknowledge all ancestor directories
+        let mut current = canonical.parent();
+        while let Some(parent) = current {
+            session.insert(parent.to_path_buf());
+            current = parent.parent();
+        }
+
+        // If it's a directory, also acknowledge default.project.json inside it
+        if project_path.is_dir() {
+            for name in &["default.project.json", "default.project.jsonc"] {
+                let project_file = project_path.join(name);
+                if let Ok(canonical_file) = project_file.canonicalize() {
+                    session.insert(canonical_file);
+                } else {
+                    session.insert(project_file);
+                }
+            }
+        }
+
+        // If it's a .project.json file, also acknowledge its parent directory
+        if let Some(parent) = project_path.parent() {
+            let parent_canonical = parent.canonicalize().unwrap_or_else(|_| parent.to_path_buf());
+            session.insert(parent_canonical);
+        }
+
+        log::debug!(
+            "GitFilter: acknowledged project path {} ({} paths total)",
+            project_path.display(),
+            session.len()
+        );
+    }
+
+    /// Finds the Git repository root for the given path.
+    pub fn find_repo_root(path: &Path) -> anyhow::Result<PathBuf> {
+        let output = Command::new("git")
+            .args(["rev-parse", "--show-toplevel"])
+            .current_dir(path)
+            .output()
+            .context("Failed to execute git rev-parse")?;
+
+        if !output.status.success() {
+            let stderr = String::from_utf8_lossy(&output.stderr);
+            bail!("Failed to find Git repository root: {}", stderr.trim());
+        }
+
+        let root = String::from_utf8_lossy(&output.stdout)
+            .trim()
+            .to_string();
+
+        Ok(PathBuf::from(root))
+    }
+
+    /// Refreshes the cache of acknowledged paths by querying Git.
+    ///
+    /// This should be called when files change to ensure newly modified files
+    /// are properly acknowledged. Once a path is acknowledged, it stays
+    /// acknowledged for the entire session (even if the file is reverted).
+    pub fn refresh(&self) -> anyhow::Result<()> {
+        let mut git_changed = HashSet::new();
+
+        // Get files changed since the base ref (modified, added, deleted)
+        let diff_output = Command::new("git")
+            .args(["diff", "--name-only", &self.base_ref])
+            .current_dir(&self.repo_root)
+            .output()
+            .context("Failed to execute git diff")?;
+
+        if !diff_output.status.success() {
+            let stderr = String::from_utf8_lossy(&diff_output.stderr);
+            bail!("git diff failed: {}", stderr.trim());
+        }
+
+        let diff_files = String::from_utf8_lossy(&diff_output.stdout);
+        let diff_count = diff_files.lines().filter(|l| !l.is_empty()).count();
+        if diff_count > 0 {
+            log::debug!("git diff found {} changed files", diff_count);
+        }
+        for line in diff_files.lines() {
+            if !line.is_empty() {
+                let path = self.repo_root.join(line);
+                log::trace!("git diff: acknowledging {}", path.display());
+                self.acknowledge_path(&path, &mut git_changed);
+            }
+        }
+
+        // Get untracked files (new files not yet committed)
+        let untracked_output = Command::new("git")
+            .args(["ls-files", "--others", "--exclude-standard"])
+            .current_dir(&self.repo_root)
+            .output()
+            .context("Failed to execute git ls-files")?;
+
+        if !untracked_output.status.success() {
+            let stderr = String::from_utf8_lossy(&untracked_output.stderr);
+            bail!("git ls-files failed: {}", stderr.trim());
+        }
+
+        let untracked_files = String::from_utf8_lossy(&untracked_output.stdout);
+        for line in untracked_files.lines() {
+            if !line.is_empty() {
+                let path = self.repo_root.join(line);
+                self.acknowledge_path(&path, &mut git_changed);
+            }
+        }
+
+        // Get staged files (files added to index but not yet committed)
+        let staged_output = Command::new("git")
+            .args(["diff", "--name-only", "--cached", &self.base_ref])
+            .current_dir(&self.repo_root)
+            .output()
+            .context("Failed to execute git diff --cached")?;
+
+        if staged_output.status.success() {
+            let staged_files = String::from_utf8_lossy(&staged_output.stdout);
+            for line in staged_files.lines() {
+                if !line.is_empty() {
+                    let path = self.repo_root.join(line);
+                    self.acknowledge_path(&path, &mut git_changed);
+                }
+            }
+        }
+
+        // Update the git changed paths cache
+        {
+            let mut cache = self.git_changed_paths.write().unwrap();
+            *cache = git_changed.clone();
+        }
+
+        // Merge newly changed paths into session acknowledged paths
+        // Once acknowledged, a path stays acknowledged for the entire session
+        {
+            let mut session = self.session_acknowledged_paths.write().unwrap();
+            for path in git_changed {
+                session.insert(path);
+            }
+            log::debug!(
+                "GitFilter refreshed: {} paths acknowledged in session",
+                session.len()
+            );
+        }
+
+        Ok(())
+    }
+
+    /// Acknowledges a path and all its ancestors, plus associated meta files.
+    fn acknowledge_path(&self, path: &Path, acknowledged: &mut HashSet<PathBuf>) {
+        // Canonicalize the path if possible, otherwise use as-is
+        let path = path.canonicalize().unwrap_or_else(|_| path.to_path_buf());
+
+        // Add the path itself
+        acknowledged.insert(path.clone());
+
+        // Add all ancestor directories
+        let mut current = path.parent();
+        while let Some(parent) = current {
+            acknowledged.insert(parent.to_path_buf());
+            current = parent.parent();
+        }
+
+        // Add associated meta files
+        self.acknowledge_meta_files(&path, acknowledged);
+    }
+
+    /// Acknowledges associated meta files for a given path.
+    fn acknowledge_meta_files(&self, path: &Path, acknowledged: &mut HashSet<PathBuf>) {
+        if let Some(file_name) = path.file_name().and_then(|n| n.to_str()) {
+            if let Some(parent) = path.parent() {
+                // For a file like "foo.lua", also acknowledge "foo.meta.json"
+                // Strip known extensions to get the base name
+                let base_name = strip_lua_extension(file_name);
+
+                let meta_path = parent.join(format!("{}.meta.json", base_name));
+                if let Ok(canonical) = meta_path.canonicalize() {
+                    acknowledged.insert(canonical);
+                } else {
+                    acknowledged.insert(meta_path);
+                }
+
+                // For init files, also acknowledge "init.meta.json" in the same directory
+                if file_name.starts_with("init.") {
+                    let init_meta = parent.join("init.meta.json");
+                    if let Ok(canonical) = init_meta.canonicalize() {
+                        acknowledged.insert(canonical);
+                    } else {
+                        acknowledged.insert(init_meta);
+                    }
+                }
+            }
+        }
+    }
+
+    /// Checks if a path is acknowledged (should be synced).
+    ///
+    /// Returns `true` if the path or any of its descendants have been changed
+    /// at any point during this session. Once a file is acknowledged, it stays
+    /// acknowledged even if its content is reverted to match the git reference.
+    pub fn is_acknowledged(&self, path: &Path) -> bool {
+        let session = self.session_acknowledged_paths.read().unwrap();
+
+        // Try to canonicalize the path
+        let canonical = path.canonicalize().unwrap_or_else(|_| path.to_path_buf());
+
+        // Check if this exact path is acknowledged
+        if session.contains(&canonical) {
+            log::trace!("Path {} is directly acknowledged", path.display());
+            return true;
+        }
+
+        // Also check without canonicalization in case of path differences
+        if session.contains(path) {
+            log::trace!("Path {} is acknowledged (non-canonical)", path.display());
+            return true;
+        }
+
+        // For directories, check if any descendant is acknowledged
+        // This is done by checking if any acknowledged path starts with this path
+        for acknowledged in session.iter() {
+            if acknowledged.starts_with(&canonical) {
+                log::trace!(
+                    "Path {} has acknowledged descendant {}",
+                    path.display(),
+                    acknowledged.display()
+                );
+                return true;
+            }
+            // Also check non-canonical
+            if acknowledged.starts_with(path) {
+                log::trace!(
+                    "Path {} has acknowledged descendant {} (non-canonical)",
+                    path.display(),
+                    acknowledged.display()
+                );
+                return true;
+            }
+        }
+
+        log::trace!(
+            "Path {} is NOT acknowledged (canonical: {})",
+            path.display(),
+            canonical.display()
+        );
+        false
+    }
+
+    /// Returns the base reference being compared against.
+    pub fn base_ref(&self) -> &str {
+        &self.base_ref
+    }
+
+    /// Returns the repository root path.
+    pub fn repo_root(&self) -> &Path {
+        &self.repo_root
+    }
+
+    /// Explicitly acknowledges a path and all its ancestors.
+    /// This is useful for ensuring certain paths are always synced regardless of git status.
+    pub fn force_acknowledge(&self, path: &Path) {
+        let mut acknowledged = HashSet::new();
+        self.acknowledge_path(path, &mut acknowledged);
+
+        let mut session = self.session_acknowledged_paths.write().unwrap();
+        for p in acknowledged {
+            session.insert(p);
+        }
+    }
+}
+
+/// Strips Lua-related extensions from a file name to get the base name.
+fn strip_lua_extension(file_name: &str) -> &str {
+    const EXTENSIONS: &[&str] = &[
+        ".server.luau",
+        ".server.lua",
+        ".client.luau",
+        ".client.lua",
+        ".luau",
+        ".lua",
+    ];
+
+    for ext in EXTENSIONS {
+        if let Some(base) = file_name.strip_suffix(ext) {
+            return base;
+        }
+    }
+
+    // If no Lua extension, try to strip the regular extension
+    file_name
+        .rsplit_once('.')
+        .map(|(base, _)| base)
+        .unwrap_or(file_name)
+}
+
+/// A wrapper around GitFilter that can be shared across threads.
+pub type SharedGitFilter = Arc<GitFilter>;
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_strip_lua_extension() {
+        assert_eq!(strip_lua_extension("foo.server.lua"), "foo");
+        assert_eq!(strip_lua_extension("foo.client.luau"), "foo");
+        assert_eq!(strip_lua_extension("foo.lua"), "foo");
+        assert_eq!(strip_lua_extension("init.server.lua"), "init");
+        assert_eq!(strip_lua_extension("bar.txt"), "bar");
+        assert_eq!(strip_lua_extension("noextension"), "noextension");
+    }
+}

