docs: record open-array M2 tag and next M3

docs/git-branches-tags.md

@@ -1,10 +1,10 @@
 # Git branches and tags — how this repository is organised
 
-**Snapshot:** 2026-10-23, after `v3-finally`. `master` =
-`c0c227c` (module finalization) plus a docs follow-up;
-`origin/master` = `4017d8f`.  The FINALLY work is local and **not
-pushed yet**; earlier exceptions/pointer/functionException work is on
-the remote.  307 tags (305 `v3-*` checkpoints).
+**Snapshot:** 2026-10-23, after open-array M2.  `master` =
+`4616e51` (fixed multi-dimensional storage); `origin/master` =
+`b3d049f`.  The open-array M1/M2 work is local and **not pushed yet**;
+earlier exceptions/pointer/functionException/finally work is also local
+where noted.  308 tags (306 `v3-*` checkpoints).
 
 Mental model:
 
@@ -49,6 +49,7 @@ Each points at the commit that landed a feature, all with green gates:
 | `v3-ptrchain` | `e804e57` | self-referential record layout and `p^.next^.value` |
 | `v3-function-exception` | `4238f67` | result function falling off its end |
 | `v3-finally` | `c0c227c` | module FINALLY / termination |
+| `v3-open-arrays-m2` | `4616e51` | fixed rank-2/3 flat storage + views |
 
 These are immutable checkpoints.  Useful commands:
 
@@ -100,9 +101,10 @@ recent ones above matter for the current session.
 
 ## Current state
 
-- `master` = `c0c227c` + docs, **1 commit ahead** of
-  `origin/master` (`4017d8f`).
-- `v3-finally` is local; push it with `master` when ready.  Earlier
-  exception/pointer/functionException tags are already on the remote.
+- `master` = `4616e51` (open-array M2), **3 commits ahead** of
+  `origin/master` (`b3d049f`): the open-array design, M1 helpers and M2.
+- `v3-finally` and `v3-open-arrays-m2` are local; push them with
+  `master` when ready.  Earlier exception/pointer/functionException
+  tags are already on the remote.
 - Next session: start from `master` and read
-  `docs/handoff-2026-10-23-next.md`.
+  `docs/handoff-2026-10-23-next.md`; continue with open-array M3.