Add prune retention planning

internal/state/prune_test.go

@@ -0,0 +1,96 @@
+package state
+
+import (
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestPlanPruneOlderThan(t *testing.T) {
+	now := time.Date(2026, 6, 8, 12, 0, 0, 0, time.UTC)
+	olderThan := 48 * time.Hour
+	plan := PlanPrune([]PruneCandidate{
+		{Path: "old.txt", UpdatedAt: now.Add(-72 * time.Hour)},
+		{Path: "fresh.txt", UpdatedAt: now.Add(-24 * time.Hour)},
+	}, PrunePlanOptions{Now: now, OlderThan: &olderThan})
+
+	if got, want := pruneCandidatePaths(plan.Pruned), "old.txt"; got != want {
+		t.Fatalf("pruned = %q, want %q", got, want)
+	}
+	if got, want := pruneCandidatePaths(plan.Preserved), "fresh.txt"; got != want {
+		t.Fatalf("preserved = %q, want %q", got, want)
+	}
+}
+
+func TestPlanPruneKeepLatest(t *testing.T) {
+	now := time.Date(2026, 6, 8, 12, 0, 0, 0, time.UTC)
+	keepLatest := 2
+	plan := PlanPrune([]PruneCandidate{
+		{Path: "old.txt", UpdatedAt: now.Add(-72 * time.Hour)},
+		{Path: "new.txt", UpdatedAt: now.Add(-1 * time.Hour)},
+		{Path: "middle.txt", UpdatedAt: now.Add(-24 * time.Hour)},
+	}, PrunePlanOptions{KeepLatest: &keepLatest})
+
+	if got, want := pruneCandidatePaths(plan.Pruned), "old.txt"; got != want {
+		t.Fatalf("pruned = %q, want %q", got, want)
+	}
+	if got, want := pruneCandidatePaths(plan.Preserved), "new.txt,middle.txt"; got != want {
+		t.Fatalf("preserved = %q, want %q", got, want)
+	}
+}
+
+func TestPlanPruneCombinedPolicyPreservesLatestBeforeAgeCheck(t *testing.T) {
+	now := time.Date(2026, 6, 8, 12, 0, 0, 0, time.UTC)
+	olderThan := 48 * time.Hour
+	keepLatest := 1
+	plan := PlanPrune([]PruneCandidate{
+		{Path: "oldest.txt", UpdatedAt: now.Add(-96 * time.Hour)},
+		{Path: "old.txt", UpdatedAt: now.Add(-72 * time.Hour)},
+		{Path: "fresh.txt", UpdatedAt: now.Add(-24 * time.Hour)},
+	}, PrunePlanOptions{Now: now, OlderThan: &olderThan, KeepLatest: &keepLatest})
+
+	if got, want := pruneCandidatePaths(plan.Pruned), "oldest.txt,old.txt"; got != want {
+		t.Fatalf("pruned = %q, want %q", got, want)
+	}
+	if got, want := pruneCandidatePaths(plan.Preserved), "fresh.txt"; got != want {
+		t.Fatalf("preserved = %q, want %q", got, want)
+	}
+}
+
+func TestPlanPruneDeterministicTieBreaking(t *testing.T) {
+	now := time.Date(2026, 6, 8, 12, 0, 0, 0, time.UTC)
+	keepLatest := 1
+	plan := PlanPrune([]PruneCandidate{
+		{Path: "b.txt", UpdatedAt: now},
+		{Path: "a.txt", UpdatedAt: now},
+		{Path: "c.txt", UpdatedAt: now.Add(-time.Hour)},
+	}, PrunePlanOptions{KeepLatest: &keepLatest})
+
+	if got, want := pruneCandidatePaths(plan.Preserved), "a.txt"; got != want {
+		t.Fatalf("preserved = %q, want %q", got, want)
+	}
+	if got, want := pruneCandidatePaths(plan.Pruned), "c.txt,b.txt"; got != want {
+		t.Fatalf("pruned = %q, want %q", got, want)
+	}
+}
+
+func TestSharedRootPruneCandidatesPreserveOtherOwners(t *testing.T) {
+	sharedRoot := validSharedRootState(t)
+	scope := CurrentOwnerScope("reports", "archive")
+	candidates := SharedRootPruneCandidates(sharedRoot, scope)
+
+	if got, want := pruneCandidatePaths(candidates), "report.md"; got != want {
+		t.Fatalf("candidates = %q, want %q", got, want)
+	}
+	if candidates[0].Owner == nil || *candidates[0].Owner != scope {
+		t.Fatalf("candidate owner = %#v, want current owner", candidates[0].Owner)
+	}
+}
+
+func pruneCandidatePaths(candidates []PruneCandidate) string {
+	paths := make([]string, 0, len(candidates))
+	for _, candidate := range candidates {
+		paths = append(paths, candidate.Path)
+	}
+	return strings.Join(paths, ",")
+}