Prune the package cache before updating

[dhh]

The pacman cache grows without bound across updates and nothing in the update flow ever reclaimed it. On this machine it had reached 7.4G across 732 archives, ~3.75 GiB of which are superseded versions nothing will install again.

Adds omarchy-update-pkg-prune, running paccache -rk2 as the first step of an update.

Why that placement

Both halves of it are load-bearing.

Before the packages update. The cache is Arch's only offline downgrade path — when an update breaks one package, reinstalling its predecessor from here is the surgical fix, where a snapshot rollback reverts every other package too. Pruning beforehand means the installed version is still the newest cached, so it survives along with a spare. Pruning after would make the newest cached version the freshly installed one, and cutting down to a single copy would delete exactly what a broken update needs.

Before the snapshot. The cache sits on the snapshotted root subvolume, so a prune taken after omarchy-snapshot create leaves the fresh snapshot holding those extents and reclaims nothing until it ages out of the number cleanup. Ordering it first is what makes the space actually come back.

-k2 reclaims 3.75 GiB here, against 4.95 for -k1 (which leaves no rollback candidate) and 3.11 for -k3.

Failure handling

A failed prune warns and continues rather than aborting. Cache housekeeping shouldn't trip the update's ERR trap and tell the user their update went wrong. This got exercised for real: an early test run hit the unstubbed command with no sudo password available, and it warned and carried on with the cache untouched.

Known limitations

Two things this deliberately does not do, both worth a second opinion:

• It runs after omarchy-update-requires-free-space, so it reclaims space during healthy updates but does not rescue a machine already under the 10 GiB gate — the case where the cache itself is what's blocking the update. Folding the prune into that gate and rechecking would fix it, at the cost of mutating the system before the user confirms.
• paccache retains by version order and never consults what is installed. The rollback guarantee therefore holds only while the installed version is among the two newest cached. A deliberate downgrade held with IgnorePkg, or repeated failed transactions, can stack newer archives on top of the installed one, and its copy becomes prunable like any other. Exempting installed versions is possible but needs real filename parsing.

Not included: paccache -ruk0 for uninstalled packages, which is strictly safe and pairs naturally with omarchy-update-orphan-pkgs.

Testing

New test/shell.d/update-pkg-prune-test.sh covers the keep count, the non-fatal failure path, and both ordering invariants by asserting line order in omarchy-update.

Also stubs the new command in update-disk-space-test.sh and update-lock-test.sh, both of which execute the real updater. Without that, ./test/shell reaches a real sudo paccache -rk2 and would prune the developer's own cache on a box with passwordless sudo. update-lock-test.sh was caught by a Codex review pass, not by me.

./test/shell (160 files) and ./test/cli both green.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds safe pacman cache pruning before snapshots and package updates.

Changes:

• Keeps two cached package versions via paccache -rk2.
• Treats pruning failures as non-fatal.
• Tests retention, failure handling, ordering, and updater isolation.

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Reviewed changes

Copilot reviewed 3 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
bin/omarchy-update	Runs cache pruning before snapshot creation.
bin/omarchy-update-pkg-cache	Implements non-fatal cache pruning.
test/shell.d/update-pkg-cache-test.sh	Tests pruning arguments, failure, and ordering.
test/shell.d/update-disk-space-test.sh	Stubs pruning during updater tests.
test/shell.d/update-lock-test.sh	Stubs pruning during lock tests.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 5 changed files in this pull request and generated no new comments.

Suppressed comments (1)

test/shell.d/update-pkg-prune-test.sh:34

• This regex also accepts values such as -rk20, so a regression that retains far more than the intended two versions could still pass while defeating the pruning goal. Compare the recorded invocation exactly with paccache -rk2 so the retention contract is pinned.

grep -qE 'paccache .*-rk2' "$test_tmp/args" ||

[Copilot]

Pull request overview

Copilot reviewed 3 out of 5 changed files in this pull request and generated no new comments.