bubbles: new Map(), // bubble_id -> bubble record (see ensureBubble) lastSeq: 0, // de-dup gate against re-fires of the same payload // Current chat epoch — bumped server-side every time the user clicks // "+" / new_chat. Each delta payload carries the epoch it was // produced under; deltas whose epoch doesn't match ours are dropped // (they're tail bytes from a stream the user already abandoned). // Initialised lazily from the first payload that arrives so legacy // payloads without an epoch field still apply. currentEpoch: null, }; // ─── DOM helpers ─────────────────────────────────────────────────────── function ensureHost() { if (state.host && document.contains(state.host)) return state.host; state.host = document.getElementById("hy-chat"); return state.host; } function escapeHtml(s) { return String(s) .replace(/&/g, "&") .replace(//g, ">") .replace(/"/g, """) .replace(/'/g, "'"); } // ─── Markdown + math renderer ────────────────────────────────────────── // We DELIBERATELY do not sanitize here. The rest of the app depends // on the model being able to emit raw HTML (e.g. //

, the HTML-preview workflow on raw // HTML code blocks). The model is trusted output for this product // surface; if that ever changes, swap marked for a sanitizing parser // like markdown-it + DOMPurify. const MARKED_OPTS = { gfm: true, breaks: false }; const KATEX_DELIMS = [ { left: "$$", right: "$$", display: true }, { left: "$", right: "$", display: false }, // We pre-convert \[…\] / $…$ → $$…$$ / $…$ via normalizeMathDelims // BEFORE marked.parse runs (see below) — so the auto-render scan // never needs to worry about them. They are NOT listed here on // purpose: marked treats ``\[`` and ``$`` as backslash escapes // and silently drops the leading ``\`` in the rendered HTML, so by // the time KaTeX scans the DOM the original bracket delimiters are // already gone. Pre-conversion is the only reliable fix. ]; // ─── Math handling: two-stage pipeline ──────────────────────────────── // // The model emits LaTeX in any of four delimiter styles: ``$$…$$``, // ``\[…\]``, ``$…$``, ``\(…$``. We need KaTeX (via auto-render) to // pick all of them up while still letting ``marked.parse`` handle the // surrounding markdown. // // Two problems block the naïve approach: // // 1. ``marked`` treats ``\[``, ``\]``, ``$``, ``$`` as backslash // escapes and silently drops the ``\``. By the time KaTeX scans // the rendered HTML the bracket delimiters are gone. // // 2. Even inside ``$$…$$``, ``marked`` strips backslashes before // ``\{``, ``\}``, ``\_``, etc. — so things like ``\{(0:0:1:0)\}`` // lose their literal-brace escapes and KaTeX renders an empty // group instead of the intended literal braces. // // The fix is two passes that together keep marked away from the math // content: // // Stage A — ``normalizeMathDelims`` converts ``\[/\]`` → ``$$`` and // ``$/$`` → ``$`` OUTSIDE fenced/inline code blocks. After this // pass every math region is delimited with dollars. // // Stage B — ``protectMath`` extracts every ``$$…$$`` / ``$…$`` from // the text and replaces it with a unique placeholder token (a NUL // character that ``marked`` will leave alone). After ``marked.parse`` // we substitute the original math source back in. ``ignoredTags`` // already keeps KaTeX out of ``

``/````, so the only
  //   regions that end up containing dollars in the rendered HTML are
  //   the math ones — exactly what we want.
  //
  // The placeholder uses NUL as a delimiter because ``marked`` cannot
  // produce a literal NUL on its own (every input source we'd see is
  // valid Unicode text without NULs), so the ``restoreMath`` regex is
  // unambiguous.
  function normalizeMathDelims(text) {
    if (!text) return text;
    let out = "";
    let i = 0;
    const n = text.length;
    while (i < n) {
      const ch = text[i];

      // Triple-backtick or triple-tilde fenced block — passthrough until
      // matching closing fence on its own (or anywhere on a) line.
      if ((ch === "`" && text.startsWith("```", i)) ||
          (ch === "~" && text.startsWith("~~~", i))) {
        const marker = text.substr(i, 3);
        out += marker;
        i += 3;
        const close = text.indexOf(marker, i);
        if (close < 0) {
          // Unclosed fence — emit rest verbatim and stop.
          out += text.slice(i);
          return out;
        }
        out += text.slice(i, close + 3);
        i = close + 3;
        continue;
      }