src/lib.rs

@@ -9,6 +9,7 @@ mod tree_view;
 
 mod auth_cookie;
 mod change_processor;
+mod git;
 mod glob;
 mod json;
 mod lua_ast;
@@ -28,6 +29,7 @@ mod web;
 
 // TODO: Work out what we should expose publicly
 
+pub use git::{GitFilter, SharedGitFilter};
 pub use project::*;
 pub use rojo_ref::*;
 pub use session_id::SessionId;

src/serve_session.rs

@@ -13,6 +13,7 @@ use thiserror::Error;
 
 use crate::{
     change_processor::ChangeProcessor,
+    git::SharedGitFilter,
     message_queue::MessageQueue,
     project::{Project, ProjectError},
     session_id::SessionId,
@@ -94,7 +95,14 @@ impl ServeSession {
     /// The project file is expected to be loaded out-of-band since it's
     /// currently loaded from the filesystem directly instead of through the
     /// in-memory filesystem layer.
-    pub fn new<P: AsRef<Path>>(vfs: Vfs, start_path: P) -> Result<Self, ServeSessionError> {
+    ///
+    /// If `git_filter` is provided, only files that have changed since the
+    /// specified Git reference will be synced.
+    pub fn new<P: AsRef<Path>>(
+        vfs: Vfs,
+        start_path: P,
+        git_filter: Option<SharedGitFilter>,
+    ) -> Result<Self, ServeSessionError> {
         let start_path = start_path.as_ref();
         let start_time = Instant::now();
 
@@ -102,12 +110,28 @@ impl ServeSession {
 
         let root_project = Project::load_initial_project(&vfs, start_path)?;
 
+        // If git filter is active, ensure the project file location is acknowledged
+        // This is necessary so the project structure exists even with no git changes
+        if let Some(ref filter) = git_filter {
+            filter.force_acknowledge(start_path);
+            filter.force_acknowledge(&root_project.file_location);
+            filter.force_acknowledge(root_project.folder_location());
+            log::debug!(
+                "Force acknowledged project at {}",
+                root_project.file_location.display()
+            );
+        }
+
         let mut tree = RojoTree::new(InstanceSnapshot::new());
 
         let root_id = tree.get_root_id();
 
