docs(canon): amend ADR-012 decision 7 — reset retires, it does not delete

Discovered before implementation: discard-and-rebuild cannot exist. Progress
events, tasks, decisions and review contracts reference workplans with ON DELETE
RESTRICT, and 1067 of 1075 workplans carry such a reference. Deleting a workplan
would delete the hub-native records attached to it, which ADR-010 decision 4
forbids and the schema refuses.

The database is enforcing this ADR's own boundary one layer down. A progress
event is a fact that happened; destroying it to tidy a derived projection loses
hub-native truth to fix a derived-state problem.

Reset now reconciles: create what is missing, update what differs, retire what no
longer derives — and retirement must be visible rather than silent.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

canon/architecture/adr-012-projection-source-and-preliminary-overlay.md

@@ -112,8 +112,27 @@ the gap where "central derives" was policy while "the laptop pushes" was
 practice.
 
 **7. The projection must be resettable from the forge, as a routine operation.**
-There must be a supported way to discard the projection — for one repository or
-for the whole fleet — and rebuild it from what Forgejo holds.
+There must be a supported way to reconcile the projection — for one repository or
+for the whole fleet — against what Forgejo holds: create what is missing, update
+what differs, and **retire what no longer derives**.
+
+> **Amended 2026-08-25, before implementation.** This decision originally said
+> *discard and rebuild*. That operation cannot exist, and the reason is a good
+> one. `progress_events`, `tasks`, `decisions` and `review_contracts` all
+> reference workplans with `ON DELETE RESTRICT`, and 1067 of 1075 workplans carry
+> at least one such reference. Deleting a workplan would mean deleting the
+> hub-native records attached to it — which `ADR-010` decision 4 forbids, and
+> which the schema refuses to allow.
+>
+> The database is enforcing this ADR's own boundary one layer down. A progress
+> event recording work on a workplan is a fact that happened; destroying it to
+> tidy a derived projection would be losing hub-native truth to fix a
+> derived-state problem, which is exactly backwards.
+>
+> Retirement achieves what reset is for — the projection converges on the forge,
+> and records that no longer derive stop appearing as live work — without
+> erasing anything that only the hub holds. Reset reconciles; it does not
+> destroy.
 
 This is the decision that makes the others checkable rather than merely stated.
 A read model that cannot be rebuilt from its source is not a projection; it is a
@@ -164,6 +183,11 @@ Three properties make it real rather than ceremonial:
   Derived identifiers (`ADR-007`) are what make this possible: the same commit
   yields the same record identities every time.
 
+**Retirement must be visible, not silent.** A retired record states that the
+forge no longer derives it, and remains inspectable — including from whatever
+hub-native history is still attached. A record that merely disappears from a
+listing is indistinguishable from one that was never there.
+
 **Reset does not restore the preliminary overlay.** Overlay records exist
 precisely because the forge does not hold them, so a rebuild from the forge
 cannot reproduce them and must not pretend to. Reset therefore discards
@@ -189,8 +213,8 @@ repository where it earns its keep; this ADR neither mandates nor forbids it.
 
 ## Consequences
 
-**Positive.** The hub becomes provably a projection: rebuildable on demand, and
-therefore knowable to be one. Truth becomes checkable by anyone, from anywhere,
+**Positive.** The hub becomes provably a projection: reconcilable on demand
+against its source, and therefore knowable to be one. Truth becomes checkable by anyone, from anywhere,
 without a clone.
 Multiple contributors share one baseline instead of overwriting each other's
 views. Provenance becomes auditable — every record can name its commit. The