julian
e579fe5b6e
Occupancy is a fold over the signed ledger (entries minus exits per identity);
getOccupancy returns {count, capacity, free, full}. Capacity is a single-row
site_config table (admin-set; null = uncapped; migration 0001, additive).
FULL gate lives in the transient entry flow: when full, refuse (no ticket, no
vehicle_entry, no open) and sign an anomaly. Permit entry is NOT gated --
subscribers are admitted past transient-full (their own maxConcurrent still
applies), so occupancy can read over capacity by design (reserve-for-permits).
Routes: GET /api/occupancy + GET /api/site-config (any role), PUT
/api/site-config (admin; non-negative int or null). Web SiteSettings: live
occupancy + FULL badge (everyone), capacity editor (admin).
Verified: fill to cap -> 3rd transient refused; permit admitted past full; exit
frees a slot; RBAC (operator can't set, -5 -> 400); verifyChain ok. Physical
FULL-sign relay output deferred.
68 lines
3.6 KiB
Markdown
68 lines
3.6 KiB
Markdown
---
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type: concept
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tags: [parking, domain, business, occupancy]
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sources: []
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updated: 2026-06-15
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status: open
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---
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# Capacity & Occupancy
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How many vehicles are inside, how many spaces remain, and what happens when the lot is full.
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## Occupancy is a projection (like everything else)
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`occupancy = count(open [[parking-session|sessions]])` — an entry with no matching exit. It is a
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**fold over the signed [[append-only-event-chain]]**, never a hand-maintained counter (a counter is
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editable and drifts; the chain is the truth). Spaces-free = `capacity − occupancy`.
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- **`capacity`** is admin-set per site (and per **zone/level** if the lot has sections — model a
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`zone` on capacity + on the entry so multi-level is a later addition, not a rewrite).
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- Permit concurrency (`maxConcurrent`, see [[permit]]) is the same kind of fold, scoped to one
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permit's open sessions.
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## Full → refuse entry + FULL sign
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- When `occupancy ≥ capacity`, the entry flow **refuses** (no `vehicle_entry`, no barrier open) and
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can drive a **"FULL" sign** (a relay/output, via the device adapter layer).
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- **Safety/policy nuance:** "full" blocks *entry* only — **exit always works** ([[fail-state-safety]]:
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exit fails open; never trap a vehicle). Permit holders may be allowed in past a "transient full"
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threshold (reserve spaces for subscribers) — an optional policy knob.
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- **Counting drift is real:** tailgating (two cars, one entry) and missed reads make the live count
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diverge from physical reality. The count is the *system's* occupancy; periodic ground-truth (a
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loop count, or the [[opencv-anpr-service|vision]] count) reconciles it — surfaced as an anomaly,
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not silently corrected.
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## "Full" is a soft, operator-configurable policy
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Refusing at capacity is the **default**, not an absolute. An operator may opt into
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**[[valet-overcapacity|valet over-capacity]]** — accept the car into operator custody (keys handed
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over, stacked beyond the marked count) instead of refusing. So the FULL gate is a policy knob
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(refuse vs. valet-accept), set by the operator per site. Valet is a manned-mode feature with its
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own custody/session shape — see [[valet-overcapacity]] (deferred).
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## As-built (2026-06-16)
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- **Occupancy** = `occupancyCount` (`apps/server/src/occupancy.ts`): a fold over the ledger —
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entries minus exits per identity, count those `> 0`. `getOccupancy` returns `{count, capacity,
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free, full}`.
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- **Capacity** is a single-row `site_config` table (admin-set; `null` = uncapped). Routes
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(`routes/site.ts`): `GET /api/occupancy` + `GET /api/site-config` (any role), `PUT /api/site-config`
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(admin; non-negative int or null).
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- **FULL gate** is in the **transient entry flow**: `occupancy.full` → refuse (no ticket, no
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`vehicle_entry`, no open) + signed `anomaly`. **Permit entry is NOT gated** here — subscribers are
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admitted past transient-full (their own `maxConcurrent` still applies); occupancy can read
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over-capacity (`free` negative) when permits enter a full lot, as intended.
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- **UI** `SiteSettings`: live occupancy + FULL badge (everyone); capacity editor (admin).
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- Verified: fill to cap → 3rd transient refused; permit still admitted past full; exit frees a
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slot; RBAC (operator can't set capacity); verifyChain ok. Physical FULL-sign relay output is
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**deferred** (needs a sign device).
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## Open
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- Zone/level granularity at launch vs. single capacity number.
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- Reserve-for-permits **threshold** (a soft transient cap below the hard capacity) — currently
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permits are simply ungated; a tunable threshold is the richer version.
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- Physical FULL-sign relay output (a sign-device role).
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- The valet over-capacity mode + custody model ([[valet-overcapacity]]).
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