feat: streaming via extension

src/api.ts

@@ -89,3 +89,135 @@ export async function sendChat(
     body: JSON.stringify(req),
   })) as ChatResponse;
 }
+
+export interface StreamChatCallbacks {
+  // Fires for every intermediate snapshot (full file content as the
+  // gateway would have written it, frontmatter included). Caller is
+  // responsible for splicing it into the editor — we don't ship the
+  // diff because the gateway already renders the canonical view and we
+  // don't want two slightly-different renderers to drift.
+  onDelta(newContent: string): void;
+  // Fires exactly once at end-of-turn (success or nothing_to_do).
+  onDone(response: ChatResponse): void;
+}
+
+// Server-Sent Events arrive as ``event: <name>\ndata: <json>\n\n``
+// frames. We can't use ``requestUrl`` (it buffers the whole body), so
+// SSE is the one place in the plugin that goes through native
+// ``fetch``. CORS is allowed by the gateway's ``CORSMiddleware``; auth
+// is the same bearer token as the other endpoints.
+export async function sendChatStream(
+  settings: BeaverSettings,
+  req: ChatRequest,
+  cb: StreamChatCallbacks,
+  signal?: AbortSignal,
+): Promise<void> {
+  const url = `${baseUrl(settings)}/chat/stream`;
+  const headers: Record<string, string> = {
+    ...authHeader(settings),
+    "Content-Type": "application/json",
+    Accept: "text/event-stream",
+  };
+  const res = await fetch(url, {
+    method: "POST",
+    headers,
+    body: JSON.stringify(req),
+    signal,
+  });
+  if (!res.ok || !res.body) {
+    // Drain the body so we can surface a useful detail. 409 in
+    // particular returns JSON; the rest may be JSON or plain text.
+    const text = await res.text().catch(() => "");
+    let detail: unknown = text;
+    try {
+      const parsed = JSON.parse(text) as { detail?: unknown };
+      detail =
+        parsed && typeof parsed === "object" && "detail" in parsed
+          ? parsed.detail
+          : parsed;
+    } catch {
+      // not JSON; leave detail as the raw text
+    }
+    const msg =
+      typeof detail === "string" && detail
+        ? detail
+        : `HTTP ${res.status}`;
+    throw new BeaverApiError(res.status, msg, detail);
+  }
+
+  const reader = res.body.getReader();
+  const decoder = new TextDecoder();
+  // SSE frames are separated by a blank line (``\n\n``). We buffer
+  // partial frames across reads, then flush full ones in order.
+  let buf = "";
+  let done = false;
+  while (!done) {
+    const chunk = await reader.read();
+    done = chunk.done;
+    if (chunk.value) buf += decoder.decode(chunk.value, { stream: !done });
+    let sep = buf.indexOf("\n\n");
+    while (sep >= 0) {
+      const frame = buf.slice(0, sep);
+      buf = buf.slice(sep + 2);
+      const handled = handleSseFrame(frame, cb);
+      if (handled === "stop") {
+        // ``done``/``error`` is terminal — stop reading even if the
+        // server sends extra padding before closing.
+        try {
+          await reader.cancel();
+        } catch {
+          // best-effort cleanup
+        }
+        return;
+      }
+      sep = buf.indexOf("\n\n");
+    }
+  }
+}
+
+function handleSseFrame(
+  frame: string,
+  cb: StreamChatCallbacks,
+): "continue" | "stop" {
+  // SSE lines: ``event: <name>`` / ``data: <json>``. ``data`` may span
+  // multiple lines (concatenated with ``\n``) per the spec; we honour
+  // that even though the gateway emits single-line ``data:`` today.
+  let event = "message";
+  const dataLines: string[] = [];
+  for (const rawLine of frame.split("\n")) {
+    const line = rawLine.replace(/\r$/, "");
+    if (!line || line.startsWith(":")) continue;
+    const colon = line.indexOf(":");
+    if (colon < 0) continue;
+    const field = line.slice(0, colon);
+    let value = line.slice(colon + 1);
+    if (value.startsWith(" ")) value = value.slice(1);
+    if (field === "event") event = value;
+    else if (field === "data") dataLines.push(value);
+  }
+  if (dataLines.length === 0) return "continue";
+  let data: unknown;
+  try {
+    data = JSON.parse(dataLines.join("\n"));
+  } catch {
+    return "continue";
+  }
+  const obj = data as Record<string, unknown>;
+  if (event === "delta") {
+    const content = obj.new_content;
+    if (typeof content === "string") cb.onDelta(content);
+    return "continue";
+  }
+  if (event === "done") {
+    cb.onDone(obj as unknown as ChatResponse);
+    return "stop";
+  }
+  if (event === "error") {
+    const code =
+      typeof obj.status_code === "number" ? obj.status_code : 500;
+    const detail =
+      typeof obj.detail === "string" ? obj.detail : `HTTP ${code}`;
+    throw new BeaverApiError(code, detail, obj);
+  }
+  return "continue";
+}

src/main.ts

@@ -9,7 +9,7 @@ import {
   BeaverApiError,
   ChatResponse,
   listAgents,
-  sendChat,
+  sendChatStream,
 } from "./api";
 import { pickAgent } from "./agentPicker";
 import {
@@ -20,6 +20,135 @@ import {
 
 const AGENT_CACHE_TTL_MS = 5 * 60 * 1000;
 
