Put @@ hunk headers before their context lines.

CHANGELOG.md

@@ -7,6 +7,7 @@ All notable changes to this project will be documented in this file.
 - `c` copies the complete loaded file preview to the terminal clipboard without line numbers or display wrapping; while a preview is open, drift releases the mouse to the terminal so its text can also be selected directly
 
 ### Fixed
+- unified diff `@@` headers sat after their context lines, so a hunk starting at line 1 showed a block of unchanged lines and then the marker. The header is the first row of the hunk now, with context underneath
 - tabbing through the diff file list could punch large black holes in the layout when a file used CRLF line endings. A leftover `\r` sent the terminal cursor back to column 0, so the padded diff background painted over the file list. Line splits now drop CR, and the renderer ignores any that remain
 - a directory marked in the remote pane of an FTP or FTPS host ended up in the diff view as a file, with a red "is a directory" where the diff belongs, instead of being expanded into the files below it. `Stat` treated a successful `SIZE` as proof of a file, but vsftpd, ProFTPD and others answer `SIZE` for directories too. It asks `MLST` first now, which reports the entry type. One command also replaces `SIZE` plus `MDTM`, and its timestamps have second precision, so the diff loader skips more downloads on files that match. Servers without `MLST` keep the old behaviour and the old ambiguity
 

internal/diff/hunks.go

@@ -36,6 +36,7 @@ func (r DisplayRow) SourceLine() int {
 }
 
 // Flatten builds display rows: hunk headers, limited context, and fold markers.
+// Each @@ header is the first row of its hunk, followed by context then changes.
 // expanded holds GapIDs whose equal runs should be shown in full.
 func Flatten(lines []DiffLine, context int, expanded map[int]struct{}) []DisplayRow {
 	if context < 0 {
@@ -56,9 +57,13 @@ func Flatten(lines []DiffLine, context int, expanded map[int]struct{}) []Display
 
 	foldBudget := 2 * context
 	out := make([]DisplayRow, 0, len(lines)+len(runs))
+	var leading []DisplayRow
 	for i, r := range runs {
 		if r.equal {
-			out = append(out, flattenEqualRun(runs, i, context, foldBudget, expanded)...)
+			prefix, fold, suffix := splitEqualRun(runs, i, context, foldBudget, expanded)
+			out = append(out, prefix...)
+			out = append(out, fold...)
+			leading = suffix
 			continue
 		}
 		hStart, hEnd := hunkRange(runs, i, context, foldBudget, expanded)
@@ -67,6 +72,8 @@ func Flatten(lines []DiffLine, context int, expanded map[int]struct{}) []Display
 			LineIndex: r.start,
 			Header:    formatHunkHeader(lines, hStart, hEnd),
 		})
+		out = append(out, leading...)
+		leading = nil
 		for idx := r.start; idx < r.end; idx++ {
 			out = append(out, DisplayRow{Kind: DisplayLine, LineIndex: idx})
 		}
@@ -139,34 +146,55 @@ func hasChangeRun(runs []run) bool {
 	return false
 }
 
-func flattenEqualRun(runs []run, i, context, foldBudget int, expanded map[int]struct{}) []DisplayRow {
+// splitEqualRun splits an equal run into trailing context of the previous hunk
+// (prefix), an optional fold, and leading context of the next hunk (suffix).
+// Flatten emits the next @@ header between fold and suffix so the header is
+// the first row of its hunk.
+func splitEqualRun(runs []run, i, context, foldBudget int, expanded map[int]struct{}) (prefix, fold, suffix []DisplayRow) {
 	r := runs[i]
 	length := r.end - r.start
 	_, shown := expanded[r.start]
-	if length <= foldBudget || shown {
-		out := make([]DisplayRow, 0, length)
-		for idx := r.start; idx < r.end; idx++ {
-			out = append(out, DisplayRow{Kind: DisplayLine, LineIndex: idx})
+	preN, sufN := equalContext(runs, i, context)
+
+	if length > foldBudget && !shown {
+		hiddenStart := r.start + preN
+		hiddenEnd := r.end - sufN
+		prefix = lineRows(r.start, hiddenStart)
+		if hiddenEnd > hiddenStart {
+			fold = []DisplayRow{{
+				Kind:      DisplayFold,
+				GapID:     r.start,
+				Hidden:    hiddenEnd - hiddenStart,
+				FoldStart: hiddenStart,
+				FoldEnd:   hiddenEnd,
+			}}
 		}
-		return out
+		suffix = lineRows(hiddenEnd, r.end)
+		return prefix, fold, suffix
+	}
+
+	switch {
+	case preN == 0 && sufN > 0:
+		return nil, nil, lineRows(r.start, r.end)
+	case sufN == 0:
+		return lineRows(r.start, r.end), nil, nil
+	default:
+		if sufN > length {
+			sufN = length
+		}
+		split := r.end - sufN
+		return lineRows(r.start, split), nil, lineRows(split, r.end)
 	}
+}
 
-	prefix, suffix := equalContext(runs, i, context)
-	out := make([]DisplayRow, 0, prefix+suffix+1)
-	for idx := r.start; idx < r.start+prefix; idx++ {
-		out = append(out, DisplayRow{Kind: DisplayLine, LineIndex: idx})
-	}
-	hiddenStart := r.start + prefix
-	hiddenEnd := r.end - suffix
-	out = append(out, DisplayRow{
-		Kind:      DisplayFold,
-		GapID:     r.start,
-		Hidden:    hiddenEnd - hiddenStart,
-		FoldStart: hiddenStart,
-		FoldEnd:   hiddenEnd,
-	})
-	for idx := hiddenEnd; idx < r.end; idx++ {
-		out = append(out, DisplayRow{Kind: DisplayLine, LineIndex: idx})
+func lineRows(start, end int) []DisplayRow {
+	n := end - start
+	if n <= 0 {
+		return nil
+	}
+	out := make([]DisplayRow, n)
+	for i := 0; i < n; i++ {
+		out[i] = DisplayRow{Kind: DisplayLine, LineIndex: start + i}
 	}
 	return out
 }

internal/diff/hunks_test.go

@@ -57,6 +57,14 @@ func TestFlattenShortGapStaysOpen(t *testing.T) {
 			t.Fatalf("6-line gap should not fold: %+v", rows)
 		}
 	}
+	headers := headerIndexes(rows)
+	if len(headers) != 2 {
+		t.Fatalf("headers at %v, want 2", headers)
+	}
+	// Gap is indices 3–8. The second header sits before the last 3 of those.
+	if rows[headers[1]+1].LineIndex != 6 {
+		t.Fatalf("second header at %d is followed by line %d, want 6", headers[1], rows[headers[1]+1].LineIndex)
+	}
 }
 
