Pad/internal/test/e2e/restore_test.go

package e2e_test

// Relaunch state restoration (spec §7): the last file, cursor, scroll,
// selection and find bar state are persisted as a tiny JSON snapshot and
// restored on the next launch. These tests drive the same entry points the
// cmd layer uses: Logic.BeginRestore before Run (restore) and the session
// saver callback (persist).

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"testing"
	"time"

	"pad/internal/editor"
	"pad/internal/io/pool/real"
	"pad/internal/test/e2e"
	"pad/internal/ui"
)

// restoreHarness writes content to <tempdir>/name, builds a harness over the
// real filesystem, hands sess to the logic BEFORE Run (as the cmd layer does
// on relaunch), starts it with the standard 390x844@2x window, and waits for
// the restored file to fully load (content + line index).
func restoreHarness(t *testing.T, name, content string, sess editor.SessionState) *e2e.Harness {
	t.Helper()
	dir := t.TempDir()
	diskPath := filepath.Join(dir, name)
	if err := os.WriteFile(diskPath, []byte(content), 0644); err != nil {
		t.Fatal(err)
	}
	sess.File = "/" + name

	h := e2e.NewHarness(e2e.WithFileSystem(real.NewRealFileSystem(dir), "/"))
	h.Logic().BeginRestore(sess)
	h.Run()
	h.SendConfig(780, 1688) // 390x844 @ 2x scale
	h.SendScale(2.0)

	// "Loaded" means both async results are fully applied: the ReadFile
	// content AND the BuildLineIndex result (same contract as
	// realFileHarness: FileLen>0 && LineIndex!=nil alone is a race).
	for i := 0; i < 100; i++ {
		v, err := h.Inspect(func(st *editor.State) any {
			cb := st.Editor.ChunkedBuffer
			if cb == nil || cb.FileLen() == 0 || cb.LineIndex == nil {
				return false
			}
			full, err := cb.FullContent()
			return err == nil && int64(len(full)) == cb.FileLen() &&
				cb.LineIndex.Size == cb.FileLen()
		})
		if err != nil {
			t.Fatalf("Inspect: %v", err)
		}
		if v.(bool) {
			return h
		}
		time.Sleep(50 * time.Millisecond)
	}
	t.Fatal("timed out waiting for restored file to load")
	return nil
}

// TestRestore_FileCursorScrollSelection restores a file with a cursor, a
// non-zero scroll and a live selection; all three must land once the content
// arrives, on the editor page (not the browser).
func TestRestore_FileCursorScrollSelection(t *testing.T) {
	content := strings.Repeat("hello world line\n", 100)
	h := restoreHarness(t, "notes.txt", content, editor.SessionState{
		Cursor:   123,
		Scroll:   100,
		SelStart: 100,
		SelEnd:   110,
	})
	defer h.Cleanup()

	v, err := h.Inspect(func(st *editor.State) any {
		return struct {
			Page     editor.Page
			File     string
			Cursor   int
			Scroll   ui.Dp
			SelStart int
			SelEnd   int
			Anchor   int
		}{st.Page(), st.Editor.Filename, st.Editor.CursorPosition, st.ScrollOffset,
			st.Editor.SelectionStart, st.Editor.SelectionEnd, st.Editor.SelectionAnchor}
	})
	if err != nil {
		t.Fatalf("Inspect: %v", err)
	}
	got := v.(struct {
		Page     editor.Page
		File     string
		Cursor   int
		Scroll   ui.Dp
		SelStart int
		SelEnd   int
		Anchor   int
	})
	if got.Page != editor.EditorPage {
		t.Errorf("page = %v, want EditorPage (restore lands straight in the editor)", got.Page)
	}
	if got.File != "/notes.txt" {
		t.Errorf("file = %q, want /notes.txt", got.File)
	}
	if got.Cursor != 123 {
		t.Errorf("cursor = %d, want 123", got.Cursor)
	}
	if got.Scroll != ui.Dp(100) {
		t.Errorf("scroll = %v, want 100", got.Scroll)
	}
	if got.SelStart != 100 || got.SelEnd != 110 || got.Anchor != 100 {
		t.Errorf("selection = [%d,%d) anchor %d, want [100,110) anchor 100",
			got.SelStart, got.SelEnd, got.Anchor)
	}
}

