a chain that deletes itself still gives back the file it displaced

(on-conflict overwrite) trashes the file in the way; §7.4 promises undo
restores it. Walking a file's log entries stopped dead at a permanent
delete, so the displace written earlier in the same chain was never
reached: the user's file stayed in the Trash, the refusal named only
the file they did not care about, and krino log called the run undone.

The displaced file is a different file, so it is offered as its own
entry in the undo plan, keyed by its own path - the deleted file stays
refused, since nothing of it can come back, and the copy or move that
preceded the delete stays unreversed too (undoing a copy whose original
was then deleted would destroy the last remaining copy).

The accounting matched: every reversible step of a deleted file was
subtracted, its displace included, so the run read (undone). Only what
genuinely cannot come back is subtracted now.

End to end, the scenario from the review: the only copy of a file is
displaced by an incoming one that is then permanently deleted.

  before: archive/ empty, "(undone)", nothing offered
  after:  archive/a.pdf restored, run reads partly undone

1 files changed, 17 insertions, 2 deletions

diff --git a/internal/journal/read.go b/internal/journal/read.go
index aa79118..a41cd8a 100644
--- a/internal/journal/read.go
+++ b/internal/journal/read.go
@@ -236,6 +236,7 @@ func Runs(path string, n int) ([]Run, error) {
 	type fileOf struct{ run, dir, file string }
 	reversibleOf := map[fileOf]int{}
 	deletedFile := map[fileOf]bool{}
+	displacedOf := map[fileOf]int{}
 
 	for _, line := range lines {
 		e, ok := parseLine(line)
@@ -259,6 +260,13 @@ func Runs(path string, n int) ([]Run, error) {
 			if e.Action == "delete" {
 				deletedFile[fileOf{e.Run, e.Dir, e.File}] = true
 			}
+			if e.Action == "displace" {
+				// Counted apart from the rest of its file: a permanent
+				// delete ends the file it deleted, but the file that chain
+				// trashed to make room is a different file and can still
+				// come back.
+				displacedOf[fileOf{e.Run, e.Dir, e.File}]++
+			}
 		}
 		if e.Action == "run-start" {
 			if orig, ok := strings.CutPrefix(e.Detail, undoOfPrefix); ok && orig != "" {
@@ -298,9 +306,16 @@ func Runs(path string, n int) ([]Run, error) {
 		if r.Undone {
 			took := 0
 			for f, n := range reversibleOf {
-				if f.run == r.ID && !deletedFile[f] {
-					took += n
+				if f.run != r.ID {
+					continue
+				}
+				if deletedFile[f] {
+					// Nothing of a permanently deleted file comes back
+					// except what it displaced.
+					took += displacedOf[f]
+					continue
 				}
+				took += n
 			}
 			r.PartlyUndone = reversed[r.ID] < took
 		}