julian
e14e31a840
Closes the three known follow-ups of the Tills decision (venue-modules.md): - Activity log per till: `tillOfEvent(type, payload)` in @parking/shared (money events by payload till, other events by their owning module's till, everything else booth), applied by `/api/events?till=` in SQL and passed by the hub log, the Drawer "today" panel and the booth feed (history + live pushes). The events route admits a role that holds a module feed permission without event:read and returns only that module's event types — the live-socket rule. - Booth Z-report: `chargesByModuleMinor` sums the chargeLines on the till's payments by module; the ticket bucket excludes them (Bileta = parking only); printed "Lavazh (në biletë)" only when any was taken. The wash till's slip prints "Lavazh:". - Printer role `wash-desk`: the wash till's Z-report and vouchers print there, falling back to the booth printer; nothing falls back to the desk. `printerRoleOf()` is the one reading of the role field (the entry/booth loaders treated any non-booth role as an entry dispenser). Footer label "at wash desk". Also: `GET /api/carwash/settings` opens to carwash:read OR site:read (new requireAnyPermission) — the Wash operator job could not load the desk's category and service pickers. Tests for all four; wiki (shift, printer-roles-failover, venue-modules, log) updated. Claude-Session: https://claude.ai/code/session_01FWncR69HgGPuei1dLrW3cU
66 lines
3.4 KiB
Markdown
66 lines
3.4 KiB
Markdown
---
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type: concept
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tags: [parking, printer, device, reliability]
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sources: []
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updated: 2026-06-14
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---
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# Printer roles & failover
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A lane runs **more than one printer**, and the system knows each one's job so it can fail over
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automatically. This is a reliability decision, not a threat-model one: an entry ticket must
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still print when the outside dispenser jams or drops off the network.
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## Roles
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Each printer instance (a `devices` row, category `printer`) declares a **role** in its
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config:
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- **`entry-dispenser`** — outside, at the lane. Prints the entry ticket the driver takes.
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- **`booth-receipt`** — inside the booth. Prints receipts at exit/payment, the booth till's
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Z-reports and vouchers, AND serves as the **backup** for entry tickets (and for wash slips).
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- **`wash-desk`** — at the Car Wash desk (added 2026-09-06). Prints the wash till's slips:
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its Z-report and drawer vouchers (see [[shift]] §Tills). Nothing else ever prints here.
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It also declares a **`failoverRank`** (higher = preferred within a role) to order multiple
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printers of the same role deterministically (ties broken by id).
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## Failover rule (asymmetric, on purpose)
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For an **entry ticket** (`wantRole = entry-dispenser`): try the entry dispensers (best rank
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first), then fall back to the **booth printer**. So a driver still gets a ticket when the
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outside unit is offline — the operator hands it over from the booth.
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The reverse is **deliberately not** done: a **receipt** never prints on the outside dispenser.
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Receipts are a booth-only job; an entry dispenser falling back to print receipts makes no
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physical sense.
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For a **wash slip** (`wantRole = wash-desk`): the desk printers first, then the **booth
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printer** — a site that has not bought a desk printer keeps printing the wash till's Z-report
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and vouchers in the booth, exactly as it did before the role existed. Nothing falls back *to*
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the wash desk: a booth receipt or an entry ticket never prints there. `ShiftService` resolves
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the role from the till (`TILL_PRINTER_ROLE`: booth → `booth-receipt`, carwash → `wash-desk`)
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and keeps one legacy fallback — a booth with a single printer that carries no booth role still
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prints its slips on it. `printerRoleOf(config)` is the one reading of the saved `role` field,
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so every loader (entry flow, booth receipts, shift slips) agrees on what a printer is; the
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device footer shows a desk printer as "at wash desk".
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## Where the logic lives
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- The driver (`rongta`) is **role-agnostic** — role/rank are just config; the transport doesn't
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care. Keeps [[device-adapter-pattern|adapters]] swappable.
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- Selection is pure logic in `packages/devices/printer-routing.ts`: `orderForRole()` ranks
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candidates; `printWithFailover()` attempts the print down the list and throws
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`NoPrinterAvailableError` only when every candidate fails.
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- It **attempts the print directly** rather than racing a `healthCheck` first — the print is
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the real reachability test, and a health probe that passes can still be followed by a failed
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print.
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## Open: the all-printers-down policy
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When `printWithFailover` exhausts every candidate, what should entry do — raise the barrier
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with no paper ticket (the plate/[[lpr-camera]] is the independent record), or hold? That policy
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belongs to the **entry flow** ([[device-input-flow]], [[fail-state-safety]]), not the printer
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layer, and is **not yet decided**. The signed event ([[append-only-event-chain]]) is created
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regardless of whether paper prints.
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