// TestRestore_ScrollLandsWhenScalePrecedesSize reproduces the on-device
// startup ordering, where the first FrameEvent (and hence the ScaleEvent)
// arrives before the size ConfigEvent. The scroll must still land, clamped
// by the layout at the real scale: an earlier revision applied it at the
// ScaleEvent against a not-yet-sized viewport and lost it.
func TestRestore_ScrollLandsWhenScalePrecedesSize(t *testing.T) {
	content := strings.Repeat("hello world line\n", 100)
	dir := t.TempDir()
	diskPath := filepath.Join(dir, "late.txt")
	if err := os.WriteFile(diskPath, []byte(content), 0644); err != nil {
		t.Fatal(err)
	}
	h := e2e.NewHarness(e2e.WithFileSystem(real.NewRealFileSystem(dir), "/"))
	h.Logic().BeginRestore(editor.SessionState{File: "/late.txt", Cursor: 123, Scroll: 100})
	h.Run()
	h.SendScale(2.0)        // scale first
	h.SendConfig(780, 1688) // size second (on-device ordering)
	defer h.Cleanup()

	for i := 0; i < 100; i++ {
		v, err := h.Inspect(func(st *editor.State) any {
			cb := st.Editor.ChunkedBuffer
			if cb == nil || cb.FileLen() == 0 || cb.LineIndex == nil {
				return false
			}
			full, err := cb.FullContent()
			return err == nil && int64(len(full)) == cb.FileLen() &&
				cb.LineIndex.Size == cb.FileLen() && st.ScrollOffset == ui.Dp(100)
		})
		if err != nil {
			t.Fatalf("Inspect: %v", err)
		}
		if v.(bool) {
			return
		}
		time.Sleep(50 * time.Millisecond)
	}
	t.Fatal("timed out: scroll did not land when the scale event preceded the size")
}

// TestRestore_ClampsToShorterFile: the file was truncated since the last
// session; the cursor and selection must clamp to the shorter content, not
// restore past EOF.
func TestRestore_ClampsToShorterFile(t *testing.T) {
	content := "0123456789" // 10 bytes
	h := restoreHarness(t, "short.txt", content, editor.SessionState{
		Cursor:   57, // far past EOF
		SelStart: 5,
		SelEnd:   99, // spans EOF
	})
	defer h.Cleanup()

	v, err := h.Inspect(func(st *editor.State) any {
		return struct{ Cursor, SelStart, SelEnd int }{
			st.Editor.CursorPosition, st.Editor.SelectionStart, st.Editor.SelectionEnd,
		}
	})
	if err != nil {
		t.Fatalf("Inspect: %v", err)
	}
	got := v.(struct{ Cursor, SelStart, SelEnd int })
	if got.Cursor != 10 {
		t.Errorf("cursor = %d, want 10 (clamped to EOF)", got.Cursor)
	}
	if got.SelStart != 5 || got.SelEnd != 10 {
		t.Errorf("selection = [%d,%d), want [5,10) (end clamped to EOF)", got.SelStart, got.SelEnd)
	}
}

// TestRestore_MissingFileFallsBackToBrowser: the restored file was deleted
// since the last session; the app must land on the browser page with a clean
// editor, not an empty editor page.
func TestRestore_MissingFileFallsBackToBrowser(t *testing.T) {
	dir := t.TempDir()
	h := e2e.NewHarness(e2e.WithFileSystem(real.NewRealFileSystem(dir), "/"))
	h.Logic().BeginRestore(editor.SessionState{File: "/gone.txt", Cursor: 10})
	h.Run()
	defer h.Cleanup()
	h.SendConfig(780, 1688)
	h.SendScale(2.0)

	deadline := time.Now().Add(5 * time.Second)
	for {
		v, err := h.Inspect(func(st *editor.State) any {
			return st.Page() == editor.BrowserPage && st.Editor.Filename == "" &&
				st.Editor.ChunkedBuffer == nil
		})
		if err != nil {
			t.Fatalf("Inspect: %v", err)
		}
		if v.(bool) {
			return
		}
		if time.Now().After(deadline) {
			t.Fatal("timed out: restore of a missing file did not fall back to the browser")
		}
		time.Sleep(25 * time.Millisecond)
	}
}

