Merge pull request #399 from storytold/fix/issue-367

Fix #367: keep a paused browser tab's recovery copies

ROADMAP.md

@@ -143,7 +143,7 @@ grade by behaviour against `plan/illustrator/`, not by whether a menu item exist
 - **Colour, type and file workflows:** Recolor Artwork (dialog with harmonies), Edit Colors, Find & Replace, Change Case, Smart Punctuation, Guides, Lock/Hide Above, Transform Each, Rasterize.
 - **Fonts:** a font is found by any of its names (family and style in every language of its name table, legacy family/style pairs, PostScript name), so documents from other apps open with the font they name; Find Font and `text.fonts` say for each font whether it was found exactly, by another name, substituted or missing, and how many glyphs are missing. PDF and `.ai` import brings Japanese text back as live type: CID fonts without a ToUnicode map read through the standard CMaps, vertical columns (WMode 1) as vertical type, letter spacing as tracking; a glyph is live type only when the installed font (in the closest style of its family) draws the same glyph, and text in a font that isn't installed comes in as live type shown in the fallback font until the font is installed (exports that draw it — PDF, EPS, EMF/WMF, raster, SVG outlines or embedded fonts — warn that they wrote the fallback font; `textAs: outlines` keeps the PDF's embedded glyphs).
 - **Files (M4):**
-  - `.vectorcraft` (lossless JSON, compressed, atomic saves, save down to v1), Save As with a format chooser, Save a Copy, Revert, templates, Data Recovery after a crash, background save and export.
+  - `.vectorcraft` (lossless JSON, compressed, atomic saves, save down to v1), Save As with a format chooser, Save a Copy, Revert, templates, Data Recovery after a crash (browser tabs hold their copies with Web Locks too, so a background tab's copies are never taken for a crash's, and a tab repairs copies another removed when it resumes: #367), background save and export.
   - SVG/SVGZ in and out with SVG Options, Preserve Editing, symbols, filters, rich text and physical units; PDF and PDF-compatible `.ai` in and out (layers, masks, editable text with type set along a curve coming back as type on a path, each artboard's art on its own page only, an `.ai`'s white page under its layers left out rather than coming in as art, spot colours, presets, security, marks and bleed, ICC output intents, raster effects, subset fonts, PDF/X, PDF layers, overprint, page thumbnails, fast web view, PDF 1.3). CMYK images keep their ink amounts from PDF import (and from placed CMYK TIFFs) to PDF export: a CMYK JPEG passes through unchanged, others stay CMYK (DeviceCMYK, or ICC-based CMYK in PDF/X-3/X-4) unless the Output settings convert them; the canvas shows them through the working CMYK profile (#320).
   - EPS and DXF in and out, EMF/WMF in and out; PNG (with PNG-8), JPEG, WebP, GIF, TIFF, BMP, Targa and layered PSD export. EPS import runs Illustrator's AGM/CoolType prologs (resource categories, `resourceforall`, `clipsave`/`cliprestore`, subarrays and substrings that share storage, the standard dictionaries in `systemdict`, `dictstack`, `internaldict`, executable filters, `cshow`, metadata skipped with `flushfile`), so Illustrator 30 EPS files open as vectors, and falls back to its palette TIFF preview. DXF TEXT justified Fit or Aligned spans its two points (stretched, or scaled as a whole).
   - Place and the Links panel, Package, File Info, Print with print presets, PostScript output and print tiling, slices and Save for Web, Export for Screens and Asset Export, CSS Properties, PNG/PDF/SVG/text clipboard flavours.

apps/vectorcraft-web/Cargo.toml

@@ -27,4 +27,4 @@ rfd = { workspace = true }
 wasm-bindgen = "0.2"
 wasm-bindgen-futures = "0.4"
 js-sys = "0.3"
-web-sys = { version = "0.3", features = ["Window", "Document", "Element", "HtmlElement", "HtmlCanvasElement", "HtmlIFrameElement", "HtmlAnchorElement", "Blob", "BlobPropertyBag", "Url", "Location", "CssStyleDeclaration", "Event", "EventTarget", "MouseEvent", "DragEvent", "Storage"] }
+web-sys = { version = "0.3", features = ["Window", "Document", "Element", "HtmlElement", "HtmlCanvasElement", "HtmlIFrameElement", "HtmlAnchorElement", "Blob", "BlobPropertyBag", "Url", "Location", "CssStyleDeclaration", "Event", "EventTarget", "MouseEvent", "DragEvent", "Storage", "Navigator"] }

