feat(taxcode): prevent deletion of add-on-referenced tax codes

[borbelyr-kong]

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[borbelyr-kong]

@greptileai review this draft

[greptile-apps]

Greptile Summary

This PR introduces a pre-delete guard that prevents a tax code from being deleted while it is still referenced by add-on rate cards. It follows the same hook pattern as the existing plan-validator hook.

• Adds a TaxCodes filter to ListAddonsInput and the Ent adapter query, joining through addon_ratecards with a deleted_at IS NULL guard so soft-deleted rate cards are excluded.
• Wires the new AddonHook into the tax code service via the existing RegisterHooks mechanism; both unit tests (stub service) and integration tests (Postgres) are included.

Confidence Score: 4/5

The change is safe to merge; the core guard logic correctly blocks deletion whenever any add-on holds a live rate-card reference to the tax code.

The hook and adapter filter are well-structured and closely mirror the proven plan-validator hook. The only gap is that add-ons in Invalid status (effectiveTo < effectiveFrom) are not checked, so a tax code could be deleted while a broken add-on still references it, preventing that add-on from ever being repaired. Both unit and integration tests cover the happy and blocking paths.

openmeter/taxcode/service/hooks/addonhook.go — the status list in PreDelete warrants a second look

Important Files Changed

Filename	Overview
openmeter/taxcode/service/hooks/addonhook.go	New PreDelete hook that queries add-ons by tax code ID before allowing deletion; mirrors the plan validator hook but omits AddonStatusInvalid from the status filter
openmeter/productcatalog/addon/adapter/addon.go	Adds TaxCodes filter to ListAddons — uses HasRatecardsWith with DeletedAtIsNil() predicate, correctly scoping to non-deleted rate cards
openmeter/taxcode/errors.go	Adds ErrCodeTaxCodeReferencedByAddon error type following the same pattern as the existing plan error
app/common/taxcode.go	Registers the new addon hook on the tax code service via wire; follows the same pattern as TaxCodePlanValidatorHook
openmeter/taxcode/service/hooks/addonhook_test.go	Unit tests for the addon hook with a stub addon service; covers block and allow paths
openmeter/productcatalog/addon/adapter/adapter_test.go	Integration tests for the new TaxCodes filter on ListAddons; covers filter-by-A, filter-by-B, and nonexistent tax code cases
openmeter/productcatalog/addon/service.go	Adds TaxCodes field to ListAddonsInput with validation, consistent with other filter fields
cmd/server/wire_gen.go	Auto-generated wire code instantiating the addon hook after both addon and taxcode services are available

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant Client
    participant TaxCodeService
    participant AddonHook
    participant AddonService
    participant DB

    Client->>TaxCodeService: DeleteTaxCode(id)
    TaxCodeService->>AddonHook: PreDelete(taxCode)
    AddonHook->>AddonService: "ListAddons(namespace, status=[Active,Draft,Archived], taxCodes=[id], page=5)"
    AddonService->>DB: "SELECT addons WHERE has_ratecards(tax_code_id=id, deleted_at IS NULL)"
    DB-->>AddonService: []Addon
    AddonService-->>AddonHook: "Result{Items, TotalCount}"
    alt "len(Items) > 0"
        AddonHook-->>TaxCodeService: ErrTaxCodeReferencedByAddon(taxCodeID, addonIDs)
        TaxCodeService-->>Client: 409 Conflict
    else "len(Items) == 0"
        AddonHook-->>TaxCodeService: nil
        TaxCodeService->>DB: "DELETE tax_code WHERE id=id"
        TaxCodeService-->>Client: 200 OK
    end

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sequenceDiagram
    participant Client
    participant TaxCodeService
    participant AddonHook
    participant AddonService
    participant DB

    Client->>TaxCodeService: DeleteTaxCode(id)
    TaxCodeService->>AddonHook: PreDelete(taxCode)
    AddonHook->>AddonService: "ListAddons(namespace, status=[Active,Draft,Archived], taxCodes=[id], page=5)"
    AddonService->>DB: "SELECT addons WHERE has_ratecards(tax_code_id=id, deleted_at IS NULL)"
    DB-->>AddonService: []Addon
    AddonService-->>AddonHook: "Result{Items, TotalCount}"
    alt "len(Items) > 0"
        AddonHook-->>TaxCodeService: ErrTaxCodeReferencedByAddon(taxCodeID, addonIDs)
        TaxCodeService-->>Client: 409 Conflict
    else "len(Items) == 0"
        AddonHook-->>TaxCodeService: nil
        TaxCodeService->>DB: "DELETE tax_code WHERE id=id"
        TaxCodeService-->>Client: 200 OK
    end

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_{Reviews (1): Last reviewed commit: "feat(taxcode): prevent deletion of add-o..." | Re-trigger Greptile}

[greptile-apps]

The PreDelete check omits AddonStatusInvalid, unlike the plan validator hook which covers all plan statuses. An add-on enters Invalid state when effectiveTo < effectiveFrom (an already-inconsistent record), but it still holds a tax_code_id FK on its rate cards. Allowing the tax code to be deleted while such an add-on exists would deepen the inconsistency and make the add-on unrecoverable if someone later tries to fix its time range.

Suggested change

	affectedAddons, err := e.addonService.ListAddons(ctx, addon.ListAddonsInput{
	Namespaces: []string{tc.Namespace},
	Status: []productcatalog.AddonStatus{
	productcatalog.AddonStatusActive,
	productcatalog.AddonStatusDraft,
	productcatalog.AddonStatusArchived,
	},
	affectedAddons, err := e.addonService.ListAddons(ctx, addon.ListAddonsInput{
	Namespaces: []string{tc.Namespace},
	Status: []productcatalog.AddonStatus{
	productcatalog.AddonStatusActive,
	productcatalog.AddonStatusDraft,
	productcatalog.AddonStatusArchived,
	productcatalog.AddonStatusInvalid,
	},