Improved displayed error message when editor reaches bad saving state

ref https://linear.app/tryghost/issue/ONC-323

- added explicit 404 handling to the editor's save task so we can display a more direct/useful error message

ghost/admin/app/controllers/lexical-editor.js

@@ -22,7 +22,7 @@ import {inject} from 'ghost-admin/decorators/inject';
 import {isBlank} from '@ember/utils';
 import {isArray as isEmberArray} from '@ember/array';
 import {isHostLimitError, isServerUnreachableError, isVersionMismatchError} from 'ghost-admin/services/ajax';
-import {isInvalidError} from 'ember-ajax/errors';
+import {isInvalidError, isNotFoundError} from 'ember-ajax/errors';
 import {mobiledocToLexical} from '@tryghost/kg-converters';
 import {inject as service} from '@ember/service';
 import {slugify} from '@tryghost/string';
@@ -652,6 +652,17 @@ export default class LexicalEditorController extends Controller {
                 return;
             }
 
+            // This shouldn't occur but we have a bug where a new post can get
+            // into a bad state where it's not saved but the store is treating
+            // it as saved and performing PUT requests with no id. We want to
+            // be noisy about this early to avoid data loss
+            if (isNotFoundError(error)) {
+                console.error(error); // eslint-disable-line no-console
+                Sentry.captureException(error, {tags: {savePostTask: true}});
+                this._showErrorAlert(prevStatus, this.post.status, 'Editor has crashed. Please copy your content and start a new post.');
+                return;
+            }
+
             if (error && !isInvalidError(error)) {
                 console.error(error); // eslint-disable-line no-console
                 Sentry.captureException(error, {tags: {savePostTask: true}});

ghost/admin/tests/acceptance/editor-test.js

@@ -706,7 +706,8 @@ describe('Acceptance: Editor', function () {
             await pasteInEditor('Testing');
 
             // we should see an error - previously this was failing silently
-            expect(find('.gh-alert-content')).to.have.trimmed.text('Resource could not be found.');
+            // error message comes from editor's own handling rather than our generic API error fallback
+            expect(find('.gh-alert-content')).to.have.trimmed.text('Saving failed: Editor has crashed. Please copy your content and start a new post.');
         });
     });
 });