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, 19 insertions, 0 deletions

diff --git a/tests/expr_test.c b/tests/expr_test.c
index 19968d1..4745ca3 100644
--- a/tests/expr_test.c
+++ b/tests/expr_test.c
@@ -286,6 +286,25 @@ int main(void) {
   refused("a ternary without its colon", "1 ? 2");
   refused("something that is not an expression at all", "@@@");
 
+  printf("\n-- the source survives compilation\n");
+  {
+    /* The dump has to write back the line somebody wrote: bytecode cannot be
+     * un-compiled, so the program keeps its text. Byte for byte, including a
+     * constant expression -- folding must not eat the spelling. */
+    const char *src = "(y % 2) * 40";
+    char err[128] = {0};
+    expr_prog_t *p = expr_compile(src, err, sizeof err);
+    ok("a program remembers its source",
+       p && expr_source(p) && strcmp(expr_source(p), src) == 0,
+       p ? expr_source(p) : err);
+    if (p) expr_free(p);
+    p = expr_compile("1 + 2", err, sizeof err);
+    ok("even one that folded to a constant",
+       p && expr_source(p) && strcmp(expr_source(p), "1 + 2") == 0,
+       p ? expr_source(p) : err);
+    if (p) expr_free(p);
+  }
+
   printf("\n-- totality: there is no loop to write\n");
   {
     /* The language has no way to express unbounded work, so this is a