fix(comment): clear resolved mark only after reopen confirmed

Move the inline ProseMirror comment-mark clear out of the Undo toast's
onClick and into the reopen mutation's onSuccess branch. Clearing it
eagerly flipped the collab mark to unresolved before the reopen result
was known: on a non-404 failure the RQ cache rolls back to resolved but
the doc kept an active highlight the panel treats as resolved, and a
comment refetch can't heal a divergence that lives in the collab doc.
Mirrors the 404 branch's editor-liveness guard/try-catch and the safe
await-then-mark pattern in comment-list-item. The button-triggered
reopen already sets the mark, so the onSuccess call is an idempotent
no-op there.

Tests: reopen failure (500) leaves the mark untouched; null editorRef
on the success path degrades gracefully.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -392,6 +392,25 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   `@docmost/token-estimate` package) so they can never diverge. Deferred-tool
   activation is also cached in the chat metadata to avoid re-resolving it each
   turn. (#490)
+- **Cyrillic (and any non-ASCII) draw.io labels no longer turn into mojibake
+  when a diagram is opened in the draw.io editor.** Agent-created diagrams
+  (`drawioCreate`) and Confluence-imported diagrams stored their model in the
+  SVG's `content=` attribute as base64; the draw.io editor decodes that via
+  Latin-1 `atob` (no UTF-8 step), so every non-ASCII char (e.g. `Старт-бит`,
+  `ё`, `—`) split into garbage and the editor's autosave then persisted the
+  corrupted model, breaking the page preview too. Both write paths
+  (`buildDrawioSvg`, the import service's `createDrawioSvg`) now write `content=`
+  as XML-entity-escaped mxfile XML — draw.io's own native form, decoded by the
+  DOM as UTF-8 — so labels open intact. The decoder reads both the new
+  entity-encoded form and the old base64 form, so existing diagrams still open.
+  *Healing pre-fix diagrams:* only a diagram that still holds its original
+  (correct-UTF-8) base64 — i.e. one not yet opened/autosaved in the draw.io
+  editor — can be repaired in place by `drawioGet` → `drawioUpdate` with the
+  same XML (rewrites the attachment in the new form); no migration script is
+  needed. A diagram that was already opened in the editor persisted the
+  mojibake at rest, so `drawioGet` reads the already-corrupted text and
+  `drawioUpdate` faithfully rewrites it — that text is lost and is not
+  recoverable by a rewrite. (#507)
 - **A chat with one malformed message part no longer 500s on every turn, and a
   failed send no longer duplicates the user's message.** Incoming client parts
   are now whitelisted to `text` (a forged tool-result part can no longer reach

apps/client/public/locales/en-US/translation.json

@@ -239,6 +239,8 @@
   "Comment re-opened successfully": "Comment re-opened successfully",
   "Comment unresolved successfully": "Comment unresolved successfully",
   "Failed to resolve comment": "Failed to resolve comment",
+  "Failed to re-open comment": "Failed to re-open comment",
+  "Comment no longer exists": "Comment no longer exists",
   "Resolve comment": "Resolve comment",
   "Unresolve comment": "Unresolve comment",
   "Resolve Comment Thread": "Resolve Comment Thread",

apps/client/public/locales/ru-RU/translation.json

@@ -239,6 +239,8 @@
   "Comment re-opened successfully": "Комментарий успешно открыт повторно",
   "Comment unresolved successfully": "Комментарий успешно переведён в нерешённые",
   "Failed to resolve comment": "Не удалось разрешить комментарий",
+  "Failed to re-open comment": "Не удалось переоткрыть комментарий",
+  "Comment no longer exists": "Комментарий больше не существует",
   "Resolve comment": "Решить комментарий",
   "Unresolve comment": "Снять статус решённого с комментария",
   "Resolve Comment Thread": "Решить ветку комментариев",

apps/client/src/features/comment/components/comment-list-with-tabs.test.tsx

@@ -27,11 +27,15 @@ vi.mock("@/features/space/queries/space-query.ts", () => ({
 import {
   buildChildrenByParent,
   CommentEditorWithActions,
+  sortResolvedByResolvedAt,
 } from "./comment-list-with-tabs";
 
 const c = (id: string, parentCommentId: string | null = null): IComment =>
   ({ id, parentCommentId }) as IComment;
 
+const resolvedAtComment = (id: string, resolvedAt: unknown): IComment =>
+  ({ id, resolvedAt }) as unknown as IComment;
+
 describe("buildChildrenByParent (childrenByParent grouping)", () => {
   it("returns an empty map for undefined or empty input", () => {
     expect(buildChildrenByParent(undefined).size).toBe(0);
@@ -71,6 +75,48 @@ describe("buildChildrenByParent (childrenByParent grouping)", () => {
   });
 });
 
+describe("sortResolvedByResolvedAt (Resolved tab order, #542)", () => {
+  it("orders by resolvedAt DESC — newest resolve first — with ISO-STRING values", () => {
+    // At runtime resolvedAt is an ISO string (axios JSON / WS subscription), so
+    // the sort must coerce with new Date(...) before .getTime().
+    const older = resolvedAtComment("older", "2026-07-10T10:00:00.000Z");
+    const newest = resolvedAtComment("newest", "2026-07-12T10:00:00.000Z");
+    const middle = resolvedAtComment("middle", "2026-07-11T10:00:00.000Z");
+
+    const out = sortResolvedByResolvedAt([older, newest, middle]);
+    expect(out.map((x) => x.id)).toEqual(["newest", "middle", "older"]);
+  });
+
+  it("also handles Date instances (optimistic onMutate window)", () => {
+    const older = resolvedAtComment("older", new Date("2026-01-01T00:00:00Z"));
+    const newer = resolvedAtComment("newer", new Date("2026-06-01T00:00:00Z"));
+    expect(sortResolvedByResolvedAt([older, newer]).map((x) => x.id)).toEqual([
+      "newer",
+      "older",
+    ]);
+  });
+
+  it("does not mutate the input array", () => {
+    const a = resolvedAtComment("a", "2026-01-01T00:00:00.000Z");
+    const b = resolvedAtComment("b", "2026-02-01T00:00:00.000Z");
+    const input = [a, b];
+    sortResolvedByResolvedAt(input);
+    expect(input.map((x) => x.id)).toEqual(["a", "b"]);
+  });
+
+  it("keeps stable order for equal resolvedAt timestamps", () => {
+    const ts = "2026-03-03T03:03:03.000Z";
+    const x = resolvedAtComment("x", ts);
+    const y = resolvedAtComment("y", ts);
+    const z = resolvedAtComment("z", ts);
+    expect(sortResolvedByResolvedAt([x, y, z]).map((c) => c.id)).toEqual([
+      "x",
+      "y",
+      "z",
+    ]);
+  });
+});
+
 function renderReplyEditor() {
   return render(
     <MantineProvider>

apps/client/src/features/comment/components/comment-list-with-tabs.tsx

@@ -53,6 +53,22 @@ export function buildChildrenByParent(
   return m;
 }
 
+// Sort the Resolved tab by resolve time, newest first, on a COPY (never mutate
+// the react-query cache array). `resolvedAt` is typed `Date` but at runtime it
+// is an ISO STRING (from the axios-JSON onSuccess and the WS subscription) — a
+// real Date only during the optimistic onMutate window — so it MUST be coerced
+// with `new Date(...)` before `.getTime()`, or a raw `.getTime()` on the string
+// throws / yields NaN. ES2019's stable sort preserves order for equal
+// timestamps. Callers pass a list already filtered to a truthy `resolvedAt`, so
+// the non-null assertion is safe.
+// Exported for unit testing.
+export function sortResolvedByResolvedAt(resolved: IComment[]): IComment[] {
+  return [...resolved].sort(
+    (a, b) =>
+      new Date(b.resolvedAt!).getTime() - new Date(a.resolvedAt!).getTime(),
+  );
+}
+
 function CommentListWithTabs({ onClose }: CommentListWithTabsProps) {
   const { t } = useTranslation();
   const { pageSlug } = useParams();
@@ -91,7 +107,10 @@ function CommentListWithTabs({ onClose }: CommentListWithTabsProps) {
       (comment: IComment) => comment.resolvedAt,
     );
 