+// Obsidian's ``Editor`` is a thin shim over a CodeMirror 6
+// ``EditorView``; reaching for it directly is the only way to grab
+// the real scrollable DOM node (``.cm-scroller``). Property name is
+// unofficial but stable across recent Obsidian releases.
+interface CMHandle {
+  scrollDOM: HTMLElement;
+}
+function cmOf(editor: Editor): CMHandle | null {
+  const cm = (editor as unknown as { cm?: CMHandle }).cm;
+  return cm && cm.scrollDOM instanceof HTMLElement ? cm : null;
+}
+
+// Boundary of the YAML frontmatter block. ``---\n…---\n`` at the very
+// start of the file; anything else is a no-frontmatter file and we
+// return 0.
+function frontmatterEnd(s: string): number {
+  if (!s.startsWith("---\n")) return 0;
+  const idx = s.indexOf("\n---\n", 4);
+  return idx >= 0 ? idx + 5 : 0;
+}
+
+// Replace only the regions that actually changed instead of
+// ``editor.setValue`` (which resets cursor + scroll and is expensive
+// on every snapshot for long files).
+//
+// Fast path: when the body after the frontmatter is identical except
+// for a tail append (the common case for the final write — gateway
+// refreshes frontmatter at the top and appends USER_SCAFFOLD at the
+// bottom, body in between is unchanged), we apply TWO small edits
+// instead of one huge one. The frontmatter rewrite stays a small,
+// localised change; the tail append touches only the very last bytes.
+// A single big ``replaceRange`` spanning the frontmatter triggers
+// Obsidian's Properties-widget rebuild + an asynchronous scroll-to-
+// start-of-content that's hard to override.
+//
+// Slow path: prefix/suffix-trimmed single splice for any other shape.
+//
+// After every edit we restore scroll on the scrollDOM directly,
+// repeatedly across several frames, because the widget rebuild keeps
+// resetting scroll asynchronously and a single restore loses the
+// race.
+function spliceIntoEditor(editor: Editor, newContent: string): void {
+  const current = editor.getValue();
+  if (current === newContent) return;
+  const cm = cmOf(editor);
+  const savedScrollTop = cm?.scrollDOM.scrollTop ?? null;
+
+  const oldFmEnd = frontmatterEnd(current);
+  const newFmEnd = frontmatterEnd(newContent);
+  const oldBody = current.slice(oldFmEnd);
+  const newBody = newContent.slice(newFmEnd);
+  const fmsDiffer =
+    current.slice(0, oldFmEnd) !== newContent.slice(0, newFmEnd);
+
+  if (newBody.startsWith(oldBody) && (fmsDiffer || newBody.length > oldBody.length)) {
+    // Tail append first, then (maybe) frontmatter rewrite. Order
+    // matters: appending at the current end keeps the frontmatter
+    // splice positions valid. Reversing the order would invalidate
+    // the append offset after the frontmatter grew.
+    if (newBody.length > oldBody.length) {
+      const appendStart = editor.offsetToPos(current.length);
+      editor.replaceRange(newBody.slice(oldBody.length), appendStart);
+    }
+    if (fmsDiffer) {
+      const fmStart = editor.offsetToPos(0);
+      const fmEnd = editor.offsetToPos(oldFmEnd);
+      editor.replaceRange(newContent.slice(0, newFmEnd), fmStart, fmEnd);
+    }
+  } else if (oldBody.startsWith(newBody) && (fmsDiffer || oldBody.length > newBody.length)) {
+    // Symmetric case: tail truncation. Unlikely on the streaming
+    // path but cheap to handle.
+    if (oldBody.length > newBody.length) {
+      const truncStart = editor.offsetToPos(oldFmEnd + newBody.length);
+      const truncEnd = editor.offsetToPos(current.length);
+      editor.replaceRange("", truncStart, truncEnd);
+    }
+    if (fmsDiffer) {
+      const fmStart = editor.offsetToPos(0);
+      const fmEnd = editor.offsetToPos(oldFmEnd);
+      editor.replaceRange(newContent.slice(0, newFmEnd), fmStart, fmEnd);
+    }
+  } else {
+    // Generic single-splice fallback: trim common prefix + suffix.
+    let prefix = 0;
+    const cap = Math.min(current.length, newContent.length);
+    while (
+      prefix < cap &&
+      current.charCodeAt(prefix) === newContent.charCodeAt(prefix)
+    ) {
+      prefix++;
+    }
+    let suffix = 0;
+    const maxSuffix = cap - prefix;
+    while (
+      suffix < maxSuffix &&
+      current.charCodeAt(current.length - 1 - suffix) ===
+        newContent.charCodeAt(newContent.length - 1 - suffix)
+    ) {
+      suffix++;
+    }
+    const start = editor.offsetToPos(prefix);
+    const end = editor.offsetToPos(current.length - suffix);
+    editor.replaceRange(
+      newContent.slice(prefix, newContent.length - suffix),
+      start,
+      end,
+    );
+  }
+
+  if (cm != null && savedScrollTop != null) {
+    // Race against Obsidian's deferred scroll-reset. Sync restore +
+    // two animation frames + two timeouts; whichever fires after
+    // Obsidian's own scroll write wins. Cheap noop on the
+    // already-correct frames.
+    const restore = () => {
+      if (cm.scrollDOM.scrollTop !== savedScrollTop) {
+        cm.scrollDOM.scrollTop = savedScrollTop;
+      }
+    };
+    restore();
+    requestAnimationFrame(() => {
+      restore();
+      requestAnimationFrame(restore);
+    });
+    window.setTimeout(restore, 50);
+    window.setTimeout(restore, 200);
+  }
+}
+
 export default class BeaverPlugin extends Plugin {
   settings: BeaverSettings = { ...DEFAULT_SETTINGS };
 
