Add case true of pattern for long condition chains

Follow-up from PR review: nested if is the right answer for two or three
dependent conditions, but past that the nesting becomes the problem. AL's
case statement is the flat alternative — the control statements
documentation states a value set "must be an expression or a range" and
that the first matching value set executes, so case true of / case false of
accept boolean expressions and stop at the first match. That is the
laziness the boolean operators do not provide.

Adds case-true-of-for-long-condition-chains.md with good/bad AL companions:
case false of for guard chains where every condition must hold, case true of
for first-match dispatch. The bad sample shows both failure shapes — a
five-level if ladder, and the worse escape of collapsing it into an and
chain, which trades nesting for a real defect.

Cross-links both articles, and adds the threshold to the short-circuit
article's Best Practice so following it does not lead to a deep ladder.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

community/knowledge/performance/case-true-of-for-long-condition-chains.good.al

@@ -0,0 +1,48 @@
+codeunit 50542 "Perf Sample CaseChain Good"
+{
+    procedure IsShippableLine(SalesLine: Record "Sales Line"): Boolean
+    var
+        Item: Record Item;
+    begin
+        // 'case false of' evaluates the value sets in order and stops at the first
+        // match, so each condition is reached only when the previous one passed —
+        // and Item.Get is never called for a non-item line.
+        case false of
+            (SalesLine.Type = SalesLine.Type::Item):
+                exit(false);
+            (SalesLine."No." <> ''):
+                exit(false);
+            (SalesLine."Qty. to Ship" > 0):
+                exit(false);
+            Item.Get(SalesLine."No."):
+                exit(false);
+            (not Item.Blocked):
+                exit(false);
+        end;
+        exit(true);
+    end;
+
+    procedure FindOpenDocumentType(CustomerNo: Code[20]): Text
+    begin
+        // 'case true of' stops at the first condition that holds, so the later
+        // lookups never run once an earlier one matched.
+        case true of
+            HasOpenDocument(CustomerNo, "Sales Document Type"::Quote):
+                exit('Quote');
+            HasOpenDocument(CustomerNo, "Sales Document Type"::Order):
+                exit('Order');
+            HasOpenDocument(CustomerNo, "Sales Document Type"::Invoice):
+                exit('Invoice');
+        end;
+        exit('None');
+    end;
+
+    local procedure HasOpenDocument(CustomerNo: Code[20]; DocumentType: Enum "Sales Document Type"): Boolean
+    var
+        SalesHeader: Record "Sales Header";
+    begin
+        SalesHeader.SetRange("Document Type", DocumentType);
+        SalesHeader.SetRange("Sell-to Customer No.", CustomerNo);
+        exit(not SalesHeader.IsEmpty());
+    end;
+}