web: XREFs, data links & extraction, ARCHIVE transmittals, worker-side saves

The last four big web-vs-desktop gaps.

XREFs: XATTACH reads the picked drawing's bytes and registers them
name-keyed (the image/PDF-underlay pattern), pre-parses on the web
worker, and the commit merge produces the same xref block flow as
native. Opened drawings resolve xrefs from the registry (trailing-name
match) before cache build; unresolved references produce ONE warning
listing the names and the fix — drop the referenced files on the page
(drops and picker opens now register their bytes) and reopen or
XRELOAD. XRELOAD works off the registry on unsaved drawings too.

Data Link & Extraction: spreadsheet links read picked xlsx/csv bytes
(calamine from slices / CSV from string) through a session registry,
so preview, refresh, and table-insert work on web; extraction takes
external drawings via a multi-file picker parsed on the worker, and
outputs CSV/TXT/.dxex via download_bytes. The disabled 'Add folder'
button explains why.

ARCHIVE/ETRANSMIT: assembles the drawing plus registered images, PDF
underlays, and session plot tables into a ZIP delivered as
{stem}_transmit.zip; skipped dependencies are reported by name.

Save/autosave off the UI thread: the parse worker gains a serialize
action (protocol v5) — the document is prepared once on the main
thread (clone, styles, dimension bake), then the DWG/DXF writer pass,
the dominant cost, runs on the worker; any worker failure falls back
to inline serialization with the identical shared implementation.
The save path also clears the dirty flag only when the tab didn't
change mid-write, and the runtime-fields sidecar now carries
graphic_data, fixing a pre-existing loss of raw DWG round-trip bytes
on web-opened documents.

(cherry picked from commit 2e100634)

Ported onto main (#1717 review): the new ocs_save crate builds on the
pinned codec; the hand-written ZIP writer is replaced by the zip crate
already in the tree; ARCHIVE packs registered xref bytes too and
serializes document_for_save() like a web Save; the web save prepares
document_for_save() (prepare_document_for_save now takes the copy by
value, so no second clone); the wasm resolve_path consults the xref
registry, so every reference lookup — not just resolve — finds dropped
files; XRELOAD keeps main's undo, unload and stale-baseline handling;
native data extraction streams the source drawings one at a time.

src/app/annotation_data.rs

@@ -1,5 +1,7 @@
-use std::collections::{BTreeMap, BTreeSet};
+use std::collections::{BTreeMap, BTreeSet, HashMap};
+use std::io::Cursor;
 use std::path::{Path, PathBuf};
+use std::sync::{Arc, Mutex, OnceLock};
 
 use codec::entities::{table::CellRange, TableBuilder};
 use codec::objects::{ClassObject, ClassObjectData, DataLink, DataLinkCustomData, ObjectType};
@@ -25,6 +27,100 @@ struct ExtractionRecord {
     details: String,
 }
 
+// ── In-session picked-file registries (web) ───────────────────────────────
+//
+// The browser exposes no reusable filesystem path: a picked file's bytes exist
+// only while the app keeps them. Both registries below hold those bytes (and
+// what was parsed from them) keyed by the reference the drawing or wizard
+// carries, following the image-model / PDF-raster pattern. Native builds never
+// fill them — the real path stays readable — but the lookup and matching
+// logic compiles everywhere so it stays unit-testable.
+
+fn picked_sources() -> &'static Mutex<HashMap<String, Arc<Vec<u8>>>> {
+    static SOURCES: OnceLock<Mutex<HashMap<String, Arc<Vec<u8>>>>> = OnceLock::new();
+    SOURCES.get_or_init(|| Mutex::new(HashMap::new()))
+}
+
+#[cfg_attr(not(target_arch = "wasm32"), allow(dead_code))]
+fn extraction_documents() -> &'static Mutex<HashMap<String, Arc<CadDocument>>> {
+    static DOCUMENTS: OnceLock<Mutex<HashMap<String, Arc<CadDocument>>>> = OnceLock::new();
+    DOCUMENTS.get_or_init(|| Mutex::new(HashMap::new()))
+}
+
+/// Lower-cased trailing component of a path-style reference. Links and wizard
+/// sources carry whatever the author stored, so the file name — not the full
+/// path — is the only component a re-picked file can be expected to match.
+fn source_name_key(path: &str) -> String {
+    path.rsplit(['/', '\\'])
+        .next()
+        .unwrap_or_default()
+        .to_ascii_lowercase()
+}
+
+/// Do two source references name the same file? Compares trailing components
+/// case-insensitively (Windows paths are case-insensitive where the link was
+/// authored, and the web has no path beyond the name at all).
+fn same_source_name(a: &str, b: &str) -> bool {
+    let (a, b) = (source_name_key(a), source_name_key(b));
+    !a.is_empty() && a == b
+}
+
+/// Keep the bytes of a spreadsheet or settings file chosen through a picker.
+/// Re-opening the link in-session re-reads these instead of demanding a new
+/// pick; re-picking the same file overwrites the entry.
+// Only the web registers sources (native re-reads the real file, so a file
+// edited after picking is picked up); tests exercise the registry directly.
+#[cfg_attr(not(target_arch = "wasm32"), allow(dead_code))]
+pub(crate) fn register_picked_source(path: &str, bytes: Arc<Vec<u8>>) {
+    picked_sources()
+        .lock()
+        .unwrap_or_else(|error| error.into_inner())
+        .insert(path.to_string(), bytes);
+}
+
+/// Bytes registered for this reference — exact key first, then any entry that
+/// names the same file (the web fallback for links whose stored path is the
+/// original author's, while the user picked only the bare file).
+pub(crate) fn picked_source_bytes(path: &str) -> Option<Arc<Vec<u8>>> {
+    let cache = picked_sources()
+        .lock()
+        .unwrap_or_else(|error| error.into_inner());
+    if let Some(bytes) = cache.get(path) {
+        return Some(Arc::clone(bytes));
+    }
+    cache
+        .iter()
+        .find(|(key, _)| same_source_name(key, path))
+        .map(|(_, bytes)| Arc::clone(bytes))
+}
+
+/// Keep a source drawing parsed at pick time, keyed by the name the wizard
+/// lists. The extraction pipeline reads these on the web instead of calling
+/// the path-based `load_file`.
+#[cfg_attr(not(target_arch = "wasm32"), allow(dead_code))]
+pub(crate) fn register_extraction_document(name: &str, document: CadDocument) {
+    extraction_documents()
+        .lock()
+        .unwrap_or_else(|error| error.into_inner())
+        .insert(name.to_string(), Arc::new(document));
+}
+
+/// The parsed drawing registered under this source reference, matched by exact
+/// key or by file name.
+#[cfg_attr(not(target_arch = "wasm32"), allow(dead_code))]
+pub(crate) fn extraction_document(path: &str) -> Option<Arc<CadDocument>> {
+    let cache = extraction_documents()
+        .lock()
+        .unwrap_or_else(|error| error.into_inner());
+    if let Some(document) = cache.get(path) {
+        return Some(Arc::clone(document));
+    }
+    cache
+        .iter()
+        .find(|(key, _)| same_source_name(key, path))
+        .map(|(_, document)| Arc::clone(document))
+}
+
 impl ExtractionRecord {
     fn value(&self, key: &str) -> String {
         match key {
@@ -88,11 +184,15 @@ fn data_link_choices(doc: &CadDocument) -> Vec<DataLinkChoice> {
             ObjectType::ClassObject(object) => match &object.data {
                 ClassObjectData::DataLink(link) => {
                     let path = resolve_link_path(doc, link);
+                    let path_text = path.to_string_lossy().into_owned();
+                    // The web has no filesystem: a link is valid when its
+                    // picked bytes are still registered in-session.
+                    let valid = path.is_file() || picked_source_bytes(&path_text).is_some();
                     Some(DataLinkChoice {
                         handle: *handle,
                         name: link_display_name(link),
-                        path: path.to_string_lossy().into_owned(),
-                        valid: path.is_file(),
+                        path: path_text,
+                        valid,
                     })
                 }
                 _ => None,
@@ -180,6 +280,12 @@ fn workbook_metadata(path: &Path) -> Result<(Vec<String>, Vec<String>), String>
     if ext == "csv" || ext == "txt" {
         return Ok((Vec::new(), Vec::new()));
     }
+    if let Some(bytes) = picked_source_bytes(&path.to_string_lossy()) {
+        return workbook_metadata_bytes(&bytes);
+    }
+    if cfg!(target_arch = "wasm32") {
+        return Err(crate::t!("Pick the file again to load its contents in the browser.").into_owned());
+    }
     use calamine::{open_workbook_auto, Reader};
     let workbook = open_workbook_auto(path).map_err(|error| error.to_string())?;
     let sheets = workbook.sheet_names();
@@ -191,6 +297,20 @@ fn workbook_metadata(path: &Path) -> Result<(Vec<String>, Vec<String>), String>
     Ok((sheets, names))
 }
 
+/// Sheet and defined-name catalog read straight from bytes (a picked file on
+/// the web, where no path exists to reopen).
+fn workbook_metadata_bytes(bytes: &[u8]) -> Result<(Vec<String>, Vec<String>), String> {
+    use calamine::{open_workbook_auto_from_rs, Reader};
+    let workbook = open_workbook_auto_from_rs(Cursor::new(bytes)).map_err(|error| error.to_string())?;
+    let sheets = workbook.sheet_names();
+    let names = workbook
+        .defined_names()
+        .iter()
+        .map(|(name, _)| name.clone())
+        .collect();
+    Ok((sheets, names))
+}
+
 fn named_range_target(formula: &str) -> Option<(String, String)> {
     let formula = formula.trim().trim_start_matches('=');
     let (sheet, range) = formula.rsplit_once('!')?;
@@ -199,6 +319,66 @@ fn named_range_target(formula: &str) -> Option<(String, String)> {
     (!sheet.is_empty() && !range.is_empty()).then_some((sheet, range))
 }
 
+/// Read the text of a CSV/TXT (or settings) source: registered picked bytes
+/// first, then the native filesystem. On the web an unregistered path has
+/// nothing behind it, so it asks for the pick instead of failing on I/O.
+fn read_text_source(path: &Path) -> Result<String, String> {
+    if let Some(bytes) = picked_source_bytes(&path.to_string_lossy()) {
+        return Ok(String::from_utf8_lossy(&bytes).into_owned());
+    }
+    if cfg!(target_arch = "wasm32") {
+        return Err(crate::t!("Pick the file again to load its contents in the browser.").into_owned());
+    }
+    std::fs::read_to_string(path).map_err(|error| error.to_string())
+}
+
+/// Sheet selection + range resolution shared by the path- and bytes-based
+/// workbook readers. Returns the raw rows and the cell range to crop to, if
+/// any.
+fn workbook_rows<RS: std::io::Read + std::io::Seek>(
+    workbook: &mut calamine::Sheets<RS>,
+    sheet: Option<&str>,
+    range_kind: LinkRange,
+    range_value: Option<&str>,
+) -> Result<(Vec<Vec<String>>, Option<String>), String> {
+    use calamine::Reader;
+    let (selected_sheet, cell_range) = if range_kind == LinkRange::NamedRange {
+        let name = range_value
+            .filter(|value| !value.trim().is_empty())
+            .ok_or_else(|| crate::t!("Select a named range.").into_owned())?;
+        let formula = workbook
+            .defined_names()
+            .iter()
+            .find(|(candidate, _)| candidate.eq_ignore_ascii_case(name))
+            .map(|(_, formula)| formula.clone())
+            .ok_or_else(|| crate::t!("The named range was not found.").into_owned())?;
+        named_range_target(&formula)
+            .ok_or_else(|| crate::t!("The named range does not refer to a worksheet cell range.").into_owned())?
+    } else {
+        let selected_sheet = sheet
+            .filter(|value| !value.trim().is_empty())
+            .map(str::to_string)
+            .or_else(|| workbook.sheet_names().first().cloned())
+            .ok_or_else(|| crate::t!("The spreadsheet contains no worksheets.").into_owned())?;
+        let range = (range_kind == LinkRange::CellRange)
+            .then_some(range_value)
+            .flatten()
+            .filter(|value| !value.trim().is_empty())
+            .map(str::to_string)
+            .unwrap_or_default();
+        (selected_sheet, range)
+    };
+    let data = workbook
+        .worksheet_range(&selected_sheet)
+        .map_err(|error| error.to_string())?;
+    Ok((
+        data.rows()
+            .map(|row| row.iter().map(ToString::to_string).collect())
+            .collect(),
+        (!cell_range.is_empty()).then_some(cell_range),
+    ))
+}
+
 pub(crate) fn read_tabular_file(
     path: &Path,
     sheet: Option<&str>,
@@ -214,53 +394,24 @@ pub(crate) fn read_tabular_file(
         if range_kind == LinkRange::NamedRange {
             return Err(crate::t!("Named ranges require a spreadsheet file.").into_owned());
         }
-        let text = std::fs::read_to_string(path).map_err(|error| error.to_string())?;
         (
-            crate::app::commands::display::parse_csv_table(&text),
+            crate::app::commands::display::parse_csv_table(&read_text_source(path)?),
             (range_kind == LinkRange::CellRange)
                 .then_some(range_value)
                 .flatten()
                 .map(str::to_string),
         )
-    } else {
-        use calamine::{open_workbook_auto, Reader};
-        let mut workbook = open_workbook_auto(path).map_err(|error| error.to_string())?;
-        let (selected_sheet, cell_range) = if range_kind == LinkRange::NamedRange {
-            let name = range_value
-                .filter(|value| !value.trim().is_empty())
-                .ok_or_else(|| crate::t!("Select a named range.").into_owned())?;
-            let formula = workbook
-                .defined_names()
-                .iter()
-                .find(|(candidate, _)| candidate.eq_ignore_ascii_case(name))
-                .map(|(_, formula)| formula.clone())
-                .ok_or_else(|| crate::t!("The named range was not found.").into_owned())?;
-            named_range_target(&formula).ok_or_else(|| {
-                crate::t!("The named range does not refer to a worksheet cell range.").into_owned()
-            })?
-        } else {
-            let selected_sheet = sheet
-                .filter(|value| !value.trim().is_empty())
-                .map(str::to_string)
-                .or_else(|| workbook.sheet_names().first().cloned())
-                .ok_or_else(|| crate::t!("The spreadsheet contains no worksheets.").into_owned())?;
-            let range = (range_kind == LinkRange::CellRange)
-                .then_some(range_value)
-                .flatten()
-                .filter(|value| !value.trim().is_empty())
-                .map(str::to_string)
-                .unwrap_or_default();
-            (selected_sheet, range)
-        };
-        let data = workbook
-            .worksheet_range(&selected_sheet)
+    } else if let Some(bytes) = picked_source_bytes(&path.to_string_lossy()) {
+        use calamine::open_workbook_auto_from_rs;
+        let mut workbook = open_workbook_auto_from_rs(Cursor::new(bytes.as_slice()))
             .map_err(|error| error.to_string())?;
-        (
-            data.rows()
-                .map(|row| row.iter().map(ToString::to_string).collect())
-                .collect(),
-            (!cell_range.is_empty()).then_some(cell_range),
-        )
+        workbook_rows(&mut workbook, sheet, range_kind, range_value)?
+    } else if cfg!(target_arch = "wasm32") {
+        return Err(crate::t!("Pick the file again to load its contents in the browser.").into_owned());
+    } else {
+        use calamine::open_workbook_auto;
+        let mut workbook = open_workbook_auto(path).map_err(|error| error.to_string())?;
+        workbook_rows(&mut workbook, sheet, range_kind, range_value)?
     };
     let rows = match cell_range
         .as_deref()
@@ -471,12 +622,14 @@ fn collect_records(
     }
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 fn is_drawing_file(path: &Path) -> bool {
     path.extension()
         .and_then(|value| value.to_str())
         .is_some_and(|value| value.eq_ignore_ascii_case("dwg") || value.eq_ignore_ascii_case("dxf"))
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 fn collect_drawing_paths(
     path: &Path,
     recursive: bool,
@@ -505,6 +658,7 @@ fn collect_drawing_paths(
     Ok(())
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 fn extraction_drawing_paths(state: &DataExtractionState) -> Result<Vec<PathBuf>, String> {
     let mut paths = Vec::new();
     for source in &state.source_files {
@@ -515,6 +669,31 @@ fn extraction_drawing_paths(state: &DataExtractionState) -> Result<Vec<PathBuf>,
     Ok(paths)
 }
 
