julian
8a8e74561d
Pivot from the hardware/integrity layer to the parking operation. All wiki-only; no code yet. Core principle throughout: business entities are projections over the signed append-only event log, never mutable tables. New concepts: parking-session, tariff (composable/versioned, FX-ready), shift (manned-only Z-report), capacity-occupancy, validation-discounts, reporting-analytics, clock-integrity, ticket-encoding, anti-passback. New entities: permit, opencv-anpr-service, blocklist. Decisions: session-model, vision-service (host-side ANPR + vehicle verification; scoped AGPL exception for the isolated service). Updates: append-only-event-chain (new event types + vision witness), local-jwt-auth (drop 8h expiry -> until logout; code change pending), lpr-camera (host-side recognition supersedes edge-AI), standing-decisions (AGPL exception), open-questions (+FX, +pay-station money corners, backup). Deferred + flagged: intercom/help-call, receipts/refunds/change, FX engine, lane topology (#1).
41 lines
1.9 KiB
Markdown
41 lines
1.9 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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## Open
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- Whether "FULL" is a hard block or a soft warning (operator can wave one in) — operator policy.
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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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