docs(remediation): bank D-42 — the head-pin's negative control has never been observed

merge-gate.md says it outright: a successful merge is NOT evidence the pin worked, only the negative
case is. On mosaicstack Gitea a merge against a WRONG head_commit_id has never been attempted, so every
head-pinned merge to date is equally consistent with the pin working and with the pin being ignored.

That is D-23's class — the queue guard "ran" and returned pass for every possible input; the pin
"holds" on every merge that would have succeeded anyway. By the mission's own standard (every
gate-introducing task carries a registered must-fail negative control; a gate with no proven failure
path manufactures evidence) the head-pin is unregistered in substance however it reads in the runbook.

Not blocking #1033: that head is coordinator-frozen with both the orchestrator and coder-mos1 holding,
so there is no concurrent pusher for the pin to defend against — its protection is only load-bearing on
a contested head. Raised by Mos while assigning the merge; Mos owns it and has filed it as an infra
task in the D-37/D-41 cluster, to be proven before any contested-head merge.

Requirement on RM-02: the negative-control clause must cover provider-side enforcement mechanisms, not
only in-repo checks. "The API accepted our parameter" is not evidence the API honours it — the same
true-answer-to-a-different-question shape as D-24 and D-38.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

docs/remediation/BOARD.md

@@ -29,8 +29,8 @@
 
 1. **Nothing is waiting on you that is urgent.** RM-03 waits on Jason; RM-61 is gate-ready and waits on
    Mos; RM-02 unblocks once RM-61 merges. Read the record before touching any lane.
-2. **`docs/remediation/TASKS.md` is authoritative**, not the newest voice in a chat. It holds 42 findings
-   (D-1…D-6 in `BOARD-LEDGER.md`, D-7…D-41 + D-38c in TASKS.md), every ruling with its rationale, and the
+2. **`docs/remediation/TASKS.md` is authoritative**, not the newest voice in a chat. It holds 43 findings
+   (D-1…D-6 in `BOARD-LEDGER.md`, D-7…D-42 + D-38c in TASKS.md), every ruling with its rationale, and the
    requirements each finding placed on RM-02/RM-34/RM-50/RM-55.
 3. **`MISSION.md` carries five first-class principles**, all earned by live failures — observe the
    property not the proxy · pre-registration prevents retrofitting and nothing else · never ship an
@@ -91,7 +91,7 @@ board is one of the six stale restatements below.
 
 ## Decisions log — full record in [`TASKS.md`](./TASKS.md)
 
-All 42 findings (D-1…D-6 in `BOARD-LEDGER.md`, D-7…D-41 + D-38c in `TASKS.md`) and every ruling with its
+All 43 findings (D-1…D-6 in `BOARD-LEDGER.md`, D-7…D-42 + D-38c in `TASKS.md`) and every ruling with its
 rationale live there. **Not duplicated here** — a second copy is a second thing to go stale, which this
 board had done three times in one night (gate list, capability registry, DECISION-1 status), and three
 more times by the next rotation seam (RM-61 "building", "nothing implemented yet", DECISION-1/2/3