+/// Visit the source drawings the extraction pipeline reads beyond the current
+/// one. Native loads them from disk one at a time (folders walked
+/// recursively), so only one foreign drawing is in memory at once; the web
+/// reads the documents parsed at pick time from the in-session registry —
+/// every listed source must have been picked, or it asks for the pick again.
+fn for_each_extraction_document(
+    state: &DataExtractionState,
+    mut visit: impl FnMut(&CadDocument),
+) -> Result<(), String> {
+    #[cfg(target_arch = "wasm32")]
+    for source in &state.source_files {
+        let document = extraction_document(source).ok_or_else(|| {
+            crate::tf!("Drawing not loaded in the browser: {name}.", name = source).into_owned()
+        })?;
+        visit(&document);
+    }
+    #[cfg(not(target_arch = "wasm32"))]
+    for source in extraction_drawing_paths(state)? {
+        let document = crate::io::load_file(&source)
+            .map_err(|error| format!("{}: {error}", source.display()))?;
+        visit(&document);
+    }
+    Ok(())
+}
+
 fn collect_type_counts(
     doc: &CadDocument,
     allowed_handles: Option<&BTreeSet<Handle>>,
@@ -560,11 +739,9 @@ fn extraction_preview(
             if state.include_current {
                 collect_records(current, None, &allowed_types, &mut records);
             }
-            for source in extraction_drawing_paths(state)? {
-                let doc = crate::io::load_file(&source)
-                    .map_err(|error| format!("{}: {error}", source.display()))?;
-                collect_records(&doc, None, &allowed_types, &mut records);
-            }
+            for_each_extraction_document(state, |document| {
+                collect_records(document, None, &allowed_types, &mut records);
+            })?;
         }
     }
     let props = state
@@ -693,11 +870,25 @@ fn save_extraction_settings(state: &DataExtractionState) -> Result<(), String> {
         "tableTitle": state.table_title,
     });
     let text = serde_json::to_string_pretty(&value).map_err(|error| error.to_string())?;
-    std::fs::write(&state.settings_path, text).map_err(|error| error.to_string())
+    #[cfg(target_arch = "wasm32")]
+    {
+        // No filesystem to write to: hand the settings to the browser as a
+        // download, mirroring the native write of the same JSON.
+        let name = Path::new(state.settings_path.trim())
+            .file_name()
+            .map(|value| value.to_string_lossy().into_owned())
+            .unwrap_or_else(|| "extraction.dxex".into());
+        crate::sys::download_bytes(&name, text.as_bytes());
+        Ok(())
+    }
+    #[cfg(not(target_arch = "wasm32"))]
+    {
+        std::fs::write(&state.settings_path, text).map_err(|error| error.to_string())
+    }
 }
 
 fn load_extraction_settings(state: &mut DataExtractionState) -> Result<(), String> {
-    let text = std::fs::read_to_string(&state.settings_path).map_err(|error| error.to_string())?;
+    let text = read_text_source(Path::new(state.settings_path.trim()))?;
     let value: serde_json::Value =
         serde_json::from_str(&text).map_err(|error| error.to_string())?;
     state.source = match value["source"].as_str() {
@@ -1075,7 +1266,7 @@ impl OpenCADStudio {
     pub(super) fn on_data_link_browse(&mut self) -> Task<Message> {
         Task::perform(
             async {
-                crate::sys::file_dialog()
+                let Some(handle) = crate::sys::file_dialog()
                     .set_title(crate::t!("Choose a Spreadsheet File").as_ref())
                     .add_filter(
                         crate::t!("Spreadsheet Files").as_ref(),
@@ -1084,7 +1275,16 @@ impl OpenCADStudio {
                     .add_filter(crate::t!("All Files").as_ref(), &["*"])
                     .pick_file()
                     .await
-                    .map(|handle| crate::sys::handle_path(&handle))
+                else {
+                    return None;
+                };
+                let path = crate::sys::handle_path(&handle);
+                // The browser forgets the file the moment the pick resolves:
+                // keep its bytes so preview, save, and later re-opens read
+                // them instead of asking for the picker again.
+                #[cfg(target_arch = "wasm32")]
+                register_picked_source(&path.to_string_lossy(), Arc::new(handle.read().await));
+                Some(path)
             },
             Message::DataLinkBrowseResult,
         )
@@ -1403,11 +1603,9 @@ impl OpenCADStudio {
                 if state.include_current {
                     collect_type_counts(current, None, &mut counts);
                 }
-                for path in extraction_drawing_paths(&state)? {
-                    let doc = crate::io::load_file(&path)
-                        .map_err(|error| format!("{}: {error}", path.display()))?;
-                    collect_type_counts(&doc, None, &mut counts);
-                }
+                for_each_extraction_document(&state, |document| {
+                    collect_type_counts(document, None, &mut counts);
+                })?;
             }
         }
         let previous = self
@@ -1570,18 +1768,21 @@ impl OpenCADStudio {
                     .set_title(crate::t!("Data Extraction Settings").as_ref())
                     .add_filter(crate::t!("Data Extraction Settings").as_ref(), &["dxex"])
                     .add_filter(crate::t!("All Files").as_ref(), &["*"]);
-                if save {
-                    dialog
-                        .set_file_name("extraction.dxex")
-                        .save_file()
-                        .await
-                        .map(|handle| crate::sys::handle_path(&handle))
+                let handle = if save {
+                    dialog.set_file_name("extraction.dxex").save_file().await
                 } else {
-                    dialog
-                        .pick_file()
-                        .await
-                        .map(|handle| crate::sys::handle_path(&handle))
+                    dialog.pick_file().await
+                };
+                let handle = handle?;
+                let path = crate::sys::handle_path(&handle);
+                // Loading settings in the browser: the picked .dxex has no
+                // path to read back from, so its bytes are kept for the load
+                // that follows this message.
+                #[cfg(target_arch = "wasm32")]
+                if !save {
+                    register_picked_source(&path.to_string_lossy(), Arc::new(handle.read().await));
                 }
+                Some(path)
             },
             Message::DataExtractionBrowseSettingsResult,
         )
@@ -1604,10 +1805,11 @@ impl OpenCADStudio {
         Task::none()
     }
 
+    #[cfg(not(target_arch = "wasm32"))]
     pub(super) fn on_data_extraction_add_drawings(&mut self) -> Task<Message> {
         Task::perform(
             async {
-                crate::sys::file_dialog()
+                Ok(crate::sys::file_dialog()
                     .set_title(crate::t!("Add Drawings").as_ref())
                     .add_filter(
                         crate::t!("CAD Files").as_ref(),
@@ -1619,7 +1821,42 @@ impl OpenCADStudio {
                     .unwrap_or_default()
                     .into_iter()
                     .map(|handle| crate::sys::handle_path(&handle))
-                    .collect()
+                    .collect())
+            },
+            Message::DataExtractionAddDrawingsResult,
+        )
+    }
+
+    /// Web: the picked drawings have no paths to re-open later, so each one is
+    /// parsed on the shared worker right here and the document registered
+    /// under its name — the pipeline then reads the registry instead of the
+    /// filesystem. The first file that fails to parse aborts the add with the
+    /// same `name: error` shape the native refresh reports.
+    #[cfg(target_arch = "wasm32")]
+    pub(super) fn on_data_extraction_add_drawings(&mut self) -> Task<Message> {
+        Task::perform(
+            async {
+                let handles = crate::sys::file_dialog()
+                    .set_title(crate::t!("Add Drawings").as_ref())
+                    .add_filter(
+                        crate::t!("CAD Files").as_ref(),
+                        &["dwg", "dxf", "DWG", "DXF"],
+                    )
+                    .add_filter(crate::t!("All Files").as_ref(), &["*"])
+                    .pick_files()
+                    .await
+                    .unwrap_or_default();
+                let mut paths = Vec::new();
+                for handle in handles {
+                    let name = handle.file_name();
+                    let bytes = handle.read().await;
+                    let document = crate::io::parse_drawing_bytes_web(&name, &bytes)
+                        .await
+                        .map_err(|error| format!("{name}: {error}"))?;
+                    register_extraction_document(&name, document);
+                    paths.push(PathBuf::from(name));
+                }
+                Ok(paths)
             },
             Message::DataExtractionAddDrawingsResult,
         )
@@ -1740,6 +1977,18 @@ impl OpenCADStudio {
             } else {
                 rows_to_csv(&rows)
             };
+            // Web output mirrors the native CSV/TXT write (there is no xlsx
+            // writer on either target): the browser gets the same bytes as a
+            // download under the picked name.
+            #[cfg(target_arch = "wasm32")]
+            {
+                let name = path
+                    .file_name()
+                    .map(|value| value.to_string_lossy().into_owned())
+                    .unwrap_or_else(|| "extraction.csv".into());
+                crate::sys::download_bytes(&name, text.as_bytes());
+            }
+            #[cfg(not(target_arch = "wasm32"))]
             if let Err(error) = std::fs::write(&path, text) {
                 self.data_extraction.error = error.to_string();
                 return Task::none();
@@ -1835,4 +2084,47 @@ mod tests {
             vec![vec!["x".to_string()]]
         );
     }
+
+    #[test]
+    fn csv_links_read_from_registered_bytes() {
+        let name = format!("ocs-registry-{}-{}.csv", std::process::id(), line!());
+        register_picked_source(&name, Arc::new(b"a,b,c\nd,e,f\n".to_vec()));
+        let rows = read_tabular_file(Path::new(&name), None, LinkRange::CellRange, Some("B1:C2"));
+        assert_eq!(
+            rows.unwrap(),
+            vec![
+                vec!["b".to_string(), "c".to_string()],
+                vec!["e".to_string(), "f".to_string()],
+            ]
+        );
+    }
+
+    #[test]
+    fn registered_bytes_match_by_file_name() {
+        let key = format!("ocs-match-{}-{}.xlsx", std::process::id(), line!());
+        register_picked_source(
+            &format!(r"C:\drawings\{key}"),
+            Arc::new(Vec::new()),
+        );
+        // Exact key…
+        assert!(picked_source_bytes(&format!(r"C:\drawings\{key}")).is_some());
+        // …same file under a differently-cased bare name (the web stores only
+        // the name, links may store the author's path)…
+        assert!(picked_source_bytes(&key.to_ascii_uppercase()).is_some());
+        // …and not another file.
+        assert!(picked_source_bytes("ocs-match-other.xlsx").is_none());
+    }
+
+    #[test]
+    fn registered_extraction_documents_match_by_file_name() {
+        let key = format!("ocs-doc-{}-{}.dwg", std::process::id(), line!());
+        register_extraction_document(&key, CadDocument::new());
+        assert!(extraction_document(&key.to_ascii_uppercase()).is_some());
+        assert!(extraction_document("ocs-doc-other.dwg").is_none());
+    }
+
+    #[test]
+    fn workbook_metadata_bytes_rejects_non_workbooks() {
+        assert!(workbook_metadata_bytes(b"not a workbook").is_err());
+    }
 }

src/app/commands/blocks.rs

@@ -1612,9 +1612,20 @@ impl OpenCADStudio {
             "XRELOAD" => {
                 // Reload all xrefs for the current drawing. Every direct key
                 // leaves the session-unloaded set (reloaded content is live
-                // again) with fresh stat baselines on the next refresh.
-                if let Some(path) = &self.tabs[i].current_path.clone() {
-                    if let Some(base_dir) = path.parent() {
+                // again) with fresh stat baselines on the next refresh. Web:
+                // xrefs re-read from the in-session bytes registry, so an
+                // unsaved drawing reloads too; native needs the drawing's own
+                // folder for relative xref paths.
+                #[cfg(target_arch = "wasm32")]
+                let base_dir: Option<std::path::PathBuf> = Some(std::path::PathBuf::new());
+                #[cfg(not(target_arch = "wasm32"))]
+                let base_dir: Option<std::path::PathBuf> = self.tabs[i]
+                    .current_path
+                    .as_ref()
+                    .and_then(|path| path.parent().map(std::path::Path::to_path_buf));
+                if let Some(base_dir) = base_dir {
+                    {
+                        let base_dir: &std::path::Path = &base_dir;
                         let reload_keys: Vec<u64> = crate::io::xref::collect_entries_with_prev(
                             &self.tabs[i].scene.document,
                             base_dir,
@@ -1631,7 +1642,7 @@ impl OpenCADStudio {
                         }
                         let (infos, _dropped) = crate::io::xref::resolve_xrefs(
                             &mut self.tabs[i].scene.document,
-                            base_dir,
+                            &base_dir,
                         );
                         // `resolve_xrefs` re-merges ALL references — refresh stat
                         // baselines for every currently-Loaded entry so no row
@@ -1652,8 +1663,17 @@ impl OpenCADStudio {
                             }
                         }
                         for info in &infos {
+                            // Web: unresolved references surface once below,
+                            // with the drop hint, instead of a filesystem path
+                            // no browser can open.
+                            #[cfg(target_arch = "wasm32")]
+                            if info.status == crate::io::xref::XrefStatus::NotFound {
+                                continue;
+                            }
                             self.report_xref_status(info);
                         }
+                        #[cfg(target_arch = "wasm32")]
+                        self.warn_unresolved_xrefs(&infos);
                         self.post_ref_op(i);
                     }
                 } else {

