Collapse _build_posts double sort into one comparator (#50)

[jmacdotorg]

Closes #50.

Diagnosis

_build_posts did two sorts:

my @posts = sort { $b->date <=> $a->date }
            map { Plerd::Post->new( ... ) }
            sort { $a->basename cmp $b->basename }   # <-- this pass
            grep { /\.markdown$|\.md$/ }
            $self->source_directory->children;

The inner basename sort isn't thrown away (it's the tiebreak for posts that share a date, preserved through the stable outer sort), but doing it as a separate pass is redundant work, as noted on the issue.

Fix

Collapse to a single sort with an explicit comparator — date descending, basename ascending:

sort {
    $b->date <=> $a->date
    || $a->source_file->basename cmp $b->source_file->basename
}

This is the same comparator _ordered_basenames already uses on the incremental publish path, so a full publish and an incremental publish now provably agree on ordering. The grep still accepts both .md and .markdown.

Behavior

Output order is unchanged (the old stable-sort + pre-sort produced the same result); this drops the redundant pass and makes the tiebreak explicit. t/post_sort.t pins the contract — newest-first with a basename tiebreak — and was written against the old code first to confirm the order doesn't change, including the mixed .md/.markdown, same-date case. Full suite green.

🤖 Generated with Claude Code