Fix self-inflicted edit conflicts: dialogs no longer pin a stale node version

Properties, Raw JSON and AI proposals sent the version captured when the
dialog opened. Any other edit to the node meanwhile (style chip, drag handle,
inline text, child insert/move) bumped it, so the save 409'd against the
user's own work. Save through ctrl.saveData instead: compare only the keys
being written against the current node (a real conflict is a key someone else
changed) and send no version. 409 toasts now show the server's reason.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

test/assistant.test.ts

@@ -8,8 +8,10 @@ const node = { id: 'n1', dataType: 'hero', version: 3, data: { title: 'Hello wro
 
 function fakeCtrl() {
   const setData = vi.fn(async () => ({}))
+  const saveData = vi.fn(async () => ({}))
   return {
     setData,
+    saveData,
     ctrl: {
       store: { get: () => ({ selected: 'n1', blocks: [{ id: 'n1', type: 'hero', depth: 0 }] }) },
       block: (id: string) => (id === 'n1' ? { id } : undefined),
@@ -19,6 +21,7 @@ function fakeCtrl() {
       schema: async () => schema,
       labelFor: () => 'Hero',
       setData,
+      saveData,
     } as any,
   }
 }
@@ -80,10 +83,10 @@ describe('runAgent + tools', () => {
 })
 
 describe('applyProposal', () => {
-  it('rebuilds the nested patch from the fresh node and saves with its version', async () => {
-    const { ctrl, setData } = fakeCtrl()
+  it('rebuilds the nested patch from the fresh node and saves it through the key-level conflict check', async () => {
+    const { ctrl, saveData } = fakeCtrl()
     await applyProposal(ctrl, { id: 1, kind: 'set', nodeId: 'n1', label: 'Hero', path: 'links.0.text', before: 'a', after: 'b' })
-    expect(setData).toHaveBeenCalledWith('n1', { links: [{ text: 'b' }] }, { version: 3 })
+    expect(saveData).toHaveBeenCalledWith('n1', node.data, { links: [{ text: 'b' }] })
   })
 })