slosh: defaults most people can live in, said by shaders

The out-of-the-box look, rethought as one piece:

- the compiled-in palette calms down: muted blue #7aa2f7 on the same
  neutral darks, with the colours that mean something kept semantic --
  amber bell, red-orange dead. sl0p stays one include away as the house
  style, and contrib/themes/default.kdl is the starting point written
  down (theme-tour shows it).

- derived state defaults now actually follow the theme: the scrolled
  wash is rebuilt from scroll_bg after the theme block (it used to bake
  the compiled accent), and declaring a state -- in any file of an
  include chain -- still wins. The dump writes derived states as
  comments so C-a e cannot pin what is meant to keep following.

- a bell you can see: the frame blinks three times in theme's bell
  colour then breathes until answered, and a soft diagonal shimmer --
  the bell colour halved towards default_fg, width breathing on a sine
  -- crosses the body for the same 900ms. bell_indicator false silences
  all of it; states { bell { } } replaces it like any state. since
  carries the clock dependency, so an idle session pays nothing.

- scrollback says where it continues: while scrolled, the viewport's
  top and bottom rows melt towards an edge with content past it and
  turn solid at the buffer's end. New expression variables above/below
  (lines hidden past each edge, own dependency bit, cached per scroll
  position), carried in shade_ctx_t -- SLOSH_SHADER_ABI 3 -> 4.

- expressions survive the dump: a program keeps its source and cb_chain
  writes it back, so amount="(y % 2) * 40" no longer dumps as a number.

- headers move to include/, -Iinclude everywhere; the plugin Makefile's
  SLOSH var becomes SLOSH_DIR because slosh exports SLOSH=1 into every
  pane it runs, and building from inside a session read that as a path.

- comment drift culled where features outran the prose, and the
  derivation boilerplate folded into derived_pass()/ctx_scroll().

1 files changed, 94 insertions, 0 deletions

diff --git a/include/input.h b/include/input.h
new file mode 100644
index 0000000..adda27a
--- /dev/null
+++ b/include/input.h
@@ -0,0 +1,94 @@
+/* Input decoding: the bytes the *outer* terminal sends us -> semantic events.
+ *
+ * libghostty-vt encodes events outward to a pane, but nothing decodes inward,
+ * so this half is ours (DESIGN.md). Decoding to a semantic event and
+ * re-encoding per pane against that pane's own modes is what makes kitty
+ * keyboard passthrough correct instead of approximate.
+ *
+ * The event carries GhosttyKey / GHOSTTY_MODS_* values as plain integers so
+ * this header stays free of libghostty-vt.
+ */
+#ifndef SLOSH_INPUT_H
+#define SLOSH_INPUT_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+typedef enum {
+  EV_NONE = 0,
+  EV_KEY,
+  EV_MOUSE,
+  EV_PASTE,
+  EV_FOCUS,
+} ev_kind_t;
+
+/* mirrors GhosttyKeyAction */
+enum { KEY_RELEASE = 0, KEY_PRESS = 1, KEY_REPEAT = 2 };
+/* mirrors GhosttyMouseAction */
+enum { MOUSE_PRESS = 0, MOUSE_RELEASE = 1, MOUSE_MOTION = 2 };
+/* mirrors GhosttyMouseButton */
+enum {
+  MBTN_UNKNOWN = 0,
+  MBTN_LEFT = 1,
+  MBTN_RIGHT = 2,
+  MBTN_MIDDLE = 3,
+  MBTN_FOUR = 4,
+  MBTN_FIVE = 5,
+  MBTN_SIX = 6,
+  MBTN_SEVEN = 7,
+};
+/* mirrors GHOSTTY_MODS_* */
+enum {
+  MOD_SHIFT = 1 << 0,
+  MOD_CTRL = 1 << 1,
+  MOD_ALT = 1 << 2,
+  MOD_SUPER = 1 << 3,
+  MOD_CAPS = 1 << 4,
+  MOD_NUM = 1 << 5,
+};
+
+typedef struct {
+  ev_kind_t kind;
+
+  /* EV_KEY */
+  int key;        /* GhosttyKey */
+  uint16_t mods;  /* MOD_* */
+  uint8_t action; /* KEY_* */
+  char text[16];  /* UTF-8 the key produced, if any */
+  uint8_t text_len;
+  uint32_t unshifted; /* unshifted codepoint, 0 if unknown */
+
+  /* EV_MOUSE */
+  uint8_t button;  /* MBTN_* */
+  uint8_t maction; /* MOUSE_* */
+  uint16_t mx, my; /* 0-indexed cell coordinates */
+
+  /* EV_PASTE */
+  const char *paste;
+  size_t paste_len;
+
+  /* EV_FOCUS */
+  bool focused;
+} input_event_t;
+
+typedef struct input_parser input_parser_t;
+typedef void (*input_cb_t)(const input_event_t *ev, void *ud);
+
+input_parser_t *input_new(void);
+void input_free(input_parser_t *p);
+
+/* Feed bytes; complete events are dispatched to cb. Partial sequences are
+ * retained for the next call, so split reads are safe. */
+void input_feed(input_parser_t *p, const uint8_t *data, size_t len,
+                input_cb_t cb, void *ud);
+
+/* True when a bare ESC (or an unterminated sequence) is buffered. Call
+ * input_timeout() after ~50ms of quiet to resolve it as the Escape key. */
+bool input_pending(const input_parser_t *p);
+void input_timeout(input_parser_t *p, input_cb_t cb, void *ud);
+
+/* Debug/test rendering of an event, e.g. "key ARROW_UP mods=CTRL press". */
+void input_event_describe(const input_event_t *ev, char *buf, size_t cap);
+
+#endif /* SLOSH_INPUT_H */