      // Inline code: single or double backticks, ended by the same run
      // length. Common case is a single backtick.
      if (ch === "`") {
        let runLen = 1;
        while (i + runLen < n && text[i + runLen] === "`") runLen++;
        const open = text.substr(i, runLen);
        out += open;
        i += runLen;
        const close = text.indexOf(open, i);
        if (close < 0) {
          out += text.slice(i);
          return out;
        }
        out += text.slice(i, close + runLen);
        i = close + runLen;
        continue;
      }

      // Backslash-bracket / backslash-paren delimiters. Must be the
      // FIRST conversion check after the code-fence skip so we don't
      // mistake e.g. ``\[`` inside a code fence for math.
      if (ch === "\\") {
        if (text[i + 1] === "[") { out += "$$"; i += 2; continue; }
        if (text[i + 1] === "]") { out += "$$"; i += 2; continue; }
        if (text[i + 1] === "(") { out += "$";  i += 2; continue; }
        if (text[i + 1] === ")") { out += "$";  i += 2; continue; }
      }

      out += ch;
      i++;
    }
    return out;
  }

  // Inline math regex requires the opening ``$`` to be IMMEDIATELY
  // followed by a non-space, non-``$`` char (avoids matching prices like
  // ``I have $5 and $10``) and the closing ``$`` to be IMMEDIATELY
  // preceded by a non-space, non-``$`` char. Display math (``$$…$$``)
  // is matched first (the alternative is left-most-greedy in a JS
  // regex, but with non-greedy bodies and ``$$`` being a longer prefix
  // it wins ties naturally).
  const MATH_RE = /\$\$[\s\S]+?\$\$|\$(?=[^\s$])[^\n$]*?(?<=[^\s$])\$/g;

  function protectMath(text) {
    const stash = [];
    const escaped = text.replace(MATH_RE, (m) => {
      const idx = stash.length;
      stash.push(m);
      return `\u0000M${idx}\u0000`;
    });
    return { escaped, stash };
  }

  function restoreMath(html, stash) {
    if (!stash.length) return html;
    return html.replace(/\u0000M(\d+)\u0000/g, (_, n) => stash[+n]);
  }

  function renderMarkdownInto(el, text) {
    if (!text) {
      el.innerHTML = "";
      return;
    }
    const normalized = normalizeMathDelims(text);
    const { escaped, stash } = protectMath(normalized);
    const rawMd = (window.marked && window.marked.parse)
      ? window.marked.parse(escaped, MARKED_OPTS)
      : escapeHtml(escaped);
    el.innerHTML = restoreMath(rawMd, stash);

    // Math
    if (window.renderMathInElement) {
      try {
        window.renderMathInElement(el, {
          delimiters: KATEX_DELIMS,
          throwOnError: false,
          // Skip math-detection inside elements that should never contain
          // math (matches KaTeX auto-render defaults).
          ignoredTags: ["script", "noscript", "style", "textarea", "pre", "code"],
        });
      } catch (err) {
        console.warn("[hy-chat] katex render error:", err);
      }
    }

    // Syntax highlighting (idempotent if hljs not loaded yet)
    if (window.hljs && window.hljs.highlightElement) {
      const codes = el.querySelectorAll("pre code");
      for (let i = 0; i < codes.length; i++) {
        const c = codes[i];
        if (c.dataset.hljsDone) continue;
        try {
          window.hljs.highlightElement(c);
        } catch (err) {
          // hljs throws if the language is unknown — harmless, ignore.
        }
        c.dataset.hljsDone = "1";
      }
    }
  }

  // ─── Frozen / streaming split ──────────────────────────────────────────
  // Find the highest "safe" boundary in the current content buffer up to
  // which we can freeze the rendered DOM and never touch it again. A
  // boundary is safe iff the markdown above it forms a complete set of
  // top-level blocks — i.e. we are NOT inside an open fenced code block
  // (``` / ~~~), display math ($$), or LaTeX env (\begin{…}).
  //
  // Returns the index in ``text`` immediately after the last safe block
  // separator (\n\n).
  function findFreezeBoundary(text) {
    const len = text.length;
    let i = 0;
    let inFence = false;       // inside ``` … ``` or ~~~ … ~~~
    let fenceMarker = null;
    let inMath = false;        // inside $$ … $$
    let inEnv = false;         // inside \begin{…} … \end{…}
    let lastSafe = 0;

    while (i < len) {
      const ch = text[i];