src/app/commands/fileops.rs

@@ -169,72 +169,81 @@ impl OpenCADStudio {
 
             // ARCHIVE / ETRANSMIT — package the drawing and its referenced files
             // (xrefs + raster images) into a sibling "<name>_archive" folder.
+            // Web: there is no folder to copy into — the same dependency set is
+            // collected from the session's bytes registries and delivered as a
+            // "<name>_transmit.zip" download (`archive_web` below).
             "ARCHIVE" | "ETRANSMIT" => {
-                use std::path::PathBuf;
-                if let Some(src) = self.tabs[i].current_path.clone() {
-                    let stem = src
-                        .file_stem()
-                        .map(|s| s.to_string_lossy().into_owned())
-                        .unwrap_or_else(|| "drawing".into());
-                    let parent = src
-                        .parent()
-                        .map(|p| p.to_path_buf())
-                        .unwrap_or_else(|| PathBuf::from("."));
-                    let folder = parent.join(format!("{stem}_archive"));
-                    match std::fs::create_dir_all(&folder) {
-                        Ok(()) => {
-                            let mut copied = 0usize;
-                            if let Some(fname) = src.file_name() {
-                                if std::fs::copy(&src, folder.join(fname)).is_ok() {
-                                    copied += 1;
-                                }
-                            }
-                            let mut deps: Vec<String> = Vec::new();
-                            for br in self.tabs[i].scene.document.block_records.iter() {
-                                if !br.xref_path.trim().is_empty() {
-                                    deps.push(br.xref_path.clone());
-                                }
-                            }
-                            for e in self.tabs[i].scene.document.entities() {
-                                if let codec::EntityType::RasterImage(img) = e {
-                                    if !img.file_path.trim().is_empty() {
-                                        deps.push(img.file_path.clone());
+                #[cfg(not(target_arch = "wasm32"))]
+                {
+                    use std::path::PathBuf;
+                    if let Some(src) = self.tabs[i].current_path.clone() {
+                        let stem = src
+                            .file_stem()
+                            .map(|s| s.to_string_lossy().into_owned())
+                            .unwrap_or_else(|| "drawing".into());
+                        let parent = src
+                            .parent()
+                            .map(|p| p.to_path_buf())
+                            .unwrap_or_else(|| PathBuf::from("."));
+                        let folder = parent.join(format!("{stem}_archive"));
+                        match std::fs::create_dir_all(&folder) {
+                            Ok(()) => {
+                                let mut copied = 0usize;
+                                if let Some(fname) = src.file_name() {
+                                    if std::fs::copy(&src, folder.join(fname)).is_ok() {
+                                        copied += 1;
                                     }
                                 }
-                            }
-                            for d in deps {
-                                let dp = PathBuf::from(&d);
-                                let resolved = if dp.is_absolute() {
-                                    dp
-                                } else {
-                                    parent.join(&dp)
-                                };
-                                if resolved.exists() {
-                                    if let Some(fname) = resolved.file_name() {
-                                        if std::fs::copy(&resolved, folder.join(fname)).is_ok() {
-                                            copied += 1;
+                                let mut deps: Vec<String> = Vec::new();
+                                for br in self.tabs[i].scene.document.block_records.iter() {
+                                    if !br.xref_path.trim().is_empty() {
+                                        deps.push(br.xref_path.clone());
+                                    }
+                                }
+                                for e in self.tabs[i].scene.document.entities() {
+                                    if let codec::EntityType::RasterImage(img) = e {
+                                        if !img.file_path.trim().is_empty() {
+                                            deps.push(img.file_path.clone());
                                         }
                                     }
                                 }
+                                for d in deps {
+                                    let dp = PathBuf::from(&d);
+                                    let resolved = if dp.is_absolute() {
+                                        dp
+                                    } else {
+                                        parent.join(&dp)
+                                    };
+                                    if resolved.exists() {
+                                        if let Some(fname) = resolved.file_name() {
+                                            if std::fs::copy(&resolved, folder.join(fname)).is_ok()
+                                            {
+                                                copied += 1;
+                                            }
+                                        }
+                                    }
+                                }
+                                self.command_line.push_output(
+                                    crate::tf!(
+                                        "{cmd}: packaged {copied} file(s) into {}",
+                                        folder.display()
+                                    )
+                                    .as_ref(),
+                                );
                             }
-                            self.command_line.push_output(
-                                crate::tf!(
-                                    "{cmd}: packaged {copied} file(s) into {}",
-                                    folder.display()
-                                )
-                                .as_ref(),
-                            );
+                            Err(e) => self.command_line.push_error(
+                                crate::tf!("{cmd}: cannot create folder ({e}).").as_ref(),
+                            ),
                         }
-                        Err(e) => self
-                            .command_line
-                            .push_error(crate::tf!("{cmd}: cannot create folder ({e}).").as_ref()),
+                    } else {
+                        self.command_line.push_error(
+                            crate::t!("ARCHIVE: save the drawing first (it has no file path yet).")
+                                .as_ref(),
+                        );
                     }
-                } else {
-                    self.command_line.push_error(
-                        crate::t!("ARCHIVE: save the drawing first (it has no file path yet).")
-                            .as_ref(),
-                    );
                 }
+                #[cfg(target_arch = "wasm32")]
+                self.archive_web(i, cmd);
             }
 
             "EXIT" | "QUIT" => {
@@ -545,6 +554,216 @@ fn parse_background_color(args: &[&str]) -> Option<[f32; 4]> {
     None
 }
 
+// ── Web ARCHIVE / ETRANSMIT ──────────────────────────────────────────────────
+//
+// The browser has no folder to copy into, so the transmittal is assembled in
+// memory and downloaded as one ZIP — the same dependency set the native
+// folder walk collects (drawing, xrefs, raster images) plus the web-only
+// bytes-backed kinds (PDF underlays, session-picked plot tables). Anything
+// whose bytes never entered the session is reported as skipped rather than
+// silently dropped, the web counterpart of native's missing-file skip.
+#[cfg(target_arch = "wasm32")]
+impl OpenCADStudio {
+    pub(in crate::app) fn archive_web(&mut self, i: usize, cmd: &str) {
+        let Some(src) = self.tabs[i].current_path.clone() else {
+            self.command_line.push_error(
+                crate::t!("ARCHIVE: save the drawing first (it has no file path yet).").as_ref(),
+            );
+            return;
+        };
+        let stem = src
+            .file_stem()
+            .map(|s| s.to_string_lossy().into_owned())
+            .unwrap_or_else(|| "drawing".into());
+        let ext = src
+            .extension()
+            .map(|e| e.to_string_lossy().into_owned())
+            .unwrap_or_else(|| "dwg".into());
+        let filename = src
+            .file_name()
+            .map(|n| n.to_string_lossy().into_owned())
+            .unwrap_or_else(|| format!("{stem}.{ext}"));
+        let version = self.tabs[i].scene.document.version;
+
+        // The drawing itself: the same serialization a web Save performs
+        // (native copies the last-saved file; the web build has none, so the
+        // current document is re-serialized).
+        let document = self.tabs[i].scene.document_for_save();
+        let drawing = match crate::io::save_to_bytes(&document, &ext, version) {
+            Ok(bytes) => bytes,
+            Err(e) => {
+                self.command_line.push_error(
+                    crate::tf!("{cmd}: cannot package the drawing ({e}).").as_ref(),
+                );
+                return;
+            }
+        };
+        let mut entries: Vec<(String, Vec<u8>)> = vec![(filename, drawing)];
+        let mut skipped: Vec<String> = Vec::new();
+
+        // Xrefs — the block-record walk native copies; the bytes come from
+        // the session's xref registry (picked, dropped or opened files).
+        for br in self.tabs[i].scene.document.block_records.iter() {
+            if br.xref_path.trim().is_empty() {
+                continue;
+            }
+            match crate::io::xref::find_registered_source(&br.xref_path)
+                .and_then(|key| crate::io::xref::registered_bytes(&key))
+            {
+                Some(bytes) => push_entry(
+                    &mut entries,
+                    transmit_file_name(&br.xref_path),
+                    (*bytes).clone(),
+                ),
+                None => push_skipped(&mut skipped, &transmit_file_name(&br.xref_path)),
+            }
+        }
+
+        // Raster images — picked/dropped bytes registered for the reference
+        // stand in for the file native would copy.
+        for e in self.tabs[i].scene.document.entities() {
+            if let codec::EntityType::RasterImage(img) = e {
+                if img.file_path.trim().is_empty() {
+                    continue;
+                }
+                match crate::scene::model::image_model::registered_source_bytes(&img.file_path) {
+                    Some(bytes) => push_entry(
+                        &mut entries,
+                        transmit_file_name(&img.file_path),
+                        (*bytes).clone(),
+                    ),
+                    None => push_skipped(&mut skipped, &transmit_file_name(&img.file_path)),
+                }
+            }
+        }
+
+        // PDF underlays — bytes registered at attach time.
+        for o in self.tabs[i].scene.document.objects.values() {
+            if let codec::objects::ObjectType::UnderlayDefinition(def) = o {
+                if !matches!(def.underlay_type, codec::entities::UnderlayType::Pdf)
+                    || def.file_path.trim().is_empty()
+                {
+                    continue;
+                }
+                match crate::scene::model::pdf_raster::registered_source_bytes(&def.file_path) {
+                    Some(bytes) => push_entry(
+                        &mut entries,
+                        transmit_file_name(&def.file_path),
+                        (*bytes).clone(),
+                    ),
+                    None => push_skipped(&mut skipped, &transmit_file_name(&def.file_path)),
+                }
+            }
+        }
+
+        // Plot tables named by the layouts (and the session's active one).
+        // Only tables picked this session have bytes; the built-ins ship
+        // with the app, so they are neither packaged nor reported missing.
+        let mut style_names: Vec<String> = self.tabs[i]
+            .scene
+            .document
+            .objects
+            .values()
+            .filter_map(|o| {
+                if let codec::objects::ObjectType::Layout(l) = o {
+                    Some(l.plot_style_sheet.clone())
+                } else {
+                    None
+                }
+            })
+            .collect();
+        if let Some(table) = self.active_plot_style.as_ref() {
+            style_names.push(table.name.clone());
+        }
+        for name in style_names {
+            if name.trim().is_empty()
+                || crate::io::plot_style::PlotStyleTable::builtin(&name).is_ok()
+            {
+                continue;
+            }
+            match crate::io::plot_style::session_table(&name) {
+                Some(bytes) => push_entry(&mut entries, name, (*bytes).clone()),
+                None => push_skipped(&mut skipped, &name),
+            }
+        }
+
+        let zip_name = format!("{stem}_transmit.zip");
+        match build_zip(&entries) {
+            Ok(zip) => {
+                crate::sys::download_bytes(&zip_name, &zip);
+                // The same report shape the native folder transmittal makes.
+                let copied = entries.len();
+                self.command_line.push_output(
+                    crate::tf!("{cmd}: packaged {copied} file(s) into {}", zip_name).as_ref(),
+                );
+            }
+            Err(e) => self.command_line.push_error(
+                crate::tf!("{cmd}: cannot build the transmittal ZIP ({e}).").as_ref(),
+            ),
+        }
+        if !skipped.is_empty() {
+            let n = skipped.len();
+            let names = skipped.join(", ");
+            self.command_line.push_output(
+                crate::tf!("{cmd}: skipped {n} referenced file(s) not loaded in this session: {names}")
+                    .as_ref(),
+            );
+        }
+    }
+}
+
+/// Trailing component of a reference path — the flat name a transmittal
+/// packages it under (native copies `file_name()` into one folder).
+#[cfg(target_arch = "wasm32")]
+fn transmit_file_name(path: &str) -> String {
+    path.trim()
+        .rsplit(['/', '\\'])
+        .next()
+        .unwrap_or_default()
+        .to_string()
+}
+
+/// Add one entry under its flat name; a later dependency with the same name
+/// replaces the bytes (native's `fs::copy` overwrite into the folder).
+#[cfg(target_arch = "wasm32")]
+fn push_entry(entries: &mut Vec<(String, Vec<u8>)>, name: String, data: Vec<u8>) {
+    if let Some(slot) = entries
+        .iter_mut()
+        .find(|(entry, _)| entry.eq_ignore_ascii_case(&name))
+    {
+        slot.1 = data;
+    } else {
+        entries.push((name, data));
+    }
+}
+
+/// Pack the transmittal entries into one deflated ZIP archive in memory.
+#[cfg(target_arch = "wasm32")]
+fn build_zip(entries: &[(String, Vec<u8>)]) -> Result<Vec<u8>, String> {
+    use std::io::Write;
+    let mut writer = zip::ZipWriter::new(std::io::Cursor::new(Vec::new()));
+    let options = zip::write::SimpleFileOptions::default()
+        .compression_method(zip::CompressionMethod::Deflated);
+    for (name, data) in entries {
+        writer
+            .start_file(name.as_str(), options)
+            .map_err(|e| e.to_string())?;
+        writer.write_all(data).map_err(|e| e.to_string())?;
+    }
+    writer
+        .finish()
+        .map(std::io::Cursor::into_inner)
+        .map_err(|e| e.to_string())
+}
+
+/// Remember a missing dependency for the report, once per name.
+#[cfg(target_arch = "wasm32")]
+fn push_skipped(skipped: &mut Vec<String>, name: &str) {
+    if !name.is_empty() && !skipped.iter().any(|s| s.eq_ignore_ascii_case(name)) {
+        skipped.push(name.to_string());
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::app::{Message, OpenCADStudio};

