Cabin rental

The §6.2 two-person-AB test, played straight: a one-man AB rents out a sommarstuga by the week. No lawyer, no procurement department - a template, a booking, a deposit that must come back unless something broke. It looks trivial and it immediately breaks something: the pool model cannot say “booked for week 29”. That fracture is this example’s reason to exist.

Profile: mk-se-b2c (same gap as example 01) or mk-se-b2b for company retreats - the mechanics are identical.

The fracture, first

§8.5 models a specific cabin as a named pool: pool unit:cabin capacity 1. Draw it, it’s gone. But a rental is not consumed - it is occupied for a date range, and two bookings for different weeks must both succeed while two for the same week must not. Capacity-1 says nothing about time; the double-booking question is an interval overlap question, and the current pool flavors cannot ask it.

Proposed primitive: the keyed pool - a pool family indexed by a key from a closed domain, each cell an independent capacity pool:

pool cabin.nights   keyed-by date within validity   capacity 1 each

A booking draws the cells 2027-07-12 .. 2027-07-19; overlap = one of those cells already drawn = the §3.1 boundedness question, per cell. Nothing new mathematically - coloured Petri nets (Jensen, 1981) are exactly this: tokens carrying values, places indexed by data. §6.3’s coupon register (“each code a capacity-1 pool”) was secretly the same shape - a pool keyed by code. Hotel/GDS inventory has run per-date availability cells for fifty years. The primitive is corpus-demanded (rentals, venues, vehicles, staff scheduling, berth allocation), lint-friendly (finite key domain within validity), and it collapses the named-pool flavor into keyed-by identity.

The contract

mechanical-contract v0
id:       mk-se-2027-cabin-0007
template: tpl-stugavtal @ v1
parties:
  landlord:  org 559234-5678 "Stugbolaget AB"  sign eIDAS-seal
  guest:     party<consumer> ref booking-payment    # example 01 identity questions apply

money: currency SEK  rounding total half-up 1.00

state:
  pool  cabin.nights   keyed-by date within validity   capacity 1 each   # keyed pool
  pool  money.rent     capacity 8_400 SEK  stages available|reserved|disbursed
  pool  money.deposit  capacity 3_000 SEK  stages available|reserved|disbursed
  bind  stay           shape { from: date, to: date }  at genesis

artifacts:
  price-table   art:stuga-prices-2027   pin v1     # SEK/night by season
  house-rules   class contract-bilaga   sha256:...  # soft: prose, hashed, binding

ports:
  in  payment.confirm   from psp        payload psp-attested-settlement
  in  cancel.request    from guest      payload signed-text
  in  checkin.confirm   from landlord   payload signed-decision
  in  checkout.confirm  from landlord   payload signed-decision
  in  damage.claim      from landlord   payload signed-claim + evidence(opaque)
  in  damage.accept     from guest      payload signed-decision
  out refund.instruct   to psp
  out receipt.emit      to submitter    always

rule on genesis:
  each night in stay.from .. stay.to:                       # bounded map over the range
    if pool cabin.nights[night] drawn -> reject "double-booked"
  reserve pool cabin.nights[stay.from .. stay.to]
  reserve money.rent + money.deposit                        # deposit: escrow, §3.4

cadence:
  cancellation ladder on cancel.request:                    # pure event math: compare
    which (stay.from - event.at) is                         # payload dates to the
      >= 30 days:  refund 100% of rent                      # cancel event's timestamp
      >= 7 days:   refund 50%
      otherwise:   refund 0%
    always: refund deposit 100%; release cabin.nights cells # cells return to the pool -
                                                            # resellable, structurally
  due damage.claim   within 5 days of checkout.confirm      # claim window: silence
                                                            # releases the deposit
  due refund deposit within 7 days of claim-window close

rule on damage.claim:
  if amount > money.deposit capacity  -> reject "exceeds deposit; excess is a civil claim"
  which guest response is
    damage.accept:        draw money.deposit amount; refund remainder
    otherwise (14 days):  escalate level 1                  # disputed damage: humans
                                                            # judge, the machine holds
escalation:                                                 # the money meanwhile
  level 1  notify both, deposit frozen        resolve-within 20 working-days
  level 2  ARN / small-claims per prose       deposit stays frozen, receipts flow

What this example stresses

Edge	Spec section
Time-sliced occupancy - the keyed-pool gap	§8.5 (falsified as written)
Deposit = reserve-with-expiry escrow, claim window as due	§3.4
Cancellation ladders as which-over-event-math	§3.2, §9
Disputed human judgment (damage) parking money in escrow + escalation	§4.1-4.2
Two-person-AB authoring bar	§6.2

