fix(#355 review round-2 F9-F11): register-gate test + shutdown idle-close + DB-path metrics gate

- F10 [stability]: closeMetricsServer() now calls server.closeIdleConnections()
  + server.unref() after server.close(). server.close()'s callback doesn't fire
  until keep-alive sockets drain, and the scraper (VictoriaMetrics/vmagent) holds
  an idle keep-alive socket — so onModuleDestroy's awaited close would hang until
  the scraper disconnects or the orchestrator SIGKILLs on the kill-grace window.
  closeIdleConnections() drops idle keep-alive sockets so shutdown completes
  immediately (Node 22, per the Dockerfile base).
- F9 [test]: client-telemetry.module.spec.ts pins the E1=B register() gate — the
  core of the "public endpoint OFF by default" decision: flag unset / any non-
  "true" value ("false"/""/"0"/…) → empty controllers+providers (route absent);
  "true"/"TRUE" → registers VitalsController + VitalsService. A flag-inversion or
  truthiness regression that reopened the anonymous disk-fill surface now fails.
- F11 [regression/perf]: the db_query_duration_seconds token work (firstSqlToken
  regex + Set lookup) is now gated on isMetricsEnabled() in database.module.ts, so
  a non-metrics deployment pays NOTHING per query (previously observeDbQuery
  no-op'd but the token was still computed on every query). Also hoisted the
  13-element known-token Set to a module const (KNOWN_SQL_TOKENS) so it's built
  once, not per query.

Gate: server tsc 0; metrics + vitals + client-telemetry suites pass (incl. the
new register-gate test).

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

.env.example

@@ -242,3 +242,27 @@ MCP_DOