fix(subs): out-of-window charge was a phantom 12h span (4,100 ALL bug)

The tariff-bridge owed amount summed TWO charges — the early-entry gap +
a "late-exit" gap — and the exit gap (outOfWindowGap edge:"exit") always
measured back to the PREVIOUS window close, even for a subscriber still BEFORE
their window. So a car that entered ~30 min early showed ~12h owed (4,100 ALL)
the moment it was looked up, instead of ~100 ALL.

Replace the two-gap sum with a single correct primitive,
minutesOutsideWindow(timeframes, tz, from, to): the minutes within the actual
stay [entry, now] that fall outside the allowed window (covering early entry AND
late exit, bounded by the stay, weekend/off-days free). windowOwedBetween prices
those minutes once as a transient stay (so increments + daily cap apply) against
the tariff in force at entry. Both the exit gate (subscription-flow) and the
booth quote (pay-station) now use this one source of truth — they can't disagree.

Verified on the live occurrence: was 4,100 ALL, now 100 ALL (9 min outside →
one increment). 87 shared tests (6 new regression cases incl. the phantom span).
Build+lint 12/12.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

packages/shared/src/index.ts

@@ -1142,6 +1142,47 @@ export function outOfWindowGap(
   return { start, end: atISO, minutes: mins };
 }
 
+/**
+ * Total minutes WITHIN the stay span `[fromISO, toISO)` that fall OUTSIDE the plan's
+ * allowed window — the correct charge basis for a subscriber's out-of-window parking
+ * (early entry AND/OR late exit, in one number, bounded by the actual stay). On days the
+ * window doesn't apply (not in `days`) the whole day is allowed (0 outside minutes). The
+ * window edges are widened by `graceMin`. Pure + tz-aware. Returns 0 for an unrestricted
+ * plan / empty span. (Sampled per minute; capped so a pathological span can't spin.)
+ */
+export function minutesOutsideWindow(
+  timeframes: PlanTimeframes | null | undefined,
+  tz: string,
+  fromISO: string,
+  toISO: string,
+): number {
+  if (!timeframes) return 0;
+  if (typeof timeframes.fromMin !== "number" || typeof timeframes.toMin !== "number") return 0;
+  const fromMs = Date.parse(fromISO);
+  const toMs = Date.parse(toISO);
+  if (!Number.isFinite(fromMs) || !Number.isFinite(toMs) || toMs <= fromMs) return 0;
+
+  const zone = timeframes.tz || tz;
+  const grace = Math.max(0, timeframes.graceMin ?? 0);
+  const days = timeframes.days && timeframes.days.length > 0 ? new Set(timeframes.days) : null;
+  // Widen the allowed window by grace on both edges (so a few minutes either side is free).
+  const from = (timeframes.fromMin - grace + 1440) % 1440;
+  const to = (timeframes.toMin + grace) % 1440;
+
+  // Iterate minute-by-minute over the stay; count minutes outside the allowed window.
+  const totalMin = Math.ceil((toMs - fromMs) / 60_000);
+  const cap = 60 * 24 * 400; // ~400 days of minutes — a hard safety bound
+  let outside = 0;
+  for (let i = 0; i < totalMin && i < cap; i += 1) {
+    const wall = localBreakdown(fromMs + i * 60_000, zone);
+    // A day the window doesn't apply to ⇒ fully allowed (this minute is free).
+    if (days && !days.has(wall.dow)) continue;
+    const m = wall.hour * 60 + wall.minute;
+    if (!inWindow(m, from, to)) outside += 1;
+  }
+  return outside;
+}
+
 /** "HH:MM" → minutes-of-day (0-1439). Invalid → NaN (validation rejects those). */
 function hourToMin(hhmm: string): number {
   const m = /^(\d{2}):(\d{2})$/.exec(hhmm);

packages/shared/src/subscription-window.test.ts

@@ -1,5 +1,5 @@
 import { describe, it, expect } from "vitest";
-import { outOfWindowGap, type PlanTimeframes } from "./index.js";
+import { minutesOutsideWindow, outOfWindowGap, type PlanTimeframes } from "./index.js";
 
 // The "tariff bridge" gap for a subscriber scan outside their allowed window. UTC tz
 // keeps the wall-clock arithmetic obvious in the tests. See wiki/entities/subscription.md.
@@ -86,3 +86,28 @@ describe("outOfWindowGap — unrestricted", () => {
     expect(outOfWindowGap(null, "UTC", monday("09:00"), "entry")).toBeNull();
   });
 });
+
+describe("minutesOutsideWindow — the charge basis (regression: no phantom span)", () => {
+  // entered 30 min before the 20:00 window; STILL inside, only a few minutes elapsed.
+  it("early entry, barely elapsed → only the elapsed pre-window minutes (NOT back to a prior close)", () => {
+    // 19:30 entry, now 19:33 → 3 minutes outside (the bug charged ~12h here).
+    expect(minutesOutsideWindow(night, "UTC", monday("19:30"), monday("19:33"))).toBe(3);
+  });
+  it("early entry until the window opens = the full pre-window gap, then 0 inside", () => {
+    // 19:30 → 22:00: 30 min outside (19:30→20:00), the rest in-window.
+    expect(minutesOutsideWindow(night, "UTC", monday("19:30"), monday("22:00"))).toBe(30);
+  });
+  it("in-window the whole stay → 0", () => {
+    expect(minutesOutsideWindow(night, "UTC", monday("22:00"), monday("23:30"))).toBe(90 - 90); // fully inside
+  });
+  it("late exit after close adds the post-close minutes", () => {
+    // enter 22:00 (in window), exit 08:30 → 30 min outside (08:00→08:30).
+    expect(minutesOutsideWindow(night, "UTC", monday("22:00"), `2026-06-23T08:30:00.000Z`)).toBe(30);
+  });
+  it("a day the window doesn't apply contributes 0 (weekend free)", () => {
+    expect(minutesOutsideWindow(night, "UTC", saturday("09:00"), saturday("18:00"))).toBe(0);
+  });
+  it("unrestricted plan → 0", () => {
+    expect(minutesOutsideWindow(null, "UTC", monday("09:00"), monday("23:00"))).toBe(0);
+  });
+});