Questions this example forced

• Keyed pools. As argued above: §8.5’s four flavors cannot express occupancy over time; the named flavor is the degenerate case of a pool keyed by identity. Proposed: adopt keyed-by <domain> as a vetted primitive (coloured-Petri semantics, finite key domain, per-cell boundedness). This is precisely the §9 mechanism working as designed - the corpus demanded, the primitive gets vetted. Proposed; it touches the core data model.
• Partial refunds are computed money flows. refund 50% is the first place a RULE computes an amount that then moves through a linear pool - the linter must prove refund ≤ reserved for every ladder branch (conservation, §6.4’s lesson applied to rules). Cheap to check, must be named as a lint promise.
• “Silence releases the deposit.” The claim window closing with no event is what triggers the refund due - an obligation triggered by the absence of an event. §3.4’s expiry machinery covers it (event-math over the window), but note the honest dependency: nothing HAPPENS until someone pokes the contract (§3.4’s untrusted alarm clock / §3.6 heartbeat). For a consumer-facing deposit, the profile should mandate a heartbeat so the guest’s refund never waits for the landlord’s goodwill to evaluate.

The meta-finding: the smallest examples break the most. The ramavtal of §2 fit the primitives because the primitives were forged against it; the sommarstuga found a real gap in an afternoon. That is exactly why these examples exist.

The contract, in mk

The full fixture in the working v0.1 grammar - Swedish clauses governing, English mk blocks:

---
mk: v0
id: tpl-stugavtal
title: Hyresvillkor - sommarstuga per vecka
prose-lang: sv (governs)
profile: mk-se-b2c
template: true
---

# Hyresvillkor Stugbolaget AB

## § 1 Parterna och bokningen  {#klausul-1 .implemented}

Uthyrare är Stugbolaget AB, org.nr 559234-5678. Hyresgäst är den konsument
som genomför bokningen. Bokningen avser stugan för de nätter som anges
vid bokningstillfället. Ångerrätt gäller inte vid upplåtelse av logi
[law:se/sfs/2005:59#kap2-p11]. <!-- statutory exemption: no angerratt
module here, deliberately - absence is readable -->

```mk
parameters:
  stay    shape: { from: date, to: date }
  rent    money SEK

parties:
  landlord  org: 559234-5678 "Stugbolaget AB"  sign: eIDAS-seal
  guest     from: parameters                   sign: payment-authorization

state:
  pool cabin.nights  keyed-by: date within validity  capacity: 1 each   # keyed pool
  pool money.rent    capacity: {rent}  stages: available|reserved|disbursed

rule on genesis:
  each night in stay.from .. stay.to:
    require cabin.nights[night] available
      else reject "dubbelbokad"
  reserve cabin.nights[stay.from .. stay.to]
  reserve money.rent
  accept
  implements: [#klausul-1]

§ 2 Avbokning {#klausul-2 .implemented}

Vid avbokning senast 30 dagar före ankomst återbetalas hela hyran; senast 7 dagar före ankomst halva hyran; därefter sker ingen återbetalning. Depositionen återbetalas alltid vid avbokning.

ports:
  in  payment.confirm   from: psp       payload: psp-attested-settlement
  in  cancel.request    from: guest     payload: signed-text
  in  checkin.confirm   from: landlord  payload: signed-decision
  in  checkout.confirm  from: landlord  payload: signed-decision
  out receipt.emit      to: submitter   always

cadence: cancellation on cancel.request   kind: ladder    # first-match, top-down:
  | notice before stay.from | refund of rent |            # rows overlap BY DESIGN,
  |--------------------------|----------------|           # order disambiguates
  | >= 30 days               | 100%           |
  | >= 7 days                | 50%            |
  | otherwise                | 0%             |
  implements: [#klausul-2]
  caption: "Avbokning 30 dagar före: full återbetalning; 7 dagar: halva hyran."

rule on cancel.request:
  refund := cancellation[stay.from - event.at] of {rent}   # the ladder, applied
  emit refund.instruct amount: refund
  release cabin.nights[stay.from .. stay.to]               # nights resellable,
  accept                                                   # structurally

§ 3 Deposition {#klausul-3 .implemented}

Hyresgästen erlägger en deposition om 3 000 kronor som återbetalas efter avresa om skadeanspråk inte framställts inom fem dagar.

use module:market/deposit@v2          # THIRD-PARTY module (Marknadsjuristerna AB),
  with: { amount: 3_000 SEK,          # publisher-sealed, hash-pinned via the tag:
          holder: party:landlord,     # @v2 resolves ONCE at flatten, recorded
          payer: party:guest,         # as sha256 beside the tag
          end-event: checkout.confirm,
          claim-window: 5 days }
  implements: [#klausul-3]

§ 4 Tvist {#klausul-4 .soft}

Tvist som inte kan lösas mellan parterna kan prövas av Allmänna reklamationsnämnden.

use module:std/se/dispute-arn@v1      # STANDARD module - same ladder the
  with: { notify-window: 5 working-days }   # webshop uses: ONE vetted artifact,
  implements: [#klausul-4]                  # many consuming contracts (§5.3)