      // Fence detection (must check before single-char paths)
      if (!inMath && !inEnv) {
        if (ch === "`" && text.startsWith("```", i)) {
          if (!inFence) { inFence = true; fenceMarker = "```"; }
          else if (fenceMarker === "```") { inFence = false; fenceMarker = null; }
          i += 3;
          continue;
        }
        if (ch === "~" && text.startsWith("~~~", i)) {
          if (!inFence) { inFence = true; fenceMarker = "~~~"; }
          else if (fenceMarker === "~~~") { inFence = false; fenceMarker = null; }
          i += 3;
          continue;
        }
      }

      if (inFence) { i++; continue; }

      // Display math $$ … $$
      if (!inEnv && ch === "$" && text[i + 1] === "$") {
        inMath = !inMath;
        i += 2;
        continue;
      }

      if (inMath) { i++; continue; }

      // \begin{env} … \end{env}
      if (ch === "\\") {
        if (text.startsWith("\\begin{", i)) { inEnv = true; i += 7; continue; }
        if (text.startsWith("\\end{", i))   { inEnv = false; i += 5; continue; }
      }

      if (inEnv) { i++; continue; }

      // Paragraph break outside any block — candidate freeze point.
      if (ch === "\n" && text[i + 1] === "\n") {
        // Skip past the entire run of blank lines so we don't freeze
        // mid-blank-paragraph.
        let j = i + 2;
        while (j < len && (text[j] === "\n" || text[j] === " " || text[j] === "\t")) j++;
        lastSafe = j;
        i = j;
        continue;
      }

      i++;
    }

    return lastSafe;
  }

  // ─── Bubble lifecycle ──────────────────────────────────────────────────
  function ensureBubble(id) {
    return state.bubbles.get(id);
  }

  // Re-fire ``hy-chat:updated`` so the scroll-lock in app.js reconsiders
  // whether to re-pin to the bottom now that geometry may have changed.
  // Coalesced via rAF so a flurry of layout changes (e.g. KaTeX +
  // hljs + table column-width pass all in the same frame) only
  // dispatches once.
  let _nudgePending = false;
  function nudgeScrollSoon() {
    if (_nudgePending) return;
    _nudgePending = true;
    requestAnimationFrame(() => {
      _nudgePending = false;
      if (!state.host) return;
      state.host.dispatchEvent(new CustomEvent("hy-chat:updated", {
        bubbles: false,
      }));
    });
  }

  // Forces ``row`` to flush any pending layout, then schedules a
  // single rAF-coalesced ``hy-chat:updated`` dispatch. Used both
  // when a ```` toggles and as the ``ResizeObserver``
  // callback for each row.
  function nudgeScrollAfterToggle(b) {
    if (!b || !b.row) return;
    void b.row.offsetHeight;
    nudgeScrollSoon();
  }

  // Per-row ResizeObserver. Many things that change a row's height
  // happen ASYNCHRONOUSLY after the streaming op that created the
  // content: KaTeX glyphs render once their fonts arrive, hljs
  // decorates code blocks on the next idle tick, browsers do a
  // second column-width pass on tables once all rows are in. None
  // of these go through ``applyDelta`` so the scroll-lock would
  // otherwise miss them, leaving the user stuck at a now-stale
  // ``scrollHeight - clientHeight``. Wiring a ResizeObserver per
  // row covers all of them with one mechanism.
  const _rowResizeObserver =
    typeof ResizeObserver !== "undefined"
      ? new ResizeObserver(() => nudgeScrollSoon())
      : null;

  function createAssistantBubble(id) {
    const row = document.createElement("div");
    row.className = "message-row bot-row";
    row.dataset.testid = "bot";
    row.dataset.role = "assistant";
    row.dataset.bubbleId = id;

    const msg = document.createElement("div");
    msg.className = "message bot";

    const md = document.createElement("div");
    md.className = "markdown hy-markdown";

    const typing = document.createElement("div");
    typing.className = "typing-indicator hy-typing";
    typing.innerHTML = "";
    md.appendChild(typing);

    msg.appendChild(md);
    row.appendChild(msg);
    state.host.appendChild(row);
    if (_rowResizeObserver) _rowResizeObserver.observe(row);