-    return { activeComments: active, resolvedComments: resolved };
+    return {
+      activeComments: active,
+      resolvedComments: sortResolvedByResolvedAt(resolved),
+    };
   }, [comments]);
 
   // Index replies by their parent once, instead of an O(n^2) filter per thread.

apps/client/src/features/comment/queries/comment-query.resolve-undo.test.tsx

@@ -0,0 +1,353 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import React from "react";
+import { renderHook, waitFor } from "@testing-library/react";
+import {
+  QueryClient,
+  QueryClientProvider,
+  InfiniteData,
+} from "@tanstack/react-query";
+
+/**
+ * Coverage for the resolve/reopen mutation (#542): the Undo-in-toast reopen and
+ * its double-click guard, the terminal 404 branch (drop from cache + clear the
+ * inline mark, no rollback), and the directional error copy.
+ */
+
+// A fake TipTap editor injected via the mocked pageEditorAtom, so we can assert
+// the mutation clears the inline comment mark (unsetComment / setCommentResolved).
+const editorMock = vi.hoisted(() => ({
+  current: {
+    isDestroyed: false,
+    commands: { unsetComment: vi.fn(), setCommentResolved: vi.fn() },
+  } as {
+    isDestroyed: boolean;
+    commands: {
+      unsetComment: (id: string) => void;
+      setCommentResolved: (id: string, v: boolean) => void;
+    };
+  } | null,
+}));
+
+vi.mock("@mantine/notifications", () => ({
+  notifications: { show: vi.fn(), hide: vi.fn() },
+}));
+
+vi.mock("jotai", () => ({
+  atom: (v: unknown) => v,
+  useAtomValue: () => editorMock.current,
+}));
+
+vi.mock("@/features/comment/services/comment-service", () => ({
+  applySuggestion: vi.fn(),
+  dismissSuggestion: vi.fn(),
+  createComment: vi.fn(),
+  updateComment: vi.fn(),
+  deleteComment: vi.fn(),
+  resolveComment: vi.fn(),
+  getPageComments: vi.fn(),
+}));
+
+import { notifications } from "@mantine/notifications";
+import { resolveComment } from "@/features/comment/services/comment-service";
+import {
+  useResolveCommentMutation,
+  RESOLVE_UNDO_AUTOCLOSE_MS,
+  RQ_KEY,
+} from "@/features/comment/queries/comment-query";
+import { IComment } from "@/features/comment/types/comment.types";
+
+const PAGE_ID = "page-1";
+
+function seededClient(comment: IComment) {
+  const queryClient = new QueryClient({
+    defaultOptions: { mutations: { retry: false } },
+  });
+  const seed: InfiniteData<any> = {
+    pageParams: [undefined],
+    pages: [
+      { items: [comment], meta: { hasNextPage: false, nextCursor: null } },
+    ],
+  };
+  queryClient.setQueryData(RQ_KEY(PAGE_ID), seed);
+  const wrapper = ({ children }: { children: React.ReactNode }) => (
+    <QueryClientProvider client={queryClient}>{children}</QueryClientProvider>
+  );
+  return { queryClient, wrapper };
+}
+
+function items(queryClient: QueryClient): IComment[] {
+  const cache = queryClient.getQueryData(RQ_KEY(PAGE_ID)) as
+    | InfiniteData<any>
+    | undefined;
+  return cache?.pages.flatMap((p) => p.items) ?? [];
+}
+
+const comment = (over?: Partial<IComment>): IComment =>
+  ({
+    id: "c-1",
+    pageId: PAGE_ID,
+    content: "{}",
+    creatorId: "u-1",
+    workspaceId: "ws-1",
+    createdAt: new Date(),
+    resolvedAt: null,
+    ...over,
+  }) as IComment;
+
+// Pull the inline Undo button's onClick out of the success toast's message tree.
+function undoOnClickFromToast(): () => void {
+  const call = vi
+    .mocked(notifications.show)
+    .mock.calls.map((c) => c[0])
+    .find((arg: any) => arg?.autoClose === RESOLVE_UNDO_AUTOCLOSE_MS);
+  expect(call).toBeTruthy();
+  const message: any = (call as any).message;
+  // message = Group( Text, Button ); grab the Button element's onClick.
+  const children = message.props.children as any[];
+  const button = children[1];
+  return button.props.onClick;
+}
+
+describe("useResolveCommentMutation — Undo toast (#542)", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    editorMock.current = {
+      isDestroyed: false,
+      commands: { unsetComment: vi.fn(), setCommentResolved: vi.fn() },
+    };
+  });
+
+  it("resolve shows an Undo toast with autoClose=10000ms; reopen shows NO Undo", async () => {
+    vi.mocked(resolveComment).mockImplementation(async (data) =>
+      comment({
+        resolvedAt: data.resolved ? (new Date() as any) : null,
+      }),
+    );
+    const { wrapper } = seededClient(comment());
+    const { result } = renderHook(() => useResolveCommentMutation(), {
+      wrapper,
+    });
+
+    await result.current.mutateAsync({
+      commentId: "c-1",
+      pageId: PAGE_ID,
+      resolved: true,
+    });
+    await waitFor(() => expect(result.current.isSuccess).toBe(true));
+
+    const resolveToast = vi
+      .mocked(notifications.show)
+      .mock.calls.map((c) => c[0])
+      .find((a: any) => a?.autoClose === RESOLVE_UNDO_AUTOCLOSE_MS);
+    expect(resolveToast).toBeTruthy();
+    expect((resolveToast as any).id).toBe("resolve-undo-c-1");
+    expect((resolveToast as any).autoClose).toBe(10000);
+
+    // Now a reopen → plain toast, no autoClose/Undo, no id.
+    vi.clearAllMocks();
+    await result.current.mutateAsync({
+      commentId: "c-1",
+      pageId: PAGE_ID,
+      resolved: false,
+    });
+    await waitFor(() => expect(result.current.isSuccess).toBe(true));
+    const calls = vi.mocked(notifications.show).mock.calls.map((c) => c[0]);
+    expect(
+      calls.some((a: any) => a?.autoClose === RESOLVE_UNDO_AUTOCLOSE_MS),
+    ).toBe(false);
+    expect(calls).toContainEqual({ message: "Comment re-opened successfully" });
+  });
+
+  it("double/fast Undo click fires reopen EXACTLY once (guard)", async () => {
+    vi.mocked(resolveComment).mockImplementation(async (data) =>
+      comment({ resolvedAt: data.resolved ? (new Date() as any) : null }),
+    );
+    const { wrapper } = seededClient(comment());
+    const { result } = renderHook(() => useResolveCommentMutation(), {
+      wrapper,
+    });
+
+    await result.current.mutateAsync({
+      commentId: "c-1",
+      pageId: PAGE_ID,
+      resolved: true,
+    });
+    await waitFor(() => expect(result.current.isSuccess).toBe(true));
+
+    const onClick = undoOnClickFromToast();
+    // Fire twice synchronously (notifications.hide is not synchronous).
+    onClick();
+    onClick();
+
+    await waitFor(() => {
+      const reopenCalls = vi
+        .mocked(resolveComment)
+        .mock.calls.filter(([d]) => d.resolved === false);
+      expect(reopenCalls).toHaveLength(1);
+    });
+    // The mark was cleared once via setCommentResolved(id, false).
+    expect(editorMock.current!.commands.setCommentResolved).toHaveBeenCalledWith(
+      "c-1",
+      false,
+    );
+    // The toast was hidden.
