### System details

Omarchy 4.0.4-1

### What's wrong?

# `omarchy channel set` silently leaves packages from the previous channel installed, and `omarchy-update-orphan-pkgs` cannot detect them

## Summary

After switching from the `edge` channel back to `stable`, applications that were only ever published on `edge` remain installed. They are not reported by the update, not offered by the orphan-cleanup step, and no prompt or warning appears at any point. Because they are no longer provided by any configured repository, `pacman -Qem` lists them, which makes `omarchy-update-aur-pkgs` run `yay -Sua` against those names on every subsequent update.

## Steps to reproduce

1. `omarchy channel set edge`
2. Install an application that is only published on the `edge` channel.
3. `omarchy channel set stable`
4. `pacman -Qem` — the `edge`-only package is still listed.
5. `pacman -Qdt` — the package is **not** listed, so `omarchy-update-orphan-pkgs` never offers it for removal.
6. `omarchy update` — the AUR update step now runs on every update.

## What happened

After switching `edge` → `stable`, two packages installed from the `edge` channel stayed installed. Neither is provided by `core`, `extra`, `multilib`, or the `stable` omarchy repository any more, but both remain installed with `Install Reason: Explicitly installed`.

`omarchy-update-aur-pkgs` gates on `pacman -Qem` (`bin/omarchy-update-aur-pkgs:5`), so it ran on every update and invoked:

```
yay -Sua --noconfirm --cleanafter --ignore gcc14,gcc14-libs
```

(`bin/omarchy-update-aur-pkgs:8`)

yay resolved one of the leftover names against the AUR. An **unrelated** project in the AUR shares that name and carries a higher version number, so yay treated it as an available upgrade and built it. That project is a Rust/Tauri application: each update downloaded roughly 495 crates (~48 MiB) and started compiling 783, and the build was never able to complete, so the installed version never changed. Because the version mismatch therefore survived every run, and because `--cleanafter` removes the build directory after a successful install (which never happened), every subsequent `omarchy update` repeated the full download and compile from scratch.

yay additionally printed `Packages not in AUR: <name>` for the second leftover package on every run. That is a direct signal that a locally installed package is not resolvable, and it is currently only a passing log line.

## Root cause

Two independent gaps combine to produce this.

**1. The channel switch never computes the difference between channels.**

`bin/omarchy-channel-set` refreshes the pacman configuration for the new channel (`omarchy-refresh-pacman`, line 86), reinstalls only `omarchy` and `omarchy-settings` (line 88), and then runs `omarchy-update -y` (line 99). It never compares which packages the previous channel provided against which packages the new channel provides, so packages unique to the old channel are simply left behind.

**2. The only automated cleanup structurally cannot catch them.**

`omarchy-update-orphan-pkgs` is the existing cleanup step, but it collects candidates with:

```
mapfile -t orphans < <(pacman -Qtdq 2>/dev/null || true)
```

(`bin/omarchy-update-orphan-pkgs:8`)

`pacman -Qtdq` returns only *orphaned* packages — those installed as a dependency, or auto-installed. A package the user installed explicitly that has since lost its repository is **not** an orphan, so this step can never surface the exact failure mode of a channel switch.

## Impact

Leaving an `edge`-only package installed has consequences beyond a stale package:

- `pacman -Qem` stays non-empty, so the AUR update step runs on every `omarchy update` even for users with no AUR packages at all.
- Any leftover name that happens to match an unrelated, higher-versioned AUR project triggers a full source build on every update, indefinitely.
- `--cleanafter` guarantees the build directory is not reused, so nothing is cached between runs.

The user receives no indication that a channel switch left anything behind, and the one cleanup step that exists reports nothing.

## Expected behavior

Either of these would prevent it:

- `omarchy channel set` reports packages that are installed but no longer provided by any configured repository, and offers to remove them as part of the switch; or
- `omarchy-update-orphan-pkgs` additionally considers installed packages that are not provided by any repository, not just `pacman -Qtdq` orphans.

## Environment

- Omarchy 4.0.4-1
- Arch Linux, yay 13.0.1
- Reproduced by switching `edge` → `stable`