Re: [PATCH v2 8/8] repack: include required packs in incremental MIDX writes

On Wed, Sep 30, 2026 at 11:12:05PM -0500, Taylor Blau wrote:

The geometric plan from 1da62fb5c86 (repack: implement incremental MIDX
repacking, 2026-05-19) can omit kept and cruft packs, since neither
necessarily participates in the geometric repack. Such packs can also be
lost when replacing a tip layer that contains them. Neither plan
consults `midx_included_packs()`, so the rules for retaining cruft in
ordinary MIDX writes do not protect incremental writes.

Use that selection logic to add missing packs to each plan's write step.
Skip packs in retained base layers, but include required packs from a
replaced tip. Count added objects when choosing which layers to compact,
without changing the preferred pack.

I admit I had a hard time following this patch. I think the point is
that we're going to include some packs in the midx that were not covered
previously. But it was hard to see where that happens. I think the magic
bit is this:

where we rely on midx_included_packs() to do that selection.

So I _think_ this is doing the right thing, but my confidence in my
review is kind of low. To some degree I'd just rely on the functional
tests here.

-Peff