src/app/mod.rs

@@ -2650,6 +2650,22 @@ pub enum Message {
         bounds: Option<iced::Rectangle>,
         screenshot: Option<iced::window::Screenshot>,
     },
+    /// Web SAVE: the serializer worker (or the inline fallback) produced the
+    /// drawing bytes; download them and finish the save bookkeeping. The
+    /// epoch/revision/camera markers snapshot the tab when serialization
+    /// started — the web counterpart of native's `snapshot_is_current`, so a
+    /// save that raced user edits does not wipe the newer dirty flag.
+    #[cfg(target_arch = "wasm32")]
+    WebSaveSerialized {
+        tab_id: u64,
+        filename: String,
+        autosave_key: String,
+        version: codec::DxfVersion,
+        geometry_epoch: u64,
+        edit_revision: u64,
+        camera_generation: u64,
+        result: Result<Vec<u8>, String>,
+    },
     /// Retry the failed save after the other application releases the file.
     #[cfg(not(target_arch = "wasm32"))]
     SaveFileInUseRetry,
@@ -4127,7 +4143,9 @@ pub enum Message {
     DataExtractionBrowseSettings,
     DataExtractionBrowseSettingsResult(Option<std::path::PathBuf>),
     DataExtractionAddDrawings,
-    DataExtractionAddDrawingsResult(Vec<std::path::PathBuf>),
+    /// Picked source drawings — `Err` carries a pick/parse failure (web
+    /// parses each file on the worker at pick time).
+    DataExtractionAddDrawingsResult(Result<Vec<std::path::PathBuf>, String>),
     DataExtractionAddFolder,
     DataExtractionAddFolderResult(Option<std::path::PathBuf>),
     DataExtractionClearSources,

src/app/update/file.rs

@@ -1958,11 +1958,18 @@ impl OpenCADStudio {
                         crate::tf!("XREF  Recovered with warnings: \"{}\"", info.name).as_ref(),
                     );
                 }
+                // Web: NotFound xrefs are summarized in one warning after the
+                // loop (see below) — the per-reference line carries a
+                // filesystem path no browser can open, and a drawing with
+                // several unresolved xrefs would repeat the same hint.
+                #[cfg(not(target_arch = "wasm32"))]
                 crate::io::xref::XrefStatus::NotFound => {
                     self.command_line.push_error(
                         crate::tf!("XREF  Not found: \"{}\" ({})", info.name, info.path).as_ref(),
                     );
                 }
+                #[cfg(target_arch = "wasm32")]
+                crate::io::xref::XrefStatus::NotFound => {}
                 crate::io::xref::XrefStatus::Failed => {
                     self.command_line.push_error(
                         crate::tf!("XREF  Recovery failed: \"{}\" ({})", info.name, info.path)
@@ -1976,6 +1983,11 @@ impl OpenCADStudio {
                 }
             }
         }
+        // Web: one warning per open lists every unresolved xref and the way
+        // to fix it — dropping the files on the page registers their bytes,
+        // and reopening the drawing (or XRELOAD) then resolves them.
+        #[cfg(target_arch = "wasm32")]
+        self.warn_unresolved_xrefs(&caches.xrefs);
         #[cfg(not(target_arch = "wasm32"))]
         let thumbs_task = self.push_recent(path.clone());
         #[cfg(target_arch = "wasm32")]
@@ -2589,83 +2601,144 @@ impl OpenCADStudio {
             self.tabs[i].scene.document.preview = Some(preview);
         }
 
-        let mut recent_task = Task::none();
         // The name the autosave snapshot for this tab is keyed by — capture it
         // before the save re-points `current_path` at the download name.
         let autosave_key = Self::web_autosave_key(&self.tabs[i]);
-        let document = self.tabs[i].scene.document_for_save();
-        let saved = match crate::io::save_to_bytes(&document, &ext, version) {
-            Ok(bytes) => {
-                crate::sys::download_bytes(&filename, &bytes);
-                let cache_name = std::path::Path::new(&filename)
-                    .file_name()
-                    .map(|name| name.to_string_lossy().into_owned())
-                    .unwrap_or_else(|| filename.clone());
-                let path = std::path::PathBuf::from(cache_name);
-                self.tabs[i].current_path = Some(path.clone());
-                self.tabs[i].scene.document.version = version;
-                self.tabs[i].dirty = false;
-                self.tabs[i].recovery_save_as_required = false;
-                recent_task = Task::perform(
-                    async move {
-                        crate::io::web_recent::store(&path.to_string_lossy(), &bytes)
-                            .await
-                            .map(|_| path)
-                    },
-                    Message::WebRecentStored,
-                );
-                // A clean save supersedes any crash-recovery snapshot for this
-                // drawing — drop the old key and the new one so stale copies
-                // don't resurface in the next boot scan. But an autosave
-                // round may still be writing the same key: its write would
-                // land AFTER the remove and resurrect the snapshot (with a
-                // newer mtime, so the next scan would offer it as
-                // recoverable). Defer the removes to the end of the round.
-                let new_key = self.tabs[i]
-                    .current_path
-                    .as_ref()
-                    .map(|path| path.to_string_lossy().into_owned())
-                    .unwrap_or_default();
-                if self.web_autosave_in_flight {
-                    self.web_autosave_clear_after.push(autosave_key);
-                    if !new_key.is_empty() {
-                        self.web_autosave_clear_after.push(new_key);
-                    }
-                } else {
-                    recent_task = Task::batch([
-                        recent_task,
-                        Task::perform(
-                            async move {
-                                let _ = crate::io::web_autosave::remove(&autosave_key).await;
-                                let _ = crate::io::web_autosave::remove(&new_key).await;
-                            },
-                            |_| Message::Noop,
-                        ),
-                    ]);
-                }
-                self.command_line
-                    .push_output(crate::tf!("Saved: {filename}").as_ref());
-                true
-            }
+        // Race guard (the web counterpart of native's `snapshot_is_current`):
+        // completion only clears the dirty flag if the tab did not change
+        // while the writer ran off-thread.
+        let geometry_epoch = self.tabs[i].scene.geometry_epoch;
+        let edit_revision = self.tabs[i].edit_revision;
+        let camera_generation = self.tabs[i].scene.camera_generation;
+        // Prepare the document here (clone + style sync + dimension bake — the
+        // app-side half of the pipeline), then hand the DWG/DXF writer pass to
+        // the browser worker so the UI thread stays responsive on large
+        // drawings. Completion (download + bookkeeping) continues in
+        // `on_web_save_serialized`.
+        let prepared =
+            crate::io::prepare_document_for_save(self.tabs[i].scene.document_for_save(), version);
+        Task::perform(
+            async move { crate::io::serialize_prepared_document(&prepared, &ext).await },
+            move |result| Message::WebSaveSerialized {
+                tab_id,
+                filename,
+                autosave_key,
+                version,
+                geometry_epoch,
+                edit_revision,
+                camera_generation,
+                result,
+            },
+        )
+    }
+
+    /// Web SAVE completion: the serializer worker (or inline fallback) has the
+    /// drawing bytes. The download and tab bookkeeping that used to run
+    /// synchronously inside `on_web_save_screenshot`, unchanged in semantics —
+    /// except the dirty flag is only cleared when the serialized snapshot is
+    /// still the tab's current state.
+    #[cfg(target_arch = "wasm32")]
+    pub(super) fn on_web_save_serialized(
+        &mut self,
+        tab_id: u64,
+        filename: String,
+        autosave_key: String,
+        version: codec::DxfVersion,
+        geometry_epoch: u64,
+        edit_revision: u64,
+        camera_generation: u64,
+        result: Result<Vec<u8>, String>,
+    ) -> Task<Message> {
+        let bytes = match result {
+            Ok(bytes) => bytes,
             Err(error) => {
                 self.command_line
                     .push_error(crate::tf!("Save failed: {error}").as_ref());
-                false
+                return self.finish_web_save(false);
             }
         };
+        // The download is the only artifact of the save — fire it even if the
+        // tab was closed while serialization was in flight.
+        crate::sys::download_bytes(&filename, &bytes);
+        let cache_name = std::path::Path::new(&filename)
+            .file_name()
+            .map(|name| name.to_string_lossy().into_owned())
+            .unwrap_or_else(|| filename.clone());
+        let path = std::path::PathBuf::from(cache_name);
+        let mut recent_task = Task::perform(
+            async move {
+                crate::io::web_recent::store(&path.to_string_lossy(), &bytes)
+                    .await
+                    .map(|_| path)
+            },
+            Message::WebRecentStored,
+        );
+        let Some(i) = self.tabs.iter().position(|tab| tab.id == tab_id) else {
+            return recent_task;
+        };
+        self.tabs[i].current_path = Some(
+            std::path::Path::new(&filename)
+                .file_name()
+                .map(|name| std::path::PathBuf::from(name.to_string_lossy().into_owned()))
+                .unwrap_or_else(|| std::path::PathBuf::from(filename.clone())),
+        );
+        self.tabs[i].scene.document.version = version;
+        self.tabs[i].recovery_save_as_required = false;
+        let snapshot_is_current = self.tabs[i].scene.geometry_epoch == geometry_epoch
+            && self.tabs[i].edit_revision == edit_revision
+            && self.tabs[i].scene.camera_generation == camera_generation;
+        if snapshot_is_current {
+            self.tabs[i].dirty = false;
+        }
+        // A clean save supersedes any crash-recovery snapshot for this
+        // drawing — drop the old key and the new one so stale copies don't
+        // resurface in the next boot scan. But an autosave round may still be
+        // writing the same key: its write would land AFTER the remove and
+        // resurrect the snapshot (with a newer mtime, so the next scan would
+        // offer it as recoverable). Defer the removes to the end of the round.
+        let new_key = self.tabs[i]
+            .current_path
+            .as_ref()
+            .map(|path| path.to_string_lossy().into_owned())
+            .unwrap_or_default();
+        if self.web_autosave_in_flight {
+            self.web_autosave_clear_after.push(autosave_key);
+            if !new_key.is_empty() {
+                self.web_autosave_clear_after.push(new_key);
+            }
+        } else {
+            recent_task = Task::batch([
+                recent_task,
+                Task::perform(
+                    async move {
+                        let _ = crate::io::web_autosave::remove(&autosave_key).await;
+                        let _ = crate::io::web_autosave::remove(&new_key).await;
+                    },
+                    |_| Message::Noop,
+                ),
+            ]);
+        }
+        self.command_line
+            .push_output(crate::tf!("Saved: {filename}").as_ref());
+        Task::batch([recent_task, self.finish_web_save(true)])
+    }
+
+    /// Tail of the web save flow: continue a pending close when the save
+    /// succeeded, or re-open the unsaved-changes dialog when it failed.
+    #[cfg(target_arch = "wasm32")]
+    fn finish_web_save(&mut self, saved: bool) -> Task<Message> {
         if self.save_dialog_for_unsaved {
             if saved {
                 if let Some(crate::app::PendingClose::Tab(tab_id)) = self.pending_close.take() {
                     let continuation = self.update(Message::TabClose(tab_id));
                     let rest = self.continue_tab_close_queue();
-                    return Task::batch([recent_task, continuation, rest]);
+                    return Task::batch([continuation, rest]);
                 }
             } else if self.pending_close.is_some() {
-                let retry = self.open_unsaved_dialog_window();
-                return Task::batch([recent_task, retry]);
+                return self.open_unsaved_dialog_window();
             }
         }
-        recent_task
+        Task::none()
     }
 
     #[cfg(not(target_arch = "wasm32"))]
@@ -3661,7 +3734,10 @@ impl OpenCADStudio {
     /// native `.sv$` copy — best-effort and non-destructive: no download, no
     /// recents update, dirty flag untouched. Snapshots run serially in one
     /// round; while it lasts (or a web save's thumbnail capture is pending)
-    /// further ticks are dropped, not queued.
+    /// further ticks are dropped, not queued. Each tab is prepared (clone +
+    /// style sync + dimension bake) once up front, then the DWG/DXF writer
+    /// pass runs on the serializer worker — the UI thread only awaits the
+    /// result between OPFS writes.
     #[cfg(target_arch = "wasm32")]
     pub(super) fn on_autosave(&mut self) -> Task<Message> {
         if self.web_autosave_in_flight || self.pending_web_thumbnail_save.is_some() {
@@ -3688,7 +3764,11 @@ impl OpenCADStudio {
             let is_dxf = crate::io::source_is_dxf(tab.current_path.as_deref(), &tab.scene.document);
             let ext = if is_dxf { "dxf" } else { "dwg" }.to_string();
             let version = tab.scene.document.version;
-            pending.push((name, ext, version, tab.scene.document.clone()));
+            pending.push((
+                name,
+                ext,
+                crate::io::prepare_document_for_save(tab.scene.document.clone(), version),
+            ));
         }
         if pending.is_empty() {
             return Task::none();
@@ -3697,10 +3777,10 @@ impl OpenCADStudio {
         Task::perform(
             async move {
                 let mut failure = None;
-                for (name, ext, version, doc) in pending {
+                for (name, ext, prepared) in pending {
                     // Autosave exists to recover geometry, not pretty recents:
                     // no thumbnail capture, just bytes into OPFS.
-                    match crate::io::save_to_bytes(&doc, &ext, version) {
+                    match crate::io::serialize_prepared_document(&prepared, &ext).await {
                         Ok(bytes) => {
                             if let Err(error) =
                                 crate::io::web_autosave::snapshot(&name, &bytes, None).await
@@ -8132,3 +8212,23 @@ mod background_task_tests {
         assert!(error.contains("worker exploded"), "error = {error}");
     }
 }
+
+impl OpenCADStudio {
+    /// Web: one warning lists every unresolved xref and the way to fix it —
+    /// dropping the files on the page registers their bytes, and reopening
+    /// the drawing (or XRELOAD) then resolves them.
+    #[cfg(target_arch = "wasm32")]
+    pub(in crate::app) fn warn_unresolved_xrefs(&mut self, infos: &[crate::io::xref::XrefInfo]) {
+        let unresolved = crate::io::xref::unresolved_xref_names(infos);
+        if unresolved.is_empty() {
+            return;
+        }
+        let names = unresolved.join(", ");
+        self.command_line.push_warning(
+            crate::tf!(
+                "XREF  Unresolved external references: {names} — drop the referenced DWG/DXF files on the page to register them, then reopen this drawing or run XRELOAD."
+            )
+            .as_ref(),
+        );
+    }
+}