+    expect(notifications.hide).toHaveBeenCalledWith("resolve-undo-c-1");
+  });
+
+  it("404 → drops the comment from cache, clears the inline mark, no rollback, no Undo", async () => {
+    vi.mocked(resolveComment).mockRejectedValue({ response: { status: 404 } });
+    const { queryClient, wrapper } = seededClient(comment());
+    const { result } = renderHook(() => useResolveCommentMutation(), {
+      wrapper,
+    });
+
+    await result.current
+      .mutateAsync({ commentId: "c-1", pageId: PAGE_ID, resolved: true })
+      .catch(() => undefined);
+    await waitFor(() => expect(result.current.isError).toBe(true));
+
+    // Removed from cache (NOT rolled back to a phantom).
+    expect(items(queryClient)).toHaveLength(0);
+    // Inline mark cleared via unsetComment (mandatory — no panel row left to do it).
+    expect(editorMock.current!.commands.unsetComment).toHaveBeenCalledWith(
+      "c-1",
+    );
+    // Neutral message, red, and crucially NOT the success copy and NO Undo toast.
+    expect(notifications.show).toHaveBeenCalledWith({
+      message: "Comment no longer exists",
+      color: "red",
+    });
+    const calls = vi.mocked(notifications.show).mock.calls.map((c) => c[0]);
+    expect(
+      calls.some((a: any) => a?.autoClose === RESOLVE_UNDO_AUTOCLOSE_MS),
+    ).toBe(false);
+  });
+
+  it("404 does not crash when the editor is gone (read-only / panel closed)", async () => {
+    editorMock.current = null;
+    vi.mocked(resolveComment).mockRejectedValue({ response: { status: 404 } });
+    const { queryClient, wrapper } = seededClient(comment());
+    const { result } = renderHook(() => useResolveCommentMutation(), {
+      wrapper,
+    });
+
+    await result.current
+      .mutateAsync({ commentId: "c-1", pageId: PAGE_ID, resolved: true })
+      .catch(() => undefined);
+    await waitFor(() => expect(result.current.isError).toBe(true));
+    expect(items(queryClient)).toHaveLength(0);
+    expect(notifications.show).toHaveBeenCalledWith({
+      message: "Comment no longer exists",
+      color: "red",
+    });
+  });
+
+  it("non-404 error on REOPEN shows 'Failed to re-open comment' and rolls back", async () => {
+    vi.mocked(resolveComment).mockRejectedValue({ response: { status: 500 } });
+    // Seed a RESOLVED comment (the reopen target).
+    const resolved = comment({ resolvedAt: new Date() as any });
+    const { queryClient, wrapper } = seededClient(resolved);
+    const { result } = renderHook(() => useResolveCommentMutation(), {
+      wrapper,
+    });
+
+    await result.current
+      .mutateAsync({ commentId: "c-1", pageId: PAGE_ID, resolved: false })
+      .catch(() => undefined);
+    await waitFor(() => expect(result.current.isError).toBe(true));
+
+    expect(notifications.show).toHaveBeenCalledWith({
+      message: "Failed to re-open comment",
+      color: "red",
+    });
+    expect(notifications.show).not.toHaveBeenCalledWith(
+      expect.objectContaining({ message: "Failed to resolve comment" }),
+    );
+    // Rolled back: the comment is still present and still resolved.
+    expect(items(queryClient)).toHaveLength(1);
+    expect(items(queryClient)[0].resolvedAt).toBeTruthy();
+  });
+
+  it("reopen via Undo FAILS (non-404) → inline mark is NOT left cleared (doc↔panel stay consistent)", async () => {
+    // First resolve succeeds → produces the Undo toast (no mark change on resolve).
+    vi.mocked(resolveComment).mockResolvedValueOnce(
+      comment({ resolvedAt: new Date() as any }),
+    );
+    const { queryClient, wrapper } = seededClient(comment());
+    const { result } = renderHook(() => useResolveCommentMutation(), {
+      wrapper,
+    });
+
+    await result.current.mutateAsync({
+      commentId: "c-1",
+      pageId: PAGE_ID,
+      resolved: true,
+    });
+    await waitFor(() => expect(result.current.isSuccess).toBe(true));
+
+    // Now the reopen fired by Undo fails with a 500.
+    vi.mocked(resolveComment).mockRejectedValue({ response: { status: 500 } });
+    const onClick = undoOnClickFromToast();
+    onClick();
+
+    await waitFor(() => expect(result.current.isError).toBe(true));
+
+    // Core F1 guarantee: the mark-clear now lives in the reopen onSuccess, so a
+    // FAILED reopen must never flip the inline mark to unresolved — otherwise the
+    // doc would show an active highlight the panel still treats as resolved and
+    // the collab mark would diverge with nothing committed on the server.
+    expect(
+      editorMock.current!.commands.setCommentResolved,
+    ).not.toHaveBeenCalledWith("c-1", false);
+    // Cache rolled back: the comment stays resolved and present.
+    expect(items(queryClient)).toHaveLength(1);
+    expect(items(queryClient)[0].resolvedAt).toBeTruthy();
+  });
+
+  it("reopen success with a null editorRef degrades gracefully (no throw, no-op)", async () => {
+    // Read-only view / panel closed: pageEditorAtom is null on the success path.
+    editorMock.current = null;
+    vi.mocked(resolveComment).mockResolvedValue(comment({ resolvedAt: null }));
+    const resolved = comment({ resolvedAt: new Date() as any });
+    const { queryClient, wrapper } = seededClient(resolved);
+    const { result } = renderHook(() => useResolveCommentMutation(), {
+      wrapper,
+    });
+
+    await result.current.mutateAsync({
+      commentId: "c-1",
+      pageId: PAGE_ID,
+      resolved: false,
+    });
+    await waitFor(() => expect(result.current.isSuccess).toBe(true));
+
+    // No crash from the reopen mark-clear; the plain reopen toast is still shown.
+    expect(notifications.show).toHaveBeenCalledWith({
+      message: "Comment re-opened successfully",
+    });
+    // Cache updated to reopened (resolvedAt cleared by the server payload).
+    expect(items(queryClient)).toHaveLength(1);
+    expect(items(queryClient)[0].resolvedAt).toBeFalsy();
+  });
+
+  it("non-404 error on RESOLVE shows 'Failed to resolve comment' and rolls back", async () => {
+    vi.mocked(resolveComment).mockRejectedValue({ response: { status: 500 } });
+    const { queryClient, wrapper } = seededClient(comment());
+    const { result } = renderHook(() => useResolveCommentMutation(), {
+      wrapper,
+    });
+
+    await result.current
+      .mutateAsync({ commentId: "c-1", pageId: PAGE_ID, resolved: true })
+      .catch(() => undefined);
+    await waitFor(() => expect(result.current.isError).toBe(true));
+
+    expect(notifications.show).toHaveBeenCalledWith({
+      message: "Failed to resolve comment",
+      color: "red",
+    });
+    // Rolled back to open (previousCache), still present.
+    expect(items(queryClient)).toHaveLength(1);
+    expect(items(queryClient)[0].resolvedAt).toBeFalsy();
+  });
+});

