feat: title = filename — wikilink resolution + slug collision detection

- Wikilink resolution order: filename stem (primary) → alias → title (fallback)
- Slug collision detection: auto-suffix (-2, -3, etc.) on note creation
- Add slugCollides utility for frontend collision checking
- resolveNewNote accepts entries param for collision-aware creation
- Title editing via H1 heading already triggers file rename (existing flow)
- Update docs/ARCHITECTURE.md with migrate_to_flat_vault command

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/hooks/useNoteActions.test.ts

@@ -20,6 +20,7 @@ import {
   useNoteActions,
   DEFAULT_TEMPLATES,
   resolveTemplate,
+  slugCollides,
 } from './useNoteActions'
 import type { NoteActionsConfig } from './useNoteActions'
 
@@ -111,6 +112,38 @@ describe('needsRenameOnSave', () => {
   })
 })
 
+describe('slugCollides', () => {
+  it('detects collision with existing filename', () => {
+    const entries = [makeEntry({ filename: 'my-note.md', path: '/vault/my-note.md' })]
+    expect(slugCollides('My Note', entries)).toBe(true)
+  })
+
+  it('returns false when no collision', () => {
+    const entries = [makeEntry({ filename: 'other.md', path: '/vault/other.md' })]
+    expect(slugCollides('My Note', entries)).toBe(false)
+  })
+
+  it('excludes the current note path from collision check', () => {
+    const entries = [makeEntry({ filename: 'my-note.md', path: '/vault/my-note.md' })]
+    expect(slugCollides('My Note', entries, '/vault/my-note.md')).toBe(false)
+  })
+})
+
+describe('resolveNewNote slug collision', () => {
+  it('auto-suffixes slug when collision detected', () => {
+    const entries = [makeEntry({ filename: 'my-project.md', path: '/vault/my-project.md' })]
+    const { entry } = resolveNewNote('My Project', 'Project', '/vault', null, entries)
+    expect(entry.path).toBe('/vault/my-project-2.md')
+    expect(entry.filename).toBe('my-project-2.md')
+  })
+
+  it('skips suffix when no collision', () => {
+    const entries = [makeEntry({ filename: 'other.md', path: '/vault/other.md' })]
+    const { entry } = resolveNewNote('My Project', 'Project', '/vault', null, entries)
+    expect(entry.path).toBe('/vault/my-project.md')
+  })
+})
+
 describe('buildNewEntry', () => {
   it('creates a VaultEntry with correct fields', () => {
     const entry = buildNewEntry({
@@ -190,8 +223,8 @@ describe('entryMatchesTarget', () => {
     expect(entryMatchesTarget(entry, 'mp')).toBe(true)
   })
 
-  it('matches by path suffix (type/slug)', () => {
-    const entry = makeEntry({ path: '/Users/luca/Laputa/project/my-project.md' })
+  it('matches by filename stem from path-style wikilink', () => {
+    const entry = makeEntry({ path: '/Users/luca/Laputa/my-project.md', filename: 'my-project.md' })
     expect(entryMatchesTarget(entry, 'project/my-project')).toBe(true)
   })
 

src/hooks/useNoteActions.ts

@@ -95,6 +95,12 @@ export function needsRenameOnSave(title: string, filename: string): boolean {
   return `${slugify(title)}.md` !== filename
 }
 
+/** Check if a slug would collide with an existing entry's filename. */
+export function slugCollides(title: string, entries: VaultEntry[], excludePath?: string): boolean {
+  const slug = slugify(title)
+  return entries.some(e => e.filename === `${slug}.md` && e.path !== excludePath)
+}
+
 /** Generate a unique "Untitled <type>" name by checking existing entries and pending names. */
 export function generateUntitledName(entries: VaultEntry[], type: string, pending?: Set<string>): string {
   const baseName = `Untitled ${type.toLowerCase()}`
@@ -190,8 +196,16 @@ export function buildNoteContent(title: string, type: string, status: string | n
   return `${lines.join('\n')}\n\n# ${title}\n${body}`
 }
 
-export function resolveNewNote(title: string, type: string, vaultPath: string, template?: string | null): { entry: VaultEntry; content: string } {
-  const slug = slugify(title)
+export function resolveNewNote(title: string, type: string, vaultPath: string, template?: string | null, entries?: VaultEntry[]): { entry: VaultEntry; content: string } {
+  let slug = slugify(title)
+  // Detect slug collision and auto-suffix
+  if (entries) {
+    let counter = 2
+    while (entries.some(e => e.filename === `${slug}.md`)) {
+      slug = `${slugify(title)}-${counter}`
+      counter++
+    }
+  }
   const status = NO_STATUS_TYPES.has(type) ? null : 'Active'
   const entry = buildNewEntry({ path: `${vaultPath}/${slug}.md`, slug, title, type, status })
   return { entry, content: buildNoteContent(title, type, status, template) }
@@ -363,7 +377,7 @@ export function useNoteActions(config: NoteActionsConfig) {
 
   const handleCreateNote = useCallback((title: string, type: string) => {
     const template = resolveTemplate(entries, type)
-    persistNew(resolveNewNote(title, type, config.vaultPath, template))
+    persistNew(resolveNewNote(title, type, config.vaultPath, template, entries))
   }, [entries, persistNew, config.vaultPath])
 
   const handleCreateNoteImmediate = useCallback((type?: string) => {
@@ -372,7 +386,7 @@ export function useNoteActions(config: NoteActionsConfig) {
       const title = generateUntitledName(entries, noteType, pendingNamesRef.current)
       pendingNamesRef.current.add(title)
       const template = resolveTemplate(entries, noteType)
-      const resolved = resolveNewNote(title, noteType, config.vaultPath, template)
+      const resolved = resolveNewNote(title, noteType, config.vaultPath, template, entries)
       openTabWithContent(resolved.entry, resolved.content)
       addEntryWithMock(resolved.entry, resolved.content, addEntry)
       config.trackUnsaved?.(resolved.entry.path)
@@ -389,7 +403,7 @@ export function useNoteActions(config: NoteActionsConfig) {
    *  Returns true on success, false on failure (shows toast on error). */
   const handleCreateNoteForRelationship = useCallback(async (title: string): Promise<boolean> => {
     const template = resolveTemplate(entries, 'Note')
-    const resolved = resolveNewNote(title, 'Note', config.vaultPath, template)
+    const resolved = resolveNewNote(title, 'Note', config.vaultPath, template, entries)
     openTabWithContent(resolved.entry, resolved.content)
     addEntryWithMock(resolved.entry, resolved.content, addEntry)
     try {