rex-durable

Keep the programs in your Rex tabs across server restarts and reboots.

Rex saves your sessions, tabs, and splits when its server stops, and restores them when it starts again. The programs that were running in them don't come back: every tab returns as an empty shell. rex-durable remembers what was running in each tab and puts it back.

Running in the tab	After a restart
fx chat	Reopens on its conversation: fx --resume <id>
Claude Code chat	Reopens on its conversation: claude --resume <id>
Codex chat	Reopens on its conversation: codex resume <id>
Any other program	Typed at the prompt, not run. Press Enter if you want it.
Plain shell	Left alone

Chats keep their options, such as --model, and come back in the same tab, split, and folder.

Install

git clone https://github.com/fazxes/rex-durable
cd rex-durable
./install.sh --add-to-config

The installer:

1. Finds Rex's rex command. On macOS it uses the copy Rex keeps up to date in ~/Library/Application Support/com.superlogical.rex/RexServer/Versions/Current/, so Rex updates don't break it.
2. Copies durable.lua to ~/Library/Application Support/rex-durable/ on macOS, or ~/.local/share/rex-durable/ on Linux.
3. Starts it as a login service: a launchd agent on macOS, a systemd user service on Linux.
4. Adds command palette actions (rex_durable.lua in your Rex config folder). --add-to-config also loads them from init.lua for you. Without it, the installer prints the one line to add.

Run ./install.sh again to update. Use --no-service to install the files without the service, or REX=/path/to/rex ./install.sh to choose the rex command.

Requirements: Rex for Mac, or the Rex server on Linux, recent enough to have the Lua API's rex.exec, rex.json, rex.every, and rex.on. The installer checks this. You also need lsof, or /proc on Linux.

Using it

There's nothing to do day to day. Every 30 seconds, and a few seconds after any change, rex-durable saves what runs in each tab. After a restart, it brings everything back within seconds and shows a notification such as "Reopened 12 chats."

To check on it, or to do something by hand:

S="$HOME/Library/Application Support/rex-durable/durable.lua"   # Linux: ~/.local/share/rex-durable/durable.lua

rex do "$S" mode=status                    # what is saved, and the last restore
rex do "$S" mode=save                      # save now
rex do "$S" mode=reopen dry_run=true       # show what a reopen would type
rex do "$S" mode=reopen                    # reopen programs in their tabs
rex do "$S" mode=checkpoint name=before-update
rex do "$S" mode=reopen from=before-update # reopen from a pinned checkpoint
rex do "$S" mode=rebuild from=before-update yes=true  # recreate saved sessions

The command palette has the same actions: search for "durable".

Add programs=false to any mode to reopen chats only, and never type other programs' commands.

How it works

durable.lua is a Rex Lua script. The service runs it with rex do durable.lua --all, which hears events from every session. It uses only Rex's public API:

• Watching. On a timer (rex.every) and after layout and terminal events (rex.on), it starts a short rex do durable.lua mode=save. Each save runs on its own connection, so reading every session never affects the watcher.

• Saving. For each tab, it records the block ID, the folder, and the program from the terminal's process method. It then works out which conversation each chat is on:

  • fx holds a lock file for its session (~/.fx/sessions/v2/<id>/lock).
  • Codex keeps its rollout file open (~/.codex/sessions/…/rollout-…-<id>.jsonl), or the ID is on its command line (codex resume <id>).
  • Claude Code names the session on its command line (--resume <id>). Otherwise rex-durable uses the newest session file for that folder written since the chat started. If two such chats share a folder, it can't tell them apart, so they come back typed, not run.

  Saves go to ~/Library/Application Support/rex-durable/ on macOS, or ~/.local/state/rex-durable/ on Linux. It keeps the last save of each of the latest 10 servers.

• Restoring. When the watcher connects to a server instance it hasn't seen, it takes the last save from the previous server. Rex restores its own sessions with the same block IDs, so each program goes back into exactly the tab it came from, by block ID first and then by session name and position. If the server starts empty, for example after rex server stop --discard, rex-durable creates the saved sessions itself.

Safety

• It only types into a tab that is sitting at an idle shell. A tab where something is running is left alone.
• It never opens a chat twice: not if the chat is already running in a Rex tab, and not if another process holds its session file, such as the same chat open in another terminal.
• It acts once per server start. Running it again on the same server only saves.
• Programs other than chats are typed, never run.
• Saves older than 30 days are never restored on their own.
• dry_run=true shows what a reopen would type, without typing it.

Limits

• A chat that was in the middle of a reply reopens, but the reply in progress is gone, so re-ask its last step. Commands a chat had running in the background don't come back.
• Only chats in your own home folder's profile are reopened. An fx chat run with a different HOME, such as a test profile, comes back typed, not run.
• It works with the server it runs next to. For a remote Rex server, install rex-durable on that machine.
• A sudden power cut loses at most about the last 30 seconds of changes.

Uninstall

./uninstall.sh          # stop the service and remove the files, keep your saves
./uninstall.sh --purge  # remove the saves too

Your Rex sessions and the programs in them are not touched. If you added require("rex_durable") to init.lua, remove that line too.

Development

test/e2e.sh            # unit tests, then end-to-end tests on a throwaway Rex server
test/e2e.sh --unit     # unit tests only
lua5.1 test/platform.lua   # process and file helpers on Linux, without Rex

The end-to-end test needs Rex and a C compiler. It runs its own Rex server on its own socket, with fake fx, Claude Code, and Codex chats in a throwaway home folder. It never connects to your Rex server and never touches your real chats.

rex-durable is not made by or affiliated with Superlogical.

License

MIT