Frontend asset `attrs` silently drops `type`, `rel` and `href`, so JSON-LD and the documented `<link>` example cannot be emitted

[asachs01]

FrontendAsset.attrs is documented as the escape hatch for extra attributes, and names type first (src/core/plugin-sdk/types/frontend.ts:49):

/** Extra attributes (e.g. `type`, `crossorigin`, `integrity`, `data-*`). */
attrs?: Record<string, string>

formatAttrs silently drops four things that are not host-owned in the general case (server/publish/frontendInjections.ts:279-291):

const RESERVED = new Set(['src', 'href', 'rel', 'data-plugin-id', 'defer', 'async', 'type'])

The comment directly above it (:281-283) explains only src, href and data-plugin-id. rel, defer, async and type are not mentioned. git log --all -S"RESERVED = new Set" returns exactly one commit (a0ca2275d), so the list has never been revised since it landed. crossorigin, integrity, id and data-* do survive, so three of the doc comment's four examples work and only type does not.

Two things this breaks.

1. JSON-LD cannot be emitted at all.

strategy is the only route to a type (frontendInjections.ts:260-271), it exists only on kind: 'script' (frontend.ts:48), and its one type-bearing value is module. kind: 'script-inline' has no strategy field and its manifest schema is additionalProperties: false (src/core/plugins/manifest.ts:322-327), so declaring one is a validation error. That leaves no route to type for an inline script:

{
  kind: 'script-inline',
  placement: 'head-end',
  attrs: { type: 'application/ld+json' },
  content: '{"@context":"https://schema.org","@type":"Article"}',
}

emits (frontendInjections.ts:188-197):

<script data-plugin-id="<id>">{"@context":"https://schema.org","@type":"Article"}</script>

The browser parses the body as classic JavaScript and throws a SyntaxError on every published page, and no crawler reads the structured data. frontend.ts:21-22 names JSON-LD as an intended head-end payload, so the SDK advertises a use case its emitter cannot produce. The tag also flips hasInlineScript (frontendInjections.ts:146-147), which relaxes the page CSP to script-src 'self' 'unsafe-inline' (:373-380) — paid for a tag that was never meant to execute.

2. The documented <link> example emits an empty tag.

docs/features/plugin-system.md:613:

{ "kind": "link", "attrs": { "rel": "preconnect", "href": "https://cdn.example.com" } }

rel and href are both reserved, and the kind: 'link' branch (frontendInjections.ts:220-227) passes the whole bag through formatAttrs and adds nothing back, so the page gets:

<link data-plugin-id="<id>">

That is the only <link> example in the tree — no plugin under examples/ declares frontend.assets.

Suggested fix: reserve per kind instead of globally. src is host-owned on script, href and rel on link, and type only when strategy: 'module' was chosen — for every other strategy the host emits no type and the slot is free. Passing the kind (and the resolved strategy) into formatAttrs and reserving against a per-kind set would fix both cases without letting an author overwrite a tag the host actually owns.

Nothing currently pins the behaviour either way: formatAttrs and renderAsset are module-private, and src/__tests__/publisher/frontendInjections.test.ts exercises only CSP relaxation through injectFrontendAssets.

Happy to send a PR if the per-kind shape looks right to you.

Verified at 6b055cf7 (v0.0.16-3).