diff --git a/Cargo.lock b/Cargo.lock
index adf0548..cd6219d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -938,6 +938,7 @@ dependencies = [
  "libsqlite3-sys",
  "liquid",
  "liquid-core",
+ "md5",
  "mlua",
  "ort",
  "pagefind",
@@ -1021,7 +1022,6 @@ dependencies = [
  "iced",
  "muda",
  "objc2 0.6.4",
- "objc2-app-kit 0.3.2",
  "objc2-foundation 0.3.2",
  "open",
  "regex",
@@ -6129,8 +6129,8 @@ dependencies = [
  "block2 0.5.1",
  "libc",
  "objc2 0.5.2",
- "objc2-core-data 0.2.2",
- "objc2-core-image 0.2.2",
+ "objc2-core-data",
+ "objc2-core-image",
  "objc2-foundation 0.2.2",
  "objc2-quartz-core 0.2.2",
 ]
@@ -6143,17 +6143,9 @@ checksum = "d49e936b501e5c5bf01fda3a9452ff86dc3ea98ad5f283e1455153142d97518c"
 dependencies = [
  "bitflags 2.13.1",
  "block2 0.6.2",
- "libc",
  "objc2 0.6.4",
- "objc2-cloud-kit 0.3.2",
- "objc2-core-data 0.3.2",
  "objc2-core-foundation",
- "objc2-core-graphics",
- "objc2-core-image 0.3.2",
- "objc2-core-text",
- "objc2-core-video",
  "objc2-foundation 0.3.2",
- "objc2-quartz-core 0.3.2",
 ]
 
 [[package]]
@@ -6169,17 +6161,6 @@ dependencies = [
  "objc2-foundation 0.2.2",
 ]
 
-[[package]]
-name = "objc2-cloud-kit"
-version = "0.3.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "73ad74d880bb43877038da939b7427bba67e9dd42004a18b809ba7d87cee241c"
-dependencies = [
- "bitflags 2.13.1",
- "objc2 0.6.4",
- "objc2-foundation 0.3.2",
-]
-
 [[package]]
 name = "objc2-contacts"
 version = "0.2.2"
@@ -6203,17 +6184,6 @@ dependencies = [
  "objc2-foundation 0.2.2",
 ]
 
-[[package]]
-name = "objc2-core-data"
-version = "0.3.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0b402a653efbb5e82ce4df10683b6b28027616a2715e90009947d50b8dd298fa"
-dependencies = [
- "bitflags 2.13.1",
- "objc2 0.6.4",
- "objc2-foundation 0.3.2",
-]
-
 [[package]]
 name = "objc2-core-foundation"
 version = "0.3.2"
@@ -6250,16 +6220,6 @@ dependencies = [
  "objc2-metal",
 ]
 
-[[package]]
-name = "objc2-core-image"
-version = "0.3.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e5d563b38d2b97209f8e861173de434bd0214cf020e3423a52624cd1d989f006"
-dependencies = [
- "objc2 0.6.4",
- "objc2-foundation 0.3.2",
-]
-
 [[package]]
 name = "objc2-core-location"
 version = "0.2.2"
@@ -6284,31 +6244,6 @@ dependencies = [
  "objc2-security",
 ]
 