    const record = {
      row, md, typing,
      // Reasoning (optional, lazily created)
      reasoningEl: null,
      reasoningSummaryEl: null,
      reasoningBodyEl: null,
      reasoningBuf: "",
      thinkingDone: false,
      // Content (lazily created on first content_delta)
      frozenEl: null,
      streamingEl: null,
      contentBuf: "",
      frozenLen: 0,
      // Tool-call append region (lazily created)
      toolCallContainer: null,
      ended: false,
    };
    state.bubbles.set(id, record);
    return record;
  }

  function ensureReasoning(b) {
    if (b.reasoningEl) return;
    const det = document.createElement("details");
    det.className = "thinking-block";
    det.open = true;
    const sum = document.createElement("summary");
    sum.textContent = (window.HY_I18N && window.HY_I18N.thinking) || "Thinking...";
    det.appendChild(sum);
    const body = document.createElement("div");
    body.className = "hy-reasoning-body";
    body.style.whiteSpace = "pre-wrap";
    body.style.wordBreak = "break-word";
    det.appendChild(body);
    b.reasoningEl = det;
    b.reasoningSummaryEl = sum;
    b.reasoningBodyEl = body;
    if (b.typing && b.typing.parentNode) b.typing.remove();
    // Reasoning always goes ABOVE content, even if content has already
    // started rendering (rare — most models stream reasoning first).
    b.md.insertBefore(det, b.md.firstChild);
    // Keep the parent chat's scroll geometry in sync whenever the user
    // (or markThinkingDone) toggles this block. See nudgeScrollAfterToggle.
    det.addEventListener("toggle", () => nudgeScrollAfterToggle(b));
  }

  function ensureContent(b) {
    if (b.frozenEl) return;
    if (b.typing && b.typing.parentNode) b.typing.remove();
    const frozen = document.createElement("div");
    frozen.className = "hy-frozen";
    const streaming = document.createElement("div");
    streaming.className = "hy-streaming";
    b.md.appendChild(frozen);
    b.md.appendChild(streaming);
    b.frozenEl = frozen;
    b.streamingEl = streaming;
  }

  function markThinkingDone(b) {
    if (!b.reasoningEl || b.thinkingDone) return;
    b.thinkingDone = true;
    b.reasoningSummaryEl.textContent =
      (window.HY_I18N && window.HY_I18N.thinking_done) || "Thought";
    b.reasoningEl.open = false;
  }

  // ─── Op handlers ───────────────────────────────────────────────────────
  function opReset() {
    if (_rowResizeObserver) {
      for (const b of state.bubbles.values()) {
        if (b.row) _rowResizeObserver.unobserve(b.row);
      }
    }
    state.host.innerHTML = "";
    state.bubbles.clear();
    state.lastSeq = 0;
    // currentEpoch is updated by applyDelta BEFORE op dispatch when a
    // reset op is in the payload — see the epoch handling there. We
    // intentionally do NOT clear it here, otherwise we'd reopen the
    // window for stale post-reset deltas.
  }

  function opUser(op) {
    const row = document.createElement("div");
    row.className = "message-row user-row";
    row.dataset.testid = "user";
    row.dataset.role = "user";

    const msg = document.createElement("div");
    msg.className = "message user user-message";

    const md = document.createElement("div");
    md.className = "markdown hy-markdown hy-user-text";
    // Render as plain text — never run user input through marked / KaTeX.
    md.style.whiteSpace = "pre-wrap";
    md.style.wordBreak = "break-word";
    md.textContent = op.text || "";

    msg.appendChild(md);
    row.appendChild(msg);
    state.host.appendChild(row);
  }

  function opAssistantBegin(op) {
    if (state.bubbles.has(op.id)) return; // idempotent on retry
    createAssistantBubble(op.id);
  }

  function opReasoningDelta(op) {
    let b = ensureBubble(op.id);
    if (!b) b = createAssistantBubble(op.id);
    ensureReasoning(b);
    const d = op.delta || "";
    if (!d) return;
    b.reasoningBuf += d;
    // Reasoning is shown as raw text — fast and never re-renders math.
    // Append-only via textContent means even very long reasoning stays
    // O(delta) per update; the DOM tree is just a single text node.
    b.reasoningBodyEl.textContent = b.reasoningBuf;
    // Keep the latest reasoning line visible inside the (max-height-
    // scrollable) details body.
    b.reasoningBodyEl.scrollTop = b.reasoningBodyEl.scrollHeight;
  }

  function opContentDelta(op) {
    let b = ensureBubble(op.id);
    if (!b) b = createAssistantBubble(op.id);
    if (op.thinking_done) markThinkingDone(b);
    ensureContent(b);
    const d = op.delta || "";
    if (!d) return;
    b.contentBuf += d;

