Add new action skills for AL testing and documentation

- Introduced `al-test-writer` to generate AL test codeunits for production objects based on TDD principles.
- Added `al-userguide-test-writer` to create test codeunits from user guide steps, mapping actions and assertions.
- Implemented `bc-extension-test-guide` to generate a comprehensive TEST_GUIDE.md for Business Central extensions, covering various categories.
- Created `bc-webclient-runner` to automate UI testing of the Business Central web client, capturing screenshots and asserting UI states.
- Developed `page-scripting-e2e` to produce a recording plan for Page Scripting, ensuring a structured approach to browser-level testing.

custom/knowledge/integration/monitor-external-event-subscription-health.good.al

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+// Best practice: a scheduled monitor lists the LIVE external event subscriptions and diffs
+// them against the EXPECTED set. Any expected subscription that BC has silently dropped
+// (because the subscriber returned a non-408/429/5xx response) raises an alert and telemetry.
+
+table 50180 "Expected Event Subscription"
+{
+    DataClassification = SystemMetadata;
+
+    fields
+    {
+        // The expected set lives in configuration, so registering an integration also registers
+        // its monitoring expectation. The two cannot drift apart.
+        field(1; "Event Name"; Text[100]) { Caption = 'Event Name'; }
+        field(2; "Notification URL"; Text[250]) { Caption = 'Notification URL'; }
+    }
+
+    keys { key(PK; "Event Name", "Notification URL") { Clustered = true; } }
+}
+
+codeunit 50181 "Subscription Health Monitor"
+{
+    TableNo = "Job Queue Entry";
+
+    // Runs as a Job Queue entry on a schedule (for example hourly). It must run actively:
+    // a dropped subscription is indistinguishable from a quiet feed, so silence cannot be trusted.
+    trigger OnRun()
+    begin
+        CheckHealth();
+    end;
+
+    procedure CheckHealth()
+    var
+        Expected: Record "Expected Event Subscription";
+        Live: List of [Text];
+    begin
+        // GET api/microsoft/runtime/v1.0/externaleventsubscriptions and project each live
+        // subscription to a comparable key.
+        Live := FetchLiveSubscriptions();
+
+        if Expected.FindSet() then
+            repeat
+                // The diff: an expected subscription missing from the live list was dropped by
+                // the platform with no notification. That is an incident, not a warning.
+                if not Live.Contains(SubscriptionKey(Expected."Event Name", Expected."Notification URL")) then
+                    RaiseMissingSubscriptionAlert(Expected);
+            until Expected.Next() = 0;
+    end;
+
+    local procedure RaiseMissingSubscriptionAlert(Expected: Record "Expected Event Subscription")
+    var
+        Dimensions: Dictionary of [Text, Text];
+    begin
+        // Telemetry carries the event name and URL so operations can re-register it AND can read,
+        // from the telemetry timeline, roughly when delivery stopped.
+        Dimensions.Add('eventName', Expected."Event Name");
+        Dimensions.Add('notificationUrl', Expected."Notification URL");
+        Session.LogMessage('INT0001', 'External event subscription missing', Verbosity::Warning,
+            DataClassification::SystemMetadata, TelemetryScope::ExtensionPublisher, Dimensions);
+        // ... and raise an operational alert (email, Teams, ticket) so a human acts before the gap grows.
+    end;
+
+    local procedure SubscriptionKey(EventName: Text; NotificationUrl: Text): Text
+    begin
+        exit(StrSubstNo('%1|%2', EventName, NotificationUrl));
+    end;
+}