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, 111 insertions, 0 deletions

diff --git a/src/json.c b/src/json.c
new file mode 100644
index 0000000..efbe120
--- /dev/null
+++ b/src/json.c
@@ -0,0 +1,111 @@
+#define _GNU_SOURCE
+#include "json.h"
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+static void reserve(json_t *j, size_t n) {
+  if (j->len + n <= j->cap) return;
+  size_t cap = j->cap ? j->cap : 4096;
+  while (cap < j->len + n) cap *= 2;
+  j->buf = realloc(j->buf, cap);
+  j->cap = cap;
+}
+
+static void raw(json_t *j, const char *s, size_t n) {
+  reserve(j, n + 1);
+  memcpy(j->buf + j->len, s, n);
+  j->len += n;
+  j->buf[j->len] = 0;
+}
+
+static void rawz(json_t *j, const char *s) { raw(j, s, strlen(s)); }
+
+void json_init(json_t *j) {
+  memset(j, 0, sizeof *j);
+  reserve(j, 4096);
+  j->buf[0] = 0;
+}
+
+void json_free(json_t *j) {
+  free(j->buf);
+  memset(j, 0, sizeof *j);
+}
+
+static void sep(json_t *j, const char *key) {
+  if (j->need_comma) rawz(j, ",");
+  if (key) {
+    rawz(j, "\"");
+    rawz(j, key);
+    rawz(j, "\":");
+  }
+  j->need_comma = true;
+}
+
+static void escaped(json_t *j, const char *s, size_t len) {
+  rawz(j, "\"");
+  for (size_t i = 0; i < len; i++) {
+    unsigned char c = (unsigned char)s[i];
+    switch (c) {
+      case '"': rawz(j, "\\\""); break;
+      case '\\': rawz(j, "\\\\"); break;
+      case '\n': rawz(j, "\\n"); break;
+      case '\r': rawz(j, "\\r"); break;
+      case '\t': rawz(j, "\\t"); break;
+      default:
+        if (c < 0x20) {
+          char b[8];
+          snprintf(b, sizeof b, "\\u%04x", c);
+          rawz(j, b);
+        } else {
+          raw(j, (const char *)&c, 1); /* UTF-8 passes through */
+        }
+    }
+  }
+  rawz(j, "\"");
+}
+
+void json_obj_open(json_t *j, const char *key) {
+  sep(j, key);
+  rawz(j, "{");
+  j->need_comma = false;
+}
+
+void json_obj_close(json_t *j) {
+  rawz(j, "}");
+  j->need_comma = true;
+}
+
+void json_arr_open(json_t *j, const char *key) {
+  sep(j, key);
+  rawz(j, "[");
+  j->need_comma = false;
+}
+
+void json_arr_close(json_t *j) {
+  rawz(j, "]");
+  j->need_comma = true;
+}
+
+void json_str(json_t *j, const char *key, const char *val, size_t len) {
+  sep(j, key);
+  escaped(j, val, len);
+}
+
+void json_int(json_t *j, const char *key, long long val) {
+  sep(j, key);
+  char b[32];
+  snprintf(b, sizeof b, "%lld", val);
+  rawz(j, b);
+}
+
+void json_bool(json_t *j, const char *key, bool val) {
+  sep(j, key);
+  rawz(j, val ? "true" : "false");
+}
+
+void json_null(json_t *j, const char *key) {
+  sep(j, key);
+  rawz(j, "null");
+}