 func TestFlattenSevenLineGapFoldsMiddle(t *testing.T) {
@@ -97,8 +105,9 @@ func TestFlattenLeadingAndTrailingFolds(t *testing.T) {
 		kinds[i] = r.Kind
 	}
 	want := []DisplayKind{
-		DisplayFold, DisplayLine, DisplayLine, DisplayLine,
-		DisplayHunkHeader, DisplayLine,
+		DisplayFold, DisplayHunkHeader,
+		DisplayLine, DisplayLine, DisplayLine,
+		DisplayLine,
 		DisplayLine, DisplayLine, DisplayLine, DisplayFold,
 	}
 	if !reflect.DeepEqual(kinds, want) {
@@ -151,8 +160,35 @@ func TestFlattenHunkHeaderIncludesContext(t *testing.T) {
 		{Text: "c", Kind: LineEqual, LocalNum: 3, RemoteNum: 3},
 	}
 	rows := Flatten(lines, DefaultContext, nil)
-	if rows[1].Kind != DisplayHunkHeader || rows[1].Header != "@@ -1,3 +1,3 @@" {
-		t.Fatalf("header = %+v, want @@ -1,3 +1,3 @@ after first context line", rows[1])
+	if rows[0].Kind != DisplayHunkHeader || rows[0].Header != "@@ -1,3 +1,3 @@" {
+		t.Fatalf("header = %+v, want @@ -1,3 +1,3 @@ as first row", rows[0])
+	}
+	if rows[1].Kind != DisplayLine || rows[1].LineIndex != 0 {
+		t.Fatalf("row after header = %+v, want first context line", rows[1])
+	}
+}
+
+func TestFlattenHeaderComesBeforeLeadingContext(t *testing.T) {
+	lines := numberedEquals(12, 1)
+	lines = append(lines, DiffLine{Text: "old", Kind: LineRemoved, LocalNum: 13})
+
+	collapsed := Flatten(lines, DefaultContext, nil)
+	if collapsed[0].Kind != DisplayFold {
+		t.Fatalf("row 0 = %+v, want leading fold", collapsed[0])
+	}
+	if collapsed[1].Kind != DisplayHunkHeader || collapsed[1].Header != "@@ -10,4 +10,3 @@" {
+		t.Fatalf("header = %+v, want @@ -10,4 +10,3 @@ after the fold", collapsed[1])
+	}
+	if collapsed[2].LineIndex != 9 {
+		t.Fatalf("first context line index = %d, want 9", collapsed[2].LineIndex)
+	}
+
+	expanded := Flatten(lines, DefaultContext, map[int]struct{}{0: {}})
+	if expanded[0].Kind != DisplayHunkHeader || expanded[0].Header != "@@ -1,13 +1,12 @@" {
+		t.Fatalf("expanded header = %+v, want @@ -1,13 +1,12 @@ first", expanded[0])
+	}
+	if expanded[1].Kind != DisplayLine || expanded[1].LineIndex != 0 {
+		t.Fatalf("expanded row 1 = %+v, want file line 1 under the header", expanded[1])
 	}
 }
 
@@ -181,6 +217,16 @@ func TestFoldableGapIDs(t *testing.T) {
 	}
 }
 
+func headerIndexes(rows []DisplayRow) []int {
+	var out []int
+	for i, r := range rows {
+		if r.Kind == DisplayHunkHeader {
+			out = append(out, i)
+		}
+	}
+	return out
+}
+
 func TestSplitRunsGroupsByKindAndClosesTheLastRun(t *testing.T) {
 	if got := splitRuns(nil); got != nil {
 		t.Fatalf("splitRuns(nil) = %v, want nil", got)

internal/tui/diffview/update_test.go

@@ -415,10 +415,8 @@ func TestHunkJumpLandsOnRunStart(t *testing.T) {
 	if len(headers) < 2 {
 		t.Fatalf("need two hunk headers, got %v", headers)
 	}
-
-	model, _ = model.handleKey(keyMsg("]"))
-	if model.scroll != headers[0] {
-		t.Fatalf("] jumped to %d, want first hunk header at %d", model.scroll, headers[0])
+	if headers[0] != 0 {
+		t.Fatalf("first header at %d, want 0 (leading context sits under it)", headers[0])
 	}
 
 	model, _ = model.handleKey(keyMsg("]"))
@@ -428,7 +426,12 @@ func TestHunkJumpLandsOnRunStart(t *testing.T) {
 
 	model, _ = model.handleKey(keyMsg("["))
 	if model.scroll != headers[0] {
-		t.Fatalf("[ jumped to %d, want previous hunk header at %d", model.scroll, headers[0])
+		t.Fatalf("[ jumped to %d, want first hunk header at %d", model.scroll, headers[0])
+	}
+
+	model, _ = model.handleKey(keyMsg("]"))
+	if model.scroll != headers[1] {
+		t.Fatalf("] jumped to %d, want second hunk header at %d", model.scroll, headers[1])
 	}
 }