macOS CI: build from the dev clone's engines, never from scratch past the 3h runner limit (L1.8)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/scripts/ci-share.sh

@@ -0,0 +1,52 @@
+#!/usr/bin/env bash
+# ci.sh uses shared engines only through links to them.
+set -euo pipefail
+
+root=$(cd "$(dirname "$0")/../.." && pwd)
+fail() {
+  echo "FAIL: $*" >&2
+  exit 1
+}
+work=$(mktemp -d)
+trap 'rm -rf "$work"' EXIT
+share=$work/share
+mkdir -p "$share/engines" "$share/reference" "$share/engines"$'\n' "$share/reference"$'\n' "$work/elsewhere"
+version=$(awk -F'"' '/^version = / { print $2; exit }' "$root/Cargo.toml")
+# A macOS clone whose packaging stub stops before any upload.
+attempt() { # name, setup; sets status, writes the output
+  local clone=$work/$1
+  mkdir -p "$clone/scripts" "$clone/packaging/macos"
+  cp "$root/scripts/ci.sh" "$clone/scripts/"
+  printf '#!/usr/bin/env bash\necho "packaging reached"\nexit 1\n' >"$clone/packaging/macos/release.sh"
+  chmod +x "$clone/packaging/macos/release.sh"
+  cp "$root/Cargo.toml" "$clone/"
+  cp "$root/packaging/apps.tsv" "$clone/packaging/"
+  (cd "$clone" && eval "$2")
+  status=0
+  ELY_SHARE=$share ELY_RELEASE_TOKEN=unused "$clone/scripts/ci.sh" macos "v$version" >"$work/$1.out" 2>&1 ||
+    status=$?
+}
+# The target as stored plus a newline and x.
+target() { readlink "$1" && printf x; }
+passes() { # name, setup; reaches the release step
+  attempt "$1" "$2"
+  grep -q 'packaging reached' "$work/$1.out" || fail "$1 was refused: $(cat "$work/$1.out")"
+  for part in engines reference; do
+    [ "$(target "$work/$1/$part")" = "$share/$part"$'\n'x ] || fail "$1 has no $part link to $share/$part"
+  done
+}
+refused() { # name, setup; stopped before the release step
+  attempt "$1" "$2"
+  [ "$status" -ne 0 ] || fail "$1 exited 0"
+  grep -q 'is not a link to' "$work/$1.out" || fail "$1 was let through: $(cat "$work/$1.out")"
+  ! grep -q 'packaging reached' "$work/$1.out" || fail "$1 reached the release step"
+}
+passes absent ':'
+passes linked 'ln -s "$share/engines" engines && ln -s "$share/reference" reference'
+for part in engines reference; do
+  refused "built-$part" "mkdir $part"
+  refused "elsewhere-$part" "ln -s \"\$work/elsewhere\" $part"
+  refused "newline-$part" "ln -s \"\$share/$part\"\$'\\n' $part"
+  refused "dangling-$part" "ln -s \"\$work/gone\" $part"
+done
+echo "ci-share: links pass; own builds, other and newline targets refused"