Add data handling and test isolation guidance

- add SCM guidance for deriving base quantities through line unit-of-measure validation`n- add security guidance for parameterizing SetFilter with external text`n- add test isolation guidance for resetting per-test state before initialization guards`n- add web-service guidance for JSON null handling and invariant standard format 9`n- route and cover all five rules with paired evaluation fixtures

microsoft/knowledge/scm/derive-base-quantities-through-the-line-unit-of-measure.bad.al

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+codeunit 50181 "Scanner Receipt Import Bad"
+{
+    procedure PostScannedReceipt(ItemNo: Code[20]; LocationCode: Code[10]; UnitOfMeasureCode: Code[10]; ScannedQuantity: Decimal; DocumentNo: Code[20])
+    var
+        ItemJournalLine: Record "Item Journal Line";
+        ItemJnlPostLine: Codeunit "Item Jnl.-Post Line";
+    begin
+        if ScannedQuantity <= 0 then
+            Error(PositiveQuantityErr);
+
+        ItemJournalLine.Init();
+        ItemJournalLine.Validate("Posting Date", WorkDate());
+        ItemJournalLine.Validate("Entry Type", ItemJournalLine."Entry Type"::"Positive Adjmt.");
+        ItemJournalLine.Validate("Document No.", DocumentNo);
+        ItemJournalLine.Validate("Item No.", ItemNo);
+        ItemJournalLine.Validate("Location Code", LocationCode);
+        ItemJournalLine."Unit of Measure Code" := UnitOfMeasureCode;
+        ItemJournalLine.Quantity := ScannedQuantity;
+        ItemJournalLine."Quantity (Base)" := ScannedQuantity;
+
+        ItemJnlPostLine.RunWithCheck(ItemJournalLine);
+    end;
+
+    var
+        PositiveQuantityErr: Label 'The scanned quantity must be greater than zero.';
+}

microsoft/knowledge/scm/derive-base-quantities-through-the-line-unit-of-measure.good.al

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+codeunit 50180 "Scanner Receipt Import Good"
+{
+    procedure PostScannedReceipt(ItemNo: Code[20]; LocationCode: Code[10]; UnitOfMeasureCode: Code[10]; ScannedQuantity: Decimal; DocumentNo: Code[20])
+    var
+        ItemJournalLine: Record "Item Journal Line";
+        ItemJnlPostLine: Codeunit "Item Jnl.-Post Line";
+    begin
+        if ScannedQuantity <= 0 then
+            Error(PositiveQuantityErr);
+
+        ItemJournalLine.Init();
+        ItemJournalLine.Validate("Posting Date", WorkDate());
+        ItemJournalLine.Validate("Entry Type", ItemJournalLine."Entry Type"::"Positive Adjmt.");
+        ItemJournalLine.Validate("Document No.", DocumentNo);
+        ItemJournalLine.Validate("Item No.", ItemNo);
+        ItemJournalLine.Validate("Location Code", LocationCode);
+        ItemJournalLine.Validate("Unit of Measure Code", UnitOfMeasureCode);
+        ItemJournalLine.Validate(Quantity, ScannedQuantity);
+
+        ItemJnlPostLine.RunWithCheck(ItemJournalLine);
+    end;
+
+    var
+        PositiveQuantityErr: Label 'The scanned quantity must be greater than zero.';
+}

microsoft/knowledge/scm/derive-base-quantities-through-the-line-unit-of-measure.md

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+---
+bc-version: [all]
+domain: scm
+keywords: [quantity-base, qty-per-unit-of-measure, unit-of-measure-code, unit-of-measure-management, calcbaseqty, getqtyperunitofmeasure, qty-rounding-precision, item-journal-line]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Derive base quantities through the line's unit of measure
+
+## Description
+
+Inventory, item ledger entries, reservations, item tracking, and warehouse quantities are measured in the item's base unit of measure. Document and journal lines hold `Quantity` in the line's `"Unit of Measure Code"`, together with `"Qty. per Unit of Measure"` and base-unit fields such as `"Quantity (Base)"`. Ten boxes of twelve pieces are 120 base units, not 10. When a line's `Quantity` is validated, the table derives the base quantity through its `CalcBaseQty` procedure. That procedure calls `"Unit of Measure Management".CalcBaseQty` with the line's quantity rounding precision and raises an error when rounding would turn a non-zero quantity into a zero base quantity. Code that bypasses this conversion creates a line whose quantity and base quantity disagree, or makes a stock decision in the wrong unit.
+
+## Best Practice
+
+On a document or journal line, validate `"Unit of Measure Code"` before `Quantity`, and validate both. Validating the unit of measure sets `"Qty. per Unit of Measure"` from the item unit of measure; validating the quantity then fills the base fields with the correct rounding. Compare line quantities with inventory or availability in base units, for example `"Quantity (Base)"` or `"Outstanding Qty. (Base)"`.
+
+Outside a line, get the factor with `"Unit of Measure Management".GetQtyPerUnitOfMeasure(Item, UnitOfMeasureCode)` and convert with its `CalcBaseQty` or `CalcQtyFromBase` procedures instead of multiplying by hand. Pass the item unit's quantity rounding precision where the available overload accepts it.
+
+Reading these fields for display, reporting, or a temporary buffer that is never posted is not a conversion defect. Code that proves the line uses the base unit of measure (`"Qty. per Unit of Measure"` equal to 1) is also correct, but don't assume this from the item alone, because a line can use another unit.
+
+See sample: [`derive-base-quantities-through-the-line-unit-of-measure.good.al`](derive-base-quantities-through-the-line-unit-of-measure.good.al).
+
+## Anti Pattern
+
+Assigning `Quantity` directly on an item journal, sales, purchase, or transfer line and then inserting, modifying, or posting it. Also assigning a base field such as `"Quantity (Base)" := Quantity`, multiplying by a hard-coded or separately looked-up factor without the line's rounding, or comparing a line's `Quantity` with `Item.Inventory` or another base-unit value. Detection signal: a direct `:=` to `Quantity`, `"Qty. per Unit of Measure"`, or a `(Base)` quantity field on a persisted or posted line, or a comparison between a non-base line quantity and an inventory quantity.
+
+See sample: [`derive-base-quantities-through-the-line-unit-of-measure.bad.al`](derive-base-quantities-through-the-line-unit-of-measure.bad.al).
+
+## References
+
+- [Set up units of measure, including quantity rounding precision](https://learn.microsoft.com/en-us/dynamics365/business-central/inventory-how-setup-units-of-measure)
+- [BCApps: Unit of Measure Management conversions](https://github.com/microsoft/BCApps/blob/4abbb8ff848cdcb4e1187fc7a3e2da0612dd0d2b/src/Layers/W1/BaseApp/Foundation/UOM/UnitofMeasureManagement.Codeunit.al)
+- [BCApps: Item Journal Line quantity validation and CalcBaseQty](https://github.com/microsoft/BCApps/blob/4abbb8ff848cdcb4e1187fc7a3e2da0612dd0d2b/src/Layers/W1/BaseApp/Inventory/Journal/ItemJournalLine.Table.al)
+- [BCApps: Sales Line quantity validation and CalcBaseQty](https://github.com/microsoft/BCApps/blob/4abbb8ff848cdcb4e1187fc7a3e2da0612dd0d2b/src/Layers/W1/BaseApp/Sales/Document/SalesLine.Table.al)