server: pay station + fee calc — full transient loop now passes

computeFee() in @parking/shared: pure integer fee over a TariffStructure
(stepped blocks, rolling-24h cap). Two edges fixed under test: grace uses RAW
duration (not rounded-up minutes), and the block ladder resets each 24h day.

PayStation + routes (GET /api/pay/quote, POST /api/pay): look up the open
session, resolve the active tariff version (latest effectiveFrom <= entry),
computeFee, append a signed payment event (amount/currency/tender/
tariffVersionId/graceExitMin). overrideMinor handles lost-ticket/dispute. PCI
stays out of the app: tender only records cash/card.

Verified end to end: entry -> quote (300 for 90min) -> pay -> exit opens and
closes the session, verifyChain ok.

wiki/concepts/parking-session.md

@@ -111,8 +111,14 @@ follow this page and [[tariff]]; the decision is recorded in [[session-model]].
   - **Not a fail-state:** an unpaid reject keeps the barrier closed deliberately (driver returns to
     the pay station); "exit fails open" ([[fail-state-safety]]) is about the *system* being unable
     to decide (host/power loss), not an unpaid car.
-  - **Currently every transient exit rejects** — no `payment` events exist until the pay station is
-    built; the validation is the correct end-state, just not passable yet.
+- **Pay station** (`apps/server/src/pay-station.ts`, routes `GET /api/pay/quote` + `POST /api/pay`):
+  look up the open session → resolve the active tariff version (latest `effectiveFrom ≤ entry`) →
+  `computeFee` → append a signed `payment` event (amount, currency, tender, `tariffVersionId`,
+  `graceExitMin`). An operator `overrideMinor` covers lost-ticket/dispute (recorded as the charged
+  amount + the quoted amount). Pay-on-foot: payment is decoupled from the exit lane. PCI scope stays
+  out of the app — `tender` only records cash/card; card capture is the standalone P2PE terminal.
+  - **The full transient loop now passes end to end** (verified): entry → quote → pay → exit opens,
+    session closed, `verifyChain` ok.
 
 > **Design gap (flagged):** `lane_devices` has **no entry/exit direction** model. Entry is
 > button-driven and exit is read-driven, so they don't currently collide — but a lane with both an