src/app/update/mod.rs

@@ -1580,26 +1580,46 @@ impl OpenCADStudio {
 
                 Task::none()
             }
-            Message::XAttachPick => Task::perform(
-                async {
-                    let handle = crate::sys::file_dialog()
-                        .set_title(crate::t!("Select External Reference File").as_ref())
-                        .add_filter(
-                            crate::t!("CAD Files").as_ref(),
-                            &["dwg", "dxf", "bak", "DWG", "DXF", "BAK"],
-                        )
-                        .add_filter(crate::t!("DWG Files").as_ref(), &["dwg", "DWG"])
-                        .add_filter(crate::t!("DXF Files").as_ref(), &["dxf", "DXF"])
-                        .add_filter(crate::t!("Backup Files").as_ref(), &["bak", "BAK"])
-                        .pick_file()
-                        .await;
-                    match handle {
-                        Some(h) => Ok(crate::sys::handle_path(&h)),
-                        None => Err("Cancelled".to_string()),
-                    }
-                },
-                Message::XAttachPickResult,
-            ),
+            Message::XAttachPick => {
+                // Web: the browser hands back bytes, not a path — read them,
+                // register them name-keyed (so reloads and re-opens of the
+                // host drawing re-resolve the xref in-session) and pre-parse
+                // on the worker in one step. The returned name-only PathBuf
+                // is what the native branch's `handle_path` yields there.
+                #[cfg(target_arch = "wasm32")]
+                {
+                    Task::perform(
+                        crate::io::pick_and_register_xref_web(),
+                        Message::XAttachPickResult,
+                    )
+                }
+                #[cfg(not(target_arch = "wasm32"))]
+                {
+                    Task::perform(
+                        async {
+                            let handle = crate::sys::file_dialog()
+                                .set_title(crate::t!("Select External Reference File").as_ref())
+                                .add_filter(
+                                    crate::t!("CAD Files").as_ref(),
+                                    &["dwg", "dxf", "bak", "DWG", "DXF", "BAK"],
+                                )
+                                .add_filter(crate::t!("DWG Files").as_ref(), &["dwg", "DWG"])
+                                .add_filter(crate::t!("DXF Files").as_ref(), &["dxf", "DXF"])
+                                .add_filter(
+                                    crate::t!("Backup Files").as_ref(),
+                                    &["bak", "BAK"],
+                                )
+                                .pick_file()
+                                .await;
+                            match handle {
+                                Some(h) => Ok(crate::sys::handle_path(&h)),
+                                None => Err("Cancelled".to_string()),
+                            }
+                        },
+                        Message::XAttachPickResult,
+                    )
+                }
+            }
 
             Message::XAttachPickResult(Ok(path)) => {
                 self.open_xref_attach_dialog(path);
@@ -1692,9 +1712,13 @@ impl OpenCADStudio {
                 self.on_data_extraction_browse_settings_result(path)
             }
             Message::DataExtractionAddDrawings => self.on_data_extraction_add_drawings(),
-            Message::DataExtractionAddDrawingsResult(paths) => {
+            Message::DataExtractionAddDrawingsResult(Ok(paths)) => {
                 self.on_data_extraction_add_drawings_result(paths)
             }
+            Message::DataExtractionAddDrawingsResult(Err(error)) => {
+                self.data_extraction.error = error;
+                Task::none()
+            }
             Message::DataExtractionAddFolder => self.on_data_extraction_add_folder(),
             Message::DataExtractionAddFolderResult(path) => {
                 self.on_data_extraction_add_folder_result(path)
@@ -1728,13 +1752,22 @@ impl OpenCADStudio {
             }
 
             Message::DataExtractionSaveResult(csv, Some(path)) => {
-                match std::fs::write(&path, csv.as_bytes()) {
+                let fname = path
+                    .file_name()
+                    .map(|n| n.to_string_lossy().into_owned())
+                    .unwrap_or_else(|| path.to_string_lossy().into_owned());
+                // The browser has no writable path behind the picked name:
+                // the CSV leaves as a download instead of an fs::write.
+                #[cfg(target_arch = "wasm32")]
+                let write_result: Result<(), String> = {
+                    crate::sys::download_bytes(&fname, csv.as_bytes());
+                    Ok(())
+                };
+                #[cfg(not(target_arch = "wasm32"))]
+                let write_result = std::fs::write(&path, csv.as_bytes()).map_err(|e| e.to_string());
+                match write_result {
                     Ok(()) => {
                         let rows = csv.lines().count().saturating_sub(1);
-                        let fname = path
-                            .file_name()
-                            .map(|n| n.to_string_lossy().into_owned())
-                            .unwrap_or_else(|| path.to_string_lossy().into_owned());
                         self.command_line.push_output(
                             crate::tf!("DATAEXTRACTION  {rows} rows → \"{fname}\"").as_ref(),
                         );
@@ -10103,6 +10136,27 @@ impl OpenCADStudio {
                 screenshot,
             } => self.on_web_save_screenshot(tab_id, filename, ext, version, bounds, screenshot),
 
+            #[cfg(target_arch = "wasm32")]
+            Message::WebSaveSerialized {
+                tab_id,
+                filename,
+                autosave_key,
+                version,
+                geometry_epoch,
+                edit_revision,
+                camera_generation,
+                result,
+            } => self.on_web_save_serialized(
+                tab_id,
+                filename,
+                autosave_key,
+                version,
+                geometry_epoch,
+                edit_revision,
+                camera_generation,
+                result,
+            ),
+
             #[cfg(not(target_arch = "wasm32"))]
             Message::SaveFileInUseRetry => self.on_save_file_in_use_retry(),
 

src/io/mod.rs

@@ -42,8 +42,13 @@ pub mod xref_model;
 
 use crate::scene::DerivedCaches;
 use codec::entities::EntityType;
+// The path-based readers are native-only; web parsing runs through the
+// parse worker / the xref bytes registry instead.
+#[cfg(not(target_arch = "wasm32"))]
 use codec::io::dwg::DwgReader;
-use codec::{CadDocument, DwgReadOptions, DwgWriter, DxfReader, DxfReaderConfiguration, DxfWriter};
+#[cfg(not(target_arch = "wasm32"))]
+use codec::{DwgReadOptions, DxfReader, DxfReaderConfiguration};
+use codec::{CadDocument, DwgWriter, DxfWriter};
 use std::path::{Path, PathBuf};
 use std::sync::atomic::{AtomicU16, AtomicU32, AtomicU8, Ordering};
 use std::sync::Arc;
@@ -608,6 +613,10 @@ pub async fn open_bytes_web(
     bytes: Arc<[u8]>,
     progress: Arc<OpenProgressState>,
 ) -> WebOpenOutcome {
+    // The opened drawing's own bytes enter the xref registry too: another
+    // open drawing may reference it by name, and the registry — not the
+    // absent filesystem — is what re-resolves that reference in-session.
+    crate::io::xref::register_source(&name, Arc::new(bytes.to_vec()));
     let size_bytes = bytes.len() as u64;
     let result = load_web_bytes(&name, &bytes, progress.clone(), false, "", None).await;
     let keep_for_recovery = result
@@ -758,9 +767,16 @@ async fn load_web_bytes(
             recovery_available: true,
         });
     }
+    // XREFs inside the opened drawing resolve from the in-session bytes
+    // registry (see `resolve_web_xrefs`) before the caches snapshot the
+    // document, so merged xref geometry is part of the caches — the same
+    // phase order the native open uses.
+    let (xref_infos, xref_dropped) = resolve_web_xrefs(&mut doc, progress.clone()).await;
     let mut caches = crate::scene::build_derived_caches(&doc);
     caches.corrupt_dropped = dropped;
     caches.read_stats = Some(outcome.stats);
+    caches.xrefs = xref_infos;
+    caches.xref_dropped = xref_dropped;
     if source_sha256.is_none() && recovery_fingerprint_needed(&caches) {
         source_sha256 = web_worker::sha256_document(bytes).await.ok();
     }
@@ -814,6 +830,91 @@ pub async fn pick_and_parse_web(
     Ok(Some((name, document)))
 }
 
+/// Web: parse drawing bytes already in hand on the shared worker — the
+/// byte-level counterpart of `load_file` for callers that ran their own
+/// picker (Data Extraction's multi-file source list). Same normalization as
+/// every other web-opened drawing.
+#[cfg(target_arch = "wasm32")]
+pub async fn parse_drawing_bytes_web(name: &str, bytes: &[u8]) -> Result<CadDocument, String> {
+    parse_web_document(name, bytes).await
+}
+
+/// Web: resolve the XREF blocks inside a freshly opened drawing against the
+/// in-session bytes registry — the browser counterpart of the native open's
+/// xref phase. Every referenced file whose bytes are registered (picked or
+/// dropped earlier this session) is parsed on the shared worker first, so
+/// the UI thread only runs the (cheap) merge; unregistered references come
+/// back as `NotFound` for the open handler to warn about.
+#[cfg(target_arch = "wasm32")]
+async fn resolve_web_xrefs(
+    doc: &mut CadDocument,
+    progress: Arc<OpenProgressState>,
+) -> (Vec<crate::io::xref::XrefInfo>, usize) {
+    let pending: Vec<String> = doc
+        .block_records
+        .iter()
+        .filter(|br| (br.flags.is_xref || br.flags.is_xref_overlay) && !br.xref_path.is_empty())
+        .map(|br| br.xref_path.clone())
+        .collect();
+    let total = pending.len().max(1);
+    for (index, raw_path) in pending.iter().enumerate() {
+        progress.set(crate::app::OPEN_PHASE_XREF, 5900, index, total);
+        let Some(key) = crate::io::xref::find_registered_source(raw_path) else {
+            continue;
+        };
+        let Some(bytes) = crate::io::xref::registered_bytes(&key) else {
+            continue;
+        };
+        // The strict worker refuses recoverable parses; those fall through
+        // to a direct registry read inside the resolve so their stats (and
+        // the Failed status derived from them) match the native loader.
+        if let Ok((outcome, _)) = web_worker::parse_document(&key, &bytes, false, "").await {
+            crate::io::xref::register_parsed(&key, outcome);
+        }
+    }
+    progress.set(crate::app::OPEN_PHASE_XREF, 5900, total, total);
+    // `set_fraction` is native-only; the web phase reports completed/total
+    // directly, which the open overlay surfaces alongside the fixed weight.
+    let xref_progress: Arc<dyn Fn(usize, usize) + Send + Sync> = {
+        let progress = Arc::clone(&progress);
+        Arc::new(move |completed, total| {
+            progress.set(crate::app::OPEN_PHASE_XREF, 5900, completed, total);
+        })
+    };
+    crate::io::xref::resolve_xrefs_with_progress(doc, Path::new(""), Some(xref_progress))
+}
+
+/// Web XATTACH pick: read the chosen drawing's bytes, keep them in the xref
+/// registry (so later reloads and re-opens of the host drawing re-resolve
+/// the reference in-session), and pre-parse on the worker so the
+/// commit-time merge stays cheap. A parse failure defers to commit time,
+/// which re-reads the registered bytes and reports the same Failed status
+/// the native attach would. `Err("Cancelled")` mirrors the native pick.
+#[cfg(target_arch = "wasm32")]
+pub async fn pick_and_register_xref_web() -> Result<PathBuf, String> {
+    let Some(handle) = crate::sys::file_dialog()
+        .set_title(crate::t!("Select External Reference File").as_ref())
+        .add_filter(
+            crate::t!("CAD Files").as_ref(),
+            &["dwg", "dxf", "bak", "DWG", "DXF", "BAK"],
+        )
+        .add_filter(crate::t!("DWG Files").as_ref(), &["dwg", "DWG"])
+        .add_filter(crate::t!("DXF Files").as_ref(), &["dxf", "DXF"])
+        .add_filter(crate::t!("Backup Files").as_ref(), &["bak", "BAK"])
+        .pick_file()
+        .await
+    else {
+        return Err("Cancelled".to_string());
+    };
+    let name = handle.file_name();
+    let bytes = handle.read().await;
+    crate::io::xref::register_source(&name, Arc::new(bytes.clone()));
+    if let Ok((outcome, _)) = web_worker::parse_document(&name, &bytes, false, "").await {
+        crate::io::xref::register_parsed(&name, outcome);
+    }
+    Ok(PathBuf::from(name))
+}
+
 /// Parse a drawing from bytes using its name or recovery-file signature.
 #[cfg(not(target_arch = "wasm32"))]
 pub fn load_bytes(name: &str, bytes: Vec<u8>) -> Result<CadDocument, String> {
@@ -870,6 +971,8 @@ pub fn load_bytes_finalized(path: &Path, bytes: Vec<u8>) -> Result<(CadDocument,
 /// Load a DWG or DXF file directly from a path (auto-detect by extension).
 /// Peek at a file's leading bytes to tell a DWG (version tag "AC10xx") from a
 /// DXF. Used for `.bak` copies, whose extension hides the real format.
+/// Native-only: the web reads registered bytes instead of the filesystem.
+#[cfg(not(target_arch = "wasm32"))]
 fn sniff_dwg_or_dxf(path: &Path) -> String {
     use std::io::Read;
     let mut buf = [0u8; 6];
@@ -905,6 +1008,10 @@ pub fn load_file(_path: &Path) -> Result<CadDocument, String> {
     Err(crate::t!("Opening a drawing by path is not available in the browser.").into_owned())
 }
 
+/// Path-based reader with progress — native-only: on the web xrefs resolve
+/// from the bytes registry (`io::xref::read_registered_outcome`), never a
+/// filesystem path.
+#[cfg(not(target_arch = "wasm32"))]
 pub(crate) fn load_file_with_progress(
     path: &Path,
     _progress: Option<Arc<dyn Fn(u16) + Send + Sync>>,
@@ -1001,12 +1108,14 @@ fn load_file_for_open(
     finalize_loaded_outcome(path, outcome).map_err(OpenAttemptFailure::from)
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 struct ReaderFailure {
     message: String,
     #[cfg(not(target_arch = "wasm32"))]
     recoverable: bool,
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 impl ReaderFailure {
     fn from_reader(error: codec::DxfError) -> Self {
         Self {
@@ -1067,6 +1176,7 @@ fn merge_read_stats(
     }
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 fn read_file_attempt(
     path: &Path,
     progress: Option<Arc<dyn Fn(u16) + Send + Sync>>,
@@ -1094,6 +1204,7 @@ fn read_file_attempt(
     }
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 fn finalize_loaded_outcome(
     path: &Path,
     mut outcome: codec::ReadOutcome,
@@ -1116,6 +1227,7 @@ fn finalize_loaded_outcome(
     Ok(outcome)
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 fn read_dwg_path(
     path: &Path,
     progress: Option<Arc<dyn Fn(u16) + Send + Sync>>,
@@ -1236,6 +1348,7 @@ fn read_drawing_snapshot(path: &Path) -> std::io::Result<Vec<u8>> {
     }
 }
 