// TestRestore_FindBar reopens the file with the find bar open, a query and a
// current match: the query must re-scan, select the saved current match (by
// byte offset) and NOT re-scroll the restored viewport.
func TestRestore_FindBar(t *testing.T) {
	var b strings.Builder
	for i := 0; i < 50; i++ {
		fmt.Fprintf(&b, "filler line number %02d\n", i)
	}
	b.WriteString("needle at start of the interesting part\n")
	b.WriteString("middle filler\n")
	b.WriteString("needle in the middle of it\n")
	b.WriteString("tail filler\n")
	b.WriteString("needle at the end\n")
	for i := 0; i < 50; i++ {
		fmt.Fprintf(&b, "trailing filler %02d\n", i)
	}
	content := b.String()

	// Offsets of the three "needle" occurrences.
	first := strings.Index(content, "needle")
	second := strings.Index(content[first+1:], "needle") + first + 1
	third := strings.Index(content[second+1:], "needle") + second + 1
	if first < 0 || second < 0 || third < 0 {
		t.Fatal("test content lost its needles")
	}

	h := restoreHarness(t, "findme.txt", content, editor.SessionState{
		FindQuery:   "needle",
		FindVisible: true,
		FindCurByte: second,
		// Cursor/scroll restored at the top: if the re-scan wrongly
		// re-scrolls to the match, ScrollOffset would no longer be 0.
	})
	defer h.Cleanup()

	deadline := time.Now().Add(5 * time.Second)
	for {
		v, err := h.Inspect(func(st *editor.State) any {
			f := &st.Editor.Find
			return struct {
				Visible, Scanning        bool
				N, Cur, SelStart, SelEnd int
				Scroll                   ui.Dp
			}{f.Visible, f.Scanning, len(f.Matches), f.Cur,
				st.Editor.SelectionStart, st.Editor.SelectionEnd, st.ScrollOffset}
		})
		if err != nil {
			t.Fatalf("Inspect: %v", err)
		}
		got := v.(struct {
			Visible, Scanning        bool
			N, Cur, SelStart, SelEnd int
			Scroll                   ui.Dp
		})
		if !got.Scanning && got.N == 3 {
			if !got.Visible {
				t.Errorf("find bar visible = false, want true")
			}
			if got.Cur != 1 {
				t.Errorf("current match = %d, want 1 (the saved current item)", got.Cur)
			}
			if got.SelStart != second || got.SelEnd != second+len("needle") {
				t.Errorf("selection = [%d,%d), want [%d,%d)",
					got.SelStart, got.SelEnd, second, second+len("needle"))
			}
			if got.Scroll != 0 {
				t.Errorf("scroll = %v, want 0 (restore must not re-scroll to the match)", got.Scroll)
			}
			return
		}
		if time.Now().After(deadline) {
			t.Fatalf("timed out waiting for the restore re-scan (matches=%d scanning=%v)", got.N, got.Scanning)
		}
		time.Sleep(25 * time.Millisecond)
	}
}

// TestRestore_FindBarClosed keeps the query but does not open the bar: no
// scan may run at restore (it would be dropped and leave Scanning stuck);
// opening the bar afterwards must re-scan and produce the matches.
func TestRestore_FindBarClosed(t *testing.T) {
	var b strings.Builder
	for i := 0; i < 60; i++ {
		fmt.Fprintf(&b, "padding line %02d\n", i)
	}
	b.WriteString("needle one\nneedle two\nneedle three\n")
	content := b.String()

	h := restoreHarness(t, "closed.txt", content, editor.SessionState{
		FindQuery:   "needle",
		FindVisible: false,
	})
	defer h.Cleanup()