apps/vectorcraft-web/src/locks.rs

@@ -0,0 +1,122 @@
+//! The browser's Web Locks (`navigator.locks`), which tell Data Recovery whether another tab still
+//! runs ([`vectorcraft_engine::cmd::recovery::RecoveryStore::announce`]). A tab holds a lock named
+//! after its recovery area for as long as it lives; the browser releases it only when the tab is
+//! gone (closed, crashed or reloaded), not while its timers are paused in the background, which a
+//! heartbeat can't tell apart.
+//!
+//! web-sys has Web Locks only as an unstable API, so they are reached through `js_sys::Reflect`.
+//! Pages that aren't secure (plain `http://` other than localhost) and older browsers have none:
+//! heartbeats alone decide there.
+
+use std::cell::RefCell;
+use std::collections::{BTreeMap, BTreeSet};
+use std::sync::{Arc, Mutex};
+
+use js_sys::{Function, Promise, Reflect};
+use vectorcraft_engine::cmd::recovery::Hold;
+use wasm_bindgen::JsCast as _;
+use wasm_bindgen::JsValue;
+use wasm_bindgen::closure::Closure;
+
+/// How often the snapshot of the locks held is refreshed (ms).
+const REFRESH_MS: i32 = 10_000;
+/// How old a snapshot may be and still be trusted (ms). A lock asked for after the snapshot was
+/// taken comes with a heartbeat, which stays fresh for at least three minutes, so anything under
+/// that is safe; an older snapshot counts every area as held.
+const FRESH_MS: f64 = 60_000.0;
+
+thread_local! {
+    /// What releases each lock this tab holds, by name: it resolves the promise the lock is held
+    /// by (wasm runs on one thread).
+    static RELEASE: RefCell<BTreeMap<String, Function>> = const { RefCell::new(BTreeMap::new()) };
+}
+
+/// The locks of the page, named `<prefix><area>`.
+#[derive(Clone)]
+pub struct WebLocks {
+    prefix: &'static str,
+    /// The areas whose locks were held at the last snapshot, and when it was asked for (ms since
+    /// the epoch). `navigator.locks.query()` is asynchronous, so the snapshot is refreshed every
+    /// [`REFRESH_MS`] and read from here.
+    seen: Arc<Mutex<(f64, BTreeSet<String>)>>,
+}
+
+/// `navigator.locks`, if the browser has it here.
+fn manager() -> Option<JsValue> {
+    let locks = Reflect::get(&web_sys::window()?.navigator(), &"locks".into()).ok()?;
+    locks.is_object().then_some(locks)
+}
+
+/// Method `name` of `obj`.
+fn method(obj: &JsValue, name: &str) -> Option<Function> {
+    Reflect::get(obj, &name.into()).ok()?.dyn_into().ok()
+}
+
+impl WebLocks {
+    /// The page's Web Locks with a first snapshot of them, kept fresh from then on; `None` when
+    /// the browser has none or won't say which are held (heartbeats alone decide then).
+    pub async fn start(prefix: &'static str) -> Option<Self> {
+        let locks = Self { prefix, seen: Arc::new(Mutex::new((f64::NEG_INFINITY, BTreeSet::new()))) };
+        locks.refresh().await?;
+        let again = locks.clone();
+        let tick = Closure::<dyn FnMut()>::new(move || {
+            let locks = again.clone();
+            wasm_bindgen_futures::spawn_local(async move {
+                // A failed refresh leaves the snapshot to age, and every area counts as held.
+                let _ = locks.refresh().await;
+            });
+        });
+        web_sys::window()?.set_interval_with_callback_and_timeout_and_arguments_0(tick.as_ref().unchecked_ref(), REFRESH_MS).ok()?;
+        // The timer lives as long as the page.
+        tick.forget();
+        Some(locks)
+    }
+
+    /// Take a new snapshot of the locks held.
+    async fn refresh(&self) -> Option<()> {
+        let m = manager()?;
+        let asked = js_sys::Date::now();
+        let query: Promise = method(&m, "query")?.call0(&m).ok()?.dyn_into().ok()?;
+        let snapshot = wasm_bindgen_futures::JsFuture::from(query).await.ok()?;
+        let held = js_sys::Array::from(&Reflect::get(&snapshot, &"held".into()).ok()?);
+        let areas = held
+            .iter()
+            .filter_map(|l| Reflect::get(&l, &"name".into()).ok()?.as_string())
+            .filter_map(|n| n.strip_prefix(self.prefix).map(str::to_string))
+            .collect();
+        *self.seen.lock().unwrap_or_else(|e| e.into_inner()) = (asked, areas);
+        Some(())
+    }
+
+    /// Does a tab hold `area`'s lock? Yes when the last snapshot is too old to tell.
+    pub fn held(&self, area: &str) -> bool {
+        let seen = self.seen.lock().unwrap_or_else(|e| e.into_inner());
+        js_sys::Date::now() - seen.0 > FRESH_MS || seen.1.contains(area)
+    }
+
+    /// Hold `area`'s lock until the returned hold is dropped (or the page goes).
+    pub fn hold(&self, area: &str) -> Option<Hold> {
+        let m = manager()?;
+        let name = format!("{}{area}", self.prefix);
+        // The lock is held until this promise resolves: when the hold is dropped.
+        let mut release = None;
+        let until = Promise::new(&mut |resolve, _| release = Some(resolve));
+        let release = release?;
+        let granted = Closure::once_into_js(move |_lock: JsValue| until);
+        method(&m, "request")?.call2(&m, &name.clone().into(), &granted).ok()?;
+        RELEASE.with(|r| r.borrow_mut().insert(name.clone(), release));
+        Some(Box::new(LockHold(name)))
+    }
+}
+
+/// A lock this tab holds (by name), released when dropped.
+struct LockHold(String);
+
+impl Drop for LockHold {
+    fn drop(&mut self) {
+        if let Some(resolve) = RELEASE.with(|r| r.borrow_mut().remove(&self.0)) {
+            // Resolving can't fail in a way worth reporting: the lock goes with the page anyway.
+            let _ = resolve.call0(&JsValue::NULL);
+        }
+    }
+}

apps/vectorcraft-web/src/main.rs

@@ -13,6 +13,8 @@
 //!
 //! URL query flag: `?webgl` forces the WebGL2 backend instead of WebGPU.
 
