fix(frontend): use dispatchTransaction hook to detect local PM steps, eliminating echo feedback loop

templates/document_edit.html

···
                     ...plugins,
                     collab({ version: collabClient.version }),
                 ]);
+                // Override dispatchTransaction to detect local edits at the PM level.
+                // After every transaction, sendableSteps is non-null only for local
+                // (unconfirmed) edits — remote receiveTransaction steps are confirmed
+                // immediately and never appear in sendableSteps.
+                ctx.update(editorViewOptionsCtx, (prev) => ({
+                    ...prev,
+                    dispatchTransaction: function(tr) {
+                        const newState = this.state.apply(tr);
+                        this.updateState(newState);
+                        if (!applyingRemote) {
+                            const sendable = sendableSteps(newState);
+                            if (sendable) {
+                                const stepsJSON = sendable.steps.map(s => JSON.stringify(s.toJSON()));
+                                collabClient.sendSteps(stepsJSON.map(j => ({type: 'pm-step', json: j})));
+                                try {
+                                    const serializer = milkdownEditor.action(c => c.get(serializerCtx));
+                                    scheduleAutoSave(serializer(newState.doc));
+                                } catch(_) {}
+                            }
+                        }
+                    },
+                }));
             })
             .use(commonmark)
             .use(history)
             .use(listener)
             .config((ctx) => {
                 ctx.get(listenerCtx).markdownUpdated((_ctx, markdown, prevMarkdown) => {
-                    if (markdown === prevMarkdown || applyingRemote) return;
+                    // Solo-mode auto-save fallback (no collab session).
+                    if (markdown === prevMarkdown || applyingRemote || accessToken) return;
                     scheduleAutoSave(markdown);
-                    // Use prosemirror-collab to extract pending steps from the PM state.
-                    const pmView = milkdownEditor.action(c => c.get(editorViewCtx));
-                    const sendable = sendableSteps(pmView.state);
-                    if (sendable) {
-                        const stepsJSON = sendable.steps.map(s => JSON.stringify(s.toJSON()));
-                        collabClient.sendSteps(stepsJSON.map(j => ({type: 'pm-step', json: j})));
-                    }
                 });
             })
             .create();