fix: vue-seo-layer as a peer dependency

pnpm refuses a git dependency inside another package by default
(blockExoticSubdeps), so an app could not install v0.8.0. vue-seo-layer
is now a peer dependency (^0.2.0) and a development dependency pinned
to v0.2.0; apps list vue-seo-layer#v0.2.0 next to the layer.

scripts/check-git-install.sh

@@ -5,7 +5,8 @@
 #
 # Proves the layer's distribution end to end: a scratch app installs
 # vue-journal-layer from git+https://git.golem15.com/golem15/vue-journal-layer.git#<tag>
-# anonymously, the installed package.json has no local dependency, the
+# anonymously, next to vue-seo-layer (a peer dependency, listed by the app at
+# the tag's devDependencies pin) with pnpm's default settings, the installed package.json has no local dependency, the
 # lockfile pins the tag's commit, `nuxt build` of the layer's playground
 # config succeeds, and the built server passes testing/expect-acme.txt
 # against the fixture API.
@@ -144,20 +145,36 @@ TAG_SHA="$(awk -v ref="refs/tags/$TAG^{}" '$2 == ref { print $1 }' <<<"$REMOTE_R
 [[ -n "$TAG_SHA" ]] || TAG_SHA="$(awk -v ref="refs/tags/$TAG" '$2 == ref { print $1 }' <<<"$REMOTE_REFS")"
 [[ -n "$TAG_SHA" ]] || die "tag $TAG not found on $REPO_URL"
 
+# vue-seo-layer is a peer dependency of the layer, so an app lists it next to
+# the layer, as the README's Installation says. The scratch app takes the
+# spec the tag pins for its own development (devDependencies), or
+# SEO_LAYER_SPEC when set. A tag that still lists vue-seo-layer under
+# dependencies (v0.8.0) gets none: pnpm then refuses it as an exotic
+# subdependency, which is what this check is for.
+SEO_SPEC="${SEO_LAYER_SPEC:-}"
+if [[ -z "$SEO_SPEC" ]]; then
+  SRC="$(mktemp -d "${TMPDIR:-/tmp}/journal-git-install-src.XXXXXX")"
+  GIT_TERMINAL_PROMPT=0 git clone --quiet --depth 1 --branch "$TAG" "$REPO_URL" "$SRC/layer" 2>/dev/null \
+    || { rm -rf "$SRC"; die "git clone of $TAG failed"; }
+  SEO_SPEC="$(node -e '
+    const pkg = JSON.parse(require("node:fs").readFileSync(process.argv[1], "utf8"))
+    const peer = (pkg.peerDependencies || {})["vue-seo-layer"]
+    const dev = (pkg.devDependencies || {})["vue-seo-layer"]
+    process.stdout.write(peer && dev ? dev : "")
+  ' "$SRC/layer/package.json")" || { rm -rf "$SRC"; die "cannot read the tag's package.json"; }
+  rm -rf "$SRC"
+fi
+
 cd "$WORK"
 
-cat >package.json <<JSON
-{
-  "name": "acme-blog",
-  "private": true,
-  "type": "module",
-  "dependencies": {
-    "nuxt": "4.4.8",
-    "vue": "3.5.35",
-    "vue-journal-layer": "git+$REPO_URL#$TAG"
-  }
-}
-JSON
+node -e '
+  const [repo, tag, seo] = process.argv.slice(1)
+  const deps = { nuxt: "4.4.8", vue: "3.5.35" }
+  if (seo) deps["vue-seo-layer"] = seo
+  deps["vue-journal-layer"] = `git+${repo}#${tag}`
+  const pkg = { name: "acme-blog", private: true, type: "module", dependencies: deps }
+  require("node:fs").writeFileSync("package.json", JSON.stringify(pkg, null, 2) + "\n")
+' "$REPO_URL" "$TAG" "$SEO_SPEC"
 
 cat >pnpm-workspace.yaml <<'YAML'
 allowBuilds: