v0.147.2 — 4c follow-up 2: when NO counter can move, say what is being worked on

The v0.147.1 file-count fallback fixed the incremental case but not the one the
demo box actually hits. Watching a second real run: bookstack reported clean byte
progress (100%, 154.0 MB, 7/7 files — the byte path works), while immich sat at
files_done 1 of 46, bytes_done 0, for 42 seconds.

restic 0.14 only counts a file into bytes_done/files_done when it COMPLETES, so
an app dominated by a single large archive (immich's ~430MB volume tar) freezes
both counters. No percentage can move in that window, so stop trying to fake one.

restic keeps reporting current_files and seconds_elapsed throughout. The card now
names the file being processed and the elapsed time: "1 / 46 fájl (430.2 MB) ·
feldolgozás alatt: immich_upload.tar · 42 mp". "Working on this file for 42
seconds" is a completely different message from "0%", and it is the honest one.

The last known current_files value persists across ticks that omit it (restic
does not send it every tick, and blanking the label every other second is its own
flicker); switching app clears it so one app's file is never shown against
another. Both pinned by tests, with the real 42-second status line shape.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nn3VgQk9iwEGgyx6QJ2NvE

controller/internal/backup/offbox_progress_test.go

@@ -230,6 +230,50 @@ func TestParseResticStatusIncrementalRun(t *testing.T) {
 	}
 }
 
+// TestParseResticStatusKeepsCurrentFileAndElapsed — the case where NO counter can move: restic 0.14
+// only counts a file when it completes, so an app dominated by one big archive freezes bytes_done
+// AND files_done. Measured on the demo box: immich at 1 of 46 files, 0 bytes, for 42 seconds while
+// restic worked through a single ~430MB volume tar. current_files + seconds_elapsed are then the only
+// honest signals of liveness left, so losing them in parsing would put the bar back to looking hung.
+func TestParseResticStatusKeepsCurrentFileAndElapsed(t *testing.T) {
+	line := `{"message_type":"status","seconds_elapsed":42,"percent_done":0,"total_files":46,` +
+		`"files_done":1,"total_bytes":451130451,"current_files":["/mnt/hdd/felhom-data/backups/primary/immich/volumes/immich_upload.tar"]}`
+	r, ok := parseResticStatus(line)
+	if !ok {
+		t.Fatal("status line was not parsed")
+	}
+	if r.ElapsedSec != 42 {
+		t.Errorf("elapsed = %d, want 42", r.ElapsedSec)
+	}
+	if r.CurrentFile == "" {
+		t.Fatal("current_file lost — with no counter moving this is the only liveness signal left")
+	}
+	if want := "immich_upload.tar"; !strings.HasSuffix(r.CurrentFile, want) {
+		t.Errorf("current_file = %q, want it to end in %q", r.CurrentFile, want)
+	}
+}
+
+// TestProgressKeepsLastKnownCurrentFile — restic omits current_files on some status ticks. Blanking
+// the label every other second is its own kind of flicker, so the last known value must persist.
+func TestProgressKeepsLastKnownCurrentFile(t *testing.T) {
+	var st offboxProgressState
+	st.begin()
+	st.setApp("immich")
+	st.update(resticProgress{CurrentFile: "/data/big.tar", ElapsedSec: 5, TotalFiles: 46, FilesDone: 1})
+	st.update(resticProgress{CurrentFile: "", ElapsedSec: 7, TotalFiles: 46, FilesDone: 1}) // tick without current_files
+	if got := st.snapshot().CurrentFile; got != "/data/big.tar" {
+		t.Errorf("current_file = %q after a tick that omitted it, want the last known value", got)
+	}
+	if got := st.snapshot().ElapsedSec; got != 7 {
+		t.Errorf("elapsed = %d, want it to keep advancing (7)", got)
+	}
+	// A new app must clear it — otherwise the previous app's file is shown against the next one.
+	st.setApp("nextcloud")
+	if got := st.snapshot().CurrentFile; got != "" {
+		t.Errorf("current_file = %q after switching app, want cleared", got)
+	}
+}
+
 // TestParseResticStatusClampsPercent — restic has been seen to report percent_done slightly above 1
 // near completion. A bar wider than its track is a visible bug.
 func TestParseResticStatusClampsPercent(t *testing.T) {