-        let instance_context =
-            InstanceContext::with_emit_legacy_scripts(root_project.emit_legacy_scripts);
+        let instance_context = match &git_filter {
+            Some(filter) => {
+                InstanceContext::with_git_filter(root_project.emit_legacy_scripts, Arc::clone(filter))
+            }
+            None => InstanceContext::with_emit_legacy_scripts(root_project.emit_legacy_scripts),
+        };
 
         log::trace!("Generating snapshot of instances from VFS");
         let snapshot = snapshot_from_vfs(&instance_context, &vfs, start_path)?;
@@ -133,6 +157,7 @@ impl ServeSession {
             Arc::clone(&vfs),
             Arc::clone(&message_queue),
             tree_mutation_receiver,
+            git_filter,
         );
 
         Ok(Self {

src/snapshot/metadata.rs

@@ -8,6 +8,7 @@ use anyhow::Context;
 use serde::{Deserialize, Serialize};
 
 use crate::{
+    git::SharedGitFilter,
     glob::Glob,
     path_serializer,
     project::ProjectNode,
@@ -70,6 +71,12 @@ pub struct InstanceMetadata {
     /// A schema provided via a JSON file, if one exists. Will be `None` for
     /// all non-JSON middleware.
     pub schema: Option<String>,
+
+    /// A custom name specified via meta.json or model.json files. If present,
+    /// this name will be used for the instance while the filesystem name will
+    /// be slugified to remove illegal characters.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub specified_name: Option<String>,
 }
 
 impl InstanceMetadata {
@@ -82,6 +89,7 @@ impl InstanceMetadata {
             specified_id: None,
             middleware: None,
             schema: None,
+            specified_name: None,
         }
     }
 
@@ -130,6 +138,13 @@ impl InstanceMetadata {
     pub fn schema(self, schema: Option<String>) -> Self {
         Self { schema, ..self }
     }
+
+    pub fn specified_name(self, specified_name: Option<String>) -> Self {
+        Self {
+            specified_name,
+            ..self
+        }
+    }
 }
 
 impl Default for InstanceMetadata {
@@ -138,13 +153,27 @@ impl Default for InstanceMetadata {
     }
 }
 
-#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+#[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct InstanceContext {
     #[serde(skip_serializing_if = "Vec::is_empty")]
     pub path_ignore_rules: Arc<Vec<PathIgnoreRule>>,
     pub emit_legacy_scripts: bool,
     #[serde(skip_serializing_if = "Vec::is_empty")]
     pub sync_rules: Vec<SyncRule>,
+    /// Optional Git filter for --git-since mode. When set, only files that have
+    /// changed since the specified Git reference will be synced.
+    #[serde(skip)]
+    pub git_filter: Option<SharedGitFilter>,
+}
+
+impl PartialEq for InstanceContext {
+    fn eq(&self, other: &Self) -> bool {
+        // Note: git_filter is intentionally excluded from comparison
+        // since it's runtime state, not configuration
+        self.path_ignore_rules == other.path_ignore_rules
+            && self.emit_legacy_scripts == other.emit_legacy_scripts
+            && self.sync_rules == other.sync_rules
+    }
 }
 
 impl InstanceContext {
@@ -153,6 +182,7 @@ impl InstanceContext {
             path_ignore_rules: Arc::new(Vec::new()),
             emit_legacy_scripts: emit_legacy_scripts_default().unwrap(),
             sync_rules: Vec::new(),
+            git_filter: None,
         }
     }
 
@@ -165,6 +195,36 @@ impl InstanceContext {
         }
     }
 
+    /// Creates a new InstanceContext with a Git filter for --git-since mode.
+    pub fn with_git_filter(
+        emit_legacy_scripts: Option<bool>,
+        git_filter: SharedGitFilter,
+    ) -> Self {
+        Self {
+            git_filter: Some(git_filter),
+            ..Self::with_emit_legacy_scripts(emit_legacy_scripts)
+        }
+    }
+
+    /// Sets the Git filter for this context.
+    pub fn set_git_filter(&mut self, git_filter: Option<SharedGitFilter>) {
+        self.git_filter = git_filter;
+    }
+
+    /// Returns true if the given path should be acknowledged (synced).
+    /// If no git filter is set, all paths are acknowledged.
+    pub fn is_path_acknowledged(&self, path: &Path) -> bool {
+        match &self.git_filter {
+            Some(filter) => filter.is_acknowledged(path),
+            None => true,
+        }
+    }
+
+    /// Returns true if a git filter is active.
+    pub fn has_git_filter(&self) -> bool {
+        self.git_filter.is_some()
+    }
+
     /// Extend the list of ignore rules in the context with the given new rules.
     pub fn add_path_ignore_rules<I>(&mut self, new_rules: I)
     where

src/snapshot_middleware/csv.rs

@@ -109,8 +109,29 @@ pub fn syncback_csv<'sync>(
 
         if !meta.is_empty() {
             let parent = snapshot.path.parent_err()?;
+            let meta_stem = snapshot.middleware
+                .and_then(|mw| {
+                    let ext = format!(".{}", crate::syncback::extension_for_middleware(mw));
+                    snapshot.path.file_name()
+                        .and_then(|n| n.to_str())
+                        .and_then(|s| s.strip_suffix(ext.as_str()))
+                        .map(str::to_owned)
+                })
+                .unwrap_or_else(|| {
+                    let name = &new_inst.name;
+                    let base = if crate::syncback::validate_file_name(name).is_err() {
+                        crate::syncback::slugify_name(name)
+                    } else {
+                        name.clone()
+                    };
+                    if base.to_lowercase() == "init" {
+                        format!("_{base}")
+                    } else {
+                        base
+                    }
+                });
             fs_snapshot.add_file(
-                parent.join(format!("{}.meta.json", new_inst.name)),
+                parent.join(format!("{meta_stem}.meta.json")),
                 serde_json::to_vec_pretty(&meta).context("cannot serialize metadata")?,
             )
         }

src/snapshot_middleware/dir.rs

@@ -8,7 +8,7 @@ use memofs::{DirEntry, Vfs};
 
 use crate::{
     snapshot::{InstanceContext, InstanceMetadata, InstanceSnapshot, InstigatingSource},
-    syncback::{hash_instance, FsSnapshot, SyncbackReturn, SyncbackSnapshot},
+    syncback::{hash_instance, slugify_name, FsSnapshot, SyncbackReturn, SyncbackSnapshot},
 };
 
 use super::{meta_file::DirectoryMetadata, snapshot_from_vfs};
@@ -134,12 +134,39 @@ pub fn syncback_dir_no_meta<'sync>(
     let mut children = Vec::new();
     let mut removed_children = Vec::new();
 
