Process Context via manual event subscriber pattern (#145)

* Process Context via manual event subscriber pattern

* improve knowledge article

community/knowledge/events/expose-process-context-via-manually-bound-flag.bad.al

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+// Demonstration-only AL. Not compiled by CI; illustrates the article.
+
+// Anti-pattern 1: the context is kept in single-instance state.
+codeunit 50545 "Process State Bad Sample"
+{
+    SingleInstance = true;
+
+    var
+        ProcessRunning: Boolean;
+
+    procedure SetProcessRunning(NewProcessRunning: Boolean)
+    begin
+        ProcessRunning := NewProcessRunning;
+    end;
+
+    procedure IsProcessRunning(): Boolean
+    begin
+        exit(ProcessRunning);
+    end;
+}
+
+codeunit 50546 "Process Driver Bad Sample"
+{
+    procedure Run(DocumentNo: Code[20])
+    var
+        ProcessState: Codeunit "Process State Bad Sample";
+    begin
+        ProcessState.SetProcessRunning(true);
+        RunSharedCode(DocumentNo);
+        // An error above never reaches this line. The database writes roll
+        // back, the single-instance variable does not: ProcessRunning stays
+        // true until the company is closed, so every later run in this session
+        // is treated as part of the process.
+        ProcessState.SetProcessRunning(false);
+    end;
+
+    local procedure RunSharedCode(DocumentNo: Code[20])
+    begin
+    end;
+}
+
+// Anti-pattern 2: the context stays private. Flag and driver look like the
+// good sample, but the query is internal, so only the owning app can ever ask.
+codeunit 50547 "Process Ctx Bad Sample"
+{
+    internal procedure IsProcessRunning(): Boolean
+    var
+        IsRunning: Boolean;
+    begin
+        OnCheckProcessRunning(IsRunning);
+        exit(IsRunning);
+    end;
+
+    [InternalEvent(false)]
+    local procedure OnCheckProcessRunning(var IsRunning: Boolean)
+    begin
+    end;
+}
+
+reportextension 50548 "Shared Report Ext Bad Sample" extends "Standard Sales - Invoice"
+{
+    trigger OnPreReport()
+    begin
+        // No callable query exists, so the extension infers the context from
+        // something it hopes only that process does - here, running without a
+        // UI. The guess is wrong for every other background run, and breaks
+        // silently the first time the owning app changes how it works.
+        if GuiAllowed() then
+            exit;
+        // ... behaviour that was meant to apply only inside that process ...
+    end;
+}