docs: document S3 backend, auto-auth, and :Pending done command (#125)

Problem: The S3 backend had no `:Pending s3` entry in the COMMANDS
section, `:Pending auth` only mentioned Google, the `sync` config
field omitted `s3`, `_s3_sync_id` was missing from the data format
section, `:Pending done` was implemented but undocumented, and the
README lacked a features overview.

Solution: Add `:Pending s3` and `:Pending done` command docs, rewrite
`:Pending auth` to cover all backends and sub-actions, update config
and data format references, add `aws` CLI to requirements, and add a
Features section to `README.md`.

README.md

@@ -8,10 +8,27 @@ Oil-like task management for todos in Neovim, inspired by
 
 https://github.com/user-attachments/assets/f3898ecb-ec95-43fe-a71f-9c9f49628ba9
 
+## Features
+
+- Oil-style buffer editing: standard Vim motions for all task operations
+- Inline metadata: `due:`, `cat:`, `rec:` tokens parsed on `:w`
+- Rich date input: relative (`+3d`, `tomorrow`), weekdays, ordinals, custom formats, time suffixes
+- Recurring tasks with automatic next-date spawning on completion
+- Category and queue views with foldable sections
+- Multi-level undo (up to 20 saves, persisted across sessions)
+- Text objects (`at`/`it`/`aC`/`iC`) and motions (`]]`/`[[`/`]t`/`[t`)
+- Omnifunc completion for `due:`, `cat:`, and `rec:` tokens
+- Filters: `cat:X`, `overdue`, `today`, `priority`, `wip`, `blocked`
+- Google Calendar one-way push via OAuth PKCE
+- Google Tasks bidirectional sync via OAuth PKCE
+- S3 whole-store sync via AWS CLI with cross-device merge
+- Auto-authentication: sync actions trigger auth flows automatically
+
 ## Requirements
 
 - Neovim 0.10+
-- (Optionally) `curl` for Google Calendar and Google Task sync
+- (Optionally) `curl` for Google Calendar and Google Tasks sync
+- (Optionally) `aws` CLI for S3 sync
 
 ## Installation
 

doc/pending.txt

@@ -42,6 +42,7 @@ Features: ~
 - Omnifunc completion for `cat:`, `due:`, and `rec:` tokens (`<C-x><C-o>`)
 - Google Calendar one-way push via OAuth PKCE
 - Google Tasks bidirectional sync via OAuth PKCE
+- S3 whole-store sync via AWS CLI
 
 ==============================================================================
 CONTENTS                                                   *pending-contents*
@@ -76,6 +77,7 @@ REQUIREMENTS                                           *pending-requirements*
 - Neovim 0.10+
 - No external dependencies for local use
 - `curl` is required for the `gcal` and `gtasks` sync backends
+- `aws` CLI is required for the `s3` sync backend
 
 ==============================================================================
 INSTALL                                                      *pending-install*
@@ -167,13 +169,34 @@ COMMANDS                                                    *pending-commands*
     Open the list with |:copen| to navigate to each task's category.
 
                                                                *:Pending-auth*
-:Pending auth
+:Pending auth [{backend} [{sub-action}]]
-    Authorize pending.nvim to access Google services (Tasks and Calendar).
+    Authenticate a sync backend. Without arguments, prompts with
-    Prompts with |vim.ui.select| to choose gtasks, gcal, or both — all
+    |vim.ui.select| when multiple backends have auth methods. With an
-    options run the same combined OAuth flow and produce a single shared
+    explicit {backend} name, dispatches directly: >vim
-    token file. If no credentials are configured, the setup wizard runs
+        :Pending auth gcal
-    first to collect a client ID and secret.
+        :Pending auth gtasks
-    See |pending-google-auth| for full details.
+        :Pending auth s3
+        :Pending auth gcal clear
+        :Pending auth gtasks reset
+        :Pending auth s3 profile
+<
+    Google backends (gcal, gtasks): ~
+    Both share a single OAuth flow with combined scopes. If no credentials
+    are configured (bundled placeholders in use), the setup wizard runs
+    first to collect a client ID and secret. Sub-actions:
+        `clear`   Remove OAuth tokens (forces re-authentication).
+        `reset`   Remove tokens and credentials (full reset).
+    See |pending-google-auth| for details.
+
+    S3 backend: ~
+    Runs `aws sts get-caller-identity` to verify AWS credentials. If the
+    profile uses SSO and the session has expired, runs `aws sso login`
+    automatically. Sub-actions:
+        `profile`   Prompt for an AWS profile name.
+    See |pending-s3| for details.
+
+    Auth is triggered automatically when running sync actions without valid
+    credentials. See |pending-sync-auto-auth|.
 
