Aio HTML Interactive

aio-html-interactive — bridge Claude to a browser via Monitor + WebSocket

The problem this solves

Claude runs in a turn-by-turn CLI loop. It has no event loop, can't addEventListener on a browser, can't block on await userClick(). So how does an interactive UI — one the user is actually clicking on right now — drive Claude's behavior while a task is in progress?

The answer two channels, both fronted by a single Bun HTTP + WebSocket server:

• Browser → Claude (input channel). RT.send(type, payload) in the browser POSTs /api/event; the server writes one line MSG::{instance,type,payload} to stdout. The Monitor tool is configured to pattern-match MSG:: lines on that server's stdout and surface each one as a notification. Notifications are how a turn-based agent gets a "user-clicked-X" event without an event loop.
• Claude → browser (output channel). Claude POSTs /api/push {type,payload} from any shell tool call; the server broadcasts that JSON verbatim over WebSocket to every connected tab. The runtime processes a small built-in vocabulary (state merge, toast, html, js, reload) before dispatching to app-registered handlers.

UI is vendored Vue 3 + Tailwind, no build step. Claude only writes the APP REGION of app.html; the runtime, server, and vendor blocks are frozen so the protocol stays intact across edits.

Workflow

1. Copy scaffold — cp -r ${CLAUDE_PLUGIN_ROOT}/skills/aio-html-interactive/scaffold /tmp/aio-html-interactive-<slug> via Bash. Do not Read+Write to copy — that round-trips through the model and risks editing the runtime by accident. For a session that may span a reboot, copy into a stable project dir instead of /tmp (which is cleared on restart) — e.g. ./.aio-html-interactive-<slug>; the slug, launch, and cleanup steps are otherwise identical.

2. Build app — Read /tmp/aio-html-interactive-<slug>/app.html once before editing. The Edit tool requires a prior in-conversation Read; the cp above does NOT count, so skipping Read makes the first Edit fail with File has not been read yet. Read with offset/limit around the two markers (~25 lines at end of file) is enough. Edit ONLY the text between <!-- ===== APP REGION START ... --> and <!-- ===== APP REGION END ===== -->, using both marker lines as Edit anchors. Never rewrite the whole file. Never touch the runtime block, server.js, or vendor/ — and do not Read them either; the full API is documented below.

3. Launch — run bun /tmp/aio-html-interactive-<slug>/server.js through the Monitor tool. The startup line prints URL + instance id; the browser opens automatically.

4. Interact — browser events arrive as Monitor notifications: MSG::{instance,type,payload}. Claude pushes back with curl -s -X POST http://localhost:<PORT>/api/push -d '{"type":"...","payload":{...}}'.

5. Cleanup (required) — when done: TaskStop the Monitor task AND rm -rf /tmp/aio-html-interactive-<slug>. Leaving the task running holds the port; leaving the directory is litter.

Server API

• POST /api/push {type,payload} — Claude → browser. Server broadcasts the JSON verbatim over WebSocket to every connected tab.
• POST /api/event {type,payload} — browser → Claude. RT.send() calls this; server writes MSG::{instance,type,payload} to stdout. Monitor surfaces each line as a notification.
• MSG:: stdout line — JSON after the prefix; instance disambiguates when multiple aio-html-interactive apps run concurrently. The prefix is the Monitor-side contract — do not change it.

Runtime API (browser-side)

• RT.start(appDef) — the only entry point the APP REGION calls (last, exactly once). appDef is a Vue component options object: template, setup, etc. The runtime injects state / send / on into the render scope; values returned from setup() merge on top.
• RT.state — reactive global state (Vue.reactive). Template reads state.*.
• RT.send(type, payload) — emit a browser → Claude event (POSTs /api/event).
• RT.on(type, fn) — register a handler for a custom push type (non-built-in).
• Template reads state / send / on directly (runtime returns them into the render scope). Inside setup() they are NOT visible — there, address them as RT.state / RT.send / RT.on (they are runtime closures, not globals; bare send(...) inside setup() throws ReferenceError).