-    // We have to enforce unique child names for the file system.
-    let mut child_names = HashSet::with_capacity(new_inst.children().len());
+    // Build the old child map early so it can be used for deduplication below.
+    let mut old_child_map = HashMap::new();
+    if let Some(old_inst) = snapshot.old_inst() {
+        for child in old_inst.children() {
+            let inst = snapshot.get_old_instance(*child).unwrap();
+            old_child_map.insert(inst.name(), inst);
+        }
+    }
+
+    // Enforce unique filesystem names. Uses actual on-disk names for existing
+    // children and resolved names (with init-prefix) for new ones.
+    let mut fs_child_names = HashSet::with_capacity(new_inst.children().len());
     let mut duplicate_set = HashSet::new();
     for child_ref in new_inst.children() {
         let child = snapshot.get_new_instance(*child_ref).unwrap();
-        if !child_names.insert(child.name.to_lowercase()) {
+        let fs_name = old_child_map
+            .get(child.name.as_str())
+            .and_then(|old| old.metadata().relevant_paths.first())
+            .and_then(|p| p.file_name())
+            .and_then(|n| n.to_str())
+            .map(|s| s.to_lowercase())
+            .unwrap_or_else(|| {
+                let slug = slugify_name(&child.name);
+                let slug_lower = slug.to_lowercase();
+                // Mirror name_for_inst's init-prefix.
+                if slug_lower == "init" {
+                    format!("_{slug_lower}")
+                } else {
+                    slug_lower
+                }
+            });
+
+        if !fs_child_names.insert(fs_name) {
             duplicate_set.insert(child.name.as_str());
         }
     }
@@ -153,13 +180,7 @@ pub fn syncback_dir_no_meta<'sync>(
         anyhow::bail!("Instance has more than 25 children with duplicate names");
     }
 
-    if let Some(old_inst) = snapshot.old_inst() {
-        let mut old_child_map = HashMap::with_capacity(old_inst.children().len());
-        for child in old_inst.children() {
-            let inst = snapshot.get_old_instance(*child).unwrap();
-            old_child_map.insert(inst.name(), inst);
-        }
-
+    if snapshot.old_inst().is_some() {
         for new_child_ref in new_inst.children() {
             let new_child = snapshot.get_new_instance(*new_child_ref).unwrap();
             if let Some(old_child) = old_child_map.remove(new_child.name.as_str()) {
@@ -225,6 +246,12 @@ pub fn syncback_dir_no_meta<'sync>(
 mod test {
     use super::*;
 
+    use std::path::PathBuf;
+
+    use crate::{
+        snapshot::{InstanceMetadata, InstanceSnapshot},
+        Project, RojoTree, SyncbackData, SyncbackSnapshot,
+    };
     use memofs::{InMemoryFs, VfsSnapshot};
 
