[WC-3442] feat(datagrid-web): add onBeforeExport and onAfterExport event actions - #2392

AI Code Review

⚠️ Approved with suggestions — low-severity items only, safe to merge

What was reviewed

Skipped (out of scope): dist/, pnpm-lock.yaml

All CI checks could not be fetched (command requires approval in this environment).

Findings

⚠️ Low — afterexport fires while the export lock is still held

File: src/features/data-export/ExportController.ts line 138
Problem: afterexport is emitted immediately after req.send() resolves, but this.locked is not set to false until the datasource view-state has been restored — which is an async step that happens later (the sourcechange listener at line 158). If a developer's onAfterExport microflow/nanoflow completes quickly enough to trigger another export before that restoration completes, the second call to exportData() will return silently without error because this.locked is still true.

// ExportController.ts — current order
await req.send();
this.emitter.emit("afterexport", { ... });   // locked === true here

this.datasource.setLimit(snapshot.limit);
// ... async restoration ...
// locked === false only after sourcechange confirms restoration

This could be documented (e.g. "a new export triggered from onAfterExport will be deferred until the current export fully unwinds"), or the afterexport emission could be moved to after locked = false inside the sourcechange listener at line 162 — though that changes the semantics slightly.

⚠️ Low — columnTitles comma-joins column headers without escaping

File: src/features/data-export/ExportController.ts line 99
Problem: columnTitles is built by joining headers with ",". A column header that contains a comma (e.g. "Last Name, First Name") will produce an ambiguous string ("Last Name, First Name,City") that a Mendix developer parsing the variable cannot reliably split. The variable's <actionVariable> description in the XML is empty, so there is no hint about this format.

Fix (minimal): Add a description to the XML action variable so consumers know what to expect:

<actionVariable key="columnTitles" caption="Column Titles" type="String" />
<!-- add: <description>Comma-separated list of visible column header captions.</description> -->

Or, if reliable round-trip parsing matters, consider a different separator (e.g. |) or JSON-encode the array.

Positives

• The ref pattern (onBeforeExportRef.current) is correctly applied so the subscription established on mount always reads the latest ActionValue without stale-closure risk, and the single useEffect([entry]) subscription avoids redundant re-subscriptions on each render.
• canExecute is checked before every action.execute() call in useDataExport.ts, consistent with Mendix Pluggable Widgets API conventions.
• The useDataExport.spec.ts test "reads the latest ActionValue from ref without resubscribing" directly validates the most subtle invariant introduced by this PR — good targeted coverage.
• afterexport is emitted for both "success" and "aborted" paths (the abort is handled because req.abort() emits loadend, which resolves the send() promise), so the pairing with onBeforeExport is maintained in all exit paths.
• CHANGELOG entry is present, user-facing, and describes the behavior without leaking implementation details.