feat(blog): nested categories via parentSlug

[aka-sacci-ccr]

Context

Blog categories were flat. Category had no way to say it belongs under another one, so a site could not express Recipes > Desserts, and the listing filter was an exact slug match.

Model

Category.parentSlug?: string — one field, no new records, no nested object in the decofile (which would allow literal recursion in the JSON).

Chosen over a children: string[] array because the breadcrumb needs a parent walk either way, and only a parent ref makes the trail unambiguous: a child has exactly one parent, and editing a child never touches the parent's record.

Guards

Categories come from a decofile a human edits, so parentSlug may point at nothing, at itself, or around a cycle. All graph logic lives in one module, blog/core/categoryTree.ts, and every walk is bounded twice — by a visited Set and by MAX_CATEGORY_DEPTH (4). A malformed record truncates the chain instead of throwing or hanging a request.

Covered by blog/tests/categoryTree.test.ts: cycle, self-reference, dangling parent, over-deep chain, duplicated slugs, descendant walk over a cycle.

Behaviour

• BlogpostListing / BlogpostList accept a category path ("parent/child") and expand the leaf into its whole subtree, so a parent lists its children's posts.
• BlogpostListing returns categoryPath, BlogPostPage returns categories — both the ancestor chain, root first, for the UI breadcrumb.
• Canonical URLs are rewritten with the real chain. A request reaching a child through a stale or wrong path still renders and points at the one canonical URL, so Google consolidates rather than 404ing or seeing duplicates.
• GetCategories gains parentSlug to list direct children (menus).

SEO

blog/utils/jsonLD.ts is unchanged. It already derives crumbs from the pathname and resolves names by slug; now that the canonical carries the full chain and SeoBlogPost passes the ancestor chain, the breadcrumb comes out Blog > Parent > Child > Post with sequential position and only the last item without item. articleSection untouched.

Incidental cleanup

filterPostsByCategory now takes a slug or a list of them. That makes filterRelatedPosts an alias and removes the Array.isArray branch of filterPosts — net negative diff, and the list case gains term filtering for free. loadCategoryBySlug, which re-read the whole collection a second time, is gone.

Required on the site side

Route the listing as a catch-all (/blog/:category*, post /blog/:category*/:slug) for subcategory URLs to match. mod.ts documents it and Template.tsx already builds the preview URL with the full path.

Verification

deno test -A blog/tests/ — 44 passed. deno task check clean.

End to end: create parent and child (parentSlug: "parent"), publish a post in child, then check (a) /blog/parent lists the child's post, (b) /blog/parent/child has its own canonical, (c) the post's JSON-LD BreadcrumbList has 4 items in order.

🤖 Generated with Claude Code

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Summary by cubic

Adds Category.parentSlug so blog categories can nest ("Recipes > Desserts" instead of flat), and makes category listings accept a full path (parent/child) and expand into the subtree. All category-graph logic is in one module, blog/core/categoryTree.ts, with walks bounded by a visited set and a depth ceiling — cycles, self-references, and dangling parents truncate instead of hanging.

Behavior

• BlogpostListing and BlogpostList expand a category path into the leaf's whole subtree, so a parent lists its children's posts.
• Canonical URLs are rewritten with the real ancestor chain; a request through a stale or wrong path still renders and points at the one canonical URL instead of 404ing or duplicating.
• BlogpostListing returns categoryPath and BlogPostPage returns categories (the ancestor chain, root first) for breadcrumbs; JSON-LD breadcrumbs are unaffected.
• GetCategories gains parentSlug to list direct children.
• filterPostsByCategory now accepts a slug or slug list; filterRelatedPosts becomes an alias and list filtering gains term filtering for free.

Migration

• Route the listing as a catch-all: /blog/:category* and /blog/:category*/:slug.

^{Written for commit 2cc3c46. Summary will update on new commits.}

[github-actions]

Tagging Options

Should a new tag be published when this PR is merged?

• 👍 for Patch 0.163.1 update
• 🎉 for Minor 0.164.0 update
• 🚀 for Major 1.0.0 update

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Reviewing files that changed from the base of the PR and between d2a310e and 2cc3c46.

📒 Files selected for processing (12)

• blog/core/categoryTree.ts
• blog/core/handlePosts.ts
• blog/loaders/BlogPostPage.ts
• blog/loaders/BlogpostList.ts
• blog/loaders/BlogpostListing.ts
• blog/loaders/GetCategories.ts
• blog/mod.ts
• blog/sections/Seo/SeoBlogPost.tsx
• blog/sections/Template.tsx
• blog/tests/categoryTree.test.ts
• blog/tests/handlePosts.test.ts
• blog/types.ts

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