apps/client/src/features/comment/queries/comment-query.ts

@@ -20,12 +20,19 @@ import {
   ISuggestionOutcome,
 } from "@/features/comment/types/comment.types";
 import { notifications } from "@mantine/notifications";
+import { Button, Group, Text } from "@mantine/core";
 import { IPagination } from "@/lib/types.ts";
 import { useTranslation } from "react-i18next";
-import { useEffect, useMemo } from "react";
+import React, { useEffect, useMemo, useRef } from "react";
+import { useAtomValue } from "jotai";
+import { pageEditorAtom } from "@/features/editor/atoms/editor-atoms";
 
 export const RQ_KEY = (pageId: string) => ["comments", pageId];
 
+// How long the resolve success toast (with its inline Undo) stays up before it
+// auto-closes. Policy constant — no env override.
+export const RESOLVE_UNDO_AUTOCLOSE_MS = 10000;
+
 export function useCommentsQuery(params: ICommentParams) {
   const query = useInfiniteQuery({
     queryKey: RQ_KEY(params.pageId),
@@ -376,7 +383,25 @@ export function useResolveCommentMutation() {
   const queryClient = useQueryClient();
   const { t } = useTranslation();
 
-  return useMutation({
+  // Keep the live editor in a ref: the toast's Undo (and the 404 branch) must
+  // clear the inline comment mark AFTER the originating CommentListItem has
+  // unmounted (resolving pulls the comment out of the Open list, so its item is
+  // already gone by the time the 10s toast is clicked). In read-only view
+  // pageEditorAtom is null and the mark converges via the server's
+  // COMMENT_MARK_UPDATE job instead.
+  const editor = useAtomValue(pageEditorAtom);
+  const editorRef = useRef(editor);
+  editorRef.current = editor;
+
+  // Self-reference the mutation so the toast's Undo can re-invoke it (reopen)
+  // long after the triggering component unmounted. Declared BEFORE useMutation
+  // and assigned AFTER; the onClick reads mutationRef.current at CALL time, not
+  // definition time, so there is no initialization cycle.
+  const mutationRef = useRef<{
+    mutate: (vars: IResolveComment) => void;
+  } | null>(null);
+
+  const mutation = useMutation({
     mutationFn: (data: IResolveComment) => resolveComment(data),
     onMutate: async (variables) => {
       await queryClient.cancelQueries({ queryKey: RQ_KEY(variables.pageId) });
@@ -401,7 +426,39 @@ export function useResolveCommentMutation() {
 
       return { previousCache };
     },
-    onError: (_err, variables, context) => {
+    onError: (err: any, variables, context) => {
+      // Terminal 404: the comment was really deleted (missing comment or deleted
+      // page — access denial is 403, resolve is idempotent so no 400). Do NOT
+      // roll back (that would resurrect a phantom row in Resolved); instead drop
+      // it from the cache and clear its now-orphaned inline mark. Mirrors
+      // handleDeleteComment and the dismiss-mutation 404 branch.
+      if (err?.response?.status === 404) {
+        const cache = queryClient.getQueryData(RQ_KEY(variables.pageId)) as
+          | InfiniteData<IPagination<IComment>>
+          | undefined;
+        if (cache) {
+          queryClient.setQueryData(
+            RQ_KEY(variables.pageId),
+            removeCommentFromCache(cache, variables.commentId),
+          );
+        }
+        const ed = editorRef.current;
+        if (ed && !ed.isDestroyed) {
+          try {
+            ed.commands.unsetComment(variables.commentId);
+          } catch {
+            /* editor gone / mark already removed */
+          }
+        }
+        notifications.show({
+          message: t("Comment no longer exists"),
+          color: "red",
+        });
+        return;
+      }
+
+      // Generic failure: roll back the optimistic update and show a DIRECTIONAL
+      // error (resolve vs. reopen), not always "resolve".
       if (context?.previousCache) {
         queryClient.setQueryData(
           RQ_KEY(variables.pageId),
@@ -409,7 +466,9 @@ export function useResolveCommentMutation() {
         );
       }
       notifications.show({
-        message: t("Failed to resolve comment"),
+        message: variables.resolved
+          ? t("Failed to resolve comment")
+          : t("Failed to re-open comment"),
         color: "red",
       });
     },
@@ -430,11 +489,72 @@ export function useResolveCommentMutation() {
         );
       }
 
+      // Reopen keeps the plain toast without an Undo.
+      if (!variables.resolved) {
+        // Clear the inline mark ONLY after the server confirms the reopen, so a
+        // failed reopen never leaves an active highlight the panel still treats
+        // as resolved. Mirrors the 404 branch's editor-liveness guard/try-catch.
+        // The button-triggered reopen already set the mark, so this is an
+        // idempotent no-op there.
+        const ed = editorRef.current;
+        if (ed && !ed.isDestroyed) {
+          try {
+            ed.commands.setCommentResolved(variables.commentId, false);
+          } catch {
+            /* editor gone — server COMMENT_MARK_UPDATE converges it */
+          }
+        }
+        notifications.show({ message: t("Comment re-opened successfully") });
+        return;
+      }
+
+      // Resolve: attach an inline Undo (reopen) to the success toast. Built with
+      // React.createElement because this is a .ts module (no JSX).
+      const { commentId, pageId } = variables;
+      const notificationId = `resolve-undo-${commentId}`;
+      // Double-click guard: notifications.hide is NOT synchronous, so the button
+      // stays clickable for a frame or two — without this a fast double-click
+      // would fire reopen twice.
+      let done = false;
       notifications.show({
-        message: variables.resolved
-          ? t("Comment resolved successfully")
-          : t("Comment re-opened successfully"),
+        id: notificationId,
+        autoClose: RESOLVE_UNDO_AUTOCLOSE_MS,
+        message: React.createElement(
+          Group,
+          { justify: "space-between", wrap: "nowrap", gap: "md" },
+          React.createElement(
+            Text,
+            { size: "sm" },
+            t("Comment resolved successfully"),
+          ),
+          React.createElement(
+            Button,
+            {
+              variant: "subtle",
+              size: "compact-sm",
+              onClick: () => {
+                if (done) return;
+                done = true;
+                // Reopen via the SAME mutation (read at click time — the
+                // originating item is already unmounted).
+                mutationRef.current?.mutate({
+                  commentId,
+                  pageId,
+                  resolved: false,
+                });
+                // The inline mark is cleared in the reopen mutation's onSuccess
+                // (bound to server confirmation), NOT here — clearing it eagerly
+                // would desync the doc from the panel if reopen then fails.
+                notifications.hide(notificationId);
+              },
+            },
+            t("Undo"),
+          ),
+        ),
       });
     },
   });
+
+  mutationRef.current = mutation;
+  return mutation;
 }