-[[package]]
-name = "objc2-core-text"
-version = "0.3.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0cde0dfb48d25d2b4862161a4d5fcc0e3c24367869ad306b0c9ec0073bfed92d"
-dependencies = [
- "bitflags 2.13.1",
- "objc2 0.6.4",
- "objc2-core-foundation",
- "objc2-core-graphics",
-]
-
-[[package]]
-name = "objc2-core-video"
-version = "0.3.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d425caf1df73233f29fd8a5c3e5edbc30d2d4307870f802d18f00d83dc5141a6"
-dependencies = [
- "bitflags 2.13.1",
- "objc2 0.6.4",
- "objc2-core-foundation",
- "objc2-core-graphics",
- "objc2-io-surface",
-]
-
 [[package]]
 name = "objc2-encode"
 version = "4.1.0"
@@ -6441,9 +6376,9 @@ dependencies = [
  "bitflags 2.13.1",
  "block2 0.5.1",
  "objc2 0.5.2",
- "objc2-cloud-kit 0.2.2",
- "objc2-core-data 0.2.2",
- "objc2-core-image 0.2.2",
+ "objc2-cloud-kit",
+ "objc2-core-data",
+ "objc2-core-image",
  "objc2-core-location",
  "objc2-foundation 0.2.2",
  "objc2-link-presentation",
diff --git a/Cargo.toml b/Cargo.toml
index d161ef2..cb22cd7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -24,6 +24,7 @@ serde_json = "1"
 serde_yaml = "0.9"
 chrono = { version = "0.4", features = ["serde"] }
 sha2 = "0.10"
+md5 = "0.8.1"
 unicode-normalization = "0.1"
 thiserror = "2"
 anyhow = "1"
diff --git a/README.md b/README.md
index 9301536..3cdebd6 100644
--- a/README.md
+++ b/README.md
@@ -11,7 +11,7 @@ The project is under active development. Core blogging workflows are broadly ava
 - Media import, thumbnails, metadata translations, filters, validation, post assignment, and sequential drag-and-drop insertion into post editors.
 - WordPress WXR migration with saved analyses, HTML-to-Markdown and shortcode conversion, conflict/taxonomy review, recoverable 500-item execution batches, media-parent linking, progress reporting, and optional AI-assisted taxonomy mapping.
 - Post, Liquid template, and Lua script editing with dedicated syntax highlighting and explicit syntax-check feedback, including publish-time enforcement of the bDS2 Liquid tag/filter/operator subset, using a custom Ropey/Syntect/Cosmic Text editor and the documented, bDS2-signature-compatible project-scoped [`bds` host API](docs/scripting/API_REFERENCE.md) across utilities, rendered macros, and Blogmark transforms, including airplane-gated Git sync.
-- SQLite and filesystem persistence with frontmatter, sidecars, rebuild, metadata diff/repair, bDS2-compatible NFD slug generation, and FTS5 search.
+- SQLite and filesystem persistence with frontmatter, sidecars, rebuild, metadata diff/repair, bDS2-compatible checksums and NFD slug generation, and FTS5 search.
 - Optional on-device multilingual semantic search and similar-post tag suggestions backed by a persistent USearch index, plus always-available partial-name tag autocomplete and duplicate-post review in the desktop workspace.
 - Read-only in-app browsers in the Help menu for the bundled global `DOCUMENTATION.md`, the generated Lua API reference with public types and runnable examples, the [CLI/server/TUI documentation](CLI.md), and the [MCP server documentation](MCP.md), with safe GFM rendering and confirmed external links.
 - A localized OPML menu editor manages pages, submenus, and category archives with protected Home ordering, keyboard-accessible tree controls, drag-and-drop, and bDS2-compatible persistence.
diff --git a/crates/bds-core/Cargo.toml b/crates/bds-core/Cargo.toml
index 09132ce..bd18857 100644
--- a/crates/bds-core/Cargo.toml
+++ b/crates/bds-core/Cargo.toml
@@ -14,6 +14,7 @@ serde_json = { workspace = true }
 serde_yaml = { workspace = true }
 chrono = { workspace = true }
 sha2 = { workspace = true }
+md5 = { workspace = true }
 unicode-normalization = { workspace = true }
 thiserror = { workspace = true }
 walkdir = { workspace = true }
diff --git a/crates/bds-core/src/engine/media.rs b/crates/bds-core/src/engine/media.rs
index 1963f7b..4290851 100644
--- a/crates/bds-core/src/engine/media.rs
+++ b/crates/bds-core/src/engine/media.rs
@@ -20,7 +20,7 @@ use crate::util::thumbnail::{
     mime_from_extension,
 };
 use crate::util::{
-    atomic_write_str, content_hash, media_dir_path, media_sidecar_path,
+    atomic_write_str, media_dir_path, media_file_hash, media_sidecar_path,
     media_translation_sidecar_path, now_unix_ms,
 };
 
@@ -193,6 +193,7 @@ pub fn import_media(
         author,
         language,
         tags,
+        None,
         now_unix_ms(),
     )
 }
@@ -216,6 +217,7 @@ pub(crate) fn import_media_at(
     author: Option<&str>,
     language: Option<&str>,
     tags: Vec<String>,
+    checksum: Option<&str>,
     created_at: i64,
 ) -> EngineResult<Media> {
     // Validate file type per spec
@@ -254,10 +256,6 @@ pub(crate) fn import_media_at(
     // Compute sidecar path
     let sidecar_rel = media_sidecar_path(&rel_file_path);
 
