sl0ptty: M0.5 — the headless driver and the harness everything rests on

--script runs the whole compositor with no tty: commands in (send, raw,
settle, resize, snapshot, alive), composited screen out as JSON — rows of
text, style runs, cursor, and the hit list.

Styles are emitted as runs rather than per-cell objects, because a test wants
'columns 0..5 of row 0 are bold red', not 1920 objects.

The hit list is empty until M1 paints something clickable, but the type, the
JSON, and hit_test() exist now: one geometry, established before there is
anything to get wrong.

Also fixes two host-policy defaults found by the cursor never appearing.
lib-vt is a VT library, not a terminal, so it starts with DECTCEM (mode 25)
off and grapheme clustering (2027) off. Both are now set via MODE_DEFAULT, so
they survive RIS.

tests/harness.py + tests/test_screen.py: 19 checks over composition, styling,
wide chars/clusters, scrollback, resize and the full input round trip —
including the kitty/legacy re-encoding matrix, which no longer needs a pty.

make test is now 2.4s for 59 checks; make test-live keeps the four that
genuinely need a tty.

1 files changed, 15 insertions, 0 deletions

diff --git a/src/pane.c b/src/pane.c
index f5eeac7..5850a57 100644
--- a/src/pane.c
+++ b/src/pane.c
@@ -78,6 +78,21 @@ pane_t *pane_new(const char *const argv[], uint16_t cols, uint16_t rows,
   ghostty_terminal_set(p->term, GHOSTTY_TERMINAL_OPT_WRITE_PTY, &wfn);
   ghostty_terminal_set(p->term, GHOSTTY_TERMINAL_OPT_TITLE_CHANGED, &tfn);
 
+  /* lib-vt makes no assumptions a host terminal would: it starts with DECTCEM
+   * (mode 25) off, so the cursor is invisible until someone says otherwise.
+   * MODE_DEFAULT sets the current value *and* the one restored by RIS, so a
+   * program that resets the terminal does not lose its cursor.
+   *
+   * 2027 is grapheme clustering: one cell per cluster, so flags and ZWJ emoji
+   * stay whole. We are opinionated about the outer terminal (D11) and it
+   * clusters too; under a terminal that does not, wide emoji may misalign. */
+  static const uint16_t default_on[] = {25, 2027};
+  for (size_t i = 0; i < sizeof default_on / sizeof *default_on; i++) {
+    GhosttyTerminalModeConfig mc = {.mode = ghostty_mode_new(default_on[i], false),
+                                    .value = true};
+    ghostty_terminal_set(p->term, GHOSTTY_TERMINAL_OPT_MODE_DEFAULT, &mc);
+  }
+
   if (pty_spawn(&p->pty, argv, cols, rows, cwd) != 0) goto fail;
   p->alive = true;
   p->dirty = true;