iris: run-headless.sh --bin, for screenshotting a real binary not just an example

desktop-app (RUST.md's E4) is a real crate binary a person runs, not a
demo under examples/, and it needs its own argv (--ca, --link) to start
at all -- neither of which the script had a way to express. --bin swaps
`cargo build --example`/`target/debug/examples/NAME` for the `--bin`
equivalents; $RUN_HEADLESS_ARGS is word-split into the launched binary's
own argv, since no example ever needed one before.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

iris/run-headless.sh

@@ -4,6 +4,16 @@
 #   ./run-headless.sh tabs [-- cargo args]
 #   ./run-headless.sh tabs --shot /tmp/tabs.png --seconds 4
 #
+# `--bin` runs a real crate binary instead of an example (E4's
+# `desktop-app`, which is a window a person runs, not a demo) --
+# `cargo build --bin NAME` instead of `--example NAME`, and
+# `target/debug/NAME` instead of `target/debug/examples/NAME`. Its own
+# argv (the CLI flags a real binary takes, as opposed to `cargo build`'s
+# own flags after `--`) comes through `$RUN_HEADLESS_ARGS`, word-split on
+# purpose -- an example never needed one, so there was nowhere to plumb it
+# through positionally without disturbing the existing `-- cargo args`
+# convention above.
+#
 # The VM has a virtio-gpu render node (Vulkan 1.4 through Venus, GL 4.6
 # through virgl), so wgpu runs on the host's real GPU -- what is missing is
 # only a compositor to give winit a surface. So: a headless sway, the same
@@ -20,16 +30,18 @@ run="${XDG_RUNTIME_DIR:-/tmp}/iris-headless"
 seconds=3
 shot=""
 example=""
+kind=example
 
 while [ $# -gt 0 ]; do
     case "$1" in
         --shot) shot=$2; shift 2 ;;
         --seconds) seconds=$2; shift 2 ;;
+        --bin) kind=bin; shift ;;
         --) shift; break ;;
         *) example=$1; shift ;;
     esac
 done
-[ -n "$example" ] || { echo "usage: $0 EXAMPLE [--shot PNG] [--seconds N] [-- cargo args]" >&2; exit 2; }
+[ -n "$example" ] || { echo "usage: $0 NAME [--bin] [--shot PNG] [--seconds N] [-- cargo args]" >&2; exit 2; }
 
 mkdir -p "$run"
 export SWAYSOCK="$run/sway.sock"
@@ -67,10 +79,17 @@ export WAYLAND_DISPLAY
 echo "run-headless: $WAYLAND_DISPLAY (sway $(swaymsg -t get_version --raw | sed -n 's/.*"human_readable":"\([^"]*\)".*/\1/p'))" >&2
 
 cd "$here"
+if [ "$kind" = bin ]; then
+    cargo build --bin "$example" "$@" >&2
+    bin="$here/target/debug/$example"
+else
     cargo build --example "$example" "$@" >&2
     bin="$here/target/debug/examples/$example"
+fi
 
-"$bin" >"$run/$example.log" 2>&1 &
+# shellcheck disable=SC2086 -- deliberately word-split: this is the
+# binary's own argv, not a single path.
+"$bin" ${RUN_HEADLESS_ARGS:-} >"$run/$example.log" 2>&1 &
 pid=$!
 trap 'kill "$pid" 2>/dev/null || true' EXIT INT TERM