fix: handle dotted names and .lua extension in meta path + name check

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>

src/snapshot_middleware/csv.rs

@@ -117,7 +117,19 @@ pub fn syncback_csv<'sync>(
                         .and_then(|s| s.strip_suffix(ext.as_str()))
                         .map(str::to_owned)
                 })
-                .unwrap_or_else(|| new_inst.name.clone());
+                .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_stem}.meta.json")),
                 serde_json::to_vec_pretty(&meta).context("cannot serialize metadata")?,

src/snapshot_middleware/lua.rs

@@ -166,7 +166,19 @@ pub fn syncback_lua<'sync>(
                         .and_then(|s| s.strip_suffix(ext.as_str()))
                         .map(str::to_owned)
                 })
-                .unwrap_or_else(|| snapshot.new_inst().name.clone());
+                .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_stem}.meta.json")),
                 serde_json::to_vec_pretty(&meta).context("cannot serialize metadata")?,

src/snapshot_middleware/meta_file.rs

@@ -154,17 +154,12 @@ impl AdjacentMetadata {
             .old_inst()
             .and_then(|inst| inst.metadata().specified_name.clone())
             .or_else(|| {
-                // Write name when the filesystem path doesn't match the
+                // Write name when name_for_inst would produce a different
-                // instance name (invalid chars or init-prefix).
+                // filesystem stem (slugification or init-prefix).
                 if snapshot.old_inst().is_none() {
                     let instance_name = &snapshot.new_inst().name;
-                    let fs_stem = path
-                        .file_name()
-                        .and_then(|n| n.to_str())
-                        .map(|s| s.split('.').next().unwrap_or(s))
-                        .unwrap_or("");
                     if validate_file_name(instance_name).is_err()
-                        || fs_stem != instance_name.as_str()
+                        || instance_name.to_lowercase() == "init"
                     {
                         Some(instance_name.clone())
                     } else {
@@ -428,16 +423,12 @@ impl DirectoryMetadata {
             .old_inst()
             .and_then(|inst| inst.metadata().specified_name.clone())
             .or_else(|| {
-                // Write name when the directory name doesn't match the
+                // Write name when name_for_inst would produce a different
-                // instance name (invalid chars or init-prefix).
+                // directory name (slugification or init-prefix).
                 if snapshot.old_inst().is_none() {
                     let instance_name = &snapshot.new_inst().name;
-                    let fs_name = path
-                        .file_name()
-                        .and_then(|n| n.to_str())
-                        .unwrap_or("");
                     if validate_file_name(instance_name).is_err()
-                        || fs_name != instance_name.as_str()
+                        || instance_name.to_lowercase() == "init"
                     {
                         Some(instance_name.clone())
                     } else {

src/snapshot_middleware/txt.rs

@@ -66,7 +66,19 @@ pub fn syncback_txt<'sync>(
                         .and_then(|s| s.strip_suffix(ext.as_str()))
                         .map(str::to_owned)
                 })
-                .unwrap_or_else(|| new_inst.name.clone());
+                .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_stem}.meta.json")),
                 serde_json::to_vec_pretty(&meta).context("could not serialize metadata")?,