terminal: keep an OSC 133;A prompt on its own line through reflow

src/terminal/Screen.zig

@@ -1614,6 +1614,25 @@ pub fn cursorResetWrap(self: *Screen) void {
     }
 }
 
+/// Make the cursor row start a new logical line by resetting the soft wrap
+/// from the row above into it. Reflow then never joins the two rows.
+pub fn cursorBreakWrapIntoRow(self: *Screen) void {
+    const page_row = self.cursor.page_row;
+    if (!page_row.wrap_continuation) return;
+    page_row.wrap_continuation = false;
+
+    const prev = self.cursor.page_pin.up(1) orelse return;
+    const prev_row = prev.rowAndCell().row;
+    prev_row.wrap = false;
+
+    // A spacer head only exists to carry a wide character over the wrap.
+    const cells = prev.cells(.all);
+    const last = prev.node.cols() - 1;
+    if (cells[last].wide == .spacer_head) {
+        self.clearCells(prev.node.page(), prev_row, cells[last..][0..1]);
+    }
+}
+
 /// Options for scrolling the viewport of the terminal grid. The reason
 /// we have this in addition to PageList.Scroll is because we have additional
 /// scroll behaviors that are not part of the PageList.Scroll enum.

src/terminal/Terminal.zig

@@ -1973,6 +1973,13 @@ pub fn semanticPrompt(
 
             const screen: *Screen = self.screens.active;
 
+            // A prompt that starts at column 0 of a soft-wrapped row reached
+            // it through padding, such as zsh PROMPT_SP overflowing spaces
+            // after a partial line. The shell draws and redraws this prompt
+            // as the start of a line, so reflow must not join it onto the
+            // padded row above.
+            if (screen.cursor.x == 0) screen.cursorBreakWrapIntoRow();
+
             // "Subsequent text (until a OSC "133;B" or OSC "133;I" command)
             // is a prompt string (as if followed by OSC 133;P;k=i\007)."
             screen.cursorSetSemanticContent(.{
@@ -15280,6 +15287,46 @@ test "Terminal: OSC133A cl option sets click to cl value" {
     try testing.expectEqual(Screen.SemanticPrompt.SemanticClick{ .cl = .multiple }, t.screens.active.semantic_prompt.click);
 }
 
+test "Terminal: OSC133A after a padded partial line keeps the prompt on its own line across resize" {
+    const alloc = testing.allocator;
+    const io_impl = testing.io;
+    var t = try init(io_impl, alloc, .{ .cols = 10, .rows = 5 });
+    defer t.deinit(alloc);
+
+    // zsh PROMPT_SP: after output with no trailing newline, the shell prints
+    // a mark and pads with spaces past the right edge so the terminal wraps
+    // to a new row, then returns to column 0 and starts the prompt there.
+    try t.printString("ab%");
+    try t.printString("        ");
+    t.carriageReturn();
+    try t.printString(" ");
+    t.carriageReturn();
+    try t.semanticPrompt(.{
+        .action = .fresh_line_new_prompt,
+        .options_unvalidated = "redraw=0",
+    });
+    try t.printString("$ ");
+    try t.semanticPrompt(.init(.end_prompt_start_input));
+    try t.printString("ls");
+    try testing.expectEqual(@as(size.CellCountInt, 1), t.screens.active.cursor.y);
+
+    // The shell redraws its prompt from column 0 after a resize, so reflow
+    // must not join the prompt onto the padded row above it.
+    try t.resize(alloc, .{ .cols = 20, .rows = 5 });
+    try testing.expectEqual(@as(size.CellCountInt, 1), t.screens.active.cursor.y);
+    try testing.expectEqual(@as(size.CellCountInt, 4), t.screens.active.cursor.x);
+    const prompt_start = t.screens.active.pages.getCell(.{ .active = .{ .x = 0, .y = 1 } }).?;
+    try testing.expectEqual(@as(u21, '$'), prompt_start.cell.codepoint());
+
+    try t.resize(alloc, .{ .cols = 6, .rows = 5 });
+    const narrowed_start = t.screens.active.pages.getCell(.{ .active = .{
+        .x = 0,
+        .y = t.screens.active.cursor.y,
+    } }).?;
+    try testing.expectEqual(@as(u21, '$'), narrowed_start.cell.codepoint());
+    try testing.expectEqual(@as(size.CellCountInt, 4), t.screens.active.cursor.x);
+}
+
 test "Terminal: OSC133A cl=line sets click to line" {
     const alloc = testing.allocator;
     const io_impl = testing.io;