    // Compute new freeze boundary. If it advanced past the last frozen
    // length, render JUST the newly-frozen chunk (text since last
    // boundary) ONCE and APPEND its DOM to the frozen container. The
    // already-frozen DOM is never touched — KaTeX, hljs, and marked
    // run exactly once per closed block.
    //
    // Why we can render the new chunk in isolation: the boundary is
    // always at a paragraph break (\n\n) outside any open code fence /
    // display math / LaTeX env, so each chunk is a complete set of
    // top-level markdown blocks that ``marked`` parses identically
    // whether or not it has the prior context.
    const text = b.contentBuf;
    const newBoundary = findFreezeBoundary(text);
    if (newBoundary > b.frozenLen) {
      const newChunk = text.slice(b.frozenLen, newBoundary);
      const temp = document.createElement("div");
      renderMarkdownInto(temp, newChunk);
      // Move children from temp into frozenEl. Moving (not cloning)
      // preserves the KaTeX/hljs work we just did, and crucially does
      // NOT re-trigger any rendering of the already-frozen DOM.
      while (temp.firstChild) {
        b.frozenEl.appendChild(temp.firstChild);
      }
      b.frozenLen = newBoundary;
    }
    // Streaming segment (everything after the boundary) is re-rendered
    // in full on each delta. It's bounded to roughly one paragraph, so
    // the KaTeX / marked / hljs work is O(paragraph) — and since
    // ``innerHTML = ...`` wipes the previous DOM, KaTeX never
    // double-renders the same formula here either.
    const streamingText = text.slice(b.frozenLen);
    renderMarkdownInto(b.streamingEl, streamingText);
  }

  function opAssistantEnd(op) {
    const b = ensureBubble(op.id);
    if (!b) return;
    b.ended = true;
    if (b.typing && b.typing.parentNode) b.typing.remove();
    // Defer one extra nudge to the next animation frame: post-stream
    // KaTeX/hljs decoration of the just-flushed tail can run after
    // applyDelta returns, growing the bubble's height beyond what
    // ``hy-chat:updated`` already saw at the end of this op.
    nudgeScrollSoon();
    // Final flush: take whatever is still in the streaming segment and
    // append it to the frozen container as one last chunk, then empty
    // streaming. Crucially we do NOT re-render the already-frozen DOM
    // — that would re-run KaTeX over every formula the user has been
    // looking at and produce a final visible flicker.
    if (b.contentBuf) {
      ensureContent(b);
      const tail = b.contentBuf.slice(b.frozenLen);
      if (tail) {
        const temp = document.createElement("div");
        renderMarkdownInto(temp, tail);
        while (temp.firstChild) {
          b.frozenEl.appendChild(temp.firstChild);
        }
      }
      b.frozenLen = b.contentBuf.length;
      b.streamingEl.innerHTML = "";
    } else if (b.streamingEl) {
      // No content at all (might be tool-call only) — clean up.
      b.streamingEl.innerHTML = "";
    }
    if (b.reasoningEl && !b.thinkingDone) markThinkingDone(b);
  }

  function opToolCall(op) {
    let b = ensureBubble(op.id);
    if (!b) b = createAssistantBubble(op.id);
    if (b.typing && b.typing.parentNode) b.typing.remove();
    if (!b.toolCallContainer) {
      const c = document.createElement("div");
      c.className = "hy-tool-calls";
      b.md.appendChild(c);
      b.toolCallContainer = c;
    }
    const tc = document.createElement("div");
    tc.className = "hy-tool-call";
    renderMarkdownInto(tc, op.markdown || "");
    b.toolCallContainer.appendChild(tc);
  }

  function opRemoveBubble(op) {
    const b = ensureBubble(op.id);
    if (!b) return;
    if (_rowResizeObserver && b.row) _rowResizeObserver.unobserve(b.row);
    if (b.row && b.row.parentNode) b.row.parentNode.removeChild(b.row);
    state.bubbles.delete(op.id);
  }

