docs(register): IR-84 — the arm the rigs fire was the only one without a clock

The number was branch-claimed 2026-09-08 by name only; IR-85 records that it
carried no entry text in any register file in any worktree. This is that text,
filed in the lane that closes its first half rather than after it.

The entry is about a DIAGNOSTIC failure, not the stall. Measured at b0b67aaa
rather than recalled: pump/mod.rs carries four PUMP_PEER_FAIL emit sites, three
of them stamped wall_ms/mono_ms, and the fourth — the Err(e) arm of
peer_leg_outcome, which is the arm every ladder rig actually fires — was the only
unstamped site left. So the single arm a reader most needs to time was the single
arm that could not be timed.

The arithmetic stays open and the entry says so: PUMP_PEER_IO_TIMEOUT 30s plus
SUPERVISE_BACKOFF_BASE 5s accounts for 35s against 61.956-69.096s observed, and
the count of exactly one fail forbids reading it as two deadlines. Three
candidates are named and deliberately not ranked. What separates them is the
deadline's own timestamps against the fail line, which is what the log did not
carry.

Recorded as a RECURRENCE, because that is the part worth keeping: this is the
second unstamped PUMP_PEER_FAIL to cost a hunt. The PRESENCE_DIAL_FAILED arm
already carries a comment naming the 2026-07-14 unstamped seed, and
REQ-PUMP-STAGE-TRUTH already requires every peer failure stamped wall+mono and
explicitly subsumes that seed. The contract was written, three of four sites
complied, and the fourth stayed silent for eight weeks — a convention enforced by
no mechanism degrades one arm at a time, and every reader of a complying arm
reports the convention as held.

Also de-stales IR-85's own sentence about this number. It recorded, truly at
`a2f335f8`, that IR-84 was "branch-claimed by name only, with no entry text in
any register file in any worktree" — a statement this very commit falsifies. It
now says so and names PR #213, so the next reader is not sent hunting for a
missing entry by a line that was accurate when written.

Register-only. No code in this commit.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WAw9XAcTR8oSwzYPsqZoY2

Co-authored by: hertz