	// Give any (wrong) eager scan time to dispatch, then check state.
	time.Sleep(300 * time.Millisecond)
	v, err := h.Inspect(func(st *editor.State) any {
		f := &st.Editor.Find
		return struct {
			Visible, Scanning bool
			Query             string
			N                 int
		}{f.Visible, f.Scanning, f.Query, len(f.Matches)}
	})
	if err != nil {
		t.Fatalf("Inspect: %v", err)
	}
	got := v.(struct {
		Visible, Scanning bool
		Query             string
		N                 int
	})
	if got.Visible {
		t.Errorf("find bar visible = true, want false")
	}
	if got.Query != "needle" {
		t.Errorf("query = %q, want needle", got.Query)
	}
	if got.Scanning {
		t.Errorf("scanning = true after a closed-bar restore; the scan would be dropped and never re-run")
	}
	if got.N != 0 {
		t.Errorf("matches = %d, want 0 (no scan while the bar is closed)", got.N)
	}

	// Opening the bar now must re-scan (findShow) and find all three.
	if err := h.WithState(func(st *editor.State) { editor.ToggleFind(nil) }); err != nil {
		t.Fatalf("ToggleFind: %v", err)
	}
	deadline := time.Now().Add(5 * time.Second)
	for {
		n, err := h.Inspect(func(st *editor.State) any {
			return len(st.Editor.Find.Matches)
		})
		if err != nil {
			t.Fatalf("Inspect: %v", err)
		}
		if n.(int) == 3 {
			return
		}
		if time.Now().After(deadline) {
			t.Fatal("timed out: opening the find bar did not re-scan the restored query")
		}
		time.Sleep(25 * time.Millisecond)
	}
}

// TestRestore_SaverSnapshot verifies the persist side: a state change
// (cursor + selection + scroll) is picked up by the rate-limited saver as a
// snapshot with the right values.
func TestRestore_SaverSnapshot(t *testing.T) {
	dir := t.TempDir()
	if err := os.WriteFile(filepath.Join(dir, "small.txt"), []byte("hello world"), 0644); err != nil {
		t.Fatal(err)
	}
	saves := make(chan editor.SessionState, 16)
	h := e2e.NewHarness(e2e.WithFileSystem(real.NewRealFileSystem(dir), "/"))
	h.Logic().SetSessionSaver(func(s editor.SessionState) { saves <- s })
	h.Run()
	h.SendConfig(780, 1688)
	h.SendScale(2.0)
	defer h.Cleanup()

	// Open the file the usual way (browser-row tap path).
	if err := h.WithState(func(st *editor.State) { editor.OpenFile("/small.txt") }); err != nil {
		t.Fatalf("OpenFile: %v", err)
	}
	time.Sleep(300 * time.Millisecond) // let the load settle

	// Change state on the owner, then force a frame (emitFrame drives the
	// rate-limited save).
	if err := h.WithState(func(st *editor.State) {
		st.Editor.CursorPosition = 6
		st.Editor.SelectionAnchor = 0
		st.Editor.SelectionStart = 0
		st.Editor.SelectionEnd = 5
		st.ScrollOffset = 10
	}); err != nil {
		t.Fatalf("WithState: %v", err)
	}
	// The save is rate-limited to one per second; wait past the limit, then
	// force a frame (emitFrame drives the check).
	time.Sleep(1100 * time.Millisecond)
	h.SendConfig(780, 1688)

	deadline := time.Now().Add(5 * time.Second)
	for {
		remaining := time.Until(deadline)
		if remaining <= 0 {
			t.Fatal("timed out: saver did not receive the expected snapshot")
		}
		select {
		case s := <-saves:
			if s.File == "/small.txt" && s.Cursor == 6 &&
				s.SelStart == 0 && s.SelEnd == 5 && s.Scroll == 10 {
				return
			}
		case <-time.After(remaining):
			t.Fatal("timed out: saver did not receive the expected snapshot")
		}
	}
}

