feat(examples/plugins/seo): worked SEO plugin proving the runtime end-to-end — closes #269

[tayebmokni]

Summary

• examples/plugins/seo/ — a TinyGo-built plugin that ships manifest.json (apiVersion gonext.io/v1), four exported ABI symbols (gn_alloc, gn_free, gn_handle_hook, gn_handle_job), and a build script. Subscribes to the_content (filter, injects schema.org JSON-LD), wp_head (action, emits <title> + <meta> + OpenGraph + Twitter card), and save_post (action, computes SEO score). Owns one background job (seo.recompute-scores).
• domain.go — pure Go helpers (BuildTitle, BuildDescription, BuildHeadHTML, BuildJSONLD, ComputeSEOScore) split out so the test suite exercises the same code the WASM blob links — no TinyGo required to run go test.
• dummy_host_test.go — Go-side fake host bus that mirrors the wazero dispatcher path, proving the wire format the plugin speaks matches what packages/go/plugins/abi/hooks/marshal.go produces. Canonical copy at packages/go/plugins/internal/_seo_dummy.go (leading underscore so Go skips it for builds; doc-only).
• seo_test.go — manifest validates against packages/go/plugins/manifest/schema.json; unit tests for all domain functions; HTML escaping; JSON-LD parses + carries Article required fields; pinned-score table; end-to-end filter run.
• docs/04-seo-plugin-tutorial.md — a 30-minute "build this plugin from scratch" walkthrough that mirrors the implementation file by file.
• go.work — adds ./examples/plugins/seo so the example builds alongside the workspace; the example has its own go.mod so TinyGo doesn't drag in the host's Postgres/Redis/Asynq deps.

Capability rationale (the plugin uses every plumbed capability so the install dialog has a real-world cap list to render):

Capability	Why it's needed
posts.read	Read the post being saved when computing the SEO score.
posts.write	Persist score to _seo_score post meta (via host call).
hooks.subscribe	Required to register the three hook subscriptions.
jobs.enqueue	Required to enqueue seo.recompute-scores.

Test plan

• go test -race -count=1 ./examples/plugins/seo/... — 14 tests pass (manifest schema, unit tests, JSON-LD validity, score table, end-to-end filter)
• cd packages/go && go test -race -count=1 ./plugins/lifecycle/... ./plugins/abi/hooks/... — pass (runtime regression check per the brief)
• cd packages/go && go test -race -count=1 ./plugins/manifest/... — pass
• bash examples/plugins/seo/build.sh — exits with a helpful "tinygo not on PATH" message when toolchain missing; README documents the install URL
• Manual: install TinyGo, run ./build.sh, pack into seo.gnplugin via zip -j seo.gnplugin manifest.json seo.wasm, install + activate via the lifecycle Manager (deferred — requires the admin install dialog from feat(plugins/runtime): wazero-backed WASM runtime foundation (#6) #350)

🤖 Generated with Claude Code