+#[cfg(target_arch = "wasm32")]
+mod locks;
 #[cfg(target_arch = "wasm32")]
 mod web;
 

apps/vectorcraft-web/src/web.rs

@@ -6,12 +6,14 @@ use std::sync::{Arc, Mutex};
 
 use vectorcraft_engine::Session;
 use vectorcraft_engine::cmd::fileio;
-use vectorcraft_engine::cmd::recovery::RecoveryStore;
+use vectorcraft_engine::cmd::recovery::{Hold, RecoveryStore};
 use vectorcraft_ui_egui::place::{DropTarget, PlaceArrival, PlaceInbox};
 use vectorcraft_ui_egui::print::{PrintJob, PrintService, Printer};
 use vectorcraft_ui_egui::{Services, VectorcraftApp};
 use wasm_bindgen::JsCast as _;
 
+use crate::locks::WebLocks;
+
 type Inbox = Arc<Mutex<Vec<(String, Vec<u8>)>>>;
 
 /// Where the pointer was over the canvas during the last file drag (CSS px from its top-left) and
@@ -33,6 +35,8 @@ pub fn start() {
             return;
         };
         let drag = track_drag(&canvas);
+        // Before the first frame, which looks for copies a crash left behind.
+        let locks = WebLocks::start(RECOVERY_PREFIX).await;
         let mut options = eframe::WebOptions::default();
         if query().contains("webgl")
             && let eframe::egui_wgpu::WgpuSetup::CreateNew(create) = &mut options.wgpu_options.wgpu_setup
@@ -49,7 +53,7 @@ pub fn start() {
                     }
                     let inbox: Inbox = Arc::default();
                     let place_inbox: PlaceInbox = Arc::default();
-                    let app = VectorcraftApp::new(Session::new(), services(inbox.clone(), place_inbox.clone(), cc.egui_ctx.clone()));
+                    let app = VectorcraftApp::new(Session::new(), services(inbox.clone(), place_inbox.clone(), cc.egui_ctx.clone(), locks));
                     Ok(Box::new(WebShell { app, inbox, place_inbox, drag }))
                 }),
             )
@@ -132,7 +136,7 @@ impl eframe::App for WebShell {
     }
 }
 
-fn services(inbox: Inbox, place_inbox: PlaceInbox, ctx: egui::Context) -> Services {
+fn services(inbox: Inbox, place_inbox: PlaceInbox, ctx: egui::Context, locks: Option<WebLocks>) -> Services {
     let open_inbox = inbox.clone();
     let picked = place_inbox.clone();
     let place_ctx = ctx.clone();
@@ -174,7 +178,7 @@ fn services(inbox: Inbox, place_inbox: PlaceInbox, ctx: egui::Context) -> Servic
             }
         })),
         inbox: Some(inbox),
-        recovery_store: Some(Arc::new(BrowserStore)),
+        recovery_store: Some(Arc::new(BrowserStore { locks })),
         // File → Print: the browser's print dialog.
         print: Some(Box::new(BrowserPrint)),
         ..Default::default()
@@ -183,8 +187,12 @@ fn services(inbox: Inbox, place_inbox: PlaceInbox, ctx: egui::Context) -> Servic
 
 /// Data Recovery's store on the web: the browser's local storage (kept across visits and shared by
 /// the site's tabs), each entry as base64 under [`RECOVERY_PREFIX`]`<area>/<name>`. It has no
-/// locks: each tab holds its area with a heartbeat, judged by the browser's clock.
-struct BrowserStore;
+/// locks: each tab holds its area with a heartbeat, judged by the browser's clock, and with a Web
+/// Lock named after it where the browser has them (`locks`), which a tab whose timers are paused
+/// in the background keeps.
+struct BrowserStore {
+    locks: Option<WebLocks>,
+}
 
 const RECOVERY_PREFIX: &str = "vectorcraft-recovery/";
 
@@ -220,6 +228,12 @@ impl RecoveryStore for BrowserStore {
     fn now(&self) -> Option<i64> {
         Some((js_sys::Date::now() / 1000.0) as i64)
     }
+    fn announce(&self, area: &str) -> Option<Hold> {
+        self.locks.as_ref()?.hold(area)
+    }
+    fn announced(&self, area: &str) -> Option<bool> {
+        self.locks.as_ref().map(|l| l.held(area))
+    }
 }
 
 /// Trigger a browser download of `bytes` named after the last component of `path`.