// TestRestore_ShutdownSavesFinalSnapshot verifies Shutdown's unconditional
// final save: the last state is persisted even without a rate-limited tick.
func TestRestore_ShutdownSavesFinalSnapshot(t *testing.T) {
	dir := t.TempDir()
	if err := os.WriteFile(filepath.Join(dir, "a.txt"), []byte("abcdef"), 0644); err != nil {
		t.Fatal(err)
	}
	saves := make(chan editor.SessionState, 16)
	l := editor.NewLogic(real.NewRealFileSystem(dir), "/", func(string) {})
	l.SetSessionSaver(func(s editor.SessionState) { saves <- s })
	go l.Run()

	// Open the file (the goroutine-send keeps this off the owner's select).
	if _, ok := l.Inspect(func(st *editor.State) any {
		editor.OpenFile("/a.txt")
		return nil
	}); !ok {
		t.Fatal("Inspect timed out")
	}
	for i := 0; i < 100; i++ {
		loaded, ok := l.Inspect(func(st *editor.State) any {
			cb := st.Editor.ChunkedBuffer
			return cb != nil && cb.FileLen() == 6
		})
		if ok && loaded.(bool) {
			break
		}
		time.Sleep(20 * time.Millisecond)
	}
	if _, ok := l.Inspect(func(st *editor.State) any {
		st.Editor.CursorPosition = 3
		return nil
	}); !ok {
		t.Fatal("Inspect timed out")
	}
	l.Shutdown()

	deadline := time.After(3 * time.Second)
	for {
		select {
		case s := <-saves:
			if s.File == "/a.txt" && s.Cursor == 3 {
				return
			}
		case <-deadline:
			t.Fatal("timed out: Shutdown did not persist a snapshot with the final state")
		}
	}
}

// TestRestore_ScrollSurvivesWrapState reproduces the on-device report
// "relaunch lands further DOWN than where I left off": the snapshot's pixel
// scroll lives in visual-line space (wrapped lines occupy several visual
// lines, and the scroll-to-line mapping runs through the WrapIndex), but on
// relaunch the counts of every line above the restored viewport are the
// estimate (1) until shaped, and lines above the visible window are never
// shaped. Mapping the saved offset through that fresh index lands a logical
// line deeper by all the wrapped continuations above it. The snapshot
// therefore persists the logical line at the viewport top (and the sub-line
// remainder), and the restore derives the offset from the line.
func TestRestore_ScrollSurvivesWrapState(t *testing.T) {
	const lines = 300
	var b strings.Builder
	for i := 0; i < lines; i++ {
		fmt.Fprintf(&b, "line %03d content\n", i)
	}
	dir := t.TempDir()
	if err := os.WriteFile(filepath.Join(dir, "wrap.txt"), []byte(b.String()), 0644); err != nil {
		t.Fatal(err)
	}

	// First session: open the file, record the first 150 lines as wrapped
	// into 3 visual lines each (as a shaping pass would), and scroll so the
	// viewport top sits on logical line 200. In visual space that is line
	// 150*3 + 50 = 500, so the pixel offset is 500 line-heights.
	saves := make(chan editor.SessionState, 16)
	h1 := e2e.NewHarness(e2e.WithFileSystem(real.NewRealFileSystem(dir), "/"))
	h1.Logic().SetSessionSaver(func(s editor.SessionState) { saves <- s })
	h1.Run()
	h1.SendConfig(780, 1688)
	h1.SendScale(2.0)
	defer h1.Cleanup()

