pty/run after a clear answers what the command printed from the clear on, whole; cut only when its start really scrolled away

A clear (ED 2, ED 3, a reset) under a running command marked its output
lost, so `clear; ls` answered only "exit 0 cut". The output's start is
now pinned again at the screen's top after the erase: what the command
prints from there is its answer, whole, and a cut is said only when
that start leaves the scrollback.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

2 files changed, 29 insertions, 6 deletions

diff --git a/src/ninep/pty.zig b/src/ninep/pty.zig
index 2245255b..fc8eb570 100644
--- a/src/ninep/pty.zig
+++ b/src/ninep/pty.zig
@@ -971,13 +971,12 @@ test "a run's answer says cut when its output's start is gone, and reads a bound
     defer gpa.free(into);
     sh.put(p, prompt);
 
-    // `clear` while it runs erases what it printed before, and the pins then
-    // span rows that no longer hold it (ED 3 even moves one to the next page
-    // without calling it garbage), so only the erase itself tells.
+    // `clear` while it runs: what it printed after is its output, whole;
+    // what the clear erased was meant to go.
     var h = sh.send(p, node);
     sh.put(p, c ++ "before\r\n\x1b[H\x1b[2J\x1b[3Jafter\r\n" ++ d ++ prompt);
     var got = sh.answered(p, node, h, into);
-    try testing.expect(std.mem.startsWith(u8, got, "exit 0 cut\n"));
+    try testing.expectEqualStrings("exit 0\nafter\n", got);
 
 
     // A resize between its start and end reflows the pins with the text.
diff --git a/src/terminal.zig b/src/terminal.zig
index 0850267e..a0337ce7 100644
--- a/src/terminal.zig
+++ b/src/terminal.zig
@@ -106,12 +106,36 @@ pub const MarkedHandler = if (enabled) struct {
                 else => {},
             }
         }
-        if (comptime action == .erase_display_complete or action == .erase_display_scrollback or action == .full_reset) {
-            if (self.phase == .running) self.lost = true;
+        if (comptime action == .erase_display_complete or action == .erase_display_scrollback or
+            action == .erase_display_scroll_complete or action == .full_reset)
+        {
+            self.inner.vt(action, value);
+            // A `clear` under a running command: its output is what it
+            // prints from here, the screen's top, not lost. Only what the
+            // scrollback later loses is (the pin goes `garbage`).
+            if (self.phase == .running) self.pinTop(&self.out_start);
+            return;
         }
         self.inner.vt(action, value);
     }
 
+    /// Pins `slot` to the primary screen's top-left; lost when it cannot be.
+    fn pinTop(self: *@This(), slot: *?*ghostty_vt.Pin) void {
+        const screen = self.inner.terminal.screens.get(.primary) orelse return;
+        if (slot.*) |old| screen.pages.untrackPin(old);
+        slot.* = null;
+        if (self.inner.terminal.screens.active_key != .primary) {
+            self.lost = true;
+            return;
+        }
+        const top = screen.pages.pin(.{ .active = .{} }) orelse {
+            self.lost = true;
+            return;
+        };
+        slot.* = screen.pages.trackPin(top) catch null;
+        if (slot.* == null) self.lost = true;
+    }
+
     pub fn deinit(self: *@This()) void {
         self.inner.deinit();
     }