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, 68 insertions, 0 deletions

diff --git a/include/proto.h b/include/proto.h
new file mode 100644
index 0000000..e6cd42c
--- /dev/null
+++ b/include/proto.h
@@ -0,0 +1,68 @@
+/* The client/server wire, and where sessions live.
+ *
+ * Frames are `u8 type, u32 length (big endian), payload`. Deliberately dull:
+ * the interesting protocol is the JSON control channel (M3) that rides on
+ * MSG_CMD, and it speaks the same vocabulary as the headless driver.
+ */
+#ifndef SLOSH_PROTO_H
+#define SLOSH_PROTO_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+/* MSG_HELLO and MSG_RESIZE carry u16 cols, u16 rows, and since the graphics
+ * fix two more: u16 cell_w, u16 cell_h, the client's cell size in pixels.
+ * A four-byte payload is still accepted and means "I did not say", which is
+ * what an older client sends and what a terminal that reports no pixel size
+ * leads to. */
+enum {
+  MSG_HELLO = 1,  /* client -> server: u16 cols, rows[, cell_w, cell_h] */
+  MSG_INPUT = 2,  /* client -> server: raw bytes from the terminal */
+  MSG_RESIZE = 3, /* client -> server: u16 cols, rows[, cell_w, cell_h] */
+  MSG_DETACH = 4, /* client -> server: leave, but keep running */
+  MSG_OUTPUT = 5, /* server -> client: bytes for the terminal */
+  MSG_EXIT = 6,   /* server -> client: u8 reason */
+  MSG_CMD = 7,    /* client -> server: one JSON line */
+  MSG_REPLY = 8,  /* server -> client: one JSON line */
+};
+
+enum {
+  EXIT_SESSION_ENDED = 0, /* the last pane closed */
+  EXIT_DETACHED = 1,      /* the user detached */
+  EXIT_REPLACED = 2,      /* another client attached */
+};
+
+typedef struct {
+  uint8_t type;
+  uint8_t *data;
+  uint32_t len;
+} msg_t;
+
+/* Incremental framing: feed bytes, take whole messages out. */
+typedef struct {
+  uint8_t *buf;
+  size_t len, cap;
+  uint8_t *msg; /* the payload handed to the caller, lifted out of buf */
+  size_t msg_cap;
+} msg_reader_t;
+
+void msg_reader_init(msg_reader_t *r);
+void msg_reader_free(msg_reader_t *r);
+void msg_reader_feed(msg_reader_t *r, const uint8_t *data, size_t len);
+/* Returns true and fills `out` (data points into the reader's buffer, valid
+ * until the next call) when a whole message is available. */
+bool msg_reader_next(msg_reader_t *r, msg_t *out);
+
+/* Blocking send of one frame. Returns 0 on success, -1 if the peer is gone. */
+int msg_send(int fd, uint8_t type, const void *data, size_t len);
+
+/* $XDG_RUNTIME_DIR/slosh/<name>.sock, or /tmp/slosh-<uid>/<name>.sock.
+ * Creates the directory (0700). Returns 0 on success. */
+int session_socket_path(const char *name, char *out, size_t cap);
+int session_log_path(const char *name, char *out, size_t cap);
+/* Names of live sessions (sockets that answer). Caller frees each and the
+ * array. Returns the count. */
+size_t session_list(char ***out_names);
+
+#endif /* SLOSH_PROTO_H */