+#[cfg(not(target_arch = "wasm32"))]
 fn read_dxf_path(path: &Path, failsafe: bool) -> Result<codec::ReadOutcome, ReaderFailure> {
     DxfReader::from_file(path)
         .map_err(ReaderFailure::from_reader)?
@@ -1312,6 +1425,7 @@ fn normalize_block_origins(doc: &mut CadDocument) {
 /// are untouched. File handles are reused when still free so a repair +
 /// resave stays handle-stable; otherwise a fresh handle is minted and the
 /// record is pointed at it.
+#[cfg(not(target_arch = "wasm32"))]
 fn materialize_missing_block_markers(doc: &mut CadDocument) {
     use codec::entities::{Block, BlockEnd};
     use codec::{EntityType, Handle};
@@ -1386,6 +1500,9 @@ fn materialize_missing_block_markers(doc: &mut CadDocument) {
 /// that doesn't exist on this machine. Resolve each image to a usable path:
 /// the stored path if it exists, otherwise the same file name next to the
 /// drawing — and write the result onto the entity so the renderer finds it.
+/// Native-only: its callers resolve against a real folder; web images bind
+/// through the name-keyed byte registry instead.
+#[cfg(not(target_arch = "wasm32"))]
 fn resolve_raster_image_paths(doc: &mut CadDocument, base_dir: Option<&Path>) {
     use codec::objects::ObjectType;
     use codec::EntityType;
@@ -2133,6 +2250,13 @@ pub fn save(doc: &CadDocument, path: &Path) -> Result<(), String> {
 /// `doc.version`). Used by the web build, which hands the bytes to a browser
 /// download instead of writing a path — the byte-buffer counterpart to
 /// [`save_as_version`].
+///
+/// This is the *inline* path (main thread on wasm). The web SAVE/AUTOSAVE
+/// flows prefer [`prepare_document_for_save`] +
+/// [`serialize_prepared_document`], which runs the writer half on the browser
+/// worker; both routes share the same preparation and the same writer
+/// dispatch (`ocs_save::serialize_document`), so the produced bytes are
+/// identical.
 #[allow(dead_code)] // web/wasm build only; unused in the native target
 pub fn save_to_bytes(
     doc: &CadDocument,
@@ -2141,35 +2265,14 @@ pub fn save_to_bytes(
 ) -> Result<Vec<u8>, String> {
     let perf = crate::perf::enabled();
     let total_started = iced::time::Instant::now();
-    let clone_started = iced::time::Instant::now();
-    let mut doc = doc.clone();
-    let clone_ms = clone_started.elapsed().as_secs_f64() * 1000.0;
-    doc.version = version;
-    let styles_started = iced::time::Instant::now();
-    sync_current_styles_on_save(&mut doc);
-    let styles_ms = styles_started.elapsed().as_secs_f64() * 1000.0;
-    let dimensions_started = iced::time::Instant::now();
-    crate::modules::draw::modify::explode::bake_dimension_blocks(&mut doc);
-    let dimensions_ms = dimensions_started.elapsed().as_secs_f64() * 1000.0;
+    let doc = prepare_document_for_save(doc.clone(), version);
     let write_started = iced::time::Instant::now();
-    let result = match ext.to_lowercase().as_str() {
-        "dxf" => DxfWriter::new(&doc)
-            .write_to_vec()
-            .map_err(|e| e.to_string()),
-        _ => {
-            let mut buf = std::io::Cursor::new(Vec::new());
-            DwgWriter::write_to_writer(&mut buf, &doc).map_err(|e| e.to_string())?;
-            Ok(buf.into_inner())
-        }
-    };
+    let result = ocs_save::serialize_document(&doc, ext);
     if perf {
         let bytes = result.as_ref().map_or(0, Vec::len);
         crate::perf_record!(
-            "[perf] save-bytes total={:.1}ms clone={:.1} styles={:.1} dimensions={:.1} write={:.1} bytes={} entities={} objects={}",
+            "[perf] save-bytes total={:.1}ms write={:.1} bytes={} entities={} objects={}",
             total_started.elapsed().as_secs_f64() * 1000.0,
-            clone_ms,
-            styles_ms,
-            dimensions_ms,
             write_started.elapsed().as_secs_f64() * 1000.0,
             bytes,
             doc.entities().count(),
@@ -2179,6 +2282,59 @@ pub fn save_to_bytes(
     result
 }
 
+/// Prepare a save copy of a document: stamp the target DXF version, sync the
+/// current-style markers into their header handles / dictionary variables, and
+/// bake missing dimension geometry blocks. The app-side half of the save
+/// pipeline — it must run where the live document lives (the worker crate
+/// cannot reach the app's style/dimension modules). It takes the copy by
+/// value, so callers that already built one (`document_for_save`) pay no
+/// second clone and the live document is never touched. Both
+/// [`save_to_bytes`] and the web worker offload call this exactly once per
+/// save, so there is one implementation of the preparation for every target.
+pub fn prepare_document_for_save(mut doc: CadDocument, version: codec::DxfVersion) -> CadDocument {
+    let perf = crate::perf::enabled();
+    doc.version = version;
+    let styles_started = perf.then(iced::time::Instant::now);
+    sync_current_styles_on_save(&mut doc);
+    let styles_ms = crate::perf::elapsed_ms(styles_started);
+    let dimensions_started = perf.then(iced::time::Instant::now);
+    crate::modules::draw::modify::explode::bake_dimension_blocks(&mut doc);
+    let dimensions_ms = crate::perf::elapsed_ms(dimensions_started);
+    if perf {
+        crate::perf_record!(
+            "[perf] save-prepare styles={:.1} dimensions={:.1} entities={} objects={}",
+            styles_ms,
+            dimensions_ms,
+            doc.entities().count(),
+            doc.objects.len(),
+        );
+    }
+    doc
+}
+
+/// Web SAVE/AUTOSAVE: offload the DWG/DXF writer pass to the browser worker.
+/// `prepared` comes from [`prepare_document_for_save`] — the serialization
+/// itself (the expensive half) runs off the UI thread and the encoded bytes
+/// come back here. Falls back to inline serialization when the worker cannot
+/// spawn or errors, so a save never hard-fails just because the worker is
+/// unavailable.
+#[cfg(target_arch = "wasm32")]
+pub async fn serialize_prepared_document(
+    prepared: &CadDocument,
+    ext: &str,
+) -> Result<Vec<u8>, String> {
+    let encoded = match ocs_save::encode_request(prepared, ext) {
+        Ok(encoded) => encoded,
+        // The worker cannot help if the document cannot even be encoded —
+        // serialize inline from the document we still hold.
+        Err(error) => {
+            log::warn!("{error}; serializing inline");
+            return ocs_save::serialize_document(prepared, ext);
+        }
+    };
+    web_worker::serialize_document(encoded).await
+}
+
 // ── Post-load fixups ──────────────────────────────────────────────────────
 
 // Resolve the current text / dimension / multiline style from the handle the
@@ -3259,3 +3415,110 @@ mod pre_r2000_layer_plot_tests {
         );
     }
 }
+
+// ── Save-pipeline prepare tests ────────────────────────────────────────────
+//
+// `prepare_document_for_save` is the extracted app-side half of the save
+// pipeline, shared by the inline `save_to_bytes` and the web worker offload —
+// these pin the behaviours both routes depend on.
+
+#[cfg(test)]
+mod prepare_save_tests {
+    use super::*;
+    use codec::entities::{Dimension, DimensionLinear};
+    use codec::tables::TextStyle;
+    use codec::types::Vector3;
+
+    // The live document must never observe the save preparation: version
+    // stamp, style sync and dimension baking all happen on the clone only.
+    #[test]
+    fn prepare_stamps_version_and_leaves_live_document_untouched() {
+        let mut doc = CadDocument::new();
+        doc.version = codec::DxfVersion::AC1027;
+        let prepared = prepare_document_for_save(doc.clone(), codec::DxfVersion::AC1032);
+        assert_eq!(prepared.version, codec::DxfVersion::AC1032);
+        assert_eq!(doc.version, codec::DxfVersion::AC1027);
+    }
+
+    // The current text style marker must resolve from its name to the table
+    // entry's handle on the prepared clone (the DWG header stores a handle),
+    // while the live document keeps its previous marker.
+    #[test]
+    fn prepare_syncs_current_style_markers() {
+        let mut doc = CadDocument::new();
+        crate::io::linetypes::populate_document(&mut doc);
+        let mut style = TextStyle::new("ANNOT");
+        style.handle = doc.allocate_handle();
+        let style_handle = style.handle;
+        doc.text_styles.add(style).unwrap();
+        doc.header.current_text_style_name = "ANNOT".to_string();
+        let live_handle = doc.header.current_text_style_handle;
+        let prepared = prepare_document_for_save(doc.clone(), doc.version);
+        assert_eq!(prepared.header.current_text_style_handle, style_handle);
+        assert_eq!(doc.header.current_text_style_handle, live_handle);
+    }
+
+    // A dimension without its anonymous geometry block must get one baked on
+    // the clone (the writer emits the *D block), with the group-10 definition
+    // point mirrored into `base` — while the live document keeps neither.
+    #[test]
+    fn prepare_bakes_missing_dimension_blocks() {
+        let mut doc = CadDocument::new();
+        crate::io::linetypes::populate_document(&mut doc);
+        let mut dim = DimensionLinear::new(
+            Vector3::new(0.0, 0.0, 0.0),
+            Vector3::new(10.0, 0.0, 0.0),
+        );
+        dim.definition_point = Vector3::new(5.0, 7.0, 0.0);
+        dim.base.definition_point = Vector3::ZERO;
+        dim.base.common.handle = doc.allocate_handle();
+        let handle = dim.base.common.handle;
+        doc.add_entity(EntityType::Dimension(Dimension::Linear(dim)))
+            .unwrap();
+
+        let prepared = prepare_document_for_save(doc.clone(), doc.version);
+        let EntityType::Dimension(Dimension::Linear(linear)) =
+            prepared.get_entity(handle).unwrap()
+        else {
+            panic!("dimension missing from prepared clone");
+        };
+        assert!(
+            linear.base.block_name.starts_with("*D"),
+            "anonymous dimension block not baked: {}",
+            linear.base.block_name
+        );
+        assert!(prepared.block_records.get(&linear.base.block_name).is_some());
+        assert_eq!(linear.base.definition_point, linear.definition_point);
+
+        // The live document is untouched: no block name, stale group-10.
+        let EntityType::Dimension(Dimension::Linear(live)) =
+            doc.get_entity(handle).unwrap()
+        else {
+            panic!("dimension missing from live document");
+        };
+        assert!(live.base.block_name.is_empty());
+        assert_eq!(live.base.definition_point, Vector3::ZERO);
+    }
+
+    // The whole point of the split: the inline fallback (`save_to_bytes`) and
+    // the worker route (`prepare_document_for_save` → `ocs_save` on the
+    // worker) must produce identical bytes for the same input.
+    #[test]
+    fn save_to_bytes_equals_prepare_then_shared_serialize() {
+        let mut doc = CadDocument::new();
+        crate::io::linetypes::populate_document(&mut doc);
+        let mut dim = DimensionLinear::new(
+            Vector3::new(0.0, 0.0, 0.0),
+            Vector3::new(10.0, 0.0, 0.0),
+        );
+        dim.base.common.handle = doc.allocate_handle();
+        doc.add_entity(EntityType::Dimension(Dimension::Linear(dim)))
+            .unwrap();
+        for ext in ["dwg", "dxf"] {
+            let inline = save_to_bytes(&doc, ext, codec::DxfVersion::AC1032).expect("inline");
+            let prepared = prepare_document_for_save(doc.clone(), codec::DxfVersion::AC1032);
+            let shared = ocs_save::serialize_document(&prepared, ext).expect("shared");
+            assert_eq!(inline, shared, "inline and shared serialize diverge for {ext}");
+        }
+    }
+}

src/io/plot_style.rs

@@ -132,8 +132,11 @@ pub fn register_session_table(name: &str, bytes: Arc<Vec<u8>>) {
 }
 
