knowledge(performance): add community rules for JIT, locks, and false positives

These articles capture BC-specific mechanics agents still invert: partial-record JIT on writes, Reset clearing SetLoadFields, HttpClient inside write transactions, and batched number series, plus negative guidance that stops over-eager Query and IsEmpty "fixes".

Co-authored-by: Cursor <cursoragent@cursor.com>

community/knowledge/performance/countapprox-for-progress-not-count.md

@@ -0,0 +1,28 @@
+---
+bc-version: [all]
+domain: performance
+keywords: [countapprox, count, dialog, progress-bar, approximate-count]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Use CountApprox for progress UI, not Count
+
+> Contributions welcome — open a PR to refine or extend this article.
+
+## Description
+
+`Count()` asks SQL for an exact row count of the current filter. On a large table that is a `SELECT COUNT(*)` before any useful work starts — the usual cost of `Dialog.Open` with a percentage bar. `CountApprox()` exists for that UI case: it returns a cheap estimate (partition stats / metadata), accurate enough for a progress denominator. Agents default to `Count()` because the name matches "how many rows".
+
+## Best Practice
+
+Feed progress dialogs and informational messages with `CountApprox()`. Use `Count()` only when the exact integer is a business result (a posted control, a reconciliation, a test assertion).
+
+See sample: `countapprox-for-progress-not-count.good.al`.
+
+## Anti Pattern
+
+`Total := Rec.Count(); Window.Open(...);` immediately before a `FindSet` over the same filter. The exact count is discarded after the bar finishes; the user paid a full scan to draw it.
+
+See sample: `countapprox-for-progress-not-count.bad.al`.