fix: revert dev

spec/sync_spec.lua

@@ -124,6 +124,100 @@ describe('sync', function()
     end)
   end)
 
+  describe('register_backend', function()
+    it('registers a custom backend', function()
+      pending.register_backend({ name = 'custom', pull = function() end })
+      local set = pending.sync_backend_set()
+      assert.is_true(set['custom'] == true)
+      assert.is_true(vim.tbl_contains(pending.sync_backends(), 'custom'))
+    end)
+
+    it('rejects backend without name', function()
+      local msg
+      local orig = vim.notify
+      vim.notify = function(m, level)
+        if level == vim.log.levels.ERROR then
+          msg = m
+        end
+      end
+      pending.register_backend({})
+      vim.notify = orig
+      assert.truthy(msg and msg:find('non%-empty'))
+    end)
+
+    it('rejects backend with empty name', function()
+      local msg
+      local orig = vim.notify
+      vim.notify = function(m, level)
+        if level == vim.log.levels.ERROR then
+          msg = m
+        end
+      end
+      pending.register_backend({ name = '' })
+      vim.notify = orig
+      assert.truthy(msg and msg:find('non%-empty'))
+    end)
+
+    it('rejects duplicate of built-in backend', function()
+      local msg
+      local orig = vim.notify
+      vim.notify = function(m, level)
+        if level == vim.log.levels.ERROR then
+          msg = m
+        end
+      end
+      pending.register_backend({ name = 'gcal' })
+      vim.notify = orig
+      assert.truthy(msg and msg:find('already exists'))
+    end)
+
+    it('rejects duplicate registered backend', function()
+      pending.register_backend({ name = 'dup_test', pull = function() end })
+      local msg
+      local orig = vim.notify
+      vim.notify = function(m, level)
+        if level == vim.log.levels.ERROR then
+          msg = m
+        end
+      end
+      pending.register_backend({ name = 'dup_test' })
+      vim.notify = orig
+      assert.truthy(msg and msg:find('already registered'))
+    end)
+  end)
+
+  describe('resolve_backend', function()
+    it('resolves built-in backend', function()
+      local mod = pending.resolve_backend('gcal')
+      assert.is_not_nil(mod)
+      assert.are.equal('gcal', mod.name)
+    end)
+
+    it('resolves registered backend', function()
+      local custom = { name = 'resolve_test', pull = function() end }
+      pending.register_backend(custom)
+      local mod = pending.resolve_backend('resolve_test')
+      assert.is_not_nil(mod)
+      assert.are.equal('resolve_test', mod.name)
+    end)
+
+    it('returns nil for unknown backend', function()
+      assert.is_nil(pending.resolve_backend('nonexistent_xyz'))
+    end)
+
+    it('dispatches command to registered backend', function()
+      local called = false
+      pending.register_backend({
+        name = 'cmd_test',
+        pull = function()
+          called = true
+        end,
+      })
+      pending.command('cmd_test pull')
+      assert.is_true(called)
+    end)
+  end)
+
   describe('auto-discovery', function()
     it('discovers gcal and gtasks backends', function()
       local backends = pending.sync_backends()