feat(sync): unify Google auth under :Pending auth

Problem: users had to run `:Pending gtasks auth` and `:Pending gcal
auth` separately, producing two token files and two browser consents
for the same Google account.

Solution: introduce `oauth.google_client` with combined tasks +
calendar scopes and a single `google_tokens.json`. Remove per-backend
`auth`/`setup` from `gcal` and `gtasks`; add top-level `:Pending auth`
that prompts with `vim.ui.select` and delegates to the shared client's
`setup()` or `auth()` based on credential availability.

lua/pending/init.lua

@@ -828,6 +828,24 @@ function M.edit(id_str, rest)
   log.info('Task #' .. id .. ' updated: ' .. table.concat(feedback, ', '))
 end
 
+---@return nil
+function M.auth()
+  local oauth = require('pending.sync.oauth')
+  vim.ui.select({ 'gtasks', 'gcal', 'both' }, {
+    prompt = 'Authenticate:',
+  }, function(choice)
+    if not choice then
+      return
+    end
+    local creds = oauth.google_client:resolve_credentials()
+    if creds.client_id == oauth.BUNDLED_CLIENT_ID then
+      oauth.google_client:setup()
+    else
+      oauth.google_client:auth()
+    end
+  end)
+end
+
 ---@param args string
 ---@return nil
 function M.command(args)
@@ -841,6 +859,8 @@ function M.command(args)
   elseif cmd == 'edit' then
     local id_str, edit_rest = rest:match('^(%S+)%s*(.*)')
     M.edit(id_str, edit_rest)
+  elseif cmd == 'auth' then
+    M.auth()
   elseif SYNC_BACKEND_SET[cmd] then
     local action = rest:match('^(%S+)')
     run_sync(cmd, action)

lua/pending/sync/gcal.lua

@@ -7,14 +7,6 @@ local M = {}
 M.name = 'gcal'
 
 local BASE_URL = 'https://www.googleapis.com/calendar/v3'
-local SCOPE = 'https://www.googleapis.com/auth/calendar'
-
-local client = oauth.new({
-  name = 'gcal',
-  scope = SCOPE,
-  port = 18392,
-  config_key = 'gcal',
-})
 
 ---@param access_token string
 ---@return table<string, string>? name_to_id
@@ -139,15 +131,15 @@ end
 ---@param callback fun(access_token: string): nil
 local function with_token(callback)
   oauth.async(function()
-    local token = client:get_access_token()
+    local token = oauth.google_client:get_access_token()
     if not token then
-      client:auth(function()
+      oauth.google_client:auth(function()
         oauth.async(function()
-          local fresh = client:get_access_token()
+          local fresh = oauth.google_client:get_access_token()
           if fresh then
             callback(fresh)
           else
-            log.error(client.name .. ': authorization failed or was cancelled')
+            log.error(oauth.google_client.name .. ': authorization failed or was cancelled')
           end
         end)
       end)
@@ -157,14 +149,6 @@ local function with_token(callback)
   end)
 end
 
-function M.setup()
-  client:setup()
-end
-
-function M.auth()
-  client:auth()
-end
-
 function M.push()
   with_token(function(access_token)
     local calendars, cal_err = get_all_calendars(access_token)

lua/pending/sync/gtasks.lua

@@ -7,14 +7,6 @@ local M = {}
 M.name = 'gtasks'
 
 local BASE_URL = 'https://tasks.googleapis.com/tasks/v1'
-local SCOPE = 'https://www.googleapis.com/auth/tasks'
-
-local client = oauth.new({
-  name = 'gtasks',
-  scope = SCOPE,
-  port = 18393,
-  config_key = 'gtasks',
-})
 
 ---@param access_token string
 ---@return table<string, string>? name_to_id
@@ -355,15 +347,15 @@ end
 ---@param callback fun(access_token: string): nil
 local function with_token(callback)
   oauth.async(function()
-    local token = client:get_access_token()
+    local token = oauth.google_client:get_access_token()
     if not token then
-      client:auth(function()
+      oauth.google_client:auth(function()
         oauth.async(function()
-          local fresh = client:get_access_token()
+          local fresh = oauth.google_client:get_access_token()
           if fresh then
             callback(fresh)
           else
-            log.error(client.name .. ': authorization failed or was cancelled')
+            log.error(oauth.google_client.name .. ': authorization failed or was cancelled')
           end
         end)
       end)
@@ -373,14 +365,6 @@ local function with_token(callback)
   end)
 end
 
-function M.setup()
-  client:setup()
-end
-
-function M.auth()
-  client:auth()
-end
-
 function M.push()
   with_token(function(access_token)
     local tasklists, s, now_ts = sync_setup(access_token)
@@ -462,11 +446,11 @@ M._gtask_to_fields = gtask_to_fields
 ---@return nil
 function M.health()
   oauth.health(M.name)
-  local tokens = client:load_tokens()
+  local tokens = oauth.google_client:load_tokens()
   if tokens and tokens.refresh_token then
     vim.health.ok('gtasks tokens found')
   else
-    vim.health.info('no gtasks tokens — run :Pending gtasks auth')
+    vim.health.info('no gtasks tokens — run :Pending auth')
   end
 end
 

lua/pending/sync/oauth.lua

@@ -501,5 +501,14 @@ end
 
 M._BUNDLED_CLIENT_ID = BUNDLED_CLIENT_ID
 M._BUNDLED_CLIENT_SECRET = BUNDLED_CLIENT_SECRET
+M.BUNDLED_CLIENT_ID = BUNDLED_CLIENT_ID
+
+M.google_client = M.new({
+  name = 'google',
+  scope = 'https://www.googleapis.com/auth/tasks'
+    .. ' https://www.googleapis.com/auth/calendar',
+  port = 18392,
+  config_key = 'google',
+})
 
 return M