	if err := h1.WithState(func(st *editor.State) { editor.OpenFile("/wrap.txt") }); err != nil {
		t.Fatalf("OpenFile: %v", err)
	}
	for i := 0; i < 100; i++ {
		v, err := h1.Inspect(func(st *editor.State) any {
			cb := st.Editor.ChunkedBuffer
			return cb != nil && cb.FileLen() > 0 && cb.LineIndex != nil
		})
		if err == nil && v.(bool) {
			break
		}
		time.Sleep(20 * time.Millisecond)
	}
	// Set the wrapped counts and the deep scroll on the owner; the line
	// height comes from the owner too (EffectiveLineHeight reads state).
	lhAny, err := h1.Inspect(func(st *editor.State) any {
		w := st.Editor.ChunkedBuffer.WrapIndex
		for i := 0; i < 150; i++ {
			w.Set(i, 3)
		}
		st.ScrollOffset = ui.Dp(500 * float64(editor.EffectiveLineHeight()))
		return float64(editor.EffectiveLineHeight())
	})
	if err != nil {
		t.Fatalf("Inspect: %v", err)
	}
	lh := lhAny.(float64)
	// Wait past the rate limit and force a frame: the saver must capture
	// the deep scroll together with its logical line (200). Match on the
	// line, not the exact Dp: ui.Dp is float32-based, so ui.Dp(500*lh) and
	// 500*float64(lh) round differently.
	time.Sleep(300 * time.Millisecond)
	h1.SendConfig(780, 1688)
	snap := editor.SessionState{}
	deadline := time.After(5 * time.Second)
	for {
		select {
		case s := <-saves:
			if s.File == "/wrap.txt" && s.ScrollLine == 200 && s.Scroll > 0 {
				snap = s
				goto got
			}
		case <-deadline:
			t.Fatal("timed out: saver did not capture the deep-scroll snapshot")
		}
	}
got:
	if snap.Scroll < 499*lh || snap.Scroll > 501*lh {
		t.Fatalf("snapshot Scroll = %v, want ~500*lh (%v): the pixel offset must stay the visual-space value",
			snap.Scroll, 500*lh)
	}
	if snap.ScrollLine != 200 {
		t.Fatalf("snapshot ScrollLine = %d, want 200 (the logical line at the viewport top under wrap)", snap.ScrollLine)
	}
	if snap.ScrollSub >= 0.01 { // 0 apart from ui.Dp float32 rounding
		t.Errorf("snapshot ScrollSub = %v, want ~0", snap.ScrollSub)
	}

	// Second session (the relaunch): the WrapIndex is fresh, every count the
	// estimate (1). The restore must land on logical line 200, not on visual
	// line 500 mapped 1:1 (which would be line 500, far deeper).
	h2 := e2e.NewHarness(e2e.WithFileSystem(real.NewRealFileSystem(dir), "/"))
	h2.Logic().BeginRestore(snap)
	h2.Run()
	h2.SendConfig(780, 1688)
	h2.SendScale(2.0)
	defer h2.Cleanup()

	// The restore must land the scroll within one line of 200*lh (the ui.Dp
	// float32 rounding keeps an exact match out of reach); the exact
	// assertion is the window start line below.
	for i := 0; i < 100; i++ {
		v, err := h2.Inspect(func(st *editor.State) any {
			cb := st.Editor.ChunkedBuffer
			if cb == nil || cb.FileLen() == 0 || cb.LineIndex == nil {
				return false
			}
			s := float64(st.ScrollOffset)
			return s > 199*lh && s < 201*lh
		})
		if err == nil && v.(bool) {
			break
		}
		time.Sleep(20 * time.Millisecond)
	}
	// One more frame so the layout pass records the window start line for
	// the landed scroll.
	h2.SendConfig(780, 1688)
	time.Sleep(100 * time.Millisecond)
	v, err := h2.Inspect(func(st *editor.State) any {
		return struct {
			Scroll  ui.Dp
			WinLine int
		}{st.ScrollOffset, st.WindowStartLine}
	})
	if err != nil {
		t.Fatalf("Inspect: %v", err)
	}
	got := v.(struct {
		Scroll  ui.Dp
		WinLine int
	})
	if s := float64(got.Scroll); s < 199*lh || s > 201*lh {
		t.Errorf("restored scroll = %v, want ~200*lh (%v): the saved logical line's offset",
			got.Scroll, 200*lh)
	}
	if got.WinLine != 200 {
		t.Errorf("window starts at line %d, want 200 (the saved line); a deeper line is the pre-fix visual-space mapping", got.WinLine)
	}
}

