docs: make standing release windows explicit graphs

Add the mint-time membership call, the sink/source/subset invariants, and the release note while the contradictory successor-count criterion awaits triage clarification.\n\nCloses #292.

RELEASES.md

@@ -74,6 +74,13 @@ interleaving unrelated windows blurs both the release story and the evidence
 behind it. Gates open windows; they do not silently admit members, so builders
 still see one deliberately ordered queue.
 
+While a window stands — an open release-labeled issue with a non-empty
+enumerated gate — its members form a DAG whose sink is the release issue.
+Every member reaches that sink; ordering edges live on members, while the sink
+records membership only; and the `ready` set is exactly the graph's sources.
+It follows that every `ready` issue is a gate member. `epic` and `post-merge`
+issues are exempt because neither is claimable (#292).
+
 The operator may declare a parallel track at init when its footprint is
 disjoint from the primary window: another repository, another artifact, or
 provably non-overlapping clusters. The declaration names the boundary and any

TRIAGE.md

@@ -98,6 +98,13 @@ Every issue you mint carries, in this order:
   edge with `Blocked by #N`, naming the newest open carrier; there is no
   alternative for disjoint regions. This keeps every `ready` issue
   concurrently claimable and makes each close release one successor (#288).
+  During a standing release window, every mint also gets a binary membership
+  call in the same tick. A non-member names the release issue as its blocker.
+  A member is placed by naming its member predecessors on the new issue,
+  adding or re-pointing every downstream member's dependency to the new issue
+  (inserting X into A → B makes A → X → B, never a fan), and adding the new
+  issue to the release issue's gate; collision and window edges are
+  independent, so write both when both apply (#292).
 - **Labels**: type (`bug`/`enhancement`/`documentation`), `scope:*`, and
   exactly one of `ready` / `blocked` (see [LABELS.md](LABELS.md)).
 

changelog.d/292.md

@@ -0,0 +1,3 @@
+### Changed
+
+- Standing release windows are dependency DAGs: every mint is placed in the window or behind it, and only current sources are `ready` (#292).