[WC-3441] DG2: export column enhancements

[yordan-st]

Pull request type

Bug fix (non-breaking change which fixes an issue)

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Description

When export type is set to "Default" for attribute columns, the exported Excel cells now use the attribute's own formatting (number decimals/grouping, date pattern) instead of exporting raw values without formatting.

For numbers, the exported cell mirrors what the grid shows: Mendix Decimal attributes do not expose a fixed decimal precision at runtime (only whether digits are grouped), so the format uses up to 8 fractional digits with trailing zeros suppressed. This keeps 1234.56 as 1234.56, 0.5 as 0.5, and integers as integers — instead of collapsing to whole numbers.

Also hides the export type and format properties in Studio Pro for dynamic text columns, since they have no effect.

What should be covered while testing?

1. Attribute column with exportType "Default" and a Decimal attribute → exported cell is a numeric cell that mirrors the grid (e.g. 1234.56 stays 1234.56, 0.5 stays 0.5, integers stay integers; thousands grouping applied when the attribute uses it). Excel format: #,##0.######## (grouped) or 0.######## (ungrouped).
2. Attribute column with exportType "Default" and a DateTime attribute with custom pattern dd/MM/yyyy → exported cell should have Excel format dd/mm/yyyy
3. Attribute column with exportType "Number" or "Date" (custom) → still uses the manually specified export format (unchanged behavior)
4. Dynamic text column → Studio Pro should NOT show export type, export number format, or export date format properties
5. Custom content columns → unchanged behavior, all export types still work
6. Existing configurations with no changes → no regression, everything exports as before

[github-actions]

AI Code Review

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

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What was reviewed

File	Change
packages/pluggableWidgets/datagrid-web/src/features/data-export/cell-readers.ts	New getAttributeDefaultFormat() function; attribute reader now branches on exportType === "default" to apply the attribute's own formatter
packages/pluggableWidgets/datagrid-web/src/features/data-export/__tests__/cell-readers.spec.ts	7 new test cases covering number formatter, date formatter, edge cases (no decimalPrecision, whole numbers)
packages/pluggableWidgets/datagrid-web/src/Datagrid.editorConfig.ts	Hides all three export properties when showContentAs === "dynamicText"
packages/pluggableWidgets/datagrid-web/CHANGELOG.md	Added and Fixed entries under [Unreleased]
packages/pluggableWidgets/datagrid-web/openspec/*.{yaml,md}	OpenSpec tracking artifacts (design, proposal, tasks)

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

CI check output was unavailable during this review (tool approval required).

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Findings

⚠️ Low — window.mx locale path in getDefaultDateFormat has no test coverage

File: packages/pluggableWidgets/datagrid-web/src/features/data-export/cell-readers.ts line 74–78
Note: getDefaultDateFormat() has two branches: the locale-aware path (window.mx?.session.getConfig().locale.patterns.date with M→m conversion) and the fallback "dd-mm-yyyy". All tests that exercise this function—including the new ones—rely on the fallback because window.mx is not set up in jest.setup.ts. The M→m conversion on real locale patterns is never verified.

This is a pre-existing gap (function was not introduced in this PR), but the new "default exportType for date attribute" path makes it more load-bearing.

Fix (non-blocking): Add a test that sets window.mx to a mock with a custom date pattern:

beforeEach(() => {
    (window as any).mx = {
        session: { getConfig: () => ({ locale: { patterns: { date: "dd/MM/yyyy" } } }) }
    };
});
afterEach(() => { delete (window as any).mx; });

it("uses locale date pattern with M→m conversion when window.mx is available", () => {
    // exportType default, date attribute, no custom formatter config
    // expects cell.z === "dd/mm/yyyy"
});

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⚠️ Low — Per-value format derivation can produce column-inconsistent Excel formats

File: packages/pluggableWidgets/datagrid-web/src/features/data-export/cell-readers.ts line 141–143
Note: When decimalPrecision is absent from the formatter config, the decimal count is derived from each individual cell's value via countDecimalPlaces(value). This means two cells in the same column—1234.5 and 1234.567—will receive different format codes (0.0 vs 0.000). In Excel, per-cell formats are valid and each cell renders correctly, but the visual appearance of the column may be inconsistent.

This is an intentional design decision (documented in the proposal and comments), and it's the right call given Mendix doesn't expose decimalPrecision at runtime. No code change needed—just worth a doc note in the proposal/design for future reference.

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Positives

• The countDecimalPlaces(value) fallback elegantly solves the trailing-dot regression ("1983.") that a static 0.######## mask would have caused—the explanation in both comments and the proposal is excellent.
• countSignificantDigits > 15 → excelString guard is correctly retained for the new exportType === "default" path, preserving precision for long identifiers.
• Test coverage for the new feature is thorough: happy path, explicit decimalPrecision, absent decimalPrecision (grouped + ungrouped), whole-number edge case, non-custom datetime config fallback—all covered independently.
• The editorConfig.ts change is a clean structural refactor: the original flat conditionals are replaced with a clear if/else that makes the "dynamicText hides all export props" intent obvious.
• CHANGELOG entries are user-facing and accurately describe the behavior change without leaking implementation details.