-    // Compute checksum of the copied file
-    let file_bytes = fs::read(&abs_file_path)?;
-    let checksum = content_hash(&file_bytes);
-
     // Generate thumbnails (silently ignore errors for non-image files)
     let thumbnails_dir = data_dir.join("thumbnails");
     let _ = generate_all_thumbnails(&abs_file_path, &thumbnails_dir, &id);
@@ -278,7 +276,7 @@ pub(crate) fn import_media_at(
         language: language.map(|s| s.to_string()),
         file_path: rel_file_path,
         sidecar_path: sidecar_rel.clone(),
-        checksum: Some(checksum),
+        checksum: checksum.map(str::to_owned),
         tags,
         created_at,
         updated_at: created_at,
@@ -373,7 +371,7 @@ pub fn replace_media_file(
         )));
     }
 
-    let replacement_checksum = crate::util::file_hash(new_source_path)?;
+    let replacement_checksum = media_file_hash(new_source_path)?;
     if media.checksum.as_deref() == Some(replacement_checksum.as_str()) {
         return Ok(None);
     }
@@ -994,7 +992,7 @@ mod tests {
         assert_eq!(from_db.mime_type, "image/png");
         assert_eq!(from_db.width, Some(100));
         assert_eq!(from_db.height, Some(80));
-        assert!(from_db.checksum.is_some());
+        assert_eq!(from_db.checksum, None);
         assert!(from_db.size > 0);
 
         // Verify binary file exists
@@ -1234,7 +1232,12 @@ mod tests {
         )
         .unwrap();
         let stored = dir.path().join(&media.file_path);
-        let updated_at = media.updated_at;
+        let duplicate = dir.path().join("duplicate.png");
+        fs::copy(&stored, &duplicate).unwrap();
+        let established = replace_media_file(db.conn(), dir.path(), &media.id, &duplicate)
+            .unwrap()
+            .unwrap();
+        let updated_at = established.updated_at;
 
         assert!(
             replace_media_file(db.conn(), dir.path(), &media.id, &stored)
@@ -1249,6 +1252,32 @@ mod tests {
         );
     }
 
+    #[test]
+    fn import_media_at_preserves_caller_supplied_bds2_checksum() {
+        let (db, dir) = setup();
+        let source = create_test_png(dir.path());
+        let checksum = crate::util::media_file_hash(&source).unwrap();
+
+        let media = import_media_at(
+            db.conn(),
+            dir.path(),
+            "p1",
+            &source,
+            "photo.png",
+            None,
+            None,
+            None,
+            None,
+            None,
+            vec![],
+            Some(&checksum),
+            now_unix_ms(),
+        )
+        .unwrap();
+
+        assert_eq!(media.checksum.as_deref(), Some(checksum.as_str()));
+    }
+
     #[test]
     fn delete_media_removes_everything() {
         let (db, dir) = setup();
diff --git a/crates/bds-core/src/engine/post.rs b/crates/bds-core/src/engine/post.rs
index eb2c1e8..e3b887a 100644
--- a/crates/bds-core/src/engine/post.rs
+++ b/crates/bds-core/src/engine/post.rs
@@ -15,8 +15,7 @@ use crate::util::frontmatter::{
     read_post_file, read_translation_file, write_post_file, write_translation_file,
 };
 use crate::util::{
-    atomic_write_str, content_hash, ensure_unique, now_unix_ms, post_file_path, slugify,
-    translation_file_path,
+    atomic_write_str, ensure_unique, now_unix_ms, post_file_path, slugify, translation_file_path,
 };
 
 /// Report returned by `rebuild_posts_from_filesystem`.
@@ -255,10 +254,6 @@ fn publish_post_in_savepoint(
     let file_content = write_post_file(&post, &body);
     atomic_write_str(&abs_path, &file_content)?;
 
