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, 137 insertions, 0 deletions

diff --git a/tests/test_screen.py b/tests/test_screen.py
new file mode 100644
index 0000000..4156a0e
--- /dev/null
+++ b/tests/test_screen.py
@@ -0,0 +1,137 @@
+#!/usr/bin/env python3
+"""Composition, styling, cursor, scrollback, resize, and the input round trip.
+
+Everything here runs through the headless driver, so it is deterministic and
+takes milliseconds. Contrast tests/live_*.py, which exist only for the parts
+that genuinely need a tty.
+"""
+import sys
+
+from harness import Session, check, report
+
+CAT = ["/bin/sh", "-c", "stty raw -echo; cat -v"]
+SH = lambda script: ["/bin/sh", "-c", script]
+
+
+def test_text_and_cursor():
+    with Session(SH("stty raw -echo; cat"), cols=20, rows=3) as s:
+        s.settle()
+        s.raw("hello")
+        s.settle()
+        snap = s.snapshot()
+        check("text lands on row 0", snap.line(0).startswith("hello"), repr(snap.line(0)))
+        check("cursor follows the text", snap.cursor == {"visible": True, "x": 5, "y": 0},
+              str(snap.cursor))
+
+        s.raw("\\r\\nsecond")
+        s.settle()
+        snap = s.snapshot()
+        check("newline moves to row 1", snap.line(1).startswith("second"), repr(snap.line(1)))
+        check("cursor on row 1", (snap.cursor["x"], snap.cursor["y"]) == (6, 1),
+              str(snap.cursor))
+
+
+def test_styles():
+    with Session(SH(r'printf "n\033[1mB\033[31mR\033[0mn"; sleep 5'), cols=10, rows=2) as s:
+        s.settle()
+        snap = s.snapshot()
+        check("style: plain cell has no run", snap.style_at(0, 0) is None,
+              str(snap.style_at(0, 0)))
+        b = snap.style_at(1, 0)
+        check("style: bold is recorded", b and b["attrs"] == ["bold"], str(b))
+        r = snap.style_at(2, 0)
+        check("style: colour is resolved to rgb",
+              r and r["fg"] is not None and "bold" in r["attrs"], str(r))
+        check("style: reset ends the run", snap.style_at(3, 0) is None,
+              str(snap.style_at(3, 0)))
+
+
+def test_wide_and_clusters():
+    with Session(SH('printf "[\\346\\227\\245]"; sleep 5'), cols=10, rows=1) as s:
+        s.settle()
+        snap = s.snapshot()
+        check("wide char occupies one cell in the dump", snap.line(0).startswith("[日]"),
+              repr(snap.line(0)))
+
+
+def test_scrollback():
+    with Session(SH("stty raw -echo; cat"), cols=20, rows=3) as s:
+        s.settle()
+        s.raw("1\\r\\n2\\r\\n3\\r\\n4\\r\\n5")
+        s.settle()
+        snap = s.snapshot()
+        check("viewport shows the tail, not the head",
+              snap.line(0).startswith("3") and snap.line(2).startswith("5"),
+              repr(snap.text))
+
+
+def test_resize():
+    with Session(SH("stty raw -echo; cat"), cols=20, rows=3) as s:
+        s.settle()
+        s.resize(40, 5)
+        s.settle()
+        snap = s.snapshot()
+        check("resize changes the composited size",
+              snap.cols == 40 and snap.rows == 5 and len(snap.line(0)) == 40,
+              f"{snap.cols}x{snap.rows} line={len(snap.line(0))}")
+
+        s.raw("\\033[999;999H\\033[6n")  # ask the pane where it thinks it is
+        s.settle()
+        check("pane still responds after resize", s.alive())
+
+
+def test_input_round_trip():
+    """The decoder and the per-pane encoder, without a pty in sight."""
+    with Session(CAT, cols=40, rows=4) as s:
+        s.settle()
+        s.send(r"\e[1;5A")  # legacy ctrl-up
+        s.settle()
+        check("legacy key reaches the pane", "^[[1;5A" in s.snapshot().screen())
+
+    with Session(CAT, cols=40, rows=4) as s:
+        s.settle()
+        s.send(r"\e[98;5u")  # kitty ctrl-b -> legacy pane
+        s.settle()
+        check("kitty key is re-encoded for a legacy pane",
+              "^B" in s.snapshot().screen())
+
+    with Session(CAT, cols=40, rows=4) as s:
+        s.settle()
+        s.send(r"\e[200~pasted\e[201~")
+        s.settle()
+        check("paste is unwrapped for a pane that did not ask",
+              "pasted" in s.snapshot().screen())
+
+    kitty = ["/bin/sh", "-c",
+             'stty raw -echo; printf "\\033[>1u\\033[?1000h\\033[?1006h"; cat -v']
+    with Session(kitty, cols=40, rows=4) as s:
+        s.settle()
+        s.send(r"\x02")  # legacy ctrl-b -> kitty pane
+        s.settle()
+        check("legacy key is re-encoded for a kitty pane",
+              "^[[98;5u" in s.snapshot().screen(), s.snapshot().screen())
+
+        s.send(r"\e[<0;7;3M")
+        s.settle()
+        check("mouse reaches a pane that asked for it",
+              "^[[<0;7;3M" in s.snapshot().screen())
+
+
+def test_hitlist_contract():
+    """Empty until M1 paints something clickable, but the contract is live."""
+    with Session(SH("sleep 5"), cols=10, rows=2) as s:
+        s.settle()
+        snap = s.snapshot()
+        check("hit list exists and is empty", snap.hits == [], str(snap.hits))
+        check("hit test on empty list is None", snap.hit_at(0, 0) is None)
+
+
+if __name__ == "__main__":
+    test_text_and_cursor()
+    test_styles()
+    test_wide_and_clusters()
+    test_scrollback()
+    test_resize()
+    test_input_round_trip()
+    test_hitlist_contract()
+    sys.exit(report())