crates/engine/src/cmd/recovery.rs

@@ -13,9 +13,17 @@
 //!
 //! Every running app (each browser tab) keeps its copies in an area of its own, `<area>/…`, and
 //! holds it while it runs: a lock on the area for its lifetime where the store has locks (folders:
-//! [`FolderStore`]), else a heartbeat it refreshes ([`heartbeat`]; browser storage). Only areas
-//! nobody holds any more (their app is gone) are offered, and while their copies are restored or
-//! discarded the area is held, so two apps launched together never both take it.
+//! [`FolderStore`]), else a heartbeat it refreshes ([`heartbeat`]; browser storage) plus, where the
+//! store can, an announcement that lasts as long as the app ([`RecoveryStore::announce`]: the
+//! browser's Web Locks). Only areas nobody holds any more (their app is gone) are offered, and
+//! while their copies are restored or discarded the area is held, so two apps launched together
+//! never both take it.
+//!
+//! A heartbeat alone can't tell a gone app from one whose timers stopped (a background tab), so
+//! when unsure an area counts as held, and its app repairs what another app did meanwhile: each
+//! heartbeat and each recovery save write again the copies missing from its area ([`repair`]), and
+//! a heartbeat newer than the one another app wrote when taking the area over marks it running
+//! again.
 //!
 //! Each copy is two entries: `<area>/<file>.vectorcraft` (the native document, written as a save
 //! writes it) and `<area>/<file>.json` (its title, original path and format, and when it was
@@ -86,6 +94,17 @@ pub trait RecoveryStore: Send + Sync {
     fn lock(&self, _area: &str) -> std::result::Result<Lock, String> {
         Ok(Lock::Unsupported)
     }
+    /// Stores without locks: also hold area `area` in a way other apps can see that lasts exactly as
+    /// long as this app runs, if the store has one (the browser's Web Locks) → it, until dropped.
+    fn announce(&self, _area: &str) -> Option<Hold> {
+        None
+    }
+    /// Stores without locks: does a running app hold area `area` by [`RecoveryStore::announce`]?
+    /// `None`: the store can't tell (heartbeats alone decide). A store that can tell but isn't sure
+    /// right now says `Some(true)`: a copy kept loses nothing, one deleted may.
+    fn announced(&self, _area: &str) -> Option<bool> {
+        None
+    }
     /// Tidy away area `area` once it holds no copies and nobody holds it (its lock file and folder).
     fn remove_area(&self, _area: &str) {}
     /// The clock heartbeats are judged by (Unix seconds; `None`: none, so no area counts as gone).
@@ -96,17 +115,19 @@ pub trait RecoveryStore: Send + Sync {
 
 /// A store in memory (tests, and hosts without storage). Areas are locked in memory, so sessions
 /// sharing one store behave like apps sharing a folder; [`MemoryStore::without_locks`] uses
-/// heartbeats like browser storage, judged by a clock tests set ([`MemoryStore::set_now`]).
+/// heartbeats like browser storage, judged by a clock tests set ([`MemoryStore::set_now`]), and
+/// [`MemoryStore::announcing`] adds announcements like the browser's Web Locks.
 pub struct MemoryStore {
     entries: Mutex<BTreeMap<String, Vec<u8>>>,
     held: Arc<Mutex<BTreeSet<String>>>,
     locks: bool,
+    announces: bool,
     now: Mutex<Option<i64>>,
 }
 
 impl Default for MemoryStore {
     fn default() -> Self {
-        Self { entries: Default::default(), held: Default::default(), locks: true, now: Mutex::new(Some(1_000_000)) }
+        Self { entries: Default::default(), held: Default::default(), locks: true, announces: false, now: Mutex::new(Some(1_000_000)) }
     }
 }
 
@@ -116,6 +137,19 @@ impl MemoryStore {
         Self { locks: false, ..Self::default() }
     }
 
+    /// A store without locks whose apps also announce the areas they hold for as long as they run
+    /// (as the browser's Web Locks do).
+    pub fn announcing() -> Self {
+        Self { announces: true, ..Self::without_locks() }
+    }
+
+    fn hold(&self, area: &str) -> Option<Hold> {
+        if !self.held.lock().unwrap_or_else(|e| e.into_inner()).insert(area.to_string()) {
+            return None;
+        }
+        Some(Box::new(MemoryHold { held: self.held.clone(), area: area.to_string() }))
+    }
+
     /// Set the clock heartbeats are judged by.
     pub fn set_now(&self, t: i64) {
         *self.now.lock().unwrap_or_else(|e| e.into_inner()) = Some(t);
@@ -160,10 +194,16 @@ impl RecoveryStore for MemoryStore {
         if !self.locks {
             return Ok(Lock::Unsupported);
         }
-        if !self.held.lock().unwrap_or_else(|e| e.into_inner()).insert(area.to_string()) {
-            return Ok(Lock::Busy);
+        Ok(self.hold(area).map_or(Lock::Busy, Lock::Held))
+    }
+    fn announce(&self, area: &str) -> Option<Hold> {
+        if !self.announces {
+            return None;
         }
-        Ok(Lock::Held(Box::new(MemoryHold { held: self.held.clone(), area: area.to_string() })))
+        self.hold(area)
+    }
+    fn announced(&self, area: &str) -> Option<bool> {
+        self.announces.then(|| self.held.lock().unwrap_or_else(|e| e.into_inner()).contains(area))
     }
     fn now(&self) -> Option<i64> {
         *self.now.lock().unwrap_or_else(|e| e.into_inner())
@@ -288,8 +328,11 @@ struct Own {
     /// The store it is in (copies are removed from there even after the preference moves on).
     store: Arc<dyn RecoveryStore>,
     area: String,
-    /// The lock held for the session's lifetime; none in stores with heartbeats.
+    /// What holds the area for the session's lifetime: its lock, else its announcement (stores
+    /// without locks that have them).
     hold: Option<Hold>,
+    /// Held with a heartbeat (stores without locks).
+    beats: bool,
 }
 
 /// The session's recovery store settings and its own area ([`crate::Session::recovery`]).
@@ -300,9 +343,10 @@ pub struct Recovery {
     /// The folder the desktop app keeps copies in when the `recoveryFolder` preference is empty.
     default_folder: Option<String>,
     own: Option<Own>,
-    /// Gone apps' areas this session took over by heartbeat (stores without locks), so its own
-    /// fresh heartbeat there doesn't make them look running.
-    adopted: BTreeSet<String>,
+    /// Gone apps' areas this session took over by heartbeat (stores without locks), with the
+    /// heartbeat it wrote there: that one doesn't make them look running, a newer one does (their
+    /// app was only paused and came back).
+    adopted: BTreeMap<String, i64>,
 }
 
 impl Recovery {
@@ -354,31 +398,52 @@ fn stale_after(s: &Session) -> i64 {
     (i64::from(s.prefs.autosave_interval.max(1)) * 180).max(MIN_STALE)
 }
 