// TestRestore_LinePinHoldsAcrossLateWrapFeedback reproduces the on-device
// report "relaunch lands further UP than where I left off" (Pixel 9 Pro):
// while the restore scroll is still armed, the top-of-file window is what's
// rendered, and its shaping feedback (real wrap counts for the lines ABOVE
// the restored line) can land before or just after the offset is applied.
// Those counts are correct data, but they change the offset-to-line mapping:
// the line-derived offset was synthesized for the all-estimate index, so
// once counts land below the pinned line the same offset maps to a shallower
// line and the viewport drifts up. The restore therefore pins the logical
// line: every wrap correction re-derives the offset as V(L)*lh + sub until
// the restored window itself has shaped (or a timeout, or the user scrolls).
func TestRestore_LinePinHoldsAcrossLateWrapFeedback(t *testing.T) {
	const lines = 300
	const lineLen = 17 // "line %03d content\n"
	var b strings.Builder
	for i := 0; i < lines; i++ {
		fmt.Fprintf(&b, "line %03d content\n", i)
	}
	dir := t.TempDir()
	if err := os.WriteFile(filepath.Join(dir, "wrap.txt"), []byte(b.String()), 0644); err != nil {
		t.Fatal(err)
	}

	// The harness runs at the default font scale, so the stateless variant
	// matches what the owner will compute.
	lh := float64(editor.EffectiveLineHeightAt(1))
	snap := editor.SessionState{
		File:       "/wrap.txt",
		Cursor:     0,
		Scroll:     float64(ui.Dp(500 * lh)), // the saving session's visual-space offset
		ScrollLine: 200,             // the logical line at the viewport top
		ScrollSub:  0,
	}

	h := e2e.NewHarness(e2e.WithFileSystem(real.NewRealFileSystem(dir), "/"))
	h.Logic().BeginRestore(snap)
	h.Run()
	h.SendConfig(780, 1688)
	h.SendScale(2.0)
	defer h.Cleanup()

	// Wait for the restore to land: with the fresh all-estimate index the
	// offset maps to exactly line 200.
	var winLine int
	for i := 0; i < 100; i++ {
		v, err := h.Inspect(func(st *editor.State) any {
			cb := st.Editor.ChunkedBuffer
			if cb == nil || cb.FileLen() == 0 || cb.LineIndex == nil {
				return -1
			}
			return st.WindowStartLine
		})
		if err == nil {
			winLine = v.(int)
			if winLine == 200 {
				break
			}
		}
		time.Sleep(20 * time.Millisecond)
	}
	if winLine != 200 {
		t.Fatalf("restore did not land on line 200 (window at %d)", winLine)
	}

	// Replay the on-device interleaving: the top-of-file window (lines
	// 0-49) was shaped while the scroll was still armed, and its feedback —
	// real wrap counts (3 visual lines each for those lines) — arrives now,
	// after the offset was applied.
	editSeq, err := h.Inspect(func(st *editor.State) any {
		return st.Editor.EditSeq
	})
	if err != nil {
		t.Fatalf("Inspect: %v", err)
	}
	var wt strings.Builder
	for i := 0; i < 50; i++ {
		fmt.Fprintf(&wt, "line %03d content\n", i)
	}
	windowText := wt.String()
	var starts []int
	for i := 0; i < 50; i++ {
		base := i * lineLen
		starts = append(starts, base, base+5, base+10) // 3 visual lines per line
	}
	h.Logic().LayoutChan() <- ui.LayoutFeedback{
		GlyphLayout: ui.GlyphLayout{
			VisualLineStarts: starts,
		},
		WindowText:      windowText,
		WindowStartByte: 0,
		WindowStartLine: 0,
		EditSeq:         editSeq.(uint64),
	}