  function applyOp(op) {
    if (!op || !op.type) return;
    if (!ensureHost()) return;
    switch (op.type) {
      case "reset":           opReset(); break;
      case "user":            opUser(op); break;
      case "assistant_begin": opAssistantBegin(op); break;
      case "reasoning_delta": opReasoningDelta(op); break;
      case "content_delta":   opContentDelta(op); break;
      case "assistant_end":   opAssistantEnd(op); break;
      case "tool_call":       opToolCall(op); break;
      case "remove_bubble":   opRemoveBubble(op); break;
      default:
        console.warn("[hy-chat] unknown op type:", op.type);
    }
  }

  function applyDelta(payload) {
    if (!payload || typeof payload !== "object") return;
    const seq = typeof payload.seq === "number" ? payload.seq : null;
    // Dedup: Gradio occasionally re-fires the same component value on
    // reconnect. Since each delta has a fresh global seq, anything ≤
    // lastSeq is a re-fire we've already applied.
    if (seq !== null && seq <= state.lastSeq) return;
    if (seq !== null) state.lastSeq = seq;
    const ops = Array.isArray(payload.ops) ? payload.ops : [];

    // ── Stale-epoch drop ────────────────────────────────────────────
    // The user clicked "+" mid-stream. The reset payload carries a NEW
    // epoch; we adopt it and apply the reset. Any later payload from
    // the cancelled generator still carries the OLD epoch and is
    // dropped here — without this, late content_delta ops would
    // ``createAssistantBubble`` for the old bubble id and a ghost
    // bubble would appear in the freshly-cleared chat.
    const epoch = payload.epoch;
    if (epoch !== undefined && epoch !== null) {
      const hasReset = ops.some((op) => op && op.type === "reset");
      if (hasReset) {
        state.currentEpoch = epoch;
      } else if (state.currentEpoch === null) {
        // First payload of the session: adopt whatever epoch we see.
        state.currentEpoch = epoch;
      } else if (epoch !== state.currentEpoch) {
        return;
      }
    }

    for (let i = 0; i < ops.length; i++) {
      try {
        applyOp(ops[i]);
      } catch (err) {
        console.error("[hy-chat] op failed:", ops[i], err);
      }
    }
    // Notify subscribers (the scroll lock and code-block injector in
    // app.js) that the chat DOM changed. We dispatch a single CustomEvent
    // per applied delta — coarser than per-op so subscribers can do their
    // own coalescing on top.
    if (state.host) {
      state.host.dispatchEvent(new CustomEvent("hy-chat:updated", {
        bubbles: false,
      }));
    }
  }

  // ─── Wire up the delta channel ─────────────────────────────────────────
  function startDeltaObserver() {
    const deltaHost = document.getElementById("hy-chat-delta");
    if (!deltaHost) {
      setTimeout(startDeltaObserver, 200);
      return;
    }
    let lastValue = "";
    function handle() {
      // Gradio may put the value in textContent or in a nested element
      // depending on version. Walk the subtree to be defensive.
      //
      // While a generator is actively yielding, Gradio also injects a
      // status / elapsed-time text node ("0.0s", "0.1s", …) INSIDE the
      // output component's wrapper. That node bubbles into textContent
      // and ticks every ~100ms, which would (a) make JSON.parse choke
      // on the leading "0.0s" prefix and (b) re-fire the observer on
      // every timer tick. Slice from the first '{' to the last '}' to
      // skip the status overlay entirely.
      const raw = (deltaHost.textContent || "");
      const start = raw.indexOf("{");
      const end = raw.lastIndexOf("}");
      if (start < 0 || end < start) return;
      const v = raw.slice(start, end + 1);
      if (!v || v === lastValue) return;
      lastValue = v;
      let payload;
      try {
        payload = JSON.parse(v);
      } catch (err) {
        // Real malformed payload (rare): keep visibility, but at debug
        // level so the timer overlay can't ever spam the console.
        console.debug("[hy-chat] bad delta JSON:", v.slice(0, 200), err);
        return;
      }
      applyDelta(payload);
    }
    new MutationObserver(handle).observe(deltaHost, {
      childList: true,
      subtree: true,
      characterData: true,
    });
    handle(); // pick up initial value if any
  }

  function init() {
    if (!ensureHost()) {
      setTimeout(init, 200);
      return;
    }
    startDeltaObserver();
  }

  // Public surface for the rest of the page (app.js).
  window.HY_CHAT = {
    init,
    applyDelta,
    getHost: ensureHost,
  };

  if (document.readyState === "loading") {
    document.addEventListener("DOMContentLoaded", () => setTimeout(init, 200));
  } else {
    setTimeout(init, 200);
  }
})();