     #[test]
@@ -261,4 +288,237 @@ mod test {
 
         insta::assert_yaml_snapshot!(instance_snapshot);
     }
+
+    fn make_project() -> Project {
+        serde_json::from_str(r#"{"tree": {"$className": "DataModel"}}"#).unwrap()
+    }
+
+    fn make_vfs() -> Vfs {
+        let mut imfs = InMemoryFs::new();
+        imfs.load_snapshot("/root", VfsSnapshot::empty_dir()).unwrap();
+        Vfs::new(imfs)
+    }
+
+    /// Two children whose Roblox names are identical when lowercased ("Alpha"
+    /// and "alpha") but live at different filesystem paths because of the
+    /// `name` property ("Beta/" and "Alpha/" respectively). The dedup check
+    /// must use the actual filesystem paths, not the raw Roblox names, to
+    /// avoid a false-positive duplicate error.
+    #[test]
+    fn syncback_no_false_duplicate_with_name_prop() {
+        use rbx_dom_weak::{InstanceBuilder, WeakDom};
+
+        // Old child A: Roblox name "Alpha", on disk at "/root/Beta"
+        //   (name property maps "Alpha" → "Beta" on the filesystem)
+        let old_child_a = InstanceSnapshot::new()
+            .name("Alpha")
+            .class_name("Folder")
+            .metadata(
+                InstanceMetadata::new()
+                    .instigating_source(PathBuf::from("/root/Beta"))
+                    .relevant_paths(vec![PathBuf::from("/root/Beta")]),
+            );
+        // Old child B: Roblox name "alpha", on disk at "/root/Alpha"
+        let old_child_b = InstanceSnapshot::new()
+            .name("alpha")
+            .class_name("Folder")
+            .metadata(
+                InstanceMetadata::new()
+                    .instigating_source(PathBuf::from("/root/Alpha"))
+                    .relevant_paths(vec![PathBuf::from("/root/Alpha")]),
+            );
+        let old_parent = InstanceSnapshot::new()
+            .name("Parent")
+            .class_name("Folder")
+            .children(vec![old_child_a, old_child_b])
+            .metadata(
+                InstanceMetadata::new()
+                    .instigating_source(PathBuf::from("/root"))
+                    .relevant_paths(vec![PathBuf::from("/root")]),
+            );
+        let old_tree = RojoTree::new(old_parent);
+
+        // New state: same two children in Roblox.
+        let mut new_tree = WeakDom::new(InstanceBuilder::new("ROOT"));
+        let new_parent = new_tree.insert(
+            new_tree.root_ref(),
+            InstanceBuilder::new("Folder").with_name("Parent"),
+        );
+        new_tree.insert(new_parent, InstanceBuilder::new("Folder").with_name("Alpha"));
+        new_tree.insert(new_parent, InstanceBuilder::new("Folder").with_name("alpha"));
+
+        let vfs = make_vfs();
+        let project = make_project();
+        let data = SyncbackData::for_test(&vfs, &old_tree, &new_tree, &project);
+        let snapshot = SyncbackSnapshot {
+            data,
+            old: Some(old_tree.get_root_id()),
+            new: new_parent,
+            path: PathBuf::from("/root"),
+            middleware: None,
+        };
+
+        let result = syncback_dir_no_meta(&snapshot);
+        assert!(
+            result.is_ok(),
+            "should not error when two children have the same lowercased Roblox \
+             name but map to distinct filesystem paths: {result:?}",
+        );
+    }
+
+    /// Two completely new children with the same non-init name would produce
+    /// the same filesystem entry and must be detected as a duplicate.
+    #[test]
+    fn syncback_detects_sibling_duplicate_names() {
+        use rbx_dom_weak::{InstanceBuilder, WeakDom};
+
+        let old_parent = InstanceSnapshot::new()
+            .name("Parent")
+            .class_name("Folder")
+            .metadata(
+                InstanceMetadata::new()
+                    .instigating_source(PathBuf::from("/root"))
+                    .relevant_paths(vec![PathBuf::from("/root")]),
+            );
+        let old_tree = RojoTree::new(old_parent);
+
+        let mut new_tree = WeakDom::new(InstanceBuilder::new("ROOT"));
+        let new_parent = new_tree.insert(
+            new_tree.root_ref(),
+            InstanceBuilder::new("Folder").with_name("Parent"),
+        );
+        // "Foo" is not a reserved name but two siblings named "Foo" still
+        // collide on disk.
+        new_tree.insert(new_parent, InstanceBuilder::new("Folder").with_name("Foo"));
+        new_tree.insert(new_parent, InstanceBuilder::new("Folder").with_name("Foo"));
+
+        let vfs = make_vfs();
+        let project = make_project();
+        let data = SyncbackData::for_test(&vfs, &old_tree, &new_tree, &project);
+        let snapshot = SyncbackSnapshot {
+            data,
+            old: Some(old_tree.get_root_id()),
+            new: new_parent,
+            path: PathBuf::from("/root"),
+            middleware: None,
+        };
+
+        let result = syncback_dir_no_meta(&snapshot);
+        assert!(
+            result.is_err(),
+            "should error when two new children would produce the same filesystem name",
+        );
+    }
+
+    /// A new child named "Init" (as a ModuleScript) would naively become
+    /// "Init.luau", which case-insensitively matches the parent's reserved
+    /// "init.luau". Syncback must resolve this automatically by prefixing the
+    /// filesystem name with '_' (→ "_Init.luau") rather than erroring.
+    #[test]
+    fn syncback_resolves_init_name_conflict() {
+        use rbx_dom_weak::{InstanceBuilder, WeakDom};
+
+        let old_parent = InstanceSnapshot::new()
+            .name("Parent")
+            .class_name("Folder")
+            .metadata(
+                InstanceMetadata::new()
+                    .instigating_source(PathBuf::from("/root"))
+                    .relevant_paths(vec![PathBuf::from("/root")]),
+            );
+        let old_tree = RojoTree::new(old_parent);
+
+        let mut new_tree = WeakDom::new(InstanceBuilder::new("ROOT"));
+        let new_parent = new_tree.insert(
+            new_tree.root_ref(),
+            InstanceBuilder::new("Folder").with_name("Parent"),
+        );
+        new_tree.insert(
+            new_parent,
+            InstanceBuilder::new("ModuleScript").with_name("Init"),
+        );
+
+        let vfs = make_vfs();
+        let project = make_project();
+        let data = SyncbackData::for_test(&vfs, &old_tree, &new_tree, &project);
+        let snapshot = SyncbackSnapshot {
+            data,
+            old: Some(old_tree.get_root_id()),
+            new: new_parent,
+            path: PathBuf::from("/root"),
+            middleware: None,
+        };
+
+        let result = syncback_dir_no_meta(&snapshot);
+        assert!(
+            result.is_ok(),
+            "should resolve init-name conflict by prefixing '_', not error: {result:?}",
+        );
+        // The child should have been placed at "_Init.luau", not "Init.luau".
+        let child_file_name = result
+            .unwrap()
+            .children
+            .into_iter()
+            .next()
+            .and_then(|c| c.path.file_name().map(|n| n.to_string_lossy().into_owned()))
+            .unwrap_or_default();
+        assert!(
+            child_file_name.starts_with('_'),
+            "child filesystem name should start with '_' to avoid init collision, \
+             got: {child_file_name}",
+        );
+    }
+
+    /// A child whose filesystem name is stored with a slugified prefix (e.g.
+    /// "_Init") must NOT be blocked — only the bare "init" stem is reserved.
+    #[test]
+    fn syncback_allows_slugified_init_name() {
+        use rbx_dom_weak::{InstanceBuilder, WeakDom};
+
+        // Existing child: on disk as "_Init" (slugified from a name with an
+        // illegal character), its stem is "_init" which is not reserved.
+        let old_child = InstanceSnapshot::new()
+            .name("Init")
+            .class_name("Folder")
+            .metadata(
+                InstanceMetadata::new()
+                    .instigating_source(PathBuf::from("/root/_Init"))
+                    .relevant_paths(vec![PathBuf::from("/root/_Init")]),
+            );
+        let old_parent = InstanceSnapshot::new()
+            .name("Parent")
+            .class_name("Folder")
+            .children(vec![old_child])
+            .metadata(
+                InstanceMetadata::new()
+                    .instigating_source(PathBuf::from("/root"))
+                    .relevant_paths(vec![PathBuf::from("/root")]),
+            );
+        let old_tree = RojoTree::new(old_parent);
+
+        let mut new_tree = WeakDom::new(InstanceBuilder::new("ROOT"));
+        let new_parent = new_tree.insert(
+            new_tree.root_ref(),
+            InstanceBuilder::new("Folder").with_name("Parent"),
+        );
+        new_tree.insert(new_parent, InstanceBuilder::new("Folder").with_name("Init"));
+
+        let vfs = make_vfs();
+        let project = make_project();
+        let data = SyncbackData::for_test(&vfs, &old_tree, &new_tree, &project);
+        let snapshot = SyncbackSnapshot {
+            data,
+            old: Some(old_tree.get_root_id()),
+            new: new_parent,
+            path: PathBuf::from("/root"),
+            middleware: None,
+        };
+
+        let result = syncback_dir_no_meta(&snapshot);
+        assert!(
+            result.is_ok(),
+            "should allow a child whose filesystem name is slugified away from \
+             the reserved 'init' stem: {result:?}",
+        );
+    }
 }

src/snapshot_middleware/json_model.rs

@@ -35,20 +35,14 @@ pub fn snapshot_json_model(
         format!("File is not a valid JSON model: {}", path.display())
     })?;
 
-    if let Some(top_level_name) = &instance.name {
-        let new_name = format!("{}.model.json", top_level_name);
+    // If the JSON has a name property, preserve it in metadata for syncback
+    let specified_name = instance.name.clone();
 
-        log::warn!(
-            "Model at path {} had a top-level Name field. \
-            This field has been ignored since Rojo 6.0.\n\
-            Consider removing this field and renaming the file to {}.",
-            new_name,
-            path.display()
-        );
+    // Use the name from JSON if present, otherwise fall back to filename-derived name
+    if instance.name.is_none() {
+        instance.name = Some(name.to_owned());
     }
 