@@ -129,15 +258,26 @@ export default class BeaverPlugin extends Plugin {
       : await this.app.vault.read(file);
 
     const notice = new Notice(`Beaver: sending to ${agent}…`, 0);
-    let response: ChatResponse;
+    let finalResponse: ChatResponse | null = null;
     try {
-      response = await sendChat(this.settings, {
-        filename,
-        content,
-        agent,
-      });
+      await sendChatStream(
+        this.settings,
+        { filename, content, agent },
+        {
+          onDelta: (newContent) => {
+            // Live splice into the editor only — we deliberately don't
+            // write the partial to disk. The gateway also skips its own
+            // intermediate file writes on this endpoint, so the local
+            // file (and Obsidian Sync's copy) only sees the final state
+            // once.
+            if (editor) spliceIntoEditor(editor, newContent);
+          },
+          onDone: (resp) => {
+            finalResponse = resp;
+          },
+        },
+      );
     } catch (err) {
-      notice.hide();
       if (err instanceof BeaverApiError && err.status === 409) {
         new Notice("Beaver: already running for this file", 6000);
         return;
@@ -148,13 +288,24 @@ export default class BeaverPlugin extends Plugin {
       notice.hide();
     }
 
-    if (response.status === "nothing_to_do") {
-      new Notice(`Beaver: nothing to do (${response.reason ?? "no reason"})`);
+    if (!finalResponse) {
+      // Stream ended without a ``done`` event — shouldn't happen but
+      // we surface it instead of pretending nothing was wrong.
+      this.notifyError(
+        `sending to ${agent}`,
+        new Error("stream ended without a done event"),
+      );
       return;
     }
 
-    if (typeof response.new_content === "string") {
-      await this.writeBack(file, editor, view, response.new_content);
+    const resp: ChatResponse = finalResponse;
+    if (resp.status === "nothing_to_do") {
+      new Notice(`Beaver: nothing to do (${resp.reason ?? "no reason"})`);
+      return;
+    }
+
+    if (typeof resp.new_content === "string") {
+      await this.writeBack(file, editor, view, resp.new_content);
     }
     new Notice(`Beaver: ${agent} replied`);
   }
@@ -196,14 +347,15 @@ export default class BeaverPlugin extends Plugin {
     _view: MarkdownView | null,
     newContent: string,
   ): Promise<void> {
-    if (editor && editor.getValue() !== newContent) {
-      editor.setValue(newContent);
+    if (editor) {
+      // Reuse the splice path so the final write (frontmatter refresh
+      // at the top + USER_SCAFFOLD appended at the bottom) preserves
+      // scroll just like the streaming deltas did.
+      spliceIntoEditor(editor, newContent);
       return;
     }
-    if (!editor) {
     await this.app.vault.modify(file, newContent);
   }
-  }
 
   private notifyError(action: string, err: unknown): void {
     const msg =