server+web: capacity / FULL gate (occupancy fold + transient refuse)

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.

apps/web/src/App.tsx

@@ -4,6 +4,7 @@ import { Login } from "./Login.js";
 import { PermitManager } from "./PermitManager.js";
 import { SetupWizard } from "./SetupWizard.js";
 import { ShiftControl } from "./ShiftControl.js";
+import { SiteSettings } from "./SiteSettings.js";
 import { TariffComposer } from "./TariffComposer.js";
 
 // Operator UI shell. Plain React (no admin framework) — the operator UI is
@@ -41,6 +42,7 @@ export function App() {
           </button>
         </span>
       </header>
+      <SiteSettings canEdit={user.role === "admin"} />
       {user.role !== "readonly" && <ShiftControl />}
       {user.role === "admin" ? (
         <>

apps/web/src/SiteSettings.tsx

@@ -0,0 +1,65 @@
+import { useEffect, useState } from "react";
+import { fetchOccupancy, fetchSiteConfig, setCapacity, type Occupancy } from "./api.js";
+
+// Live occupancy + capacity. Occupancy is shown to everyone (it's a fold over the
+// signed ledger); the capacity field is admin-editable. The FULL gate (refuse
+// transient entry at capacity) is enforced server-side in the entry flow.
+// See wiki/concepts/capacity-occupancy.md.
+
+export function SiteSettings({ canEdit }: { canEdit: boolean }) {
+  const [occ, setOcc] = useState<Occupancy | null>(null);
+  const [capInput, setCapInput] = useState("");
+  const [msg, setMsg] = useState<string | null>(null);
+
+  function reload() {
+    fetchOccupancy().then(setOcc).catch(() => {});
+  }
+  useEffect(() => {
+    reload();
+    fetchSiteConfig()
+      .then((c) => setCapInput(c.capacity == null ? "" : String(c.capacity)))
+      .catch(() => {});
+  }, []);
+
+  async function save() {
+    setMsg(null);
+    const raw = capInput.trim();
+    const capacity = raw === "" ? null : Math.round(Number(raw));
+    try {
+      await setCapacity(capacity);
+      reload();
+      setMsg("Capacity saved.");
+    } catch (e) {
+      setMsg((e as Error).message);
+    }
+  }
+
+  return (
+    <section style={{ marginTop: "1.5rem", padding: "0.75rem 1rem", border: "1px solid #ddd", borderRadius: 6, maxWidth: 460 }}>
+      <strong>Occupancy:</strong>{" "}
+      {occ == null ? (
+        "…"
+      ) : (
+        <>
+          <span style={{ fontWeight: 600 }}>{occ.count}</span>
+          {occ.capacity != null ? ` / ${occ.capacity}` : " (no capacity set)"}
+          {occ.capacity != null && (
+            <span style={{ color: "#666" }}> · {occ.free} free</span>
+          )}
+          {occ.full && <span style={{ color: "crimson", marginLeft: "0.5rem", fontWeight: 600 }}>FULL</span>}{" "}
+          <button type="button" onClick={reload} style={{ marginLeft: "0.5rem" }}>↻</button>
+        </>
+      )}
+      {canEdit && (
+        <div style={{ marginTop: "0.6rem" }}>
+          <label>
+            Capacity (blank = no limit):{" "}
+            <input value={capInput} onChange={(e) => setCapInput(e.target.value)} style={{ width: 80 }} placeholder="e.g. 120" />
+          </label>{" "}
+          <button type="button" onClick={save}>Save</button>
+          {msg && <span style={{ marginLeft: "0.5rem", color: "#555" }}>{msg}</span>}
+        </div>
+      )}
+    </section>
+  );
+}

apps/web/src/api.ts

@@ -304,3 +304,22 @@ export function openShift(): Promise<{ startedAt: string }> {
 export function closeShift(): Promise<ShiftReport> {
   return apiFetch("/api/shift/close", { method: "POST" });
 }
+
+// --- Site config / occupancy ----------------------------------------------
+
+export interface Occupancy {
+  count: number;
+  capacity: number | null;
+  free: number | null;
+  full: boolean;
+}
+
+export function fetchOccupancy(): Promise<Occupancy> {
+  return apiFetch("/api/occupancy");
+}
+export function fetchSiteConfig(): Promise<{ capacity: number | null }> {
+  return apiFetch("/api/site-config");
+}
+export function setCapacity(capacity: number | null): Promise<{ capacity: number | null }> {
+  return apiFetch("/api/site-config", { method: "PUT", body: JSON.stringify({ capacity }) });
+}