-    instance.name = Some(name.to_owned());
-
     let id = instance.id.take().map(RojoRef::new);
     let schema = instance.schema.take();
 
@@ -62,7 +56,8 @@ pub fn snapshot_json_model(
         .relevant_paths(vec![vfs.canonicalize(path)?])
         .context(context)
         .specified_id(id)
-        .schema(schema);
+        .schema(schema)
+        .specified_name(specified_name);
 
     Ok(Some(snapshot))
 }
@@ -81,6 +76,7 @@ pub fn syncback_json_model<'sync>(
         // schemas will ever exist in one project for it to matter, but it
         // could have a performance cost.
         model.schema = old_inst.metadata().schema.clone();
+        model.name = old_inst.metadata().specified_name.clone();
     }
 
     Ok(SyncbackReturn {

src/snapshot_middleware/lua.rs

@@ -158,8 +158,29 @@ pub fn syncback_lua<'sync>(
 
         if !meta.is_empty() {
             let parent_location = snapshot.path.parent_err()?;
+            let meta_stem = snapshot.middleware
+                .and_then(|mw| {
+                    let ext = format!(".{}", crate::syncback::extension_for_middleware(mw));
+                    snapshot.path.file_name()
+                        .and_then(|n| n.to_str())
+                        .and_then(|s| s.strip_suffix(ext.as_str()))
+                        .map(str::to_owned)
+                })
+                .unwrap_or_else(|| {
+                    let name = &snapshot.new_inst().name;
+                    let base = if crate::syncback::validate_file_name(name).is_err() {
+                        crate::syncback::slugify_name(name)
+                    } else {
+                        name.clone()
+                    };
+                    if base.to_lowercase() == "init" {
+                        format!("_{base}")
+                    } else {
+                        base
+                    }
+                });
             fs_snapshot.add_file(
-                parent_location.join(format!("{}.meta.json", new_inst.name)),
+                parent_location.join(format!("{meta_stem}.meta.json")),
                 serde_json::to_vec_pretty(&meta).context("cannot serialize metadata")?,
             );
         }

src/snapshot_middleware/meta_file.rs

@@ -10,7 +10,10 @@ use rbx_dom_weak::{
 use serde::{Deserialize, Serialize};
 
 use crate::{
-    json, resolution::UnresolvedValue, snapshot::InstanceSnapshot, syncback::SyncbackSnapshot,
+    json,
+    resolution::UnresolvedValue,
+    snapshot::InstanceSnapshot,
+    syncback::{validate_file_name, SyncbackSnapshot},
     RojoRef,
 };
 
@@ -36,6 +39,9 @@ pub struct AdjacentMetadata {
     #[serde(default, skip_serializing_if = "IndexMap::is_empty")]
     pub attributes: IndexMap<String, UnresolvedValue>,
 
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub name: Option<String>,
+
     #[serde(skip)]
     pub path: PathBuf,
 }
@@ -144,6 +150,26 @@ impl AdjacentMetadata {
             }
         }
 
+        let name = snapshot
+            .old_inst()
+            .and_then(|inst| inst.metadata().specified_name.clone())
+            .or_else(|| {
+                // Write name when name_for_inst would produce a different
+                // filesystem stem (slugification or init-prefix).
+                if snapshot.old_inst().is_none() {
+                    let instance_name = &snapshot.new_inst().name;
+                    if validate_file_name(instance_name).is_err()
+                        || instance_name.to_lowercase() == "init"
+                    {
+                        Some(instance_name.clone())
+                    } else {
+                        None
+                    }
+                } else {
+                    None
+                }
+            });
+
         Ok(Some(Self {
             ignore_unknown_instances: if ignore_unknown_instances {
                 Some(true)
@@ -155,6 +181,7 @@ impl AdjacentMetadata {
             path,
             id: None,
             schema,
+            name,
         }))
     }
 
@@ -213,11 +240,26 @@ impl AdjacentMetadata {
         Ok(())
     }
 
+    fn apply_name(&mut self, snapshot: &mut InstanceSnapshot) -> anyhow::Result<()> {
+        if self.name.is_some() && snapshot.metadata.specified_name.is_some() {
+            anyhow::bail!(
+                "cannot specify a name using {} (instance has a name from somewhere else)",
+                self.path.display()
+            );
+        }
+        if let Some(name) = &self.name {
+            snapshot.name = name.clone().into();
+        }
+        snapshot.metadata.specified_name = self.name.take();
+        Ok(())
+    }
+
     pub fn apply_all(&mut self, snapshot: &mut InstanceSnapshot) -> anyhow::Result<()> {
         self.apply_ignore_unknown_instances(snapshot);
         self.apply_properties(snapshot)?;
         self.apply_id(snapshot)?;
         self.apply_schema(snapshot)?;
+        self.apply_name(snapshot)?;
         Ok(())
     }
 
@@ -226,11 +268,13 @@ impl AdjacentMetadata {
     ///
     /// - The number of properties and attributes is 0
     /// - `ignore_unknown_instances` is None
+    /// - `name` is None
     #[inline]
     pub fn is_empty(&self) -> bool {
         self.attributes.is_empty()
             && self.properties.is_empty()
             && self.ignore_unknown_instances.is_none()
+            && self.name.is_none()
     }
 
     // TODO: Add method to allow selectively applying parts of metadata and
@@ -262,6 +306,9 @@ pub struct DirectoryMetadata {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub class_name: Option<Ustr>,
 
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub name: Option<String>,
+
     #[serde(skip)]
     pub path: PathBuf,
 }
@@ -372,6 +419,26 @@ impl DirectoryMetadata {
             }
         }
 
+        let name = snapshot
+            .old_inst()
+            .and_then(|inst| inst.metadata().specified_name.clone())
+            .or_else(|| {
+                // Write name when name_for_inst would produce a different
+                // directory name (slugification or init-prefix).
+                if snapshot.old_inst().is_none() {
+                    let instance_name = &snapshot.new_inst().name;
+                    if validate_file_name(instance_name).is_err()
+                        || instance_name.to_lowercase() == "init"
+                    {
+                        Some(instance_name.clone())
+                    } else {
+                        None
+                    }
+                } else {
+                    None
+                }
+            });
+
         Ok(Some(Self {
             ignore_unknown_instances: if ignore_unknown_instances {
                 Some(true)
@@ -384,6 +451,7 @@ impl DirectoryMetadata {
             path,
             id: None,
             schema,
+            name,
         }))
     }
 