apps/server/src/core/ai-chat/ai-chat.service.ts

@@ -189,10 +189,11 @@ export function stepBudgetWarning(stepNumber: number): string {
 //
 // `system` is the in-scope system prompt; we CONCATENATE so the original
 // persona/context is preserved — a bare `system` override would REPLACE the
-// whole system prompt for the step. `activatedTools` is PER-TURN mutable state
-// owned by the streaming loop (a closure Set grown by loadTools); it is passed
-// in (not module-global, not persisted) so this stays a pure function of its
-// arguments.
+// whole system prompt for the step. `activatedTools` is a closure Set grown by
+// loadTools and owned by the streaming loop; the caller seeds it from and
+// persists it to the chat's metadata across turns (#490), but this function only
+// READS the Set it is handed, so it stays a pure function of its arguments (not
+// module-global).
 //
 // NOTE: at AI SDK v7 the per-step `system` field is renamed to `instructions`.
 // On v6 (`^6.0.134`) `system` is the correct field — adjust when bumping.
@@ -1410,10 +1411,11 @@ export class AiChatService implements OnModuleInit, OnModuleDestroy {
       const baseTools = { ...external.tools, ...docmostTools };
 
       // Deferred tool loading state (#332), scoped to THIS streaming loop:
-      //  - `activatedTools` is per-TURN mutable state — a fresh closure Set created
-      //    per streamText call, NOT module-global and NOT persisted, so a new turn
-      //    starts cold. loadTools.execute adds to it; prepareAgentStep reads it to
-      //    widen `activeTools` on the NEXT step.
+      //  - `activatedTools` is a fresh closure Set per streamText call (not
+      //    module-global), SEEDED from the chat's persisted metadata.activatedTools
+      //    (#490, just below) so activation carries across turns. loadTools.execute
+      //    adds to it; prepareAgentStep reads it to widen `activeTools` on the NEXT
+      //    step; turn end persists it back.
       //  - `validDeferredNames` = every tool that is NOT core (the in-app deferred
       //    tools + ALL external MCP tools), computed from the ACTUAL toolset so an
       //    external tool is loadable by its namespaced name. loadTools rejects any

apps/server/src/integrations/import/services/import-attachment.service.drawio-svg.spec.ts

@@ -0,0 +1,131 @@
+// p-limit and @sindresorhus/slugify are ESM-only and not in jest's transform
+// allowlist; both are irrelevant to createDrawioSvg (a pure fs + string method),
+// so they are mocked out to keep the module graph loadable under ts-jest.
+jest.mock('p-limit', () => ({
+  __esModule: true,
+  default: () => (fn: () => unknown) => fn(),
+}));
+jest.mock('@sindresorhus/slugify', () => ({
+  __esModule: true,
+  default: (input: string) => String(input),
+}));
+
+import { promises as fs } from 'fs';
+import * as os from 'os';
+import * as path from 'path';
+import { ImportAttachmentService } from './import-attachment.service';
+
+/**
+ * Unit test for ImportAttachmentService.createDrawioSvg (issue #507).
+ *
+ * The Confluence import wraps a `.drawio` file into a `.drawio.svg` attachment.
+ * The `content=` payload MUST be the mxfile XML entity-escaped (draw.io's native
+ * form), NOT base64 — draw.io's editor decodes a base64 content= via Latin-1
+ * atob, mangling every non-ASCII char into mojibake. createDrawioSvg touches no
+ * injected dependency, so the service is built with placeholder deps.
+ */
+describe('ImportAttachmentService.createDrawioSvg (#507)', () => {
+  const service = new ImportAttachmentService(
+    {} as any,
+    {} as any,
+    {} as any,
+  );
+  const call = (p: string): Promise<Buffer> =>
+    (service as any).createDrawioSvg(p);
+
+  let tmpDir: string;
+  beforeAll(async () => {
+    tmpDir = await fs.mkdtemp(path.join(os.tmpdir(), 'drawio-507-'));
+  });
+  afterAll(async () => {
+    await fs.rm(tmpDir, { recursive: true, force: true });
+  });
+
+  const writeDrawio = async (name: string, xml: string): Promise<string> => {
+    const p = path.join(tmpDir, name);
+    await fs.writeFile(p, xml, 'utf-8');
+    return p;
+  };
+
+  it('writes content= as entity-encoded XML, not base64', async () => {
+    const drawio =
+      '<mxfile host="Confluence"><diagram name="Схема — ёж">' +
+      '<mxGraphModel><root><mxCell id="0"/>' +
+      '<mxCell id="2" value="Старт-бит" vertex="1" parent="0"/>' +
+      '</root></mxGraphModel></diagram></mxfile>';
+    const p = await writeDrawio('cyrillic.drawio', drawio);
+
+    const svg = (await call(p)).toString('utf-8');
+    const content = /content="([^"]*)"/.exec(svg)?.[1];
+    expect(content).toBeDefined();
+
+    // Entity-encoded XML form, starting with &lt;mxfile — never a base64 blob.
+    expect(content).toMatch(/^&lt;mxfile/);
+    expect(content).toContain('&lt;');
+    // Non-ASCII survives as raw UTF-8, with no Latin-1 mojibake.
+    expect(content).toContain('Старт-бит');
+    expect(content).toContain('Схема — ёж');
+    expect(content).not.toContain('Ð');
+
+    // Decoding the attribute (un-escaping) yields the original drawio file.
+    const decoded = content!
+      .replace(/&lt;/g, '<')
+      .replace(/&gt;/g, '>')
+      .replace(/&quot;/g, '"')
+      .replace(/&amp;/g, '&');
+    expect(decoded).toBe(drawio);
+  });
+
+  it('encodes literal tab/newline/CR as numeric char-refs, not literal control chars (#507 F1)', async () => {
+    // A literal tab/newline/CR inside the mxfile XML would be collapsed to a
+    // single space by XML attribute-value normalization when the draw.io editor
+    // reads content=, silently flattening multi-line labels and tab-bearing
+    // values. They must be emitted as numeric char-refs instead.
+    const drawio =
+      '<mxfile><diagram name="p">' +
+      '<mxGraphModel><root><mxCell id="0"/>' +
+      '<mxCell id="2" value="col1\tcol2" style="html=1;\nshadow=0" vertex="1" parent="0"/>' +
+      '<mxCell id="3" value="Line1\nLine2\rLine3" vertex="1" parent="0"/>' +
+      '</root></mxGraphModel></diagram></mxfile>';
+    const p = await writeDrawio('ctrl.drawio', drawio);
+
+    const svg = (await call(p)).toString('utf-8');
+    const content = /content="([^"]*)"/.exec(svg)?.[1];
+    expect(content).toBeDefined();
+    // No literal control chars survive in the attribute value.
+    expect(content).not.toMatch(/[\t\n\r]/);
+    // They round-trip as numeric char-refs.
+    expect(content).toContain('&#x9;');
+    expect(content).toContain('&#xa;');
+    expect(content).toContain('&#xd;');
+    // Decoding (char-refs back to literal, entities back) recovers the file.
+    const decoded = content!
+      .replace(/&lt;/g, '<')
+      .replace(/&gt;/g, '>')
+      .replace(/&quot;/g, '"')
+      .replace(/&#39;/g, "'")
+      .replace(/&#x9;/gi, '\t')
+      .replace(/&#xa;/gi, '\n')
+      .replace(/&#xd;/gi, '\r')
+      .replace(/&amp;/g, '&');
+    expect(decoded).toBe(drawio);
+  });
+
+  it('escapes XML metacharacters in the drawio payload', async () => {
+    const drawio = '<mxfile><diagram name="a &amp; b">"q" &lt;x&gt;</diagram></mxfile>';
+    const p = await writeDrawio('meta.drawio', drawio);
+
+    const svg = (await call(p)).toString('utf-8');
+    const content = /content="([^"]*)"/.exec(svg)?.[1];
+    expect(content).toBeDefined();
+    // The attribute value must contain no bare `<`, `>` or `"` that would break
+    // out of the content="..." attribute or the SVG element.
+    expect(content).not.toMatch(/[<>"]/);
+    const decoded = content!
+      .replace(/&lt;/g, '<')
+      .replace(/&gt;/g, '>')
+      .replace(/&quot;/g, '"')
+      .replace(/&amp;/g, '&');
+    expect(decoded).toBe(drawio);
+  });
+});

