feat(gl): add read-only ledger reconciliation scan

application/reconciliation/service.go

@@ -0,0 +1,53 @@
+// Package reconciliation provides read-only integrity checks for the GL.
+package reconciliation
+
+import (
+	"context"
+	"fmt"
+
+	"gl/domain/ledger"
+)
+
+type Repository interface {
+	List(context.Context, ledger.JournalFilter) ([]ledger.Journal, error)
+}
+
+type Report struct {
+	Scanned int
+	Valid   int
+	Invalid []Issue
+}
+
+type Issue struct {
+	JournalID string
+	Error     string
+}
+
+// Run scans all posted journals without mutating the ledger.
+func Run(ctx context.Context, repository Repository, pageSize int) (Report, error) {
+	if repository == nil {
+		return Report{}, fmt.Errorf("reconciliation repository is required")
+	}
+	if pageSize <= 0 || pageSize > 200 {
+		pageSize = 100
+	}
+	report := Report{Invalid: make([]Issue, 0)}
+	for offset := 0; ; offset += pageSize {
+		journals, err := repository.List(ctx, ledger.JournalFilter{Limit: pageSize, Offset: offset})
+		if err != nil {
+			return Report{}, fmt.Errorf("list journals at offset %d: %w", offset, err)
+		}
+		for _, journal := range journals {
+			report.Scanned++
+			if err := journal.Validate(); err != nil {
+				report.Invalid = append(report.Invalid, Issue{JournalID: journal.ID, Error: err.Error()})
+				continue
+			}
+			report.Valid++
+		}
+		if len(journals) < pageSize {
+			break
+		}
+	}
+	return report, nil
+}