@@ -393,6 +461,7 @@ impl DirectoryMetadata {
         self.apply_properties(snapshot)?;
         self.apply_id(snapshot)?;
         self.apply_schema(snapshot)?;
+        self.apply_name(snapshot)?;
 
         Ok(())
     }
@@ -464,17 +533,33 @@ impl DirectoryMetadata {
         snapshot.metadata.schema = self.schema.take();
         Ok(())
     }
+
+    fn apply_name(&mut self, snapshot: &mut InstanceSnapshot) -> anyhow::Result<()> {
+        if self.name.is_some() && snapshot.metadata.specified_name.is_some() {
+            anyhow::bail!(
+                "cannot specify a name using {} (instance has a name from somewhere else)",
+                self.path.display()
+            );
+        }
+        if let Some(name) = &self.name {
+            snapshot.name = name.clone().into();
+        }
+        snapshot.metadata.specified_name = self.name.take();
+        Ok(())
+    }
     /// Returns whether the metadata is 'empty', meaning it doesn't have anything
     /// worth persisting in it. Specifically:
     ///
     /// - The number of properties and attributes is 0
     /// - `ignore_unknown_instances` is None
     /// - `class_name` is either None or not Some("Folder")
+    /// - `name` is None
     #[inline]
     pub fn is_empty(&self) -> bool {
         self.attributes.is_empty()
             && self.properties.is_empty()
             && self.ignore_unknown_instances.is_none()
+            && self.name.is_none()
             && if let Some(class) = &self.class_name {
                 class == "Folder"
             } else {

src/snapshot_middleware/mod.rs

@@ -61,6 +61,10 @@ pub use self::{
 /// This will inspect the path and find the appropriate middleware for it,
 /// taking user-written rules into account. Then, it will attempt to convert
 /// the path into an InstanceSnapshot using that middleware.
+///
+/// If a git filter is active in the context and the path is not acknowledged
+/// (i.e., the file hasn't changed since the base git reference), this function
+/// returns `Ok(None)` to skip syncing that file.
 #[profiling::function]
 pub fn snapshot_from_vfs(
     context: &InstanceContext,
@@ -72,6 +76,16 @@ pub fn snapshot_from_vfs(
         None => return Ok(None),
     };
 
+    // Check if this path is acknowledged by the git filter.
+    // If not, skip this path entirely.
+    if !context.is_path_acknowledged(path) {
+        log::trace!(
+            "Skipping path {} (not acknowledged by git filter)",
+            path.display()
+        );
+        return Ok(None);
+    }
+
     if meta.is_dir() {
         let (middleware, dir_name, init_path) = get_dir_middleware(vfs, path)?;
         // TODO: Support user defined init paths
@@ -213,6 +227,10 @@ pub enum Middleware {
 impl Middleware {
     /// Creates a snapshot for the given path from the Middleware with
     /// the provided name.
+    ///
+    /// When a git filter is active in the context, `ignore_unknown_instances`
+    /// will be set to `true` on all generated snapshots to preserve descendants
+    /// in Studio that are not tracked by Rojo.
     fn snapshot(
         &self,
         context: &InstanceContext,
@@ -262,6 +280,14 @@ impl Middleware {
         };
         if let Ok(Some(ref mut snapshot)) = output {
             snapshot.metadata.middleware = Some(*self);
+
+            // When git filter is active, force ignore_unknown_instances to true
+            // so that we don't delete children in Studio that aren't tracked.
+            if context.has_git_filter() {
+                snapshot.metadata.ignore_unknown_instances = true;
+                // Also apply this recursively to all children
+                set_ignore_unknown_instances_recursive(&mut snapshot.children);
+            }
         }
         output
     }
@@ -365,6 +391,16 @@ impl Middleware {
     }
 }
 
+/// Recursively sets `ignore_unknown_instances` to `true` on all children.
+/// This is used when git filter is active to ensure we don't delete
+/// children in Studio that aren't tracked by Rojo.
+fn set_ignore_unknown_instances_recursive(children: &mut [InstanceSnapshot]) {
+    for child in children {
+        child.metadata.ignore_unknown_instances = true;
+        set_ignore_unknown_instances_recursive(&mut child.children);
+    }
+}
+
 /// A helper for easily defining a SyncRule. Arguments are passed literally
 /// to this macro in the order `include`, `middleware`, `suffix`,
 /// and `exclude`. Both `suffix` and `exclude` are optional.

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);
+            }
         }
     }
 
@@ -192,6 +225,17 @@ pub fn snapshot_project_node(
         }
 
         (_, None, _, Some(PathNode::Required(path))) => {
+            // If git filter is active and the path was filtered out, treat it
+            // as if the path was optional and skip this node.
+            if context.has_git_filter() {
+                log::trace!(
+                    "Skipping project node '{}' because its path was filtered by git filter: {}",
+                    instance_name,
+                    path.display()
+                );
+                return Ok(None);
+            }
+
             anyhow::bail!(
                 "Rojo project referred to a file using $path that could not be turned into a Roblox Instance by Rojo.\n\
                 Check that the file exists and is a file type known by Rojo.\n\
@@ -282,7 +326,12 @@ pub fn snapshot_project_node(
     // If the user didn't specify it AND $path was not specified (meaning
     // there's no existing value we'd be stepping on from a project file or meta
     // file), set it to true.
-    if let Some(ignore) = node.ignore_unknown_instances {
+    //
+    // When git filter is active, always set to true to preserve descendants
+    // in Studio that are not tracked by Rojo.
+    if context.has_git_filter() {
+        metadata.ignore_unknown_instances = true;
+    } else if let Some(ignore) = node.ignore_unknown_instances {
         metadata.ignore_unknown_instances = ignore;
     } else if node.path.is_none() {
         // TODO: Introduce a strict mode where $ignoreUnknownInstances is never

src/snapshot_middleware/txt.rs

@@ -58,8 +58,29 @@ pub fn syncback_txt<'sync>(
 
         if !meta.is_empty() {
             let parent = snapshot.path.parent_err()?;
+            let meta_stem = snapshot.middleware
+                .and_then(|mw| {
+                    let ext = format!(".{}", crate::syncback::extension_for_middleware(mw));
+                    snapshot.path.file_name()
+                        .and_then(|n| n.to_str())
+                        .and_then(|s| s.strip_suffix(ext.as_str()))
+                        .map(str::to_owned)
+                })
+                .unwrap_or_else(|| {
+                    let name = &new_inst.name;
+                    let base = if crate::syncback::validate_file_name(name).is_err() {
+                        crate::syncback::slugify_name(name)
+                    } else {
+                        name.clone()
+                    };
+                    if base.to_lowercase() == "init" {
+                        format!("_{base}")
+                    } else {
+                        base
+                    }
+                });
             fs_snapshot.add_file(
-                parent.join(format!("{}.meta.json", new_inst.name)),
+                parent.join(format!("{meta_stem}.meta.json")),
                 serde_json::to_vec_pretty(&meta).context("could not serialize metadata")?,
             );
         }

src/syncback/file_names.rs

@@ -8,11 +8,11 @@ use rbx_dom_weak::Instance;
 
 use crate::{snapshot::InstanceWithMeta, snapshot_middleware::Middleware};
 