apps/server/src/integrations/import/services/import-attachment.service.ts

@@ -8,6 +8,7 @@ import { createReadStream } from 'node:fs';
 import { promises as fs } from 'fs';
 import { Readable } from 'stream';
 import { getMimeType, sanitizeFileName } from '../../../common/helpers';
+import { htmlEscape } from '../../../common/helpers/html-escaper';
 import { v7 } from 'uuid';
 import { FileTask } from '@docmost/db/types/entity.types';
 import { getAttachmentFolderPath } from '../../../core/attachment/attachment.utils';
@@ -849,7 +850,12 @@ export class ImportAttachmentService {
   ): Promise<Buffer> {
     try {
       const drawioContent = await fs.readFile(drawioPath, 'utf-8');
-      const drawioBase64 = Buffer.from(drawioContent).toString('base64');
+      // Write the mxfile XML XML-entity-escaped (draw.io's native content= form),
+      // NOT base64. draw.io's editor decodes a base64 content= via Latin-1 atob
+      // (no UTF-8 step), turning every non-ASCII char (Cyrillic, ё, —) into
+      // mojibake; the entity-encoded form is decoded by the DOM as UTF-8 and
+      // opens intact. Docmost's own decoder reads both forms.
+      const drawioEscaped = this.xmlEscapeContent(drawioContent);
 
       let imageElement = '';
       // If we have a PNG, include it in the SVG
@@ -875,7 +881,7 @@ export class ImportAttachmentService {
       width="600"
       height="400"
       viewBox="0 0 600 400"
-      content="${drawioBase64}">${imageElement}</svg>`;
+      content="${drawioEscaped}">${imageElement}</svg>`;
 
       return Buffer.from(svgContent, 'utf-8');
     } catch (error) {
@@ -884,6 +890,24 @@ export class ImportAttachmentService {
     }
   }
 
+  /**
+   * Escape a string so it is safe as the value of a double-quoted XML attribute
+   * (the `content=` payload of a `.drawio.svg`). The shared `htmlEscape` covers
+   * `& < > " '` (a strict superset of what this attribute needs; the extra `'`
+   * escape is harmless in a `"`-delimited value). On top of that, the numeric
+   * char-refs for tab/newline/CR are required: a literal tab/newline/CR inside
+   * an attribute value is collapsed to a single space by XML attribute-value
+   * normalization on DOM read (both our decoder and the real draw.io editor),
+   * silently flattening multi-line labels and tab-bearing values. Char-refs
+   * survive that normalization (#507).
+   */
+  private xmlEscapeContent(s: string): string {
+    return htmlEscape(s)
+      .replace(/\t/g, '&#x9;')
+      .replace(/\n/g, '&#xa;')
+      .replace(/\r/g, '&#xd;');
+  }
+
   private async uploadWithRetry(opts: {
     abs: string;
     storageFilePath: string;

apps/server/test/integration/ai-chat-stream.int-spec.ts

@@ -322,20 +322,21 @@ describe('AiChatService.stream [integration]', () => {
   });
 
   /**
-   * #332 deferred tool loading, the ON path. The riskiest property is that the
-   * per-turn `activatedTools` Set is created FRESH inside each stream() call, so a
-   * tool a previous turn activated via loadTools is NOT still active when the next
-   * turn starts — the new turn begins "cold" (CORE + loadTools only). The unit
-   * tests only exercise pure prepareAgentStep with hand-fed Sets; this pins the
-   * real wiring end-to-end (loadTools.execute -> activatedTools -> prepareStep ->
-   * per-step activeTools) against the real streamText loop, and proves there is no
-   * cross-turn leak. We drive a MockLanguageModelV3 whose step 1 calls
-   * loadTools(['createPage']) and assert, via the model's recorded per-step
-   * CallOptions.tools (the AI SDK filters the provider tool list by activeTools),
-   * that the deferred tool becomes active on the SAME turn's next step but NOT on a
-   * fresh turn's first step.
+   * #332 + #490 deferred tool loading, the ON path. Turn 1 starts COLD (CORE +
+   * loadTools only) and activates a deferred tool via loadTools; that activation
+   * is PERSISTED into the chat's metadata.activatedTools (#490) so the NEXT turn
+   * SEEDS from it and the tool is active from the fresh turn's FIRST step — the
+   * model never re-runs loadTools to re-activate the same tool. The unit tests
+   * only exercise pure prepareAgentStep with hand-fed Sets; this pins the real
+   * wiring end-to-end (loadTools.execute -> activatedTools -> persist -> next-turn
+   * seed -> prepareStep -> per-step activeTools) against the real streamText loop.
+   * We drive a MockLanguageModelV3 whose step 1 calls loadTools(['createPage'])
+   * and assert, via the model's recorded per-step CallOptions.tools (the AI SDK
+   * filters the provider tool list by activeTools), that the deferred tool becomes
+   * active on the SAME turn's next step AND, seeded from metadata, on the next
+   * turn's first step.
    */
-  describe('deferred tool loading ON — per-turn activation, no leak (#332)', () => {
+  describe('deferred tool loading ON — cross-turn activation persistence (#332 + #490)', () => {
     // A stub deferred (non-core) tool the agent can activate. Its execute is never
     // called — the model only needs to SEE it become active — but it must be a
     // valid AI-SDK tool so the SDK includes it in a step's tool list once active.
@@ -451,7 +452,7 @@ describe('AiChatService.stream [integration]', () => {
       } as any);
     }
 
-    it('activates a deferred tool for the SAME turn, and a NEW turn starts cold (no leak)', async () => {
+    it('activates a deferred tool for the SAME turn, and a NEW turn SEEDS it from persisted chat metadata (#490)', async () => {
       const chatId = (await createChat(db, { workspaceId, creatorId: userId })).id;
 
       // --- Turn 1: loadTools(createPage) on step 1, then answer on step 2. ---
@@ -474,7 +475,7 @@ describe('AiChatService.stream [integration]', () => {
       // Step 2 of the SAME turn sees the just-activated deferred tool.
       expect(step2Tools).toContain('createPage');
 
