vms-0425: rejoin — sub-question settled + CM JOIN gate bisected (spec §4(O.24))

[baron-3dl]

What this settles

vms-944/§4(O.23) relocated the rejoin frontier to "reclaim succeeds, CM JOIN does not run" and left one open sub-question: its reclaim was demonstrated with a blatantly future incarnation pin (1-OCT-2026, chosen for SDA day-resolution visibility). Does a realistic near-now incarnation — what OVMX presents in normal operation — also trigger the reclaim, or is the reclaim an artifact of a coarse delta (which would move the frontier to "make the member see a new incarnation")?

Sub-question SETTLED — realistic incarnation reclaims identically to the future pin

Same-boot single-factor SDA bracket on a freshly-booted vaxlab-1, two brand-new identities, first-join op02 form held constant, VAX1 parked in SDA per arm:

arm	identity	return incarnation	member's CSB (SDA)	XITDONE
0425Rf	OVXR40/1975	— (first join)	built 8796AE80 → member,selected	1
0425Rr	OVXR40	default live (near-now)	8796AE80 DEALLOC → NEW 879DF540, 02040000 status_rcvd (non-member)	0
0425Ff	OVXF40/1976	— (first join)	built 879DEF00 → member,selected	1
0425Fr	OVXF40	1-OCT-2026	879DEF00 DEALLOC → NEW 879DF2C0, Incarnation 11-AUG → 1-OCT, 02040000 status_rcvd (non-member)	0

The realistic return (Rr) and the future-pinned return (Fr) produce byte-identical CSB outcomes: both deallocate the residual CSB and rebuild a fresh one at a new address (Davis pp.7-24/7-25), both reach 02040000 status_rcvd — the exact intermediate state a successful first join passes through — and both stall there, never reaching member,selected. Only the SDA-displayed date differs. The reclaim needs no coarse delta; the frontier does NOT relocate — it stays at the CM JOIN transition. §4(O.22)'s "never reclaims" was a SHOW CLUSTER-string artifact.

CM JOIN gate BISECTED on the wire — OVMX DRIVES op 0x02; the coordinator ABANDONS it

Rf-vs-Rr CM-frame wire diff (same identity/pod; docs/clean-room/tools/cmdiff.py):

step	first join 0425Rf (XITDONE=1)	return 0425Rr (XITDONE=0)
OVMX → coordinator op 0x02 (join request)	sent	sent (OVMX drives it on the return too)
coordinator → other member op 0x12 RELAY	sent	absent
coordinator → OVMX op 0x03 COMMIT	sent → OVMX 0x81-responds	absent (cm_responses=0)
what the coordinator does instead	op 0x05 / op 0x06 → joined	member↔member cat-0x06 reconcile excluding OVMX, then a transition ABORT

This bisects the frontier's either/or: it is not that OVMX omits op 0x02 (it drives it, correctly addressed — its own SCSD-I-CMCONFIG2 log confirms), and not that the member waits silently (the coordinator actively runs a different transition). Per Davis p.7-38 the coordinator, on a join request, runs admission/quorum tests and "ignores the request … and no state transition occurs" when they fail; a first join passes them, a return (against a member that just reclaimed OVMX's CSB) does not. The gate is the coordinator ignoring an op02-driven ADD for a returning identity.

Relocated frontier (next isolation)

SDA on the COORDINATOR (the member OVMX sends op 0x02 to), across departure+return, to see why it declines an op02-driven ADD for a reclaimed identity it admits when fresh — i.e. whether its CLUB nodemap / quorum-vote accounting still carries residual state for the departed OVMX so its p.7-38 tests fail. (A separate OVMX-side defect surfaced, not the gate: on the return OVMX re-drives its add-member burst with remote_conid=0x00000000 and leaves its VMS$VAXcluster VCs CONNSTUCK.)

What ships (no wire change, guard 8 — the first-join path is byte-unchanged)

• READMITMAP verdict refinement: JOIN-ABANDONED (joiner_cfg2_sent && cm_responses==0) split out of RECLAIMED-NOJOIN/NO-ENGAGE, naming the member OVMX actually drove the join request to (the coordinator) distinctly from one it only reached. Checked before the open latch (OVMX's own VC ends CONNSTUCK on the return, so vaxcluster_open_reached under-reports). Log-only; kill-switch OVMX_NO_READMITMAP unchanged.
• Live pass-post: with the refined daemon, scsd-0425Rr2.log reads coordinator verdict=JOIN-ABANDONED, non-coordinator NO-ENGAGE, SUMMARY join_abandoned=1 no_engage=1 (the old latch-first classifier read both NO-ENGAGE, masking the op02-driven fact).
• fail-pre/pass-post unit case in tests/vmsscs/test_scsd_wire.c (test_scsd_wire green).
• docs/clean-room/tools/cmdiff.py — CM-frame (category/opcode) decoder.
• spec §4(O.24) + design record docs/design-rejoin-cm-state-map.md §8.

What this does NOT claim

XITDONE did not flip (0→0, as expected): this settles the sub-question and bisects the gate; it does not fix rejoin. Still a non-admission (never ADMITTED; INV-6).

Clean-room Rule 8: VAXcluster Principles pp.7-24/7-25/7-37/7-38/7-39 cited by page number only.

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