-pub fn name_for_inst<'old>(
+pub fn name_for_inst<'a>(
     middleware: Middleware,
-    new_inst: &Instance,
-    old_inst: Option<InstanceWithMeta<'old>>,
-) -> anyhow::Result<Cow<'old, str>> {
+    new_inst: &'a Instance,
+    old_inst: Option<InstanceWithMeta<'a>>,
+) -> anyhow::Result<Cow<'a, str>> {
     if let Some(old_inst) = old_inst {
         if let Some(source) = old_inst.metadata().relevant_paths.first() {
             source
@@ -35,14 +35,34 @@ pub fn name_for_inst<'old>(
             | Middleware::CsvDir
             | Middleware::ServerScriptDir
             | Middleware::ClientScriptDir
-            | Middleware::ModuleScriptDir => Cow::Owned(new_inst.name.clone()),
+            | Middleware::ModuleScriptDir => {
+                let name = if validate_file_name(&new_inst.name).is_err() {
+                    Cow::Owned(slugify_name(&new_inst.name))
+                } else {
+                    Cow::Borrowed(new_inst.name.as_str())
+                };
+                // Prefix "init" to avoid colliding with reserved init files.
+                if name.to_lowercase() == "init" {
+                    Cow::Owned(format!("_{name}"))
+                } else {
+                    name
+                }
+            }
             _ => {
                 let extension = extension_for_middleware(middleware);
-                let name = &new_inst.name;
-                validate_file_name(name).with_context(|| {
-                    format!("name '{name}' is not legal to write to the file system")
-                })?;
-                Cow::Owned(format!("{name}.{extension}"))
+                let slugified;
+                let stem: &str = if validate_file_name(&new_inst.name).is_err() {
+                    slugified = slugify_name(&new_inst.name);
+                    &slugified
+                } else {
+                    &new_inst.name
+                };
+                // Prefix "init" stems to avoid colliding with reserved init files.
+                if stem.to_lowercase() == "init" {
+                    Cow::Owned(format!("_{stem}.{extension}"))
+                } else {
+                    Cow::Owned(format!("{stem}.{extension}"))
+                }
             }
         })
     }
@@ -94,6 +114,39 @@ const INVALID_WINDOWS_NAMES: [&str; 22] = [
 /// in a file's name.
 const FORBIDDEN_CHARS: [char; 9] = ['<', '>', ':', '"', '/', '|', '?', '*', '\\'];
 
+/// Slugifies a name by replacing forbidden characters with underscores
+/// and ensuring the result is a valid file name
+pub fn slugify_name(name: &str) -> String {
+    let mut result = String::with_capacity(name.len());
+
+    for ch in name.chars() {
+        if FORBIDDEN_CHARS.contains(&ch) {
+            result.push('_');
+        } else {
+            result.push(ch);
+        }
+    }
+
+    // Handle Windows reserved names by appending an underscore
+    let result_lower = result.to_lowercase();
+    for forbidden in INVALID_WINDOWS_NAMES {
+        if result_lower == forbidden.to_lowercase() {
+            result.push('_');
+            break;
+        }
+    }
+
+    while result.ends_with(' ') || result.ends_with('.') {
+        result.pop();
+    }
+
+    if result.is_empty() || result.chars().all(|c| c == '_') {
+        result = "instance".to_string();
+    }
+
+    result
+}
+
 /// Validates a provided file name to ensure it's allowed on the file system. An
 /// error is returned if the name isn't allowed, indicating why.
 /// This takes into account rules for Windows, MacOS, and Linux.

src/syncback/mod.rs

@@ -28,7 +28,7 @@ use crate::{
     Project,
 };
 
-pub use file_names::{extension_for_middleware, name_for_inst, validate_file_name};
+pub use file_names::{extension_for_middleware, name_for_inst, slugify_name, validate_file_name};
 pub use fs_snapshot::FsSnapshot;
 pub use hash::*;
 pub use property_filter::{filter_properties, filter_properties_preallocated};
@@ -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());
 
@@ -237,6 +238,24 @@ pub fn inst_path(dom: &WeakDom, referent: Ref) -> String {
     path.join("/")
 }
 
+impl<'sync> SyncbackData<'sync> {
+    /// Constructs a `SyncbackData` for use in unit tests.
+    #[cfg(test)]
+    pub fn for_test(
+        vfs: &'sync Vfs,
+        old_tree: &'sync RojoTree,
+        new_tree: &'sync WeakDom,
+        project: &'sync Project,
+    ) -> Self {
+        Self {
+            vfs,
+            old_tree,
+            new_tree,
+            project,
+        }
+    }
+}
+
 #[cfg(test)]
 mod test {
     use rbx_dom_weak::{InstanceBuilder, WeakDom};

tests/tests/build.rs

@@ -41,7 +41,6 @@ gen_build_tests! {
     issue_546,
     json_as_lua,
     json_model_in_folder,
-    json_model_legacy_name,
     module_in_folder,
     module_init,
     nested_runcontext,
@@ -55,6 +54,8 @@ gen_build_tests! {
     script_meta_disabled,
     server_in_folder,
     server_init,
+    slugified_name_roundtrip,
+    model_json_name_input,
     txt,
     txt_in_folder,
     unresolved_values,

tests/tests/syncback.rs

@@ -86,4 +86,9 @@ syncback_tests! {
     sync_rules => ["src/module.modulescript", "src/text.text"],
     // Ensures that the `syncUnscriptable` setting works
     unscriptable_properties => ["default.project.json"],
+    // Ensures that instances with names containing illegal characters get slugified filenames
+    // and preserve their original names in meta.json without forcing directories for leaf scripts
+    slugified_name => ["src/_Script.meta.json", "src/_Script.server.luau", "src/_Folder/init.meta.json"],
+    // Ensures that .model.json files preserve the name property
+    model_json_name => ["src/foo.model.json"],
 }