-      // --- Turn 2 on the SAME chat: must start cold again. ---
+      // --- Turn 2 on the SAME chat: seeds the persisted activation (#490). ---
       const model2 = new MockLanguageModelV3({
         doStream: async () => ({ stream: successStream() }),
       } as any);
@@ -485,9 +486,10 @@ describe('AiChatService.stream [integration]', () => {
 
       const nextTurnFirstStep = toolNames(model2.doStreamCalls[0]);
       expect(nextTurnFirstStep).toContain('loadTools');
-      // The activated set is per-turn: the prior turn's createPage did NOT leak,
-      // so the fresh turn's first step sees it deferred again.
-      expect(nextTurnFirstStep).not.toContain('createPage');
+      // #490: activation PERSISTS across turns — turn 1 wrote createPage into the
+      // chat's metadata.activatedTools, so the next turn seeds from it and the
+      // deferred tool is active from the FIRST step (no need to re-run loadTools).
+      expect(nextTurnFirstStep).toContain('createPage');
     });
   });
 });

packages/mcp/src/lib/drawio-xml.ts

@@ -178,10 +178,11 @@ function sliceModel(xml: string): string | null {
 // --- decode chain ----------------------------------------------------------
 
 /**
- * Read the `content=` attribute out of a `.drawio.svg` string. Docmost stores a
- * base64 payload there (createDrawioSvg); draw.io's own SVG export may store the
- * XML entity-encoded instead. The DOM decodes entities for us, so the caller
- * only has to distinguish "starts with '<'" (raw XML) from base64.
+ * Read the `content=` attribute out of a `.drawio.svg` string. Docmost writes
+ * the mxfile XML entity-encoded there (buildDrawioSvg / createDrawioSvg), which
+ * is also how draw.io's own SVG export stores it; older attachments stored a
+ * base64 payload instead. The DOM decodes entities for us, so the caller only
+ * has to distinguish "starts with '<'" (raw XML) from base64.
  */
 export function extractContentAttr(svg: string): string {
   const { doc, error } = parseXml(svg);
@@ -195,12 +196,23 @@ export function extractContentAttr(svg: string): string {
   // value itself never contains a double-quote (base64 / entity-encoded XML).
   const m = /content="([^"]*)"/.exec(svg);
   if (m) {
-    // Decode the handful of XML entities a raw regex would leave encoded.
+    // Decode the handful of XML entities a raw regex would leave encoded. The
+    // numeric char-refs for tab/newline/CR MUST be decoded here too: the DOM
+    // path above turns them back into the literal control chars, so this
+    // regex fallback has to agree or the two decode paths diverge (#507).
+    // `&amp;` is decoded last so an escaped `&amp;#x9;` reads back as the
+    // literal text `&#x9;`, not a tab.
     return m[1]
       .replace(/&lt;/g, "<")
       .replace(/&gt;/g, ">")
       .replace(/&quot;/g, '"')
       .replace(/&#39;/g, "'")
+      .replace(/&#x9;/gi, "\t")
+      .replace(/&#9;/g, "\t")
+      .replace(/&#xa;/gi, "\n")
+      .replace(/&#10;/g, "\n")
+      .replace(/&#xd;/gi, "\r")
+      .replace(/&#13;/g, "\r")
       .replace(/&amp;/g, "&");
   }
   throw new Error("drawio: SVG has no content= attribute to decode");
@@ -307,9 +319,16 @@ export function encodeDrawioFile(modelXml: string, title = "Page-1"): string {
 /**
  * Build the `diagram.drawio.svg` attachment. Mirrors the import service's
  * createDrawioSvg contract exactly:
- *   <svg xmlns=… xmlns:xlink=… content="${base64(drawioFile)}">${inner}</svg>
+ *   <svg xmlns=… xmlns:xlink=… content="${xmlEscape(drawioFile)}">${inner}</svg>
  * plus width/height/viewBox from the diagram bounding box and the schematic
  * preview as the visible children (`inner`).
+ *
+ * The `content=` value is the mxfile XML XML-entity-escaped (draw.io's own
+ * native form), NOT base64. draw.io's editor decodes a base64 content= via
+ * Latin-1 atob (no UTF-8 step), turning every non-ASCII char (e.g. Cyrillic,
+ * ё, —) into mojibake; the entity-encoded form is decoded by the DOM as UTF-8
+ * and opens intact. Our decoder (decodeDrawioSvg) reads both forms, so old
+ * base64 attachments still round-trip.
  */
 export function buildDrawioSvg(
   modelXml: string,
@@ -318,14 +337,14 @@ export function buildDrawioSvg(
   title = "Page-1",
 ): string {
   const file = encodeDrawioFile(modelXml, title);
-  const base64 = Buffer.from(file, "utf-8").toString("base64");
+  const content = xmlEscape(file);
   const w = Math.max(1, Math.round(bbox.width));
   const h = Math.max(1, Math.round(bbox.height));
   return (
     `<svg xmlns="http://www.w3.org/2000/svg" ` +
     `xmlns:xlink="http://www.w3.org/1999/xlink" ` +
     `width="${w}" height="${h}" viewBox="0 0 ${w} ${h}" ` +
-    `content="${base64}">${inner}</svg>`
+    `content="${content}">${inner}</svg>`
   );
 }
 
@@ -334,7 +353,15 @@ function xmlEscape(s: string): string {
     .replace(/&/g, "&amp;")
     .replace(/</g, "&lt;")
     .replace(/>/g, "&gt;")
-    .replace(/"/g, "&quot;");
+    .replace(/"/g, "&quot;")
+    // A literal tab/newline/CR inside an attribute value is collapsed to a
+    // single space by XML attribute-value normalization on DOM read (both jsdom
+    // here and the real draw.io editor), silently flattening multi-line labels
+    // and tab-bearing values. Numeric char-refs survive that normalization, so
+    // emit them the way draw.io's own native export does (#507).
+    .replace(/\t/g, "&#x9;")
+    .replace(/\n/g, "&#xa;")
+    .replace(/\r/g, "&#xd;");
 }
 
 // --- normalization + hash --------------------------------------------------

packages/mcp/test/unit/drawio-xml.test.mjs

@@ -51,6 +51,14 @@ const hasRule = (issues, rule, cellId) =>
     (i) => i.rule === rule && (cellId === undefined || i.cellId === cellId),
   );
 
+// Reverse the attribute-value XML escaping used in the `content=` payload.
+const unescapeAttr = (s) =>
+  s
+    .replace(/&lt;/g, "<")
+    .replace(/&gt;/g, ">")
+    .replace(/&quot;/g, '"')
+    .replace(/&amp;/g, "&");
+
 // --- style parsing ---------------------------------------------------------
 
 test("parseStyle: base stylename + key=value pairs", () => {
@@ -335,16 +343,20 @@ test("encode/build: a title with < > \" & round-trips without corrupting the SVG
 
   // The outer content="..." attribute must not be broken by the title: the raw
   // title metacharacters never appear literally in the SVG markup (they are
-  // base64-encoded inside content=, and escaped inside the file XML).
+  // entity-escaped inside content=, doubly so where the file XML already escaped
+  // them inside name="...").
   const contentMatch = /content="([^"]*)"/.exec(svg);
   assert.ok(contentMatch, "SVG has a single well-formed content= attribute");
 
   // The diagram model still decodes losslessly despite the exotic title.
   assert.equal(decodeDrawioSvg(svg), model);
 
