style(purchase,config): clear new-from-rev lint on OfferingClass diff

Resolve the three golangci-lint findings that --new-from-rev=origin/main
attributes to the #694 OfferingClass changes:

- errcheck: replace the silent `_ =` discard of SavePurchaseExecution on
  the processPurchaseRecommendations error path with the existing
  saveExecutionStatusBestEffort helper, which persists and logs the
  audit-save failure instead of dropping it.
- gocritic unnamedResult: name the four results of
  processPurchaseRecommendations (its return set grew to include error);
  switch the trailing assignment from := to = accordingly.
- misspell: pre-694 behaviour -> behavior in the ValidOfferingClasses doc.

No behavior change to the purchase path; base-debt Lint/Security failures
are pre-existing on main and out of scope.

Author: cristim

internal/config/validation.go

@@ -168,7 +168,7 @@ func crossProviderPaymentAlias(provider, raw string) (string, bool) {
 
 // ValidOfferingClasses lists the accepted EC2 RI offering class values for
 // GlobalConfig. The empty string is also accepted (maps to "convertible" at
-// purchase time to preserve pre-694 behaviour).
+// purchase time to preserve pre-694 behavior).
 var ValidOfferingClasses = []string{"convertible", "standard"}
 
 // ValidRampScheduleTypes lists all supported ramp schedule types

internal/purchase/execution.go

@@ -250,7 +250,7 @@ func (m *Manager) executeForAccount(ctx context.Context, baseExec *config.Purcha
 	if procErr != nil {
 		acctExec.Status = "failed"
 		acctExec.Error = procErr.Error()
-		_ = m.config.SavePurchaseExecution(ctx, &acctExec)
+		m.saveExecutionStatusBestEffort(ctx, &acctExec)
 		return false, procErr
 	}
 
@@ -507,7 +507,7 @@ type recPurchaseOutcome struct {
 	err      error
 }
 
-func (m *Manager) processPurchaseRecommendations(ctx context.Context, exec *config.PurchaseExecution, plan *config.PurchasePlan, accountID string, provCfg *provider.ProviderConfig) (float64, float64, []string, error) {
+func (m *Manager) processPurchaseRecommendations(ctx context.Context, exec *config.PurchaseExecution, plan *config.PurchasePlan, accountID string, provCfg *provider.ProviderConfig) (totalSavings, totalUpfront float64, purchaseErrors []string, procErr error) {
 	// ExecutionID is carried into PurchaseOptions so executeSinglePurchase
 	// can tag every per-rec log line with the owning exec UUID. Without
 	// this, CloudWatch filtering by exec ID returns zero hits and a stuck
@@ -590,7 +590,7 @@ func (m *Manager) processPurchaseRecommendations(ctx context.Context, exec *conf
 	// there are no concurrent writes to totals, exec.Recommendations, or
 	// purchaseErrors (05-N2). Do NOT move the aggregation inside the FanOut
 	// closure or run it concurrently with the fan-out.
-	totalSavings, totalUpfront, purchaseErrors := m.aggregatePurchaseOutcomes(ctx, exec, plan, accountID, results)
+	totalSavings, totalUpfront, purchaseErrors = m.aggregatePurchaseOutcomes(ctx, exec, plan, accountID, results)
 	return totalSavings, totalUpfront, purchaseErrors, nil
 }