feat(entries): offer to save the editor content as a new entry when the row is gone

A 404 on save meant the work had to be copied out by hand. The POST mints a fresh uuid, so this is a new entry rather than a resurrection and cannot fight the tombstone the delete left behind. Gated on status 404 AND the server message: the HTTP layer answers 404 to any request it refuses, which the status alone would misread.

js/app.js

@@ -5072,11 +5072,49 @@ async function soSaveInner() {
                 toast('Saved');
             }
         } else {
-            await api('/entries/' + soState.id, {
-                method: 'PUT',
-                headers: authHeaders({ 'Content-Type': 'application/json' }),
-                body,
-            });
+            try {
+                await api('/entries/' + soState.id, {
+                    method: 'PUT',
+                    headers: authHeaders({ 'Content-Type': 'application/json' }),
+                    body,
+                });
+            } catch (err) {
+                // The row is gone — deleted by a sync, another device, or a
+                // purge, after the editor opened it. Offer to keep the work as
+                // a NEW entry rather than making the user copy it out by hand.
+                // A fresh uuid is minted, so this is a new entry and not a
+                // resurrection: it can't fight the tombstone the delete left.
+                // Both checks matter: the HTTP layer also answers 404 to any
+                // request it refuses (token lockdown), so the status alone
+                // would misread a rejected request as a deleted entry.
+                if (err.status !== 404 || !/no longer exists/i.test(err.message || ''))
+                    throw err;
+                const again = await confirmDialog({
+                    title:   'Entry no longer exists',
+                    message: 'It was deleted after you opened it — by a sync, ' +
+                             'an import, or another device. Your changes are ' +
+                             'still here and can be saved as a new entry.',
+                    okText:  'Save as new entry',
+                });
+                if (!again) return;
+                const created = await api('/entries', {
+                    method: 'POST',
+                    headers: authHeaders({ 'Content-Type': 'application/json' }),
+                    body,
+                });
+                const newId = created && created.id;
+                toast('Saved as a new entry');
+                await loadEntries();
+                if (typeof healthCache !== 'undefined') healthCache = null;
+                // Cleared before reopening for the same reason as the normal
+                // save path: a stale soState would trigger the discard prompt.
+                soState = null;
+                if (newId) openSlideOver(newId, { noFocus: true });
+                else closeSlideOver();
+                render();
+                if (newId) flashEntry(newId);
+                return;
+            }
             toast('Saved');
         }
         await loadEntries();