NARROWING MY OWN WARNING, before you rule on it — the trap is REAL but I quoted a stale cost and it
makes the conversion cheaper than I told you.

I said "twohost.rs shares ONE `a` brain across all rungs", citing my 2026-07-25 entry. Measured at
a2f335f8 instead of quoted: it does NOT, not for these verbs. Full census of all 14 call sites of the
six verbs — 6 production, all in wansend.rs (:480 wan, :615 knock, :654 presence, :753 fork, :1658
redeem, :1714 answer) and 8 test-side:
  twohost.rs :1599 ack_brain, :1729 + :1742 answer_brain (same brain, two calls), :2918 redeem_brain,
              :2959 reply_brain, :3198 seal_brain, :3260 done_brain
  twohost_web.rs :534 its own `brain`, built Brain::cold_start at :517
Each rung builds its OWN brain — five of them through one helper, connect_retry (twohost.rs:442,
`Brain::cold_start`, 9 uses in the file), and twohost_web builds its own inline.

So the conversion surface is: one helper (or a pump-mode sibling of it), two inline constructions,
and no shared brain to thread a carrier change through. That removes the "converted verb reds the
whole ladder through a shared brain" failure I warned you about — it becomes per-rung and local,
which is the shape my own entry recommended in the first place ("give the one rung its own pump
brain rather than converting a shared one" — they already have their own).

WHAT SURVIVES the narrowing, and it is still the axis worth your ruling: the seam refusing an
unbounded carrier still breaks callers at RUNTIME, not compile time, because both carriers are the
same `&mut Brain` type. So a missed call site is a two-host-only red, not a build error. With 14
sites total and 8 of them in two rig files, that risk is enumerable rather than open-ended — I can
name every one in the commit and convert them in the same change.

Recommendation unchanged, now with a smaller price tag: refuse at the seam, convert all 14, name them
in the commit body. If you would rather not touch the ladder at all this close to the release, the
alternative is to bound only what a pump brain is handed and leave the seam permissive — cheaper
today, and it is exactly the silence that shipped this wrong the first time.

Still idle, nothing edited.