feat: add GitHub Actions CI and support hosting under a subpath

Mirrors the GitLab pipeline — typecheck, tests, feed sanity — and adds a
Pages deploy.

Pages serves from /<repo>/, and the app used absolute asset paths, so that
job would have shipped a site that 404s on everything. Assets now resolve
against a <base href> the build substitutes, the feed URL resolves against
document.baseURI so deep links work too, and the service worker derives its
paths from its own registration scope. Root-hosted builds are unchanged.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

.github/workflows/ci.yml

@@ -0,0 +1,132 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+  workflow_dispatch:
+
+# A new push supersedes the one before it on the same ref.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+# Least privilege by default; jobs opt into more where they need it.
+permissions:
+  contents: read
+
+jobs:
+  check:
+    name: Typecheck, test, feed
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: "1.3"
+
+      - run: bun install --frozen-lockfile
+
+      - name: Typecheck
+        run: bun run typecheck
+
+      - name: Test
+        # Offline by design: no fixture is re-fetched, so a red run always means
+        # the code changed, never that a source was unreachable.
+        run: bun test
+
+      - name: Build feed
+        run: bun run build:feed
+
+      - name: Feed sanity
+        # A source that quietly stops yielding events is the failure mode a
+        # parser-only pipeline is most prone to, and nothing else surfaces it.
+        run: |
+          bun -e '
+            const feed = await Bun.file("public/data/events.v1.json").json();
+            const games = new Set(feed.events.map((e) => e.game));
+            console.log(`${feed.events.length} events across ${games.size} games`);
+            if (feed.events.length < 20) {
+              throw new Error(`feed collapsed to ${feed.events.length} events`);
+            }
+            if (feed.events.some((e) => !e.startsAt)) {
+              throw new Error("events without a start date");
+            }
+          '
+
+  build:
+    name: Build site
+    runs-on: ubuntu-latest
+    needs: check
+    steps:
+      - uses: actions/checkout@v4
+      - uses: oven-sh/setup-bun@v2
+        with:
+          bun-version: "1.3"
+      - run: bun install --frozen-lockfile
+      - name: Build
+        # Pages serves from /<repo>/, so the app is built with a matching base
+        # href. Built at the domain root it would 404 on every asset.
+        env:
+          BASE_PATH: /${{ github.event.repository.name }}/
+        run: bun run build
+      - uses: actions/upload-artifact@v4
+        with:
+          name: site
+          path: public/
+          retention-days: 7
+
+  image:
+    name: Container image
+    runs-on: ubuntu-latest
+    needs: check
+    # Pushing an image for every pull request fills the registry; do it where
+    # the artefact could actually be deployed.
+    if: github.ref == 'refs/heads/main' && github.event_name != 'pull_request'
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: docker/setup-buildx-action@v3
+
+      - uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - uses: docker/build-push-action@v6
+        with:
+          context: .
+          push: true
+          tags: |
+            ghcr.io/${{ github.repository }}:latest
+            ghcr.io/${{ github.repository }}:${{ github.sha }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+
+  pages:
+    name: Deploy to Pages
+    runs-on: ubuntu-latest
+    needs: build
+    if: github.ref == 'refs/heads/main' && github.event_name != 'pull_request'
+    permissions:
+      pages: write
+      id-token: write
+    environment:
+      name: github-pages
+      url: ${{ steps.deploy.outputs.page_url }}
+    steps:
+      - uses: actions/download-artifact@v4
+        with:
+          name: site
+          path: public
+      - uses: actions/configure-pages@v5
+      - uses: actions/upload-pages-artifact@v3
+        with:
+          path: public
+      - id: deploy
+        uses: actions/deploy-pages@v4

README.md

@@ -148,10 +148,25 @@ so iteration never re-fetches. Every event links back to its source.
 
 ## CI
 
-`.gitlab-ci.yml` runs typecheck, tests and a feed sanity check on every push, then builds and
-publishes a container image from the default branch. The feed job fails if the event count collapses
-— a source that quietly stops yielding events is the failure mode a parser-only pipeline is most
-prone to, and nothing else surfaces it.
+Both `.github/workflows/ci.yml` and `.gitlab-ci.yml` run the same gates on every push — typecheck,
+tests, and a feed sanity check — then build and publish a container image from the default branch.
+GitHub Actions additionally deploys to Pages.
+
+The feed job fails if the event count collapses. A source that quietly stops yielding events is the
+failure mode a parser-only pipeline is most prone to, and nothing else would surface it. Everything
+runs offline against checked-in fixtures, so a red pipeline always means the code changed rather
+than a wiki being down.
+
+### Hosting under a subpath
+
+Assets resolve against a `<base href>` that the build substitutes, so the app works at a domain root
+and under a subpath alike:
+
+```bash
+BASE_PATH=/gacha-event-tracker/ bun run build
+```
+
+The Pages job sets this automatically. Without it, a subpath deploy 404s on every asset.
 
