shaders: -Dprebuilt-shaders, so a gui build needs no Vulkan SDK

glslc is the one build input that wants a tool a stock machine does not have,
and it is also the input that changes least often: eight GLSL files that have
outlived several rewrites of everything around them. Asking every machine that
wants to run the SDL shell for shaderc is the wrong trade.

The SPIR-V is now COMMITTED, under shaders/prebuilt/, and -Dprebuilt-shaders
embeds that copy instead of shelling out. The default stays the honest one --
compile the shaders that are actually in the tree -- because the flag trades a
dependency for a freshness problem: with it on, the .glsl sources are not build
inputs at all, so editing one changes nothing.

`zig build shaders` is the other half, and it is deliberately independent of
-Dplatform: it recompiles every shader and writes the result back into the
tracked directory, so whoever changes a shader refreshes the cache on a machine
that has the compiler and commits the diff. `jj diff shaders/prebuilt` after it
is the freshness check -- empty means the cache was already current.

The shader list is also spelled once now (gui_shaders): the eight embeds, the
eight glslc runs and the refresh step all read it, so adding a shader is a name
there plus the @embedFile in gui.zig, not three edits in two places.

Verified: -Dplatform=gui -Dprebuilt-shaders builds with glslc absent from PATH,
and image-harness passes on that binary -- real SDL GPU pipelines built from the
committed SPIR-V, 512 source pixels read back. The default gui build still runs
the eight glslc steps; tty runs none. The committed bytes are identical to a
fresh glslc run, and `zig build shaders` is idempotent.

1 files changed, 13 insertions, 13 deletions

diff --git a/test/snapshots/fsearch.snap b/test/snapshots/fsearch.snap
index b9b7ddf4..3752909b 100644
--- a/test/snapshots/fsearch.snap
+++ b/test/snapshots/fsearch.snap
@@ -1,11 +1,13 @@
 # `/` file search: the pattern types into the tag (persistent, no popup);
 # Enter searches the buffer in-core and writes `path:LINE:COL-ENDCOL text` into
 # a +Search OUTPUT BUFFER (a file pane with no file behind it — no Save in its
-# tag); n/N SELECT the next/prev row there and open nothing, and Enter — the
-# look chord — is what scrolls the file pane to the hit AND SELECTS IT: the row
-# names the match's whole span, not just where it starts. Esc abandons the
-# input; a no-match search opens an EMPTY buffer (every search gets its own,
-# stacked under the pane) with nothing in it for n to stop on.
+# tag) — AND GOES TO THE FIRST HIT, which is the step `n` is and the look Enter
+# is, run for you in that buffer. From there n/N SELECT the next/prev row and
+# open nothing, and Enter — the look chord — is what scrolls the file pane to
+# the hit AND SELECTS IT: the row names the match's whole span, not just where
+# it starts. Esc abandons the input; a no-match search opens an EMPTY buffer
+# (every search gets its own, stacked under the pane) with nothing in it for n
+# to stop on, and goes nowhere.
 file g.txt l1\nMARK a\nl3\nl4\nl5\nMARK b\nl7\nl8\nl9\nMARK c\nl11\nl12
 start 30 180 -n 3
 wait 8000 g.txt
@@ -33,15 +35,13 @@ snap typing
 key enter
 wait 10000 g.txt:2:1-4 MARK
 stable 700 10000
+# ...and the submit already looked result 1: the file scrolled to line 2 and
+# the four cells the pattern matched there came up selected — the styles below
+# are what prove the second half of that. No `n` was pressed to get here.
 snap results
-# n selects result 1 and Enter looks it: the file scrolls to line 2 and the
-# four cells the pattern matched there come up selected — the styles below are
-# what prove the second half of that
-key n
-key enter
-stable 700 15000
-snap first
-snapstyle first
+snapstyle results
+# n/N walk on from there, one row of the list per press, Enter looking what
+# the step selected
 key n
 key enter
 stable 700 15000