-/// Record that `area`'s app runs (stores without locks).
-fn beat(store: &dyn RecoveryStore, area: &str) -> std::result::Result<(), String> {
+/// Record that `area`'s app runs (stores without locks) → the heartbeat written.
+fn beat(store: &dyn RecoveryStore, area: &str) -> std::result::Result<i64, String> {
     let now = store.now().ok_or("no clock to keep a heartbeat by")?;
-    store.write(&format!("{area}/{BEAT}"), now.to_string().as_bytes())
+    store.write(&format!("{area}/{BEAT}"), now.to_string().as_bytes())?;
+    Ok(now)
 }
 
-/// Has `area`'s app said it runs within `stale` seconds (stores without locks)? Without a clock
-/// every app counts as running.
-fn beating(store: &dyn RecoveryStore, area: &str, stale: i64) -> bool {
+/// Has `area`'s app said it runs within `stale` seconds (stores without locks)? `mine`: the
+/// heartbeat this session wrote there itself when taking the area over, which doesn't count.
+/// Without a clock every app counts as running.
+fn beating(store: &dyn RecoveryStore, area: &str, stale: i64, mine: Option<i64>) -> bool {
     let Some(now) = store.now() else { return true };
     let at = store.read(&format!("{area}/{BEAT}")).ok().and_then(|b| String::from_utf8(b).ok()).and_then(|t| t.trim().parse::<i64>().ok());
-    at.is_some_and(|t| now.saturating_sub(t) <= stale)
+    at.is_some_and(|t| now.saturating_sub(t) <= stale && Some(t) != mine)
 }
 
-/// Refresh this session's heartbeat in a store without locks (the app does this every
-/// [`HEARTBEAT_EVERY`] seconds). Best effort: a missed beat only lets another app offer the copies
-/// once three intervals have passed.
-pub fn heartbeat(s: &Session) {
-    if let Some(own) = s.recovery.own.as_ref().filter(|o| o.hold.is_none()) {
+/// Refresh this session's hold on its area (the app does this every [`HEARTBEAT_EVERY`] seconds,
+/// so also on its first frame after its timers were paused): its heartbeat in a store without
+/// locks, and its copies ([`repair`]) → the documents whose copies went missing (write them now).
+/// Best effort: a missed beat only lets another app offer the copies once three intervals have
+/// passed.
+pub fn heartbeat(s: &mut Session) -> Vec<u64> {
+    if let Some(own) = s.recovery.own.as_ref().filter(|o| o.beats) {
         let _ = beat(own.store.as_ref(), &own.area);
     }
+    repair(s)
+}
+
+/// Forget this session's copies that are missing from its area, so the next recovery save writes
+/// them again → their documents' uids. Another app removes them only when it took this one for
+/// gone (its heartbeat stopped while its timers were paused, as browsers do to background tabs); a
+/// copy it restored is its own now, so both are kept. A store that can't be listed changes nothing.
+pub fn repair(s: &mut Session) -> Vec<u64> {
+    let Some(names) = s.recovery.own.as_ref().and_then(|o| o.store.list().ok()) else { return vec![] };
+    let mut lost = vec![];
+    for st in &mut s.docs {
+        if st.recovery.as_ref().is_some_and(|c| !names.iter().any(|n| n.strip_suffix(DOC_EXT) == Some(c.file.as_str()))) {
+            st.recovery = None;
+            lost.push(st.uid);
+        }
+    }
+    lost
 }
 
 /// This session's area in `store`, taken now if it has none there yet: a fresh area, held for the
-/// session's lifetime (locked, or with a heartbeat).
+/// session's lifetime (locked, or with a heartbeat and an announcement where the store has them).
 pub fn claim(s: &mut Session, store: &Arc<dyn RecoveryStore>) -> Result<String> {
     if let Some(own) = &s.recovery.own {
         if own.store.location() == store.location() {
@@ -394,15 +459,15 @@ pub fn claim(s: &mut Session, store: &Arc<dyn RecoveryStore>) -> Result<String>
         if taken.contains(&area) {
             continue;
         }
-        let hold = match store.lock(&area).map_err(EngineError::Other)? {
-            Lock::Held(h) => Some(h),
+        let (hold, beats) = match store.lock(&area).map_err(EngineError::Other)? {
+            Lock::Held(h) => (Some(h), false),
             Lock::Busy => continue,
             Lock::Unsupported => {
                 beat(store.as_ref(), &area).map_err(EngineError::Other)?;
-                None
+                (store.announce(&area), true)
             }
         };
-        s.recovery.own = Some(Own { store: store.clone(), area: area.clone(), hold });
+        s.recovery.own = Some(Own { store: store.clone(), area: area.clone(), hold, beats });
         return Ok(area);
     }
     Err(EngineError::Other("no free recovery area".into()))
@@ -413,7 +478,7 @@ pub fn release(s: &mut Session) {
     for st in &mut s.docs {
         st.recovery = None;
     }
-    let Some(Own { store, area, hold }) = s.recovery.own.take() else { return };
+    let Some(Own { store, area, hold, .. }) = s.recovery.own.take() else { return };
     let mine = |n: &String| n.split_once('/').is_some_and(|(a, _)| a == area);
     for name in store.list().unwrap_or_default().iter().filter(|n| mine(n)) {
         let _ = store.remove(name);
@@ -531,6 +596,8 @@ fn fresh_name(area: &str, stem: &str, taken: &[String]) -> String {
 /// when it has none and a copy is needed) → (jobs, skipped: `[{title, reason}]` for modified
 /// documents that get none).
 pub fn jobs(s: &mut Session, store: &Arc<dyn RecoveryStore>) -> Result<(Vec<RecoveryJob>, Vec<Value>)> {
+    // Copies another app removed are written again.
+    repair(s);
     let skipped: Vec<Value> = s
         .documents()
         .iter()
@@ -628,7 +695,9 @@ enum Owner {
 