 ## Licence
 

index.html

@@ -2,6 +2,7 @@
 <html lang="en">
   <head>
     <meta charset="utf-8" />
+    <base href="__BASE__" />
     <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover" />
     <title>Event Clock — gacha events by what expires next</title>
     <meta
@@ -15,13 +16,13 @@
       href="https://fonts.googleapis.com/css2?family=Chakra+Petch:wght@500;600;700&family=Public+Sans:ital,wght@0,400;0,500;0,600;1,400&display=swap"
       rel="stylesheet"
     />
-    <link rel="manifest" href="/manifest.webmanifest" />
-    <link rel="icon" href="/icon.svg" type="image/svg+xml" />
-    <link rel="apple-touch-icon" href="/icon.svg" />
-    <link rel="stylesheet" href="/styles.css" />
+    <link rel="manifest" href="manifest.webmanifest" />
+    <link rel="icon" href="icon.svg" type="image/svg+xml" />
+    <link rel="apple-touch-icon" href="icon.svg" />
+    <link rel="stylesheet" href="styles.css" />
   </head>
   <body>
     <div id="root"></div>
-    <script type="module" src="/main.js"></script>
+    <script type="module" src="main.js"></script>
   </body>
 </html>

package.json

@@ -11,7 +11,7 @@
     "build:js": "bun build src/client/main.tsx --outfile public/main.js --minify",
     "build": "bun run build:feed && bun run build:css && bun run build:js && bun run build:static",
     "dev": "bun run build && bun run serve.ts",
-    "build:static": "cp index.html public/index.html && cp src/client/sw.js public/sw.js && cp src/client/manifest.webmanifest public/manifest.webmanifest && cp src/client/icon.svg public/icon.svg",
+    "build:static": "mkdir -p public && sed \"s|__BASE__|${BASE_PATH:-/}|g\" index.html > public/index.html && cp src/client/sw.js public/sw.js && cp src/client/manifest.webmanifest public/manifest.webmanifest && cp src/client/icon.svg public/icon.svg",
     "serve": "bun run serve.ts"
   },
   "dependencies": {

src/client/api.ts

@@ -13,7 +13,10 @@ export type FeedState =
  * worse than one that asks you to reload.
  */
 export async function fetchFeed(signal?: AbortSignal): Promise<EventFeed> {
-  const res = await fetch("/data/events.v1.json", { signal: signal ?? null });
+  // Resolved against <base>, so this is correct at a domain root, under a
+  // GitHub Pages subpath, and on a deep link alike.
+  const feedUrl = new URL("data/events.v1.json", document.baseURI);
+  const res = await fetch(feedUrl, { signal: signal ?? null });
   if (!res.ok) {
     throw new Error(`Feed request failed (${res.status}).`);
   }

src/client/main.tsx

@@ -15,7 +15,8 @@ createRoot(root).render(
 // guarded because file:// and older browsers have no service worker at all.
 if ("serviceWorker" in navigator && location.protocol.startsWith("http")) {
   window.addEventListener("load", () => {
-    void navigator.serviceWorker.register("/sw.js").catch(() => {
+    const swUrl = new URL("sw.js", document.baseURI);
+    void navigator.serviceWorker.register(swUrl).catch(() => {
       // An unavailable worker costs offline support, nothing else. The app
       // works exactly as before.
     });

src/client/manifest.webmanifest

@@ -2,15 +2,15 @@
   "name": "Event Clock",
   "short_name": "Event Clock",
   "description": "Live and upcoming gacha events, sorted by what expires next.",
-  "start_url": "/",
-  "scope": "/",
+  "start_url": "./",
+  "scope": "./",
   "display": "standalone",
   "background_color": "#12141c",
   "theme_color": "#12141c",
   "orientation": "portrait-primary",
   "icons": [
     {
-      "src": "/icon.svg",
+      "src": "icon.svg",
       "sizes": "any",
       "type": "image/svg+xml",
       "purpose": "any maskable"

src/client/sw.js

@@ -15,8 +15,12 @@
  */
 
 const CACHE_VERSION = "event-clock-v1";
-const SHELL = ["/", "/index.html", "/styles.css", "/main.js"];
-const FEED = "/data/events.v1.json";
+// Paths are derived from the registration scope, so the same worker is
+// correct at a domain root and under a subpath (GitHub Pages) alike.
+const BASE = new URL("./", self.registration.scope);
+const at = (path) => new URL(path, BASE).toString();
+const SHELL = ["", "index.html", "styles.css", "main.js"].map(at);
+const FEED = new URL("data/events.v1.json", BASE).pathname;
 const FONT_HOSTS = new Set(["fonts.googleapis.com", "fonts.gstatic.com"]);
 
 self.addEventListener("install", (event) => {