feat(sync): add opt-in remote deletion for gcal and gtasks (#85)

Problem: push/sync permanently deleted remote Google Calendar events and
Google Tasks entries whenever a local task was marked deleted, done, or
de-due'd. There was no opt-out, so a misfire could silently cause
irreversible data loss on the remote side.

Solution: add a `remote_delete` boolean to the config (default `false`).
A unified flag at `sync.remote_delete` sets the base; per-backend
overrides at `sync.gcal.remote_delete` / `sync.gtasks.remote_delete`
take precedence when non-nil. When disabled, `_extra` remote IDs are
cleared silently (unlinking) so stale IDs don't accumulate.

lua/pending/config.lua

@@ -7,16 +7,19 @@
 ---@field category string
 
 ---@class pending.GcalConfig
+---@field remote_delete? boolean
 ---@field credentials_path? string
 ---@field client_id? string
 ---@field client_secret? string
 
 ---@class pending.GtasksConfig
+---@field remote_delete? boolean
 ---@field credentials_path? string
 ---@field client_id? string
 ---@field client_secret? string
 
 ---@class pending.SyncConfig
+---@field remote_delete? boolean
 ---@field gcal? pending.GcalConfig
 ---@field gtasks? pending.GtasksConfig
 

lua/pending/sync/gcal.lua

@@ -129,6 +129,31 @@ local function delete_event(access_token, calendar_id, event_id)
   return err
 end
 
+---@return boolean
+local function allow_remote_delete()
+  local cfg = config.get()
+  local sync = cfg.sync or {}
+  local per = (sync.gcal or {}) --[[@as pending.GcalConfig]]
+  if per.remote_delete ~= nil then
+    return per.remote_delete == true
+  end
+  return sync.remote_delete == true
+end
+
+---@param task pending.Task
+---@param extra table
+---@param now_ts string
+local function unlink_remote(task, extra, now_ts)
+  extra['_gcal_event_id'] = nil
+  extra['_gcal_calendar_id'] = nil
+  if next(extra) == nil then
+    task._extra = nil
+  else
+    task._extra = extra
+  end
+  task.modified = now_ts
+end
+
 ---@param callback fun(access_token: string): nil
 local function with_token(callback)
   oauth.async(function()
@@ -150,6 +175,7 @@ function M.push()
     end
 
     local s = require('pending').store()
+    local now_ts = os.date('!%Y-%m-%dT%H:%M:%SZ') --[[@as string]]
     local created, updated, deleted = 0, 0, 0
 
     for _, task in ipairs(s:tasks()) do
@@ -166,19 +192,20 @@ function M.push()
         )
 
       if should_delete then
-        local del_err =
-          delete_event(access_token, cal_id --[[@as string]], event_id --[[@as string]])
-        if del_err then
-          log.warn('gcal delete failed: ' .. del_err)
-        else
-          extra['_gcal_event_id'] = nil
-          extra['_gcal_calendar_id'] = nil
-          if next(extra) == nil then
-            task._extra = nil
+        if allow_remote_delete() then
+          local del_err =
+            delete_event(access_token, cal_id --[[@as string]], event_id --[[@as string]])
+          if del_err then
+            log.warn('gcal delete failed: ' .. del_err)
           else
-            task._extra = extra
+            unlink_remote(task, extra, now_ts)
+            deleted = deleted + 1
           end
-          task.modified = os.date('!%Y-%m-%dT%H:%M:%SZ') --[[@as string]]
+        else
+          log.debug(
+            'gcal: remote delete skipped (remote_delete disabled) — unlinked task #' .. task.id
+          )
+          unlink_remote(task, extra, now_ts)
           deleted = deleted + 1
         end
       elseif task.status == 'pending' and task.due then
@@ -204,7 +231,7 @@ function M.push()
               end
               task._extra['_gcal_event_id'] = new_id
               task._extra['_gcal_calendar_id'] = lid
-              task.modified = os.date('!%Y-%m-%dT%H:%M:%SZ') --[[@as string]]
+              task.modified = now_ts
               created = created + 1
             end
           end

lua/pending/sync/gtasks.lua

@@ -172,6 +172,29 @@ local function parse_notes(notes)
   return priority, recur, recur_mode
 end
 
+---@return boolean
+local function allow_remote_delete()
+  local cfg = config.get()
+  local sync = cfg.sync or {}
+  local per = (sync.gtasks or {}) --[[@as pending.GtasksConfig]]
+  if per.remote_delete ~= nil then
+    return per.remote_delete == true
+  end
+  return sync.remote_delete == true
+end
+
+---@param task pending.Task
+---@param now_ts string
+local function unlink_remote(task, now_ts)
+  task._extra['_gtasks_task_id'] = nil
+  task._extra['_gtasks_list_id'] = nil
+  task._extra['_gtasks_synced_at'] = nil
+  if next(task._extra) == nil then
+    task._extra = nil
+  end
+  task.modified = now_ts
+end
+
 ---@param task pending.Task
 ---@return table
 local function task_to_gtask(task)
@@ -240,21 +263,20 @@ local function push_pass(access_token, tasklists, s, now_ts, by_gtasks_id)
     local list_id = extra['_gtasks_list_id'] --[[@as string?]]
 
     if task.status == 'deleted' and gtid and list_id then
-      local err = delete_gtask(access_token, list_id, gtid)
-      if err then
-        log.warn('gtasks delete failed: ' .. err)
-        failed = failed + 1
+      if allow_remote_delete() then
+        local err = delete_gtask(access_token, list_id, gtid)
+        if err then
+          log.warn('gtasks delete failed: ' .. err)
+          failed = failed + 1
+        else
+          unlink_remote(task, now_ts)
+          deleted = deleted + 1
+        end
       else
-        if not task._extra then
-          task._extra = {}
-        end
-        task._extra['_gtasks_task_id'] = nil
-        task._extra['_gtasks_list_id'] = nil
-        task._extra['_gtasks_synced_at'] = nil
-        if next(task._extra) == nil then
-          task._extra = nil
-        end
-        task.modified = now_ts
+        log.debug(
+          'gtasks: remote delete skipped (remote_delete disabled) — unlinked task #' .. task.id
+        )
+        unlink_remote(task, now_ts)
         deleted = deleted + 1
       end
     elseif task.status ~= 'deleted' then