diff --git a/docs/changelog-20260731-prefer-ipv6-research.md b/docs/changelog-20260731-prefer-ipv6-research.md
index 7b1554e..ee1103d 100644
--- a/docs/changelog-20260731-prefer-ipv6-research.md
+++ b/docs/changelog-20260731-prefer-ipv6-research.md
@@ -504,3 +504,53 @@
 region scale rather than a nicety.
 
 **Revert.** `git revert` -- register item 21 and the CURRENT-STATE entry move together.
+
+## Item 16 -- OPERATOR DIRECTION: all Tailscale decisions deferred to the end of the step
+
+**Operator direction, verbatim (2026-07-31):** *"To make sure we don't muddle the in
+process deployment, queue all the tailscale decisions to the end of the step. When you
+bring them back up give me decisions choices with your recommendation for each."*
+
+All four sub-decisions in gap register item 21 (utility-band octet; admin-reachability
+model star-vs-mesh; HA count per site; SNAT on/off) are DEFERRED to the end of the
+current step. When re-raised they are to be presented as decision CHOICES, each with an
+explicit recommendation. Nothing about Tailscale is to be built or ruled before then.
+
+**Revert.** Nothing to revert.
+
+## Item 17 -- MEASUREMENT: the size of `jammy-backports` if it is added to the dc0 mirror
+
+Measured 2026-07-31 against `archive.ubuntu.com` from the dc0 rack, summing the `Size:`
+field of every entry in each component's `binary-amd64/Packages.gz`, at the EXACT scope
+`dc-mirror.sh:177-181` uses (`--section=main,restricted,universe,multiverse --arch=amd64
+--nosource --diff=none`):
+
+| component | bytes | packages |
+|---|---|---|
+| main | 859,001,998 | 338 |
+| universe | 211,685,404 | 123 |
+| restricted | 0 | 0 (empty in backports) |
+| multiverse | 0 | 0 (empty in backports) |
+| **total** | **1,070,687,402 (~1.00 GiB)** | **461** |
+
+**Context measured alongside:** the existing dc0 mirror is **951 GB**
+(`/var/lib/dc-mirror/ubuntu`), with **1.8 T free** on the rack. Backports is therefore
+**~0.1% of the mirror** and a non-issue for capacity.
+
+**Sanity checks run, because a clean total is exactly the shape this repo has been burned
+by:** the five largest entries were listed to confirm the `Size:` field was being read
+(top entry `libreoffice-dev-doc` at 190 MB -- plausible); a separate `binary-all` index
+was probed and returns **404**, so arch:all packages are already inside `binary-amd64`
+(301 of main's 338 entries) and are not double-counted or missed.
+
+**Worth knowing before choosing: ~462 MB of the 859 MB in main is LibreOffice** (two
+`libreoffice-dev-doc` versions at 190 MB + 184 MB, plus `-core` and `-common`) -- i.e.
+roughly 46% of the suite is a desktop package set no OpenStack control-plane node will
+ever install.
+
+**Transfer estimate, stated as the weak measurement it is:** a single-stream fetch of one
+Packages.gz measured **932 KB/s** egress from the rack, which puts 1.07 GB at roughly
+**19 minutes**. That is one file on one stream; debmirror parallelises, so treat it as an
+upper bound rather than a figure.
+
+**Revert.** Measurement only; nothing changed.