 /// Whose `area` of `store` is. A gone app's area is held by the caller (its lock in `hold` until
 /// dropped) and, with `take` in a store without locks, taken over with a fresh heartbeat, so
-/// another app leaves it alone meanwhile.
+/// another app leaves it alone meanwhile. In a store without locks an area is gone only when
+/// nothing says its app runs: no announcement (or the store can't tell) and no heartbeat for three
+/// intervals but the one this session wrote taking it over.
 fn owner(s: &mut Session, store: &dyn RecoveryStore, area: &str, hold: &mut Vec<Hold>, take: bool) -> Owner {
     if s.recovery.own.as_ref().is_some_and(|o| o.area == area && o.store.location() == store.location()) {
         return Owner::Mine;
@@ -640,14 +709,12 @@ fn owner(s: &mut Session, store: &dyn RecoveryStore, area: &str, hold: &mut Vec<
         }
         Ok(Lock::Busy) | Err(_) => Owner::Running,
         Ok(Lock::Unsupported) => {
-            if !s.recovery.adopted.contains(area) && beating(store, area, stale_after(s)) {
+            if store.announced(area).unwrap_or(false) || beating(store, area, stale_after(s), s.recovery.adopted.get(area).copied()) {
                 return Owner::Running;
             }
-            if take {
-                // Best effort: without it another app might offer the copies too, which loses
-                // nothing.
-                let _ = beat(store, area);
-                s.recovery.adopted.insert(area.to_string());
+            // Best effort: without it another app might offer the copies too, which loses nothing.
+            if take && let Ok(t) = beat(store, area) {
+                s.recovery.adopted.insert(area.to_string(), t);
             }
             Owner::Gone
         }

crates/engine/src/tests_recovery.rs

@@ -1,6 +1,7 @@
 //! Data Recovery: `file.recovery.save/list/restore/discard`, copies removed on save, revert and
 //! close, complex documents skipped, each app's own area (another running app's copies are never
-//! offered: locks, heartbeats), and the folder store with real file locks.
+//! offered: locks, heartbeats, announcements; a paused app repairs its copies), and the folder
+//! store with real file locks.
 
 use std::sync::Arc;
 
@@ -175,7 +176,7 @@ fn heartbeats_hold_areas_where_the_store_has_no_locks() {
     store.set_now(10_000 + 359);
     assert!(offered(&mut b).is_empty());
     // A beats (as the app does every minute): fresh again.
-    cmd::recovery::heartbeat(&a);
+    cmd::recovery::heartbeat(&mut a);
     store.set_now(10_000 + 359 + 300);
     assert!(offered(&mut b).is_empty());
     assert_eq!(restored(b.execute("file.recovery.restore", &json!({})).unwrap()), 0);
@@ -203,6 +204,71 @@ fn heartbeats_hold_areas_where_the_store_has_no_locks() {
     assert_eq!(offered(&mut b), ["Untitled-1"]);
 }
 
