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, 28 insertions, 0 deletions

diff --git a/src/json.h b/src/json.h
new file mode 100644
index 0000000..b1acc43
--- /dev/null
+++ b/src/json.h
@@ -0,0 +1,28 @@
+/* A minimal JSON writer. No parser: we only ever emit. */
+#ifndef SL0PTTY_JSON_H
+#define SL0PTTY_JSON_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+typedef struct {
+  char *buf;
+  size_t len, cap;
+  bool need_comma;
+} json_t;
+
+void json_init(json_t *j);
+void json_free(json_t *j);
+
+void json_obj_open(json_t *j, const char *key);  /* key may be NULL in arrays */
+void json_obj_close(json_t *j);
+void json_arr_open(json_t *j, const char *key);
+void json_arr_close(json_t *j);
+
+void json_str(json_t *j, const char *key, const char *val, size_t len);
+void json_int(json_t *j, const char *key, long long val);
+void json_bool(json_t *j, const char *key, bool val);
+void json_null(json_t *j, const char *key);
+
+#endif /* SL0PTTY_JSON_H */