1 files changed, 79 insertions, 4 deletions

diff --git a/internal/engine/explain_test.go b/internal/engine/explain_test.go
index 4d304f9..83011c5 100644
--- a/internal/engine/explain_test.go
+++ b/internal/engine/explain_test.go
@@ -4,10 +4,12 @@ package engine
 
 import (
 	"context"
+	"os"
 	"path/filepath"
 	"reflect"
 	"strings"
 	"testing"
+	"time"
 
 	"krino/internal/plan"
 )
@@ -26,7 +28,7 @@ func TestExplainReportsCapturesAndChain(t *testing.T) {
 	if len(errs) > 0 {
 		t.Fatal(errs)
 	}
-	x, err := e.Explain(context.Background(), filepath.Join(dl, "Screenshot_2026-09-01.png"))
+	x, err := e.ExplainWithChain(context.Background(), filepath.Join(dl, "Screenshot_2026-09-01.png"))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -38,8 +40,9 @@ func TestExplainReportsCapturesAndChain(t *testing.T) {
 	}
 }
 
-// TestExplainChainMatchesThePlan: the chain explain reports is the one the
-// directory's plan gives the same file, conflicts and skips included.
+// TestExplainChainMatchesThePlan: for a file planned on its own, the chain
+// is the one the directory's plan gives it, conflicts with files already on
+// disk included.
 func TestExplainChainMatchesThePlan(t *testing.T) {
 	h, dl := excludeTree(t, map[string]string{"a.pdf": "one", "Out/a.pdf": "taken"})
 	main := writeConfig(t, h, `(include "dl")`, map[string]string{"dl": `
@@ -55,7 +58,7 @@ func TestExplainChainMatchesThePlan(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	x, err := e.Explain(context.Background(), filepath.Join(dl, "a.pdf"))
+	x, err := e.ExplainWithChain(context.Background(), filepath.Join(dl, "a.pdf"))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -63,3 +66,75 @@ func TestExplainChainMatchesThePlan(t *testing.T) {
 		t.Errorf("explain chain %+v\nplan chain %+v", x.Chain, dp.Chains[0].Steps)
 	}
 }
+
+// TestExplainChainOnlyWhenAsked: the command line's explain does not build
+// the chain (it can hash files to resolve a conflict), and a file no rule
+// acts on has none at all (plan 13 review F1, F2).
+func TestExplainChainOnlyWhenAsked(t *testing.T) {
+	h, dl := excludeTree(t, map[string]string{"a.pdf": "one", "keep-b.pdf": "two", "new.pdf": "three"})
+	now := time.Now()
+	os.Chtimes(filepath.Join(dl, "new.pdf"), now, now)
+	main := writeConfig(t, h, `(include "dl")`, map[string]string{"dl": `
+(path "~/dl")
+(exclude (name "^keep-"))
+(rule "all" (move "Out"))
+`})
+	e, errs := Load(main)
+	if len(errs) > 0 {
+		t.Fatal(errs)
+	}
+	x, err := e.Explain(context.Background(), filepath.Join(dl, "a.pdf"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if x.Chain != nil {
+		t.Errorf("Explain built a chain: %+v", x.Chain)
+	}
+	if x, err = e.ExplainWithChain(context.Background(), filepath.Join(dl, "a.pdf")); err != nil || len(x.Chain) != 1 {
+		t.Fatalf("ExplainWithChain: %+v, %v", x.Chain, err)
+	}
+	for _, rel := range []string{"keep-b.pdf", "new.pdf"} {
+		x, err := e.ExplainWithChain(context.Background(), filepath.Join(dl, rel))
+		if err != nil {
+			t.Fatal(err)
+		}
+		if x.Chain != nil {
+			t.Errorf("%s (%s%s) has a chain: %+v", rel, x.Skip, x.Excluded, x.Chain)
+		}
+	}
+}
+
+// TestExplainChainIsThisFileAlone: with two files competing for one name,
+// the chain shows what this file alone would do; the plan is where the two
+// are resolved against each other (plan 13 review F2).
+func TestExplainChainIsThisFileAlone(t *testing.T) {
+	h, dl := excludeTree(t, map[string]string{"a.pdf": "one", "b.pdf": "two"})
+	main := writeConfig(t, h, `(include "dl")`, map[string]string{"dl": `
+(path "~/dl")
+(rule "r" (rename "same.pdf"))
+`})
+	e, errs := Load(main)
+	if len(errs) > 0 {
+		t.Fatal(errs)
+	}
+	dp, err := e.Plan(context.Background(), e.Dirs[0], plan.NewClaims())
+	if err != nil {
+		t.Fatal(err)
+	}
+	var planned string
+	for _, c := range dp.Chains {
+		if c.File.Rel == "b.pdf" {
+			planned = filepath.Base(c.Steps[0].Dst)
+		}
+	}
+	if planned != "same_1.pdf" {
+		t.Fatalf("the plan gave b.pdf %q; expected the suffix", planned)
+	}
+	x, err := e.ExplainWithChain(context.Background(), filepath.Join(dl, "b.pdf"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := filepath.Base(x.Chain[0].Dst); got != "same.pdf" {
+		t.Errorf("chain for b.pdf alone = %q, want same.pdf (the plan resolves the clash with a.pdf)", got)
+	}
+}