-    // Compute checksum
-    let hash = content_hash(file_content.as_bytes());
-    post.checksum = Some(hash);
-
     // Set published snapshot fields
     let tags_json = serde_json::to_string(&post.tags).unwrap_or_else(|_| "[]".into());
     let cats_json = serde_json::to_string(&post.categories).unwrap_or_else(|_| "[]".into());
@@ -387,7 +382,7 @@ pub fn discard_post_draft(conn: &Connection, data_dir: &Path, post_id: &str) ->
                 fm.do_not_translate,
                 fm.tags,
                 fm.categories,
-                Some(content_hash(raw.as_bytes())),
+                None,
             )
         } else {
             (
@@ -887,8 +882,6 @@ fn publish_translation(
     let file_content = write_translation_file(t, &body);
     atomic_write_str(&abs_path, &file_content)?;
 
-    let hash = content_hash(file_content.as_bytes());
-    t.checksum = Some(hash);
     t.content = None;
 
     qt::update_post_translation(conn, t)?;
@@ -984,7 +977,6 @@ pub(crate) fn rebuild_canonical_post(
         .to_string_lossy()
         .to_string();
 
-    let hash = content_hash(content.as_bytes());
     let status = match fm.status.as_str() {
         "published" => PostStatus::Published,
         "archived" => PostStatus::Archived,
@@ -1010,7 +1002,7 @@ pub(crate) fn rebuild_canonical_post(
             post.do_not_translate = fm.do_not_translate;
             post.template_slug = fm.template_slug;
             post.file_path = rel_path;
-            post.checksum = Some(hash);
+            post.checksum = None;
             post.tags = fm.tags;
             post.categories = fm.categories;
             post.created_at = fm.created_at;
@@ -1038,7 +1030,7 @@ pub(crate) fn rebuild_canonical_post(
                 do_not_translate: fm.do_not_translate,
                 template_slug: fm.template_slug,
                 file_path: rel_path,
-                checksum: Some(hash),
+                checksum: None,
                 tags: fm.tags,
                 categories: fm.categories,
                 published_title: None,
@@ -1072,8 +1064,6 @@ pub(crate) fn rebuild_translation(
         .to_string_lossy()
         .to_string();
 
-    let hash = content_hash(content.as_bytes());
-
     // Check if parent post exists
     let parent = qp::get_post_by_id(conn, &fm.translation_for);
     if parent.is_err() {
@@ -1110,7 +1100,7 @@ pub(crate) fn rebuild_translation(
             };
             t.status = status;
             t.file_path = rel_path;
-            t.checksum = Some(hash);
+            t.checksum = None;
             t.created_at = created_at;
             t.updated_at = updated_at;
             t.published_at = published_at;
@@ -1132,7 +1122,7 @@ pub(crate) fn rebuild_translation(
                 },
                 status,
                 file_path: rel_path,
-                checksum: Some(hash),
+                checksum: None,
                 created_at,
                 updated_at,
                 published_at,
@@ -1643,6 +1633,48 @@ mod tests {
         );
     }
 
+    #[test]
+    fn publish_preserves_caller_supplied_checksums() {
+        let (db, dir) = setup();
+        let mut post = create_post(
+            db.conn(),
+            dir.path(),
+            "p1",
+            "Imported",
+            Some("body"),
+            vec![],
+            vec![],
+            None,
+            None,
+            None,
+        )
+        .unwrap();
+        post.checksum = Some("bds2-post-checksum".into());
+        qp::update_post(db.conn(), &post).unwrap();
+        let mut translation = upsert_translation(
+            db.conn(),
+            dir.path(),
+            &post.id,
+            "de",
+            "Importiert",
+            None,
+            Some("Inhalt"),
+        )
+        .unwrap();
+        translation.checksum = Some("bds2-translation-checksum".into());
+        qt::update_post_translation(db.conn(), &translation).unwrap();
+
+        let published = publish_post(db.conn(), dir.path(), &post.id).unwrap();
+        let published_translation =
+            qt::get_post_translation_by_id(db.conn(), &translation.id).unwrap();
+
+        assert_eq!(published.checksum.as_deref(), Some("bds2-post-checksum"));
+        assert_eq!(
+            published_translation.checksum.as_deref(),
+            Some("bds2-translation-checksum")
+        );
+    }
+
     #[test]
     fn delete_post_removes_everything() {
         let (db, dir) = setup();
@@ -1873,12 +1905,14 @@ mod tests {
         assert_eq!(post.slug, "rebuilt-post");
         assert_eq!(post.tags, vec!["test"]);
         assert_eq!(post.updated_at, 1_705_320_000_000);
+        assert_eq!(post.checksum, None);
 
