fix(mocks): drop derived variables before staging

stagedata.sas removes the MPE_DERIVED droplist from the submitted data before
anything is staged, and writes its approval CSV from that stripped dataset - the
mock staged the derived columns into both.

sas/mocks/sasjs/services/editors/stagedata.js

@@ -104,6 +104,29 @@ if (rkName && !jsDataHeaders.some((h) => h.toUpperCase() === rkName.toUpperCase(
     jsDataHeaders.push(rkName)
 }
 
+// ─── Derived variables ───────────────────────────────────────────────────────
+// stagedata.sas drops the MPE_DERIVED droplist from the submitted data before
+// anything is staged (they are display-only), and the approval CSV is written
+// from that stripped dataset - so neither the staged rows nor the pack may
+// carry them.
+
+const derivedVars = mpeDerived({
+    libref,
+    table: dsn,
+    dataDir: mpeDataDir,
+    columns: schema
+})
+if (derivedVars.length > 0) {
+    const derivedNames = new Set(derivedVars.map((d) => d.name.toUpperCase()))
+    const keep = (key) => !derivedNames.has(key.toUpperCase())
+    jsDataHeaders = jsDataHeaders.filter(keep)
+    jsDataRows = jsDataRows.map((row) => {
+        const copy = {}
+        for (const key of Object.keys(row)) if (keep(key)) copy[key] = row[key]
+        return copy
+    })
+}
+
 // ─── Stage the data ──────────────────────────────────────────────────────────
 // One subfolder per submission (DSID) under the staging directory, so that the
 // staged data can sit alongside related artifacts (submit/approval logs,