Fix remaining correctness issues from Jesper's 2026-09-15 re-review

- commit-shared-test-fixture-inside-lazy-initialize: three sub-issues.
  Recommended TestIsolation = Codeunit instead of listing Disabled as an
  equal option - Disabled never rolls back at all ("tests are not
  isolated from each other" per the property's own docs), so a fixture
  this pattern commits under Disabled is permanent database
  contamination unless something else tears it down; Disabled is now
  only mentioned alongside that explicit teardown requirement. Added
  precedence in al-testing-review.md so the deliberate end-of-test
  asserterror Error(...) rollback sentinel isn't also flagged by the
  generic asserterror-needs-expectederror-and-code rule. Rewrote both
  fixtures to actually demonstrate the pattern: persisted fixture data
  (an Item record) instead of an empty comment, a second [Test] method
  that depends on the fixture surviving into it, and an explicit
  Subtype = TestRunner / TestIsolation = Codeunit runner codeunit.

- table-relation-test-exclude-known-invalid-relations-via-event:
  the length/type rule was stated as one global requirement. Verified
  ValidateFieldRelation in codeunit 134926 directly (BCApps reference
  clone) and split it into the two branches the source actually has:
  a field with any unconditional relation needs exact length and exact
  resolved type; a field whose relations are all conditional only fails
  on being shorter (longer is fine) than the largest related field, and
  when the required type is specifically Code, a Text source passes too
  - a tolerance that does not apply on the unconditional side and does
  not extend to a required Text.

Rebased onto upstream/main (one conflict in
transactionmodel-attribute-governs-test-transactions.md - upstream had
already linked its sample references via the READ convention, ours
added a Source section; merged both). Also converted the 3 remaining
plain-backtick sample references in this PR to the READ-convention
markdown-link form, same fix as #156/#157/#158.

microsoft/knowledge/testing/commit-shared-test-fixture-inside-lazy-initialize.bad.al

@@ -4,6 +4,7 @@ codeunit 50142 "Sample Test Library"
 
     var
         Initialized: Boolean;
+        SharedItemNo: Code[20];
         RollBackMsg: Label 'Revert back the tables to their original state.';
 
     local procedure Initialize()
@@ -12,23 +13,62 @@ codeunit 50142 "Sample Test Library"
             exit;
 
         CreateSharedFixtureData();
+        // BUG: no Commit() here. The fixture below is still inside this
+        // test method's own transaction.
         Initialized := true;
     end;
 
     local procedure CreateSharedFixtureData()
+    var
+        Item: Record Item;
     begin
-        // insert master/setup data shared across every test in this codeunit
+        Item.Init();
+        Item."No." := 'SAMPLE-SHARED';
+        Item.Insert(true);
+        SharedItemNo := Item."No.";
     end;
 
     [Test]
     procedure FirstTestUsesSharedFixture()
+    var
+        Item: Record Item;
     begin
         Initialize();
 
-        // exercise/verify against the shared fixture, then make scratch changes of its own
+        Item.Get(SharedItemNo);
+        Item.Description := 'Scratch change this test makes and does not need to keep.';
+        Item.Modify();
 
         asserterror Error(RollBackMsg);
-        // the deliberate rollback above also erases the never-committed fixture;
-        // Initialized still reads true on the next test, but the rows are gone
+        // The deliberate rollback above also erases the never-committed
+        // fixture from CreateSharedFixtureData(). Initialized still reads
+        // true on the next test, but the row it points at is gone.
+    end;
+
+    [Test]
+    procedure SecondTestStillFindsSharedFixture()
+    var
+        Item: Record Item;
+    begin
+        Initialize();
+
+        // Fails here: Initialize() saw Initialized = true and returned
+        // immediately, so it never recreated the fixture - and the first
+        // test's rollback took the original row with it.
+        Item.Get(SharedItemNo);
+    end;
+}
+
+codeunit 50143 "Sample Test Runner"
+{
+    // Codeunit isolation alone does not save this fixture: TestIsolation
+    // only controls whether committed changes survive between methods, and
+    // this fixture was never committed in the first place.
+    Subtype = TestRunner;
+    TestIsolation = Codeunit;
+
+    trigger OnRun()
+    begin
+        Codeunit.Run(Codeunit::"Sample Test Library");
     end;
 }