Built-in push types

POST /api/push with these type values is handled by the runtime directly (before app-registered handlers; an app handler cannot shadow these):

Any other type → invokes the handler registered via RT.on(); no handler → silently ignored.

Design principles

• Drive UI through state. Push a state patch; let Vue reactivity re-render. Prefer this over html / js, which are escape hatches.
• Bake initial state in setup() when Claude already has it. If Claude holds the initial dataset at the time of writing the app (list, table, config…), seed it directly into RT.state inside setup() so first paint is complete. Use push state for subsequent updates only. Launching the server and then pushing initial state is a wasted round-trip with a blank-flash for the user.
• Single writer per state key. Either the app writes locally (optimistic) OR Claude push state writes — never both for the same key. Both writing → last-writer-wins race, value flickers. Pick a model: Claude-authoritative (browser clicks only send(), only Claude pushes — no race but adds latency) or browser-authoritative (app writes local, Claude reads events but does not push that key).
• Define a small, explicit message vocabulary. A handful of type values for browser → Claude, a handful for Claude → browser. Spell them out at the top of the APP REGION.
• Explicit submission + busy flag. Claude turn-takes asynchronously and can take seconds; send() is fire-and-forget. Do NOT fire send() on every micro-interaction (every keystroke) and leave the user blind — they cannot tell whether Claude received the event, is processing, or whether further input is allowed. Collect input into local state, give the user an explicit "Send to AI" button, set a pending flag (e.g. state.busy = true) on submit so the UI shows "waiting for AI…" and/or disables input, and have Claude push state to clear the flag when done. The feedback loop must stay closed — the user always knows whose turn it is.

Starter — APP REGION skeleton (optional)

The skeleton below follows the design principles above: header, centered container, explicit "Send to AI" button, state.busy flag, initial state baked in setup(). Copy over the placeholder content and replace the body. Head-start only — different layouts are fine, this is not required.

RT.start({
  template: `
    <div class="min-h-screen pb-24">

      <!-- header — app title + one-line description -->
      <div class="bg-slate-900 text-white">
        <div class="max-w-3xl mx-auto px-6 py-5">
          <h1 class="text-lg font-semibold">{{ state.title }}</h1>
          <p class="text-slate-400 text-sm mt-0.5">{{ state.subtitle }}</p>
        </div>
      </div>

      <!-- main content — replace this block with the real app -->
      <div class="max-w-3xl mx-auto px-6 py-6">
        <div class="bg-white rounded-xl border border-slate-200 p-6 text-sm text-slate-600">
          App content here.
        </div>
      </div>

      <!-- action bar — explicit Send button, locked while waiting on AI -->
      <div class="fixed bottom-0 inset-x-0 bg-white border-t border-slate-200">
        <div class="max-w-3xl mx-auto px-6 py-3 flex items-center gap-4">
          <div class="flex-1 text-sm text-slate-500">
            {{ state.busy ? '⏳ Waiting for AI…' : 'Ready.' }}
          </div>
          <button @click="submit" :disabled="state.busy"
              class="px-5 py-2 rounded-lg text-sm font-semibold text-white
                     bg-slate-900 hover:bg-slate-700 disabled:opacity-40">
            Send to AI →
          </button>
        </div>
      </div>

    </div>
  `,
  setup() {
    // Bake initial state — first paint is complete, no blank-flash.
    RT.state.title = "App title";
    RT.state.subtitle = "One-line description";
    RT.state.busy = false;

    // Browser → AI: commit the submission and raise the busy flag so the
    // UI locks itself.
    function submit() {
      if (RT.state.busy) return;
      RT.state.busy = true;
      RT.send("submit", {});
    }

    // AI → browser: on completion, AI pushes {"type":"done"} to release
    // the busy flag.
    RT.on("done", function () {
      RT.state.busy = false;
    });

    return { submit: submit };
  },
});

Lifecycle

Server lifetime is tied to the Monitor task. TaskStop terminates the Bun process, which closes every WebSocket; subsequent browser actions silently fail (no handler reachable). The /tmp/aio-html-interactive-<slug>/ directory is Claude's responsibility to remove after TaskStop — see step 5 of the workflow.