+/// Issue #367: a tab whose timers were paused (a background tab) long enough for its heartbeat to
+/// go stale, while another tab discards the copies it takes for crash leftovers.
+#[test]
+fn a_paused_app_writes_its_copies_again_and_is_running_again() {
+    let store = Arc::new(MemoryStore::without_locks());
+    let mut a = session_in(&store);
+    a.execute("file.recovery.save", &json!({})).unwrap();
+    let a_file = format!("{}/Untitled-1-1", a.recovery.own_area().unwrap());
+    let mut b = relaunch(&store);
+    b.prefs.autosave_interval = 1;
+    assert!(b.execute("file.recovery.discard", &json!({})).unwrap()["discarded"].as_array().unwrap().is_empty());
+    // A is paused past three minutes: with heartbeats alone, B can't tell it from a crash.
+    store.set_now(1_000_000 + 186);
+    assert_eq!(b.execute("file.recovery.discard", &json!({})).unwrap()["discarded"], json!([a_file.clone()]));
+    assert!(copies(store.as_ref()).is_empty());
+    // A resumes: its heartbeat finds the copy gone and the next save writes it again, unchanged
+    // document or not.
+    store.set_now(1_000_000 + 200);
+    assert_eq!(cmd::recovery::heartbeat(&mut a), [a.doc().unwrap().uid]);
+    assert!(a.doc().unwrap().recovery.is_none());
+    let r = a.execute("file.recovery.save", &json!({})).unwrap();
+    assert_eq!(r["saved"][0]["file"], a_file.as_str(), "{r}");
+    assert_eq!(copies(store.as_ref()), ["Untitled-1-1"]);
+    assert!(cmd::recovery::heartbeat(&mut a).is_empty(), "nothing missing any more");
+    // A's heartbeat is newer than the one B wrote taking the area over: A runs again for B.
+    let l = b.execute("file.recovery.list", &json!({})).unwrap();
+    assert_eq!((l["copies"][0]["file"].as_str(), l["copies"][0]["running"].as_bool()), (Some(a_file.as_str()), Some(true)));
+    assert!(b.execute("file.recovery.discard", &json!({})).unwrap()["discarded"].as_array().unwrap().is_empty());
+    assert!(b.execute("file.recovery.discard", &json!({"file": a_file})).is_err());
+    // A recovery save alone repairs too (no heartbeat in between).
+    store.set_now(1_000_000 + 600);
+    let mut c = relaunch(&store);
+    c.prefs.autosave_interval = 1;
+    c.execute("file.recovery.discard", &json!({})).unwrap();
+    assert!(copies(store.as_ref()).is_empty());
+    assert_eq!(a.execute("file.recovery.save", &json!({})).unwrap()["saved"].as_array().unwrap().len(), 1);
+    assert_eq!(copies(store.as_ref()), ["Untitled-1-1"]);
+}
+
+/// Issue #367 where the store can tell a paused app from a gone one (the browser's Web Locks): the
+/// paused app's copies are never taken, however old its heartbeat.
+#[test]
+fn announced_areas_stay_held_while_their_app_is_paused() {
+    let store = Arc::new(MemoryStore::announcing());
+    let mut a = session_in(&store);
+    a.execute("file.recovery.save", &json!({})).unwrap();
+    let a_file = format!("{}/Untitled-1-1", a.recovery.own_area().unwrap());
+    store.set_now(1_000_000 + 3600);
+    let mut b = relaunch(&store);
+    assert!(offered(&mut b).is_empty());
+    assert!(b.execute("file.recovery.discard", &json!({})).unwrap()["discarded"].as_array().unwrap().is_empty());
+    assert_eq!(restored(b.execute("file.recovery.restore", &json!({})).unwrap()), 0);
+    assert!(b.execute("file.recovery.discard", &json!({"file": a_file})).unwrap_err().to_string().contains("running"));
+    assert_eq!(copies(store.as_ref()), ["Untitled-1-1"]);
+    // A crashes: the browser releases its lock, and its copies are offered once its heartbeat is
+    // stale too.
+    drop(a);
+    assert_eq!(offered(&mut b), ["Untitled-1"]);
+    assert_eq!(restored(b.execute("file.recovery.restore", &json!({})).unwrap()), 1);
+    // B's area is announced in turn.
+    let mut c = relaunch(&store);
+    store.set_now(1_000_000 + 7200);
+    assert!(offered(&mut c).is_empty());
+}
+
 #[test]
 fn folder_areas_are_locked_by_running_apps() {
     let dir = std::env::temp_dir().join(format!("vc-recovery-locks-{}", std::process::id()));

crates/ui-egui/src/recovery.rs

@@ -4,8 +4,10 @@
 //! left copies behind (a crash). The copies themselves are the engine's
 //! ([`vectorcraft_engine::cmd::recovery`]).
 
+use std::sync::Arc;
+
 use serde_json::{Value, json};
-use vectorcraft_engine::cmd::recovery;
+use vectorcraft_engine::cmd::recovery::{self, RecoveryStore};
 
 use crate::VectorcraftApp;
 use crate::background::{self, Writer};
@@ -36,7 +38,14 @@ pub fn frame(app: &mut VectorcraftApp, now: f64) -> Option<f64> {
     tick(app, now);
     if !(0.0..recovery::HEARTBEAT_EVERY).contains(&(now - app.recovery.beat)) {
         app.recovery.beat = now;
-        recovery::heartbeat(&app.session);
+        // Copies another app removed while this one's timers were paused (it took this one for
+        // gone) are written again at once.
+        let lost = recovery::heartbeat(&mut app.session);
+        if !lost.is_empty()
+            && let Some(store) = recovery::store(&app.session)
+        {
+            write(app, &store, |uid| lost.contains(&uid));
+        }
     }
     let interval = f64::from(app.session.prefs.autosave_interval.max(1)) * 60.0;
     let next = app.recovery.last.map(|t| t + interval - now)?;
@@ -77,10 +86,16 @@ pub fn tick(app: &mut VectorcraftApp, now: f64) -> usize {
             return 0;
         }
     }
+    write(app, &store, |_| true)
+}
+
+/// Start a recovery copy of every document that needs one and `pick` picks (by uid) → how many
+/// were started.
+fn write(app: &mut VectorcraftApp, store: &Arc<dyn RecoveryStore>, pick: impl Fn(u64) -> bool) -> usize {
     recovery::forget_clean(&mut app.session);
-    let jobs = match recovery::jobs(&mut app.session, &store) {
+    let jobs = match recovery::jobs(&mut app.session, store) {
         // A document whose save or last copy is still being written waits for the next round.
-        Ok((jobs, _)) => jobs.into_iter().filter(|j| !app.background.busy_with(j.uid)).collect::<Vec<_>>(),
+        Ok((jobs, _)) => jobs.into_iter().filter(|j| pick(j.uid) && !app.background.busy_with(j.uid)).collect::<Vec<_>>(),
         Err(e) => {
             app.status(format!("Couldn't save recovery data: {e}"));
             return 0;