 /// The bytes registered under `name` this session, matched
-/// case-insensitively the way the folder scan matches file names.
-fn session_table(name: &str) -> Option<Arc<Vec<u8>>> {
+/// case-insensitively the way the folder scan matches file names. The web
+/// ARCHIVE/ETRANSMIT packages a drawing's registered plot table into the
+/// transmittal; `None` means the table was not picked this session (the
+/// built-ins ship with the app and need no transmittal copy).
+pub fn session_table(name: &str) -> Option<Arc<Vec<u8>>> {
     session_tables()
         .lock()
         .unwrap_or_else(|poisoned| poisoned.into_inner())

src/io/web_drop.rs

@@ -130,6 +130,11 @@ pub async fn open_dropped(
     bytes: Vec<u8>,
     progress: std::sync::Arc<crate::io::OpenProgressState>,
 ) -> crate::io::WebOpenOutcome {
+    // The dropped drawing's bytes also enter the xref registry (name-keyed,
+    // like dropped raster images): another drawing may reference it by
+    // name, and the registry — not the absent filesystem — is what
+    // re-resolves that reference when its host is reopened or reloaded.
+    super::xref::register_source(&name, std::sync::Arc::new(bytes.clone()));
     progress.set(crate::app::OPEN_PHASE_READING, 500, 1, 2);
     let bytes: std::sync::Arc<[u8]> = std::sync::Arc::from(bytes);
     let size_bytes = bytes.len() as u64;

src/io/web_worker.rs

@@ -7,24 +7,10 @@ use wasm_bindgen::{JsCast, JsValue};
 use web_sys::{ErrorEvent, MessageEvent, Worker, WorkerOptions, WorkerType};
 
 const HASH_MARKER: &str = "\nreport-source-sha256:";
-const PROTOCOL_VERSION: u16 = 4;
-const WORKER_URL: &str = "ocs-parse-worker.js?v=4";
-
-#[derive(serde::Deserialize)]
-struct EntityRuntimeFields {
-    handle: u64,
-    linetype_handle: Option<u64>,
-    color_book_handle: Option<u64>,
-    face_visual_style_handle: Option<u64>,
-    edge_visual_style_handle: Option<u64>,
-    material_flags: u8,
-    material_handle: Option<u64>,
-    shadow_flags: u8,
-    plotstyle_flags: u8,
-    plotstyle_handle: Option<u64>,
-    entity_mode: Option<u8>,
-    has_ds_data: bool,
-}
+/// Version of the shared worker wire format (`ocs_save`); the `?v=` on the
+/// worker URL cache-busts to match. v5 adds the `serialize` action.
+const PROTOCOL_VERSION: u16 = ocs_save::PROTOCOL_VERSION;
+const WORKER_URL: &str = "ocs-parse-worker.js?v=5";
 
 pub(super) async fn parse_document(
     name: &str,
@@ -58,7 +44,7 @@ pub(super) async fn parse_document(
                         Result<codec::ReadOutcome, (String, Option<codec::ReadStats>)>,
                         Option<String>,
                         bool,
-                        Vec<EntityRuntimeFields>,
+                        Vec<ocs_save::EntityRuntimeFields>,
                     ) = bincode::deserialize(&bytes)
                         .map_err(|error| super::OpenLoadError::from(error.to_string()))?;
                     if payload.0 != PROTOCOL_VERSION {
@@ -69,7 +55,10 @@ pub(super) async fn parse_document(
                     }
                     match payload.1 {
                         Ok(mut outcome) => {
-                            restore_entity_runtime_fields(&mut outcome.document, payload.4);
+                            ocs_save::restore_entity_runtime_fields(
+                                &mut outcome.document,
+                                payload.4,
+                            );
                             Ok((outcome, payload.2))
                         }
                         Err((message, read_stats)) => Err(super::OpenLoadError {
@@ -136,30 +125,6 @@ pub(super) async fn parse_document(
     result
 }
 
-fn restore_entity_runtime_fields(
-    document: &mut codec::CadDocument,
-    fields: Vec<EntityRuntimeFields>,
-) {
-    let handle = |value: Option<u64>| value.map(codec::Handle::new);
-    for fields in fields {
-        let Some(entity) = document.get_entity_mut(codec::Handle::new(fields.handle)) else {
-            continue;
-        };
-        let common = entity.common_mut();
-        common.linetype_handle = handle(fields.linetype_handle);
-        common.color_book_handle = handle(fields.color_book_handle);
-        common.face_visual_style_handle = handle(fields.face_visual_style_handle);
-        common.edge_visual_style_handle = handle(fields.edge_visual_style_handle);
-        common.material_flags = fields.material_flags;
-        common.material_handle = handle(fields.material_handle);
-        common.shadow_flags = fields.shadow_flags;
-        common.plotstyle_flags = fields.plotstyle_flags;
-        common.plotstyle_handle = handle(fields.plotstyle_handle);
-        common.entity_mode = fields.entity_mode;
-        common.has_ds_data = fields.has_ds_data;
-    }
-}
-
 pub(super) async fn sha256_document(bytes: &[u8]) -> Result<String, super::OpenLoadError> {
     let options = WorkerOptions::new();
     options.set_type(WorkerType::Module);
@@ -226,6 +191,92 @@ fn decode_worker_error(message: String) -> super::OpenLoadError {
     super::OpenLoadError::new(message.to_string(), source_sha256)
 }
 
+/// Run the DWG/DXF writer pass for SAVE/AUTOSAVE on the browser worker.
+/// `encoded_request` is the shared `ocs_save` payload (prepared document +
+/// runtime-field sidecar + target extension); the worker replies with the
+/// encoded drawing bytes. Any worker failure — cannot spawn, script error,
+/// stale protocol — falls back to decoding the document here and serializing
+/// inline on this thread, so a save never hard-fails because the worker is
+/// unavailable (strict CSP, blocked worker script, out-of-memory spawn...).
+pub(super) async fn serialize_document(encoded_request: Vec<u8>) -> Result<Vec<u8>, String> {
+    match serialize_document_via_worker(&encoded_request).await {
+        Ok(bytes) => Ok(bytes),
+        Err(worker_error) => {
+            log::warn!("save worker unavailable, serializing inline: {worker_error}");
+            let (document, ext) = ocs_save::decode_request(&encoded_request)?;
+            ocs_save::serialize_document(&document, &ext)
+        }
+    }
+}
+
+async fn serialize_document_via_worker(encoded_request: &[u8]) -> Result<Vec<u8>, String> {
+    let options = WorkerOptions::new();
+    options.set_type(WorkerType::Module);
+    let worker =
+        Worker::new_with_options(WORKER_URL, &options).map_err(|error| js_error(error))?;
+
+    let (sender, receiver) =
+        iced::futures::channel::oneshot::channel::<Result<Vec<u8>, String>>();
+    let sender = Rc::new(RefCell::new(Some(sender)));
+    let message_sender = sender.clone();
+    let on_message = Closure::<dyn FnMut(MessageEvent)>::new(move |event: MessageEvent| {
+        let data = event.data();
+        let ok = Reflect::get(&data, &JsValue::from_str("ok"))
+            .ok()
+            .and_then(|value| value.as_bool())
+            .unwrap_or(false);
+        let result = if ok {
+            Reflect::get(&data, &JsValue::from_str("data"))
+                .map_err(|error| js_error(error))
+                .and_then(|value| {
+                    let bytes = Uint8Array::new(&value).to_vec();
+                    ocs_save::decode_response(&bytes)
+                })
+                .and_then(|result| result)
+        } else {
+            let message = Reflect::get(&data, &JsValue::from_str("error"))
+                .ok()
+                .and_then(|value| value.as_string())
+                .unwrap_or_else(|| "CAD serializer worker failed".to_string());
+            Err(message)
+        };
+        if let Some(sender) = message_sender.borrow_mut().take() {
+            let _ = sender.send(result);
+        }
+    });
+    worker.set_onmessage(Some(on_message.as_ref().unchecked_ref()));
+
+    let error_sender = sender;
+    let on_error = Closure::<dyn FnMut(ErrorEvent)>::new(move |event: ErrorEvent| {
+        if let Some(sender) = error_sender.borrow_mut().take() {
+            let _ = sender.send(Err(event.message()));
+        }
+    });
+    worker.set_onerror(Some(on_error.as_ref().unchecked_ref()));
+
+    let payload = Object::new();
+    Reflect::set(
+        &payload,
+        &JsValue::from_str("action"),
+        &JsValue::from_str("serialize"),
+    )
+    .map_err(|error| js_error(error))?;
+    let input = Uint8Array::from(encoded_request);
+    Reflect::set(&payload, &JsValue::from_str("document"), &input.buffer())
+        .map_err(|error| js_error(error))?;
+    let transfer = Array::new();
+    transfer.push(&input.buffer());
+    worker
+        .post_message_with_transfer(&payload, &transfer)
+        .map_err(|error| js_error(error))?;
+
+    let result = receiver
+        .await
+        .map_err(|_| "CAD serializer worker closed without a result".to_string())?;
+    worker.terminate();
+    result
+}
+
 fn js_error(value: JsValue) -> String {
     value
         .as_string()

src/io/xref.rs

@@ -7,6 +7,7 @@ use codec::types::{Handle, Vector3};
 use codec::{CadDocument, EntityType};
 use rustc_hash::{FxHashMap as HashMap, FxHashSet as HashSet};
 use std::path::{Path, PathBuf};
+use std::sync::{Arc, Mutex, OnceLock};
 
 #[cfg(not(target_arch = "wasm32"))]
 type SourceFingerprint = crate::io::edit_lock::FileFingerprint;
@@ -44,6 +45,197 @@ pub struct XrefInfo {
     pub source_sha256: Option<String>,
 }
 
+/// Names of the xrefs that resolved to nothing (`NotFound`) — the list the
+/// one-line "unresolved references" warning after a web open shows.
+pub fn unresolved_xref_names(infos: &[XrefInfo]) -> Vec<String> {
+    infos
+        .iter()
+        .filter(|info| info.status == XrefStatus::NotFound)
+        .map(|info| info.name.clone())
+        .collect()
+}
+
+// ── In-session xref byte registry (web) ────────────────────────────────
+//
+// The browser exposes no filesystem behind the path a drawing's XREF block
+// carries, so the web build keeps the bytes of every DWG/DXF the user picked
+// or dropped, keyed by file name — the xref counterpart of
+// `image_model::register_source`. Resolution matches a block-record's
+// `xref_path` against the registry by trailing file name (case-insensitive),
+// the only component two machines can be expected to agree on. Native builds
+// never consult the registry: `resolve_path` reads the real filesystem, so
+// their behaviour is byte-identical to before. The registry itself compiles
+// on every target so its pure matching logic stays unit-testable on the
+// native host.
+
+/// Lower-cased trailing component of a path-style xref reference. Drawings
+/// store xref paths as the author wrote them (often an absolute foreign
+/// path), so the file name is the only part a picked or dropped file on
+/// another machine can be expected to match.
+#[cfg_attr(not(target_arch = "wasm32"), allow(dead_code))] // unit-tested on native
+pub(crate) fn file_name_key(path: &str) -> String {
+    path.rsplit(['/', '\\'])
+        .next()
+        .unwrap_or_default()
+        .to_ascii_lowercase()
+}
+
+/// Do two xref references name the same file? Compares trailing components
+/// case-insensitively (the web has no path beyond the name at all, and the
+/// Windows paths most drawings were authored on are case-insensitive).
+#[cfg_attr(not(target_arch = "wasm32"), allow(dead_code))] // unit-tested on native
+pub(crate) fn same_file_name(a: &str, b: &str) -> bool {
+    let (a, b) = (file_name_key(a), file_name_key(b));
+    !a.is_empty() && a == b
+}
+
+fn source_cache() -> &'static Mutex<HashMap<String, Arc<Vec<u8>>>> {
+    static SOURCES: OnceLock<Mutex<HashMap<String, Arc<Vec<u8>>>>> = OnceLock::new();
+    SOURCES.get_or_init(|| Mutex::new(HashMap::default()))
+}
+
+fn parsed_cache() -> &'static Mutex<HashMap<String, codec::ReadOutcome>> {
+    static PARSED: OnceLock<Mutex<HashMap<String, codec::ReadOutcome>>> = OnceLock::new();
+    PARSED.get_or_init(|| Mutex::new(HashMap::default()))
+}
+
+/// Keep a picked or dropped drawing's bytes, keyed by the file name the
+/// drawing's xref references will be matched against. Registering supersedes
+/// any eager parse cached for the same file, so a re-pick (or a drop that
+/// finally supplies a missing reference) reloads from the new bytes.
+#[cfg_attr(not(target_arch = "wasm32"), allow(dead_code))] // mirrors image_model::register_source
+pub fn register_source(name: &str, bytes: Arc<Vec<u8>>) {
+    source_cache()
+        .lock()
+        .unwrap_or_else(|poisoned| poisoned.into_inner())
+        .insert(name.to_string(), bytes);
+    parsed_cache()
+        .lock()
+        .unwrap_or_else(|poisoned| poisoned.into_inner())
+        .retain(|parsed, _| !same_file_name(parsed, name));
+}
+
+/// Cache an off-thread parse (web parse worker) for the next resolve to
+/// merge. The entry is one-shot: a resolve consumes it, so a later reload
+/// re-reads the registered bytes instead of replaying a stale document.
+#[cfg_attr(not(target_arch = "wasm32"), allow(dead_code))]
+pub(crate) fn register_parsed(name: &str, outcome: codec::ReadOutcome) {
+    parsed_cache()
+        .lock()
+        .unwrap_or_else(|poisoned| poisoned.into_inner())
+        .insert(name.to_string(), outcome);
+}
+
+/// Registry key whose trailing file name matches `raw` (case-insensitive) —
+/// the web stand-in for `resolve_path`, which has no filesystem to consult.
+#[cfg_attr(not(target_arch = "wasm32"), allow(dead_code))] // unit-tested on native
+pub(crate) fn find_registered_source(raw: &str) -> Option<String> {
+    source_cache()
+        .lock()
+        .unwrap_or_else(|poisoned| poisoned.into_inner())
+        .keys()
+        .find(|key| same_file_name(key, raw))
+        .cloned()
+}
+
+/// Bytes registered under exactly `key`.
+#[cfg_attr(not(target_arch = "wasm32"), allow(dead_code))]
+pub(crate) fn registered_bytes(key: &str) -> Option<Arc<Vec<u8>>> {
+    source_cache()
+        .lock()
+        .unwrap_or_else(|poisoned| poisoned.into_inner())
+        .get(key)
+        .cloned()
+}
+
+/// Take the cached parse for `key`, if one is pending.
+#[cfg(any(target_arch = "wasm32", test))]
+fn take_parsed(key: &str) -> Option<codec::ReadOutcome> {
+    parsed_cache()
+        .lock()
+        .unwrap_or_else(|poisoned| poisoned.into_inner())
+        .remove(key)
+}
+
+/// Read a registered xref on the web: the cached off-thread parse when the
+/// pick/open pre-pass produced one, otherwise a direct parse of the
+/// registered bytes (the eager parse never caches recoverable outcomes —
+/// those must keep their stats so phase 2 reports them as Failed, like the
+/// native reader does).
+#[cfg(target_arch = "wasm32")]
+fn read_registered_outcome(
+    key: &str,
+    progress: Option<Arc<dyn Fn(u16) + Send + Sync>>,
+) -> Result<codec::ReadOutcome, String> {
+    if let Some(mut outcome) = take_parsed(key) {
+        finalize_xref_outcome(&mut outcome);
+        return Ok(outcome);
+    }
+    let Some(bytes) = registered_bytes(key) else {
+        return Err(format!("no registered bytes for xref \"{key}\""));
+    };
+    let mut outcome = read_outcome_from_bytes(key, bytes, progress)?;
+    finalize_xref_outcome(&mut outcome);
+    Ok(outcome)
+}
+
+/// Apply the same post-parse fixups the file-open tail applies, so merged
+/// xref content behaves like natively loaded content.
+#[cfg(target_arch = "wasm32")]
+fn finalize_xref_outcome(outcome: &mut codec::ReadOutcome) {
+    let doc = &mut outcome.document;
+    super::normalize_block_origins(doc);
+    if outcome.stats.source_format == Some(codec::SourceFormat::Dxf) {
+        super::fix_dxf_dimension_rotations(doc);
+        super::fix_dxf_layout_plot_settings(doc);
+    }
+    super::fix_viewport_status_flags(doc);
+    super::fix_current_style_names(doc);
+}
+
+/// Parse DWG/DXF bytes into a reader outcome — `load_file_with_progress`
+/// for the browser, where the "file" is the registry entry. Recoverable
+/// parse issues stay in the stats instead of failing the read, matching the
+/// native xref loader's behaviour (phase 2 turns them into Failed).
+#[cfg(target_arch = "wasm32")]
+fn read_outcome_from_bytes(
+    name: &str,
+    bytes: Arc<Vec<u8>>,
+    progress: Option<Arc<dyn Fn(u16) + Send + Sync>>,
+) -> Result<codec::ReadOutcome, String> {
+    use codec::io::dwg::DwgReader;
+    use codec::DxfReader;
+    // The readers keep their stream and want an owned, 'static buffer —
+    // take the registry `Arc`'s contents by value (one copy; the worker
+    // pre-parse makes this fallback path the exception, not the rule).
+    let bytes = bytes.to_vec();
+    let ext = name.rsplit('.').next().unwrap_or_default().to_lowercase();
+    // A `.bak`/`.sv$` copy hides the real format behind its extension —
+    // sniff the leading bytes, exactly as the path-based reader does.
+    let effective = if matches!(ext.as_str(), "bak" | "sv$") {
+        super::sniff_dwg_or_dxf_bytes(&bytes).to_string()
+    } else {
+        ext.clone()
+    };
+    let outcome = match effective.as_str() {
+        "dwg" => {
+            let mut reader = DwgReader::from_stream(std::io::Cursor::new(bytes));
+            if let Some(progress) = progress {
+                reader.set_progress_callback(progress);
+            }
+            reader.read_with_stats()
+        }
+        "dxf" => DxfReader::from_reader(std::io::Cursor::new(bytes))
+            .and_then(|reader| reader.read_with_stats()),
+        _ => return Err(format!("Unsupported file format: .{ext}")),
+    };
+    let outcome = outcome.map_err(|error| error.to_string())?;
+    if !outcome.stats.has_usable_drawing_data() {
+        return Err("initial read returned no source drawing records".to_string());
+    }
+    Ok(outcome)
+}
+
 /// Scan `doc` for XREF block-records, resolve their paths relative to
 /// `base_dir`, and populate each xref block with entities from the
 /// referenced file.
@@ -148,9 +340,16 @@ fn resolve_xrefs_with_filter(
                     });
                 callback
             });
+            #[cfg(not(target_arch = "wasm32"))]
             let xref_outcome = resolved
                 .as_ref()
                 .map(|path| super::load_file_with_progress(path, nested_progress));
+            // Web: read the registry — the cached off-thread parse when the
+            // pick/open pre-pass made one, otherwise the registered bytes.
+            #[cfg(target_arch = "wasm32")]
+            let xref_outcome = resolved
+                .as_ref()
+                .map(|path| read_registered_outcome(&path.to_string_lossy(), nested_progress));
             let source_sha256 = resolved.as_ref().and_then(|path| {
                 let needs_fingerprint = match &xref_outcome {
                     Some(Ok(outcome)) => {
@@ -414,8 +613,17 @@ pub fn layer_overrides(doc: &CadDocument, name: &str, raw_path: &str, base_dir:
     })
 }
 