	// The correction must NOT drag the viewport: the pin re-derives the
	// offset as V(200)*lh, where V(200) = 50*3 + 150 = 300 under the
	// corrected index, keeping line 200 at the top. Pre-fix, the applied
	// offset (200*lh) mapped to line ~66 under the corrected index.
	for i := 0; i < 100; i++ {
		v, err := h.Inspect(func(st *editor.State) any {
			return struct {
				Scroll  float64
				WinLine int
			}{float64(st.ScrollOffset), st.WindowStartLine}
		})
		if err == nil {
			got := v.(struct {
				Scroll  float64
				WinLine int
			})
			if got.WinLine == 200 && got.Scroll > 299*lh && got.Scroll < 301*lh {
				return // held
			}
		}
		time.Sleep(20 * time.Millisecond)
	}
	v, err := h.Inspect(func(st *editor.State) any {
		return struct {
			Scroll  float64
			WinLine int
		}{float64(st.ScrollOffset), st.WindowStartLine}
	})
	if err != nil {
		t.Fatalf("Inspect: %v", err)
	}
	got := v.(struct {
		Scroll  float64
		WinLine int
	})
	if got.WinLine != 200 {
		t.Errorf("window at line %d after late wrap feedback, want 200: the line-pin must hold the viewport on the restored line (a shallower line is the pre-fix drift)", got.WinLine)
	}
	if got.Scroll < 499*lh || got.Scroll > 501*lh {
		t.Errorf("scroll = %v after late wrap feedback, want ~300*lh (%v): V(200) under the corrected index", got.Scroll, 300*lh)
	}
}

// TestRestore_UrgentSaveOnSelection verifies the kill-race fix: a selection
// appearing (the user just highlighted text) saves immediately, even inside
// the rate-limit window that the file-open save opened. Without the urgent
// path, killing the app (recents-wipe) less than a second after highlighting
// lost the selection and cursor.
func TestRestore_UrgentSaveOnSelection(t *testing.T) {
	dir := t.TempDir()
	if err := os.WriteFile(filepath.Join(dir, "a.txt"), []byte("abcdef"), 0644); err != nil {
		t.Fatal(err)
	}
	saves := make(chan editor.SessionState, 16)
	l := editor.NewLogic(real.NewRealFileSystem(dir), "/", func(string) {})
	l.SetSessionSaver(func(s editor.SessionState) { saves <- s })
	go l.Run()
	defer l.Shutdown()

	// Open the file: the file change is itself urgent, so a save lands as
	// the load settles. Drain everything up to and including the loaded
	// snapshot.
	if _, ok := l.Inspect(func(st *editor.State) any {
		editor.OpenFile("/a.txt")
		return nil
	}); !ok {
		t.Fatal("Inspect timed out")
	}
	loaded := false
	for i := 0; i < 100 && !loaded; i++ {
		v, ok := l.Inspect(func(st *editor.State) any {
			cb := st.Editor.ChunkedBuffer
			return cb != nil && cb.FileLen() == 6
		})
		if ok {
			loaded = v.(bool)
		}
		if loaded {
			break
		}
		time.Sleep(20 * time.Millisecond)
	}
	if !loaded {
		t.Fatal("file did not load")
	}
	// Drain saves up to the first one describing the loaded file.
	deadline := time.After(3 * time.Second)
	for {
		select {
		case s := <-saves:
			if s.File == "/a.txt" {
				goto drainDone
			}
		case <-deadline:
			t.Fatal("timed out: no save for the opened file")
		}
	}
drainDone:
	// Immediately (well inside any rate-limit window after the saves above),
	// make a selection appear and force a frame: the urgent path must save it
	// now, not after the interval elapses.
	if _, ok := l.Inspect(func(st *editor.State) any {
		st.Editor.SelectionAnchor = 1
		st.Editor.SelectionStart = 1
		st.Editor.SelectionEnd = 4
		st.Editor.CursorPosition = 4
		st.ScrollOffset = 3
		return nil
	}); !ok {
		t.Fatal("Inspect timed out")
	}
	l.ConfigChan() <- editor.ConfigEvent{PixelWidth: 780, PixelHeight: 1688} // force emitFrame

	select {
	case s := <-saves:
		if s.SelStart == 1 && s.SelEnd == 4 && s.Cursor == 4 {
			return
		}
		t.Fatalf("unexpected snapshot: %+v", s)
	case <-time.After(2 * time.Second):
		t.Fatal("timed out: selection appearance was not saved immediately (urgent path)")
	}
}