         // Verify translation in DB
         let trans =
             qt::get_post_translation_by_post_and_language(db.conn(), "rebuild-post-1", "de")
                 .unwrap();
         assert_eq!(trans.title, "Wiederhergestellter Beitrag");
+        assert_eq!(trans.checksum, None);
 
         // Run rebuild again - should update, not create
         let report2 = rebuild_posts_from_filesystem(db.conn(), dir.path(), "p1").unwrap();
diff --git a/crates/bds-core/src/engine/wordpress_import.rs b/crates/bds-core/src/engine/wordpress_import.rs
index 04cfc7a..f1776e4 100644
--- a/crates/bds-core/src/engine/wordpress_import.rs
+++ b/crates/bds-core/src/engine/wordpress_import.rs
@@ -25,8 +25,8 @@ use crate::model::{
     TaxonomyKind,
 };
 use crate::util::{
-    atomic_write_str, content_hash, file_hash, media_sidecar_path, media_translation_sidecar_path,
-    now_unix_ms, post_file_path, slugify,
+    atomic_write_str, content_hash, media_file_hash, media_sidecar_path,
+    media_translation_sidecar_path, now_unix_ms, post_file_path, slugify,
 };
 
 const TRANSACTION_BATCH_SIZE: usize = 500;
@@ -678,7 +678,7 @@ fn analyze_media(
     let checksum = source_path
         .as_ref()
         .filter(|path| path.is_file())
-        .and_then(|path| file_hash(path).ok());
+        .and_then(|path| media_file_hash(path).ok());
     let existing_by_name = media_by_name.get(&item.filename.to_lowercase()).copied();
     let existing_by_checksum = checksum
         .as_ref()
@@ -1369,7 +1369,6 @@ fn import_post_item(
         imported.published_at = item.published_at.or(Some(imported.created_at));
         imported.file_path = post_file_path(imported.created_at, &imported.slug);
         let serialized = crate::util::frontmatter::write_post_file(&imported, &body);
-        imported.checksum = Some(content_hash(serialized.as_bytes()));
         atomic_write_str(&data_dir.join(&imported.file_path), &serialized)?;
         if !previous_file_path.is_empty() && previous_file_path != imported.file_path {
             remove_file_if_present(&data_dir.join(previous_file_path))?;
@@ -1476,6 +1475,7 @@ fn execute_media_phase(
                         default_author,
                         None,
                         Vec::new(),
+                        item.checksum.as_deref(),
                         item.created_at.unwrap_or_else(now_unix_ms),
                     )?
                 };
diff --git a/crates/bds-core/src/util/checksum.rs b/crates/bds-core/src/util/checksum.rs
index 2bc00c1..2a7044e 100644
--- a/crates/bds-core/src/util/checksum.rs
+++ b/crates/bds-core/src/util/checksum.rs
@@ -25,6 +25,26 @@ pub fn file_hash(path: &Path) -> std::io::Result<String> {
     Ok(encode_hex(hasher.finalize()))
 }
 
+/// Compute the bDS2-compatible lower-hex MD5 change signal for media bytes.
+pub fn media_content_hash(content: &[u8]) -> String {
+    format!("{:x}", md5::compute(content))
+}
+
+/// Compute the bDS2-compatible lower-hex MD5 change signal for a media file.
+pub fn media_file_hash(path: &Path) -> std::io::Result<String> {
+    let mut file = std::fs::File::open(path)?;
+    let mut context = md5::Context::new();
+    let mut buf = [0u8; 8192];
+    loop {
+        let n = file.read(&mut buf)?;
+        if n == 0 {
+            break;
+        }
+        context.consume(&buf[..n]);
+    }
+    Ok(format!("{:x}", context.finalize()))
+}
+
 fn encode_hex(bytes: impl AsRef<[u8]>) -> String {
     bytes
         .as_ref()
@@ -55,4 +75,13 @@ mod tests {
             "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
         );
     }
+
+    #[test]
+    fn media_hash_matches_bds2_fixture() {
+        // Base.encode16(:crypto.hash(:md5, "hello"), case: :lower) in bDS2.
+        assert_eq!(
+            media_content_hash(b"hello"),
+            "5d41402abc4b2a76b9719d911017c592"
+        );
+    }
 }
diff --git a/crates/bds-core/src/util/mod.rs b/crates/bds-core/src/util/mod.rs
index 4101413..bb493fb 100644
--- a/crates/bds-core/src/util/mod.rs
+++ b/crates/bds-core/src/util/mod.rs
@@ -10,7 +10,7 @@ pub mod timestamp;
 