+/// Web: there is no filesystem behind a stored path, so a reference resolves
+/// to the name-keyed bytes registry instead (trailing-name match); the
+/// returned path is the registry key.
+#[cfg(target_arch = "wasm32")]
+fn resolve_path(raw: &str, _base_dir: &Path) -> Option<PathBuf> {
+    find_registered_source(raw).map(PathBuf::from)
+}
+
 /// Try to build an absolute path from a raw xref path string.
 /// Handles absolute paths, relative paths, and Windows-style separators.
+#[cfg(not(target_arch = "wasm32"))]
 fn resolve_path(raw: &str, base_dir: &Path) -> Option<PathBuf> {
     let normalised = raw.replace('\\', "/");
     let p = PathBuf::from(&normalised);
@@ -3279,3 +3487,112 @@ fn relative_point_cloud_path(doc: &mut CadDocument, handle: Handle, host: &Path)
         def.source_filename = relative;
     }
 }
+
+#[cfg(test)]
+mod web_registry_tests {
+    use super::*;
+
+    fn outcome() -> codec::ReadOutcome {
+        codec::ReadOutcome::new(CadDocument::new(), codec::ReadStats::default())
+    }
+
+    #[test]
+    fn file_name_key_takes_the_trailing_component_case_folded() {
+        assert_eq!(file_name_key("Site Plan.dwg"), "site plan.dwg");
+        assert_eq!(
+            file_name_key(r"D:\Projects\Arch\XREFS\Elevation.DWG"),
+            "elevation.dwg"
+        );
+        assert_eq!(file_name_key("../consultant/model.dxf"), "model.dxf");
+        assert_eq!(file_name_key(""), "");
+    }
+
+    #[test]
+    fn same_file_name_ignores_path_and_case_but_not_empty() {
+        assert!(same_file_name(
+            r"C:\foreign\abs\PATH\Elevation.DWG",
+            "elevation.dwg"
+        ));
+        assert!(same_file_name("a/x.dwg", r"b\X.Dwg"));
+        assert!(!same_file_name("elevation.dwg", "elevation-2.dwg"));
+        // An empty trailing component names nothing — never a match, or a
+        // drawing with a blank xref path would resolve to any empty key.
+        assert!(!same_file_name("", ""));
+        assert!(!same_file_name("", "x.dwg"));
+    }
+
+    #[test]
+    fn registry_finds_a_registered_source_by_trailing_name() {
+        let registered = "Registry-Find-Site.dwg";
+        register_source(registered, Arc::new(vec![1, 2, 3]));
+        // The drawing's stored path is the author's absolute foreign path;
+        // only the trailing name can match, case-insensitively.
+        assert_eq!(
+            find_registered_source(r"E:\2009\Consultant\REGISTRY-FIND-SITE.DWG"),
+            Some(registered.to_string())
+        );
+        assert_eq!(find_registered_source("registry-find-site.dxf"), None);
+        assert_eq!(
+            registered_bytes(registered).map(|bytes| bytes.as_ref().clone()),
+            Some(vec![1, 2, 3])
+        );
+    }
+
+    #[test]
+    fn register_source_supersedes_a_cached_parse_of_the_same_file() {
+        let name = "Registry-Supersede-Plan.dwg";
+        register_parsed(name, outcome());
+        // Re-registering the same file under a differently-cased path name
+        // must drop the stale parse so a reload re-reads the new bytes.
+        register_source("registry-supersede-plan.DWG", Arc::new(vec![9]));
+        assert!(take_parsed(name).is_none());
+        // And the fresh bytes are what the registry hands back.
+        assert_eq!(
+            find_registered_source(name).as_deref(),
+            Some("registry-supersede-plan.DWG")
+        );
+    }
+
+    #[test]
+    fn unresolved_xref_names_lists_not_found_entries_only() {
+        let infos = vec![
+            XrefInfo {
+                name: "Loaded.dwg".into(),
+                path: "Loaded.dwg".into(),
+                status: XrefStatus::Loaded,
+                diagnostics: Vec::new(),
+                read_stats: None,
+                source_sha256: None,
+            },
+            XrefInfo {
+                name: "Missing A.dwg".into(),
+                path: r"C:\gone\Missing A.dwg".into(),
+                status: XrefStatus::NotFound,
+                diagnostics: Vec::new(),
+                read_stats: None,
+                source_sha256: None,
+            },
+            XrefInfo {
+                name: "Broken.dwg".into(),
+                path: "Broken.dwg".into(),
+                status: XrefStatus::Failed,
+                diagnostics: Vec::new(),
+                read_stats: None,
+                source_sha256: None,
+            },
+            XrefInfo {
+                name: "Missing B.dxf".into(),
+                path: "Missing B.dxf".into(),
+                status: XrefStatus::NotFound,
+                diagnostics: Vec::new(),
+                read_stats: None,
+                source_sha256: None,
+            },
+        ];
+        assert_eq!(
+            unresolved_xref_names(&infos),
+            vec!["Missing A.dwg".to_string(), "Missing B.dxf".to_string()]
+        );
+        assert!(unresolved_xref_names(&[]).is_empty());
+    }
+}

src/locale_catalog.rs

@@ -3756,6 +3756,7 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "new path for selection" => Some(("insert", "xref-new-path-for-selection")),
         "new path prefix" => Some(("insert", "xref-new-path-prefix")),
         "old path prefix" => Some(("insert", "xref-old-path-prefix")),
+        "XREF  Unresolved external references: {names} — drop the referenced DWG/DXF files on the page to register them, then reopen this drawing or run XRELOAD." => Some(("insert", "xref-unresolved-external-references")),
         "Y (mm)" => Some(("plot", "y-mm")),
         "Yards" => Some(("common", "yards")),
         "Yellow" => Some(("common", "yellow")),
@@ -3793,11 +3794,14 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "that object" => Some(("modal", "that-object")),
         "those objects" => Some(("modal", "those-objects")),
         "units" => Some(("common", "units")),
+        "{cmd}: cannot build the transmittal ZIP ({e})." => Some(("file", "cmd-cannot-build-the-transmittal-zip-e")),
         "{cmd}: cannot create folder ({e})." => Some(("file", "cmd-cannot-create-folder-e")),
+        "{cmd}: cannot package the drawing ({e})." => Some(("file", "cmd-cannot-package-the-drawing-e")),
         "{cmd}: no hatch objects." => Some(("view", "cmd-no-hatch-objects")),
         "{cmd}: no text or dimension objects." => Some(("view", "cmd-no-text-or-dimension-objects")),
         "{cmd}: not yet implemented." => Some(("view", "cmd-not-yet-implemented")),
         "{cmd}: packaged {copied} file(s) into {}" => Some(("file", "cmd-packaged-copied-file-s-into")),
+        "{cmd}: skipped {n} referenced file(s) not loaded in this session: {names}" => Some(("file", "cmd-skipped-n-referenced-file-s-not-loaded-in")),
         "{count} object(s) added to selection." => Some(("common", "count-object-s-added-to-selection")),
         "{count} object(s) pasted." => Some(("common", "count-object-s-pasted")),
         "{error}. External-change checks remain active." => Some(("file", "error-external-change-checks-remain-active")),
@@ -4178,6 +4182,9 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "Data Extraction Settings" => Some(("common", "data-extraction-settings")),
         "Add Drawings" => Some(("common", "add-drawings")),
         "CSV" => Some(("common", "csv")),
+        "Pick the file again to load its contents in the browser." => Some(("file", "pick-the-file-again-to-load-its-contents")),
+        "Adding folders is not available in the browser. Add drawing files instead." => Some(("file", "adding-folders-is-not-available-in-the-browser")),
+        "Drawing not loaded in the browser: {name}." => Some(("file", "drawing-not-loaded-in-the-browser")),
         "Export STL" => Some(("common", "export-stl")),
         "STL Files" => Some(("common", "stl-files")),
         "Export STEP AP203" => Some(("common", "export-step-ap203")),

src/scene/model/image_model.rs

@@ -573,6 +573,19 @@ fn registered_bytes_by_name(path: &str) -> Option<Arc<Vec<u8>>> {
         .map(|(_, bytes)| Arc::clone(bytes))
 }
 
+/// Original image file bytes registered for a reference, resolved the way
+/// `decode_reference` resolves pixels: exact reference first, then any
+/// registration that names the same file. The web ARCHIVE/ETRANSMIT
+/// packages these bytes into the transmittal; `None` means nothing was
+/// picked or dropped for the reference this session.
+pub fn registered_source_bytes(path: &str) -> Option<Arc<Vec<u8>>> {
+    let path = path.trim();
+    if path.is_empty() {
+        return None;
+    }
+    registered_bytes(path).or_else(|| registered_bytes_by_name(path))
+}
+
 /// Drop every memoised image so the next resolve re-reads / re-fetches. Called
 /// when a new document is opened — a fresh drawing shouldn't inherit a prior
 /// one's stale successes or offline failures.

src/scene/model/pdf_raster.rs

@@ -38,6 +38,18 @@ fn source_cache() -> &'static Mutex<HashMap<String, Arc<Vec<u8>>>> {
     SOURCES.get_or_init(|| Mutex::new(HashMap::new()))
 }
 
+/// Bytes registered for exactly this PDF reference (the attach flow keys by
+/// the same path the underlay definition stores). The web ARCHIVE/ETRANSMIT
+/// packages the underlay into the transmittal; `None` means no PDF was
+/// picked for this reference this session.
+pub fn registered_source_bytes(path: &str) -> Option<Arc<Vec<u8>>> {
+    source_cache()
+        .lock()
+        .unwrap_or_else(|error| error.into_inner())
+        .get(path)
+        .cloned()
+}
+
 /// Keep bytes selected through a file dialog. Browsers expose no reusable path,
 /// while native builds also benefit by avoiding a second disk read.
 pub fn register_source(path: &str, bytes: Arc<Vec<u8>>) {

src/ui/window/annotation_data.rs

@@ -899,6 +899,17 @@ pub fn data_extraction_view(
     let add_folder = button(text(t!("Add folder…")).size(12)).padding([5, 10]);
     #[cfg(not(target_arch = "wasm32"))]
     let add_folder = add_folder.on_press(Message::DataExtractionAddFolder);
+    // The web has no folder picker and no directory to walk, so the button
+    // stays disabled there — with a tooltip that says why and what to do.
+    #[cfg(target_arch = "wasm32")]
+    let add_folder = iced::widget::tooltip(
+        add_folder,
+        container(text(t!("Adding folders is not available in the browser. Add drawing files instead.")).size(11))
+            .padding([3, 6])
+            .style(container::bordered_box),
+        iced::widget::tooltip::Position::Top,
+    )
+    .gap(4);
 
     let body: Element<'_, Message> = match state.page {
         ExtractionPage::Begin => group(