julian
648d3254d6
Capture that refusing at capacity is the default, not absolute: an operator may opt into valet over-capacity (customer hands over keys, operator stacks the car into custody). Manned-only, new custody/session shape. Deferred; not built into the entry flow. Made capacity-occupancy's FULL gate a soft policy knob.
49 lines
2.3 KiB
Markdown
49 lines
2.3 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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## Open
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- Zone/level granularity at launch vs. single capacity number.
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- Reserve-for-permits threshold.
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- The valet over-capacity mode + custody model ([[valet-overcapacity]]).
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