refactor(coverage): hoist 7d default into shared DefaultRecLookbackPeriod constant

The "7d" default was hardcoded in three places after PR #992 added
--rec-lookback-period (cmd flag default, cmd-side fallback in
fetchRecommendationsForRegion, client-side fallback in fetchSingleComboRecs).
Per feedback_no_hardcoded_magic_values.md, centralise it into
recommendations.DefaultRecLookbackPeriod so the cmd flag default, the
cmd-side fallback, and the client-side fallback all reference one source
of truth, and a future change to the default only needs to flip one value.

No behavioural change: same "7d" value, same call sites.

refs #360

Author: cristim

cmd/main.go

@@ -11,6 +11,7 @@ import (
 	"github.com/LeanerCloud/CUDly/pkg/common"
 	"github.com/LeanerCloud/CUDly/pkg/provider"
 	_ "github.com/LeanerCloud/CUDly/providers/aws"
+	"github.com/LeanerCloud/CUDly/providers/aws/recommendations"
 	"github.com/LeanerCloud/CUDly/providers/aws/services/ec2"
 	"github.com/LeanerCloud/CUDly/providers/aws/services/elasticache"
 	"github.com/LeanerCloud/CUDly/providers/aws/services/memorydb"
@@ -70,9 +71,10 @@ type Config struct {
 	DryRun                 bool
 	SkipConfirmation       bool
 	// RecLookbackPeriod controls the LookbackPeriodInDays passed to
-	// GetReservationPurchaseRecommendation. Valid values: "7d", "30d", "60d".
+	// GetReservationPurchaseRecommendation. Valid values: "7d", "30d", "60d"
+	// (recommendations.DefaultRecLookbackPeriod is the shared default).
 	// A longer window smooths seasonal spikes; a shorter window weights
-	// recent demand more heavily. Default "7d" matches the CE console default.
+	// recent demand more heavily.
 	RecLookbackPeriod string
 }
 
@@ -151,7 +153,7 @@ func init() {
 			"below this threshold. Useful with --target-coverage to skip tiny pools "+
 			"that integer arithmetic forces above target (e.g. avg=1 cannot hit 80%%). "+
 			"Default 0 = no filter.")
-	rootCmd.Flags().StringVar(&toolCfg.RecLookbackPeriod, "rec-lookback-period", "7d",
+	rootCmd.Flags().StringVar(&toolCfg.RecLookbackPeriod, "rec-lookback-period", recommendations.DefaultRecLookbackPeriod,
 		"Historical window for GetReservationPurchaseRecommendation. "+
 			"Valid values: 7d, 30d, 60d. A longer window smooths seasonal spikes; "+
 			"a shorter window weights recent demand more heavily. Default 7d.")

cmd/multi_service_helpers.go

@@ -425,7 +425,7 @@ func fetchRecommendationsForRegion(
 
 	lookback := cfg.RecLookbackPeriod
 	if lookback == "" {
-		lookback = "7d"
+		lookback = recommendations.DefaultRecLookbackPeriod
 	}
 	params := common.RecommendationParams{
 		Service:        service,

providers/aws/recommendations/client.go

@@ -22,6 +22,16 @@ import (
 // payer org we have seen. Exceeding the cap returns a diagnostic error (issue #692).
 const maxRecommendationPages = 20
 
+// DefaultRecLookbackPeriod is the LookbackPeriod string forwarded to
+// GetReservationPurchaseRecommendation when --rec-lookback-period is not
+// specified. Kept in the recommendations package so the cmd flag default,
+// the cmd-side fallback, and the client-side fallback all refer to a single
+// source of truth (avoids the magic-value duplication called out by
+// feedback_no_hardcoded_magic_values.md). Valid CE values are 7d/30d/60d
+// (see convertLookbackPeriodE); 7d matches the prior hardcoded behaviour
+// from before --rec-lookback-period existed.
+const DefaultRecLookbackPeriod = "7d"
+
 // CostExplorerAPI defines the interface for Cost Explorer operations
 type CostExplorerAPI interface {
 	GetReservationPurchaseRecommendation(ctx context.Context, params *costexplorer.GetReservationPurchaseRecommendationInput, optFns ...func(*costexplorer.Options)) (*costexplorer.GetReservationPurchaseRecommendationOutput, error)
@@ -254,7 +264,7 @@ func (c *Client) fetchSingleComboRecs(ctx context.Context, service common.Servic
 	}
 	lookback := c.recLookbackPeriod
 	if lookback == "" {
-		lookback = "7d"
+		lookback = DefaultRecLookbackPeriod
 	}
 	params := common.RecommendationParams{
 		Service:        service,