fix: more work on metadata-diff

specs/frontmatter.allium

@@ -88,7 +88,6 @@ config {
 
 value PostFrontmatter {
     -- File path: posts/{YYYY}/{MM}/{slug}.md
-    -- For translations: posts/{YYYY}/{MM}/{slug}.{language}.md
     id: String              -- UUID v4
     title: String
     slug: String
@@ -105,6 +104,29 @@ value PostFrontmatter {
     categories: List<String> -- Always written, even if empty
 }
 
+value TranslationFrontmatter {
+    -- File path: posts/{YYYY}/{MM}/{slug}.{language}.md
+    -- Translation files only store language-specific metadata.
+    -- Shared publication state and timestamps are inherited from the
+    -- canonical post file and are not duplicated here.
+    id: String              -- UUID v4
+    translation_for: String -- Canonical post UUID
+    language: String        -- ISO 639-1 language code
+    title: String           -- Translated title
+    excerpt: String?        -- Only written when the translated excerpt differs
+}
+
+surface TranslationFrontmatterSurface {
+    context frontmatter: TranslationFrontmatter
+
+    exposes:
+        frontmatter.id
+        frontmatter.translation_for
+        frontmatter.language
+        frontmatter.title
+        frontmatter.excerpt when frontmatter.excerpt != null
+}
+
 invariant PostFileLayout {
     -- Posts are stored in date-based directory structure
     -- YYYY and MM derived from created_at (zero-padded)
@@ -125,6 +147,13 @@ invariant PostTranslationFileLayout {
             lang: t.language)
 }
 
+invariant TranslationFilesInheritCanonicalMetadata {
+    -- Missing status and timestamp fields in translation files are expected.
+    -- Rebuild and metadata diff must resolve those values from the canonical post.
+    for t in PostTranslations where file_path != "":
+        parse_frontmatter(read_file(t.file_path)) = translation_frontmatter_fields(t)
+}
+
 rule WritePostFile {
     when: PublishPostRequested(post)
     ensures: FileWritten(

specs/metadata_diff.allium

@@ -46,6 +46,20 @@ rule RunMetadataDiff {
         if diffs.count > 0:
             ensures: DiffReport.created(entity_type: "post", entity_id: post.id, differences: diffs)
 
+    -- Translation files only carry language-specific metadata. Shared status and
+    -- timestamp fields come from the canonical post and must not be reported as
+    -- missing when they are absent from the translation file.
+    for translation in project.post_translations:
+        let translation_file_data = parse_post_file(translation.file_path)
+        let translation_diffs = compare_translation_specific_fields(translation, translation_file_data)
+        if translation_diffs.count > 0:
+            ensures:
+                DiffReport.created(
+                    entity_type: "post_translation",
+                    entity_id: translation.id,
+                    differences: translation_diffs
+                )
+
     -- Detect orphan files (on disk but not in DB)
     for file in scan_directory(project.effective_data_dir + "/posts", "*.md"):
         let matching = Posts where file_path = file

specs/translation.allium

@@ -64,6 +64,15 @@ entity PostTranslation {
     }
 }
 
+invariant TranslationFilesStoreOnlyLanguageSpecificMetadata {
+    -- Translation markdown files persist only fields that differ by language.
+    -- Shared metadata such as publication status and timestamps belongs to the
+    -- canonical post file and is inherited from the canonical post when
+    -- rebuilding or diffing translation files.
+    for t in PostTranslations where file_path != "":
+        translation_file(t).omits_shared_metadata = true
+}
+
 surface PostTranslationSurface {
     context translation: PostTranslation