                                                               *:Pending-gtasks*
 :Pending gtasks {action}
@@ -207,6 +230,34 @@ COMMANDS                                                    *pending-commands*
     Tab completion after `:Pending gcal ` lists available actions.
     See |pending-gcal| for full details.
 
+                                                                *:Pending-s3*
+:Pending s3 {action}
+    Run an S3 sync action. An explicit action is required.
+
+    Actions: ~
+        `sync`    Pull remote changes then push merged result.
+        `push`    Upload the local store to S3.
+        `pull`    Download the remote store and merge into local.
+
+    Examples: >vim
+        :Pending s3 sync            " pull then push
+        :Pending s3 push            " upload local → S3
+        :Pending s3 pull            " download S3 → local
+<
+
+    Tab completion after `:Pending s3 ` lists available actions.
+    See |pending-s3| for full details.
+
+                                                              *:Pending-done*
+:Pending done [{id}]
+    Mark a task as done without opening the buffer. {id} is the numeric task
+    ID. When {id} is omitted and the task buffer is open, the task under the
+    cursor is used. Recurring tasks spawn a new pending instance with the
+    next due date. >vim
+        :Pending done 5
+        :Pending done
+<
+
                                                             *:Pending-filter*
 :Pending filter {predicates}
     Apply a filter to the task buffer. {predicates} is a space-separated list
@@ -862,9 +913,11 @@ Fields: ~
     {sync}               (table, default: {})          *pending.SyncConfig*
                          Sync backend configuration. Each key is a backend
                          name and the value is the backend-specific config
-                         table. Built-in backends: `gcal`, `gtasks`. Both
+                         table. Built-in backends: `gcal`, `gtasks`, `s3`.
-                         ship bundled OAuth credentials so no setup is
+                         Google backends ship bundled OAuth credentials so
-                         needed beyond `:Pending <backend> auth`.
+                         no setup is needed beyond `:Pending auth`. The S3
+                         backend delegates to the AWS CLI credential chain.
+                         See |pending-gcal|, |pending-gtasks|, |pending-s3|.
 
     {icons}              (table)                          *pending.Icons*
                          Icon characters displayed in the buffer. The
@@ -1424,10 +1477,11 @@ Task fields: ~
     {order}       (integer) Relative ordering within a category.
 
 Any field not in the list above is preserved in `_extra` and written back on
-save. This is used internally to store the Google Calendar event ID
+save. This is used internally to store sync backend metadata:
-(`_gcal_event_id`) and Google Tasks IDs (`_gtasks_task_id`,
+- Google Calendar: `_gcal_event_id`, `_gcal_calendar_id`
-`_gtasks_list_id`), and allows third-party tooling to annotate tasks without
+- Google Tasks: `_gtasks_task_id`, `_gtasks_list_id`
-data loss.
+- S3: `_s3_sync_id` (UUID for cross-device merge)
+Third-party tooling can annotate tasks via `_extra` without data loss.
 
 The `version` field is checked on load. If the file version is newer than the
 version the plugin supports, loading is aborted with an error message asking