feat: add optimistic error recovery for note creation (#69)

Note creation was already optimistic (UI updates before disk write) but
errors were silently swallowed. Now if the disk write fails, the
optimistic entry is reverted (tab closed, entry removed) and the user
sees an error toast. Each note creation is independent, so one failure
in rapid Cmd+N presses doesn't affect the others.

- Add removeEntry to useVaultLoader for reverting optimistic adds
- Refactor persistNewNote to return a Promise for error handling
- Extract navigateWikilink, persistOptimistic, createAndPersist,
  and runFrontmatterAndApply helpers to reduce hook complexity
- Add tests for error recovery: single note, type, success path,
  and rapid creation with partial failure
- Code health: 8.93→9.01 (CC fixed: 10→7, primitive obsession improved)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/hooks/useNoteActions.test.ts

@@ -1,5 +1,7 @@
 import { describe, it, expect, vi, beforeEach } from 'vitest'
 import { renderHook, act } from '@testing-library/react'
+import { invoke } from '@tauri-apps/api/core'
+import { isTauri } from '../mock-tauri'
 import type { VaultEntry } from '../types'
 import {
   slugify,
@@ -17,7 +19,7 @@ import type { NoteActionsConfig } from './useNoteActions'
 // Mock dependencies
 vi.mock('@tauri-apps/api/core', () => ({ invoke: vi.fn() }))
 vi.mock('../mock-tauri', () => ({
-  isTauri: () => false,
+  isTauri: vi.fn(() => false),
   addMockEntry: vi.fn(),
   updateMockContent: vi.fn(),
   mockInvoke: vi.fn().mockResolvedValue(''),
@@ -280,16 +282,18 @@ describe('frontmatterToEntryPatch', () => {
 
 describe('useNoteActions hook', () => {
   const addEntry = vi.fn()
+  const removeEntry = vi.fn()
   const updateContent = vi.fn()
   const updateEntry = vi.fn()
   const setToastMessage = vi.fn()
 
   const makeConfig = (entries: VaultEntry[] = []): NoteActionsConfig => ({
-    addEntry, updateContent, entries, setToastMessage, updateEntry,
+    addEntry, removeEntry, updateContent, entries, setToastMessage, updateEntry,
   })
 
   beforeEach(() => {
     vi.clearAllMocks()
+    vi.mocked(isTauri).mockReturnValue(false)
   })
 
   it('handleCreateNote calls addEntry and creates correct entry', () => {
@@ -436,4 +440,61 @@ describe('useNoteActions hook', () => {
     expect(updateEntry).not.toHaveBeenCalled()
     expect(setToastMessage).toHaveBeenCalledWith('Property updated')
   })
+
+  describe('optimistic error recovery (Tauri mode)', () => {
+    beforeEach(() => {
+      vi.mocked(isTauri).mockReturnValue(true)
+    })
+
+    it.each([
+      ['handleCreateNote', 'Failing Note', 'Note', 'note/failing-note.md'],
+      ['handleCreateType', 'Recipe', 'Type', 'type/recipe.md'],
+    ])('reverts optimistic creation via %s when disk write fails', async (method, title, type, pathFragment) => {
+      vi.mocked(invoke).mockRejectedValueOnce(new Error('disk full'))
+      const { result } = renderHook(() => useNoteActions(makeConfig()))
+
+      await act(async () => {
+        if (method === 'handleCreateNote') result.current.handleCreateNote(title, type)
+        else result.current.handleCreateType(title)
+        await new Promise((r) => setTimeout(r, 0))
+      })
+
+      expect(addEntry).toHaveBeenCalledTimes(1)
+      expect(removeEntry).toHaveBeenCalledWith(expect.stringContaining(pathFragment))
+      expect(setToastMessage).toHaveBeenCalledWith('Failed to create note — disk write error')
+    })
+
+    it('does not revert when disk write succeeds', async () => {
+      vi.mocked(invoke).mockResolvedValueOnce(undefined)
+      const { result } = renderHook(() => useNoteActions(makeConfig()))
+
+      await act(async () => {
+        result.current.handleCreateNote('Good Note', 'Note')
+        await new Promise((r) => setTimeout(r, 0))
+      })
+
+      expect(removeEntry).not.toHaveBeenCalled()
+      expect(setToastMessage).not.toHaveBeenCalled()
+    })
+
+    it('handles rapid creation with one failure independently', async () => {
+      vi.mocked(invoke)
+        .mockResolvedValueOnce(undefined)
+        .mockRejectedValueOnce(new Error('disk full'))
+        .mockResolvedValueOnce(undefined)
+
+      const { result } = renderHook(() => useNoteActions(makeConfig()))
+
+      await act(async () => {
+        result.current.handleCreateNoteImmediate()
+        result.current.handleCreateNoteImmediate()
+        result.current.handleCreateNoteImmediate()
+        await new Promise((r) => setTimeout(r, 0))
+      })
+
+      expect(addEntry).toHaveBeenCalledTimes(3)
+      expect(removeEntry).toHaveBeenCalledTimes(1)
+      expect(removeEntry).toHaveBeenCalledWith(expect.stringContaining('untitled-note-2.md'))
+    })
+  })
 })