ABN-298: Extended net terms and surcharge configuration

[dgjlindsay]

Summary

Based on #80 (dev tooling).

• Extended net terms: Multi-term selection (14/30/60/90 + custom), per-term surcharge config via admin grid, surcharge calculator with pricing API integration, checkout term selector, VAT auto-detect
• Differential surcharge (commit 2, ABN-specific): "Surcharge Calculation Basis" option that charges buyers only for the fee difference vs the default payment term — delegates calculation to the pricing API via buyer_fee_share.reference_terms

Key design decisions

• Surcharge config stored as flat keys — no migration, per-field scope inheritance
• Admin grid via custom frontend_model Block replacing 12 sequential fields
• SurchargeCalculator delegates percentage + differential to /v1/pricing/order/fee API (single call), applies fixed amount and limit cap locally
• Differential mode (last commit) is cleanly revertable for the standard build

Commit structure

#	Commit	Scope
1	Extended net terms + surcharge	Full feature, 103 tests
2	Differential surcharge	ABN-specific, +6 tests = 109 total

Test plan

• Unit tests pass (make test — 109 tests)
• E2E pricing tests pass (make test-e2e)
• Admin: surcharge grid renders, columns toggle per surcharge type
• Admin: custom payment term adds grid row dynamically
• Checkout: term selector + surcharge line item on order
• Differential: default term = zero surcharge, extended term = fee delta

🤖 Generated with Claude Code

[claude]

Reviewed the surcharge + extended net terms implementation. One critical issue flagged inline; the rest of the approach looks sound.

[gemini-code-assist]

Code Review

This pull request introduces a comprehensive surcharge and payment terms system for the Two payment gateway, featuring an admin configuration grid, a calculation service, and a frontend term selector. It also modernizes the local development environment with Docker, Xdebug, and FRP proxy support, supported by new unit and E2E tests. Feedback focuses on improving code maintainability by refactoring duplicated logic in the order service and moving inline styles to external CSS files or standard Magento admin classes.

[claude]

All previously flagged issues are resolved:

• selectedTerm validation (critical): getSelectedTermDays() now validates against getAllBuyerTerms() and falls back to the default term. Fix matches the suggestion exactly.
• Inline styles: moved to _surcharge-grid.less (auto-loaded via _module.less).
• buildTermObject() duplication: extracted into shared helper.

No new critical issues found in the updated commits. Ready for human approval.

[claude]

The selectedTerm validation from the previous review is correctly fixed. One new critical issue flagged inline: SurchargeGrid::afterSave() reads from getValue() which beforeSave() already cleared — surcharge config is never saved to the database.

[claude]

Both previously flagged critical issues are resolved:

• selectedTerm validation (Service/Order/ComposeOrder.php): getSelectedTermDays() now validates the buyer-supplied value against getAllBuyerTerms() before use. ✓
• afterSave() not persisting values (Model/Config/Backend/SurchargeGrid.php): now reads from getData('groups') instead of getValue() (which beforeSave() had cleared). ✓

No new critical issues found in the updated commits. Ready for human approval.

[claude]

Both issues flagged in my previous review are confirmed fixed:

• selectedTerm validation — getSelectedTermDays() now validates against getAllBuyerTerms() before trusting the buyer-supplied value; invalid/unconfigured terms fall back to the configured default.
• SurchargeGrid::afterSave() data source bug — now reads grid values from getData('groups') instead of getValue() (which beforeSave() clears to ''), so surcharge config is actually persisted.

No new critical issues found in the updated diff. Ready for human review.