 pub use app_paths::{application_data_dir, application_database_path, default_project_data_dir};
 pub use atomic_write::{atomic_write, atomic_write_str};
-pub use checksum::{content_hash, file_hash};
+pub use checksum::{content_hash, file_hash, media_content_hash, media_file_hash};
 pub use paths::*;
 pub use slug::{ensure_unique, slugify};
 pub use timestamp::{
diff --git a/crates/bds-core/tests/wordpress_import.rs b/crates/bds-core/tests/wordpress_import.rs
index 9457b1d..11e9575 100644
--- a/crates/bds-core/tests/wordpress_import.rs
+++ b/crates/bds-core/tests/wordpress_import.rs
@@ -163,7 +163,7 @@ fn analysis_distinguishes_new_updates_conflicts_duplicates_and_missing_media() {
         .unwrap();
     let old_different = dir.path().join("old-different.png");
     DynamicImage::new_rgb8(2, 2).save(&old_different).unwrap();
-    bds_core::engine::media::import_media(
+    let same = bds_core::engine::media::import_media(
         db.conn(),
         dir.path(),
         &project.id,
@@ -177,7 +177,14 @@ fn analysis_distinguishes_new_updates_conflicts_duplicates_and_missing_media() {
         Vec::new(),
     )
     .unwrap();
-    bds_core::engine::media::import_media(
+    bds_core::engine::media::replace_media_file(
+        db.conn(),
+        dir.path(),
+        &same.id,
+        &uploads.join("same.png"),
+    )
+    .unwrap();
+    let different = bds_core::engine::media::import_media(
         db.conn(),
         dir.path(),
         &project.id,
@@ -191,6 +198,13 @@ fn analysis_distinguishes_new_updates_conflicts_duplicates_and_missing_media() {
         Vec::new(),
     )
     .unwrap();
+    bds_core::engine::media::replace_media_file(
+        db.conn(),
+        dir.path(),
+        &different.id,
+        &old_different,
+    )
+    .unwrap();
 
     let same_body = "Hello **world**.\n\n[[gallery ids=\"1,2\"]]";
     let update = post::create_post(
diff --git a/crates/bds-ui/Cargo.toml b/crates/bds-ui/Cargo.toml
index b33f82c..e8373e3 100644
--- a/crates/bds-ui/Cargo.toml
+++ b/crates/bds-ui/Cargo.toml
@@ -25,7 +25,6 @@ wry = "0.55.1"
 [target.'cfg(target_os = "macos")'.dependencies]
 objc2 = "0.6"
 objc2-foundation = { version = "0.3", features = ["objc2-core-services"] }
-objc2-app-kit = "0.3"
 
 [dev-dependencies]
 fluent-syntax = { workspace = true }
diff --git a/specs/import.allium b/specs/import.allium
index ae833fb..07cbed1 100644
--- a/specs/import.allium
+++ b/specs/import.allium
@@ -264,6 +264,8 @@ invariant WxrConversionParity {
 }
 
