fix: enforce open-limit rules proactively in the foreground

RuleEnforcer.refresh only shielded a limit rule once its budget was
spent, so it tore down the background's proactive open-limit "turnstile"
shield (the shield is how opens are counted) whenever the app was
foregrounded, and a freshly created open-limit rule did nothing until
the next midnight reset.

refresh now applies the same proactive gate as
LimitEnforcement.handleDayStart: an enabled, scheduled-today, un-paused
open-limit rule is shielded even before its budget is spent, so it takes
effect immediately. A new app-group OpenSessionStore records a granted
"Open" session's expiry so neither enforcement path re-shields (and cuts
short) a sanctioned ~15-minute session.

Overlapping rules already enforce strictly: each rule shields its own
ManagedSettingsStore and Screen Time unions them, so an app is blocked
if any covering rule blocks it. Document that model in the spec (§4.8)
and lock it in with tests, including a time limit blocking during an
open-limit's granted session and a daily opens reset.

Co-Authored-By: Claude <noreply@anthropic.com>

Shared/OpenSessionStore.swift

@@ -0,0 +1,59 @@
+//
+//  OpenSessionStore.swift
+//  OpenAppLock
+//
+
+import Foundation
+
+/// Read access to in-progress granted "Open" sessions, keyed by rule.
+protocol OpenSessionReading: AnyObject {
+    /// Whether a granted open for `ruleID` is still running at `now`.
+    func hasActiveSession(for ruleID: UUID, at now: Date) -> Bool
+}
+
+/// Records when a granted "Open" expires, per rule, in the shared app-group
+/// defaults. Pressing the shield's "Open" button lifts an open-limit rule's
+/// shield for ~15 minutes (`MonitoringPlan.openSessionMinutes`); this marker
+/// lets the foreground enforcer leave that one rule un-shielded for the life of
+/// the session instead of re-locking the app mid-session. The monitor clears it
+/// when the session's one-shot activity ends.
+final class OpenSessionStore: OpenSessionReading {
+    private static let key = "openSessionExpiry"
+    private let defaults: UserDefaults
+
+    init(defaults: UserDefaults = AppGroup.defaults) {
+        self.defaults = defaults
+    }
+
+    func hasActiveSession(for ruleID: UUID, at now: Date = .now) -> Bool {
+        guard let expiry = expiries[ruleID.uuidString] else { return false }
+        return Date(timeIntervalSince1970: expiry) > now
+    }
+
+    /// Marks a granted open for `ruleID` running until `expiry`.
+    func startSession(for ruleID: UUID, until expiry: Date) {
+        var map = expiries
+        map[ruleID.uuidString] = expiry.timeIntervalSince1970
+        defaults.set(map, forKey: Self.key)
+    }
+
+    /// Ends a granted open (its one-shot activity fired, or it is being reset).
+    func endSession(for ruleID: UUID) {
+        var map = expiries
+        map[ruleID.uuidString] = nil
+        defaults.set(map, forKey: Self.key)
+    }
+
+    private var expiries: [String: TimeInterval] {
+        defaults.dictionary(forKey: Self.key) as? [String: TimeInterval] ?? [:]
+    }
+}
+
+/// In-memory granted sessions for tests and UI-test launches.
+final class MockOpenSessionStore: OpenSessionReading {
+    var activeRuleIDs: Set<UUID> = []
+
+    func hasActiveSession(for ruleID: UUID, at now: Date) -> Bool {
+        activeRuleIDs.contains(ruleID)
+    }
+}