crates/ui-egui/src/tests_recovery.rs

@@ -176,3 +176,25 @@ fn the_timer_asks_for_frames_while_idle() {
     app.session.prefs.autosave_recovery = false;
     assert!(recovery::frame(&mut app, 1.0).is_none());
 }
+
+/// Issue #367: a tab whose timers were paused (in the background) long enough for another tab to
+/// take it for gone and discard its copy writes the copy again on its first heartbeat after it
+/// resumes, even with the timer off (the copy was written by hand).
+#[test]
+fn a_resumed_tab_writes_again_the_copies_another_tab_discarded() {
+    let store = Arc::new(MemoryStore::without_locks());
+    let mut a = app_with(&store, Services::default());
+    a.session.prefs.autosave_recovery = false;
+    a.run("file.recovery.save", json!({})).unwrap();
+    recovery::frame(&mut a, 0.0);
+    store.set_now(1_000_000 + 400);
+    let mut b = VectorcraftApp::new(Session::new(), Services { recovery_store: Some(store.clone()), ..Default::default() });
+    b.run("file.recovery.discard", json!({})).unwrap();
+    assert_eq!(copies(&store), 0);
+    store.set_now(1_000_000 + 410);
+    recovery::frame(&mut a, 30.0);
+    assert_eq!(copies(&store), 0, "the store is looked at with the heartbeat, not every frame");
+    recovery::frame(&mut a, 410.0);
+    assert_eq!(copies(&store), 1);
+    assert_eq!(a.ui.status, "Saved recovery data for Untitled-1");
+}

docs/development.md

@@ -21,6 +21,7 @@ How the web shell (`apps/vectorcraft-web/src/web.rs`) differs from desktop:
 - **Open** sets `Services::open_async`, which shows `rfd::AsyncFileDialog`. The bytes arrive in `Services::inbox`, which the app drains every frame.
 - **Save / Save As / Export** go through `Services::download`: a Blob, an object URL and a temporary `<a download>`, all created from Rust. There is no save dialog, so the suggested name becomes the download name.
 - **Drag-and-drop:** `WebShell` takes the frame's `dropped_files` before the app sees them, reads each with `DroppedFile::bytes_async` and pushes the bytes into the inbox (files dropped on a canvas go to `Services::place_inbox` with their `place::DropAt`: the document they were dropped on, by uid, and the point). A file that arrives after another document became active still lands in its own document, which becomes active again; if that document closed meanwhile, the file is not placed and the status bar says so. (The app's synchronous drop path is compiled out on wasm32.)
+- **Data Recovery** keeps its copies in `localStorage` (`vectorcraft-recovery/<area>/<name>`, shared by the site's tabs), so tabs can't lock their areas the way desktop apps lock a folder (`RecoveryStore::lock`). Each tab holds its area with a heartbeat it refreshes every minute and, where the browser has Web Locks (secure pages: `https://` or localhost), with a Web Lock named after the area (`apps/vectorcraft-web/src/locks.rs`, through `js_sys::Reflect` since web-sys has them only as an unstable API). The browser releases the lock only when the tab is gone, not while its timers are paused in the background, which a heartbeat can't tell apart (#367). `navigator.locks.query()` is asynchronous, so the shell keeps a snapshot refreshed every 10 seconds (taken once before the first frame); a snapshot older than a minute counts every area as held. An area is offered as a crash's leftovers only when no tab holds its lock and its heartbeat is older than three intervals. Without Web Locks a paused tab can still be taken for gone; it repairs that when it resumes: its next heartbeat (or recovery save) writes again the copies missing from its area, and a heartbeat newer than the one the other tab wrote taking the area over makes the area running again for that tab.
 - **No control server:** browsers can't listen on TCP. To automate the web build, drive headless Chrome with `--remote-debugging-port`.
 - Quick smoke test: `"/Applications/Google Chrome.app/Contents/MacOS/Google Chrome" --headless=new --enable-unsafe-webgpu --screenshot=web.png --window-size=1440,900 --virtual-time-budget=15000 http://127.0.0.1:8766/` (headless Chrome on macOS gets a real WebGPU adapter).
 

docs/mcp.md

@@ -1554,9 +1554,12 @@ The copies live in the `recoveryFolder` preference's folder (default: `Data Reco
 none when the app runs with `VECTORCRAFT_NO_PREFS`) or, on the web, in browser storage.
 
 Each running app (each browser tab) keeps its copies in an area of its own (`<area>/<name>`): a sub-folder whose
-`.lock` file it keeps locked while it runs, or on the web an area with a heartbeat it refreshes every minute. Only
-areas nobody holds are offered: their lock is free, or their heartbeat is older than three intervals (at least three
-minutes). Several apps running at once (agents' instances included) never see each other's copies as crash leftovers,
+`.lock` file it keeps locked while it runs, or on the web an area with a heartbeat it refreshes every minute and a Web
+Lock the browser holds until the tab is gone (where the browser has Web Locks: secure pages). Only areas nobody holds
+are offered: their lock is free, or no tab holds their Web Lock and their heartbeat is older than three intervals (at
+least three minutes). A background tab whose timers are paused therefore keeps its copies. Without Web Locks another
+tab can take such a tab for gone; when it resumes, its next heartbeat or recovery save writes its missing copies
+again. Several apps running at once (agents' instances included) never see each other's copies as crash leftovers,
 and an area being restored or discarded is held, so two apps launched together never both take it.
 
 `file.recovery.list` → `{copies: [{file, title, path, format, saved, open, running}], location}` (`open`: the copy of a