 invariant AnalysisClassification {
+    -- Post/page checksums are lower-hex SHA-256 of converted Markdown; media
+    -- checksums are lower-hex MD5 of source bytes, matching bDS2.
     -- Posts/pages: same slug and checksum => update; same slug with different
     -- content => conflict; checksum matching another post => content duplicate;
     -- otherwise new. Media applies the same rules by original filename and
diff --git a/specs/media_processing.allium b/specs/media_processing.allium
index 688d0c6..816d4bd 100644
--- a/specs/media_processing.allium
+++ b/specs/media_processing.allium
@@ -254,7 +254,8 @@ invariant MediaTranslationFileLayout {
 rule ImportMedia {
     when: ImportMediaRequested(source_path, project, metadata)
     -- metadata is optional import context: title, alt, caption, author,
-    -- language, and tags may be supplied by the caller.
+    -- language, tags, and a checksum may be supplied by the caller. WXR
+    -- supplies a lower-hex MD5 checksum; interactive imports leave it nil.
     -- 1. Validate file type (must be supported image)
     -- 2. Generate UUID v4 filename
     -- 3. Copy to media/{YYYY}/{MM}/{uuid}.{ext}
@@ -276,7 +277,7 @@ rule ImportMedia {
         tags: metadata.tags,
         file_path: format("media/{yyyy}/{mm}/{uuid}.{ext}"),
         sidecar_path: format("media/{yyyy}/{mm}/{uuid}.{ext}.meta"),
-        checksum: sha256(source_path)
+        checksum: metadata.checksum
     )
     ensures: ThumbnailsGenerated(media_id)
     ensures: SearchIndexUpdated(media_id)
diff --git a/specs/post.allium b/specs/post.allium
index 530fa40..9078d77 100644
--- a/specs/post.allium
+++ b/specs/post.allium
@@ -98,6 +98,8 @@ entity Post {
     template_slug: String?
     file_path: String
     checksum: String?
+        -- Caller-supplied SHA-256 content change signal. Publish preserves it;
+        -- filesystem rebuild/sync clears it to match bDS2.
     tags: List<String>
     categories: List<String>
     created_at: Timestamp
@@ -210,6 +212,7 @@ rule PublishPost {
         -- Writes frontmatter + markdown to posts/YYYY/MM/{slug}.md
     ensures: post.content = null
         -- Content cleared from DB; now lives in filesystem only
+    -- post.checksum is preserved unchanged.
     ensures: SearchIndexUpdated(post)
     ensures: PostLinksUpdated(post)
         -- Parse inter-post links, update link graph
@@ -242,6 +245,7 @@ rule SyncPostFromFile {
     -- record from it (the filesystem is treated as truth for that one post).
     -- Re-syncs the post's link graph. Errors out if the file is missing.
     ensures: PostFieldsUpdated(post, parse_post_file(post.file_path))
+    ensures: post.checksum = null
     ensures: PostLinksUpdated(post)
 }
 
diff --git a/specs/schema.allium b/specs/schema.allium
index 5c642f9..d27f9ea 100644
--- a/specs/schema.allium
+++ b/specs/schema.allium
@@ -55,7 +55,7 @@ entity Post {
     updated_at: Timestamp
     published_at: Timestamp?
     file_path: String       -- Empty for never-published drafts
-    checksum: String?       -- SHA-256 of content
+    checksum: String?       -- Caller-supplied SHA-256 content change signal; nil after filesystem rebuild
     tags: Set<String>       -- JSON array stored as text
     categories: Set<String> -- JSON array stored as text
     template_slug: String?  -- User template override
@@ -83,7 +83,7 @@ entity PostTranslation {
     updated_at: Timestamp
     published_at: Timestamp?
     file_path: String
-    checksum: String?
+    checksum: String?       -- Caller-supplied content change signal; nil after filesystem rebuild
 }
 
 entity Media {
@@ -103,7 +103,7 @@ entity Media {
     sidecar_path: String    -- Path to .meta sidecar file
     created_at: Timestamp
     updated_at: Timestamp
-    checksum: String?
+    checksum: String?       -- Lower-hex MD5 of media bytes when known
     tags: Set<String>       -- JSON array stored as text
     language: String?       -- ISO 639-1 code
 }
diff --git a/specs/translation.allium b/specs/translation.allium
index 6f96ba3..e5bade5 100644
--- a/specs/translation.allium
+++ b/specs/translation.allium
@@ -51,6 +51,8 @@ entity PostTranslation {
     status: PostTranslationStatus
     file_path: String
     checksum: String?
+        -- Caller-supplied content change signal. Publish preserves it;
+        -- filesystem rebuild/sync clears it to match bDS2.
     created_at: Timestamp
     updated_at: Timestamp
     published_at: Timestamp?
@@ -143,6 +145,7 @@ rule PublishTranslation {
     ensures: TranslationFileWritten(translation)
     ensures: translation.content = null
         -- Content moves to filesystem
+    -- translation.checksum is preserved unchanged.
 }
 
 rule ReopenPublishedTranslation {