+  // content= is now entity-encoded XML (draw.io's native form), never base64.
+  assert.match(contentMatch[1], /^&lt;mxfile/);
+
   // The file XML is well-formed: the title lives in name="..." as escaped
   // entities, so unescaping recovers the original title byte-for-byte.
-  const fileXml = Buffer.from(contentMatch[1], "base64").toString("utf-8");
+  const fileXml = unescapeAttr(contentMatch[1]);
   const nameMatch = /<diagram id="[^"]*" name="([^"]*)">/.exec(fileXml);
   assert.ok(nameMatch, "the diagram name attribute is intact and quote-safe");
   const decodedTitle = nameMatch[1]
@@ -358,3 +370,112 @@ test("encode/build: a title with < > \" & round-trips without corrupting the SVG
   const file = encodeDrawioFile(model, title);
   assert.match(file, /name="A &lt; B &gt; C &quot; D &amp; E">/);
 });
+
+// --- #507: content= is entity-encoded XML, never base64 --------------------
+
+// A model whose cell values carry Cyrillic, ё and an em dash — exactly the
+// characters draw.io's Latin-1 atob mangles when content= is base64.
+const CYRILLIC_MODEL =
+  "<mxGraphModel><root>" +
+  '<mxCell id="0"/><mxCell id="1" parent="0"/>' +
+  '<mxCell id="2" value="Старт-бит — ёж" style="rounded=1;html=1;" vertex="1" parent="1">' +
+  '<mxGeometry x="100" y="100" width="120" height="60" as="geometry"/></mxCell>' +
+  "</root></mxGraphModel>";
+
+test("#507: buildDrawioSvg writes content= as entity-encoded XML (not base64)", () => {
+  const model = normalizeXml(CYRILLIC_MODEL);
+  const svg = buildDrawioSvg(model, "<g/>", { width: 200, height: 120 }, "Диаграмма");
+
+  const contentMatch = /content="([^"]*)"/.exec(svg);
+  assert.ok(contentMatch, "SVG has a single well-formed content= attribute");
+  const content = contentMatch[1];
+
+  // The content= value is the entity-encoded mxfile XML — starts with `&lt;mxfile`.
+  assert.match(content, /^&lt;mxfile/, "content= is entity-encoded mxfile XML");
+  // It must NOT be a base64 blob: base64 has no XML entities and no literal `<`.
+  assert.ok(content.includes("&lt;"), "content= carries XML entities, not base64");
+
+  // Cyrillic / ё / — survive verbatim in the attribute (raw UTF-8, not atob-mangled).
+  assert.ok(content.includes("Старт-бит — ёж"), "non-ASCII value is raw UTF-8 in content=");
+  assert.ok(content.includes("Диаграмма"), "non-ASCII title is raw UTF-8 in content=");
+  // The mojibake that base64+atob would have produced must be absent.
+  assert.ok(!content.includes("Ð"), "no Latin-1 mojibake in content=");
+});
+
+test("#507: Cyrillic model round-trips byte-stable through buildDrawioSvg -> decodeDrawioSvg", () => {
+  const model = normalizeXml(CYRILLIC_MODEL);
+  const svg = buildDrawioSvg(model, "<g/>", { width: 200, height: 120 }, "Заголовок — ё");
+  assert.equal(decodeDrawioSvg(svg), model);
+});
+
+test("#507 back-compat: an OLD base64-form .drawio.svg still decodes losslessly", () => {
+  const model = normalizeXml(CYRILLIC_MODEL);
+  // Reproduce the pre-fix write path: encodeDrawioFile -> base64 in content=.
+  const file = encodeDrawioFile(model, "Старая диаграмма");
+  const base64 = Buffer.from(file, "utf-8").toString("base64");
+  const svg =
+    `<svg xmlns="http://www.w3.org/2000/svg" content="${base64}"><g/></svg>`;
+  // No XML entities, purely base64 alphabet — this is the legacy form.
+  assert.ok(!base64.includes("<") && !base64.includes("&"));
+  assert.equal(decodeDrawioSvg(svg), model);
+});
+
+test("#507 negative: non-ASCII in a cell value AND in the title round-trip clean", () => {
+  const model = normalizeXml(CYRILLIC_MODEL);
+  const title = "Тест — ёмкость № 5";
+  const svg = buildDrawioSvg(model, "<g/>", { width: 200, height: 120 }, title);
+
+  // Model recovered byte-for-byte.
+  assert.equal(decodeDrawioSvg(svg), model);
+
+  // Title lands in the <diagram name="..."> of the decoded file XML, intact.
+  const content = /content="([^"]*)"/.exec(svg)[1];
+  const fileXml = unescapeAttr(content);
+  const nameMatch = /<diagram id="[^"]*" name="([^"]*)">/.exec(fileXml);
+  assert.ok(nameMatch, "diagram name attribute present");
+  assert.equal(unescapeAttr(nameMatch[1]), title);
+});
+
+// --- #507 F1: literal tab/newline/CR in an attribute value survive the
+// content= round-trip. The whole mxfile XML lives in one content="..." attr;
+// XML attribute-value normalization collapses a LITERAL tab/newline/CR to a
+// single space on DOM read, so the escape must emit numeric char-refs instead.
+const CTRL_MODEL =
+  "<mxGraphModel><root>" +
+  '<mxCell id="0"/><mxCell id="1" parent="0"/>' +
+  '<mxCell id="2" value="col1\tcol2" style="html=1;\nshadow=0" vertex="1" parent="1">' +
+  '<mxGeometry x="10" y="10" width="120" height="60" as="geometry"/></mxCell>' +
+  '<mxCell id="3" value="Line1\nLine2\rLine3" vertex="1" parent="1">' +
+  '<mxGeometry x="10" y="100" width="120" height="60" as="geometry"/></mxCell>' +
+  "</root></mxGraphModel>";
+
+test("#507 F1: literal tab/newline/CR in a value round-trip byte-stable (DOM decode)", () => {
+  const svg = buildDrawioSvg(CTRL_MODEL, "<g/>", { width: 200, height: 200 });
+  const content = /content="([^"]*)"/.exec(svg)[1];
+  // The tab/newline/CR must be emitted as numeric char-refs, never as literal
+  // control chars (which DOM attribute-value normalization would eat).
+  assert.ok(
+    !/[\t\n\r]/.test(content),
+    "no literal tab/newline/CR survive in the content= attribute",
+  );
+  assert.ok(
+    content.includes("&#x9;") &&
+      content.includes("&#xa;") &&
+      content.includes("&#xd;"),
+    "tab/newline/CR are emitted as numeric char-refs",
+  );
+  // Full DOM decode recovers the model byte-for-byte, control chars intact.
+  assert.equal(decodeDrawioSvg(svg), CTRL_MODEL);
+});
+
+test("#507 F1: regex fallback decodes tab/newline/CR char-refs (agrees with DOM path)", () => {
+  const svg = buildDrawioSvg(CTRL_MODEL, "<g/>", { width: 200, height: 200 });
+  const content = /content="([^"]*)"/.exec(svg)[1];
+  // A bare `&` makes the SVG wrapper malformed, forcing extractContentAttr onto
+  // its regex fallback branch. That branch must decode the tab/newline/CR
+  // char-refs exactly like the DOM path, or the two decoders diverge.
+  const malformedSvg = `<svg content="${content}">&</svg>`;
+  assert.equal(decodeDrawioSvg(malformedSvg), CTRL_MODEL);
+  // The well-formed (DOM) path yields the identical result.
+  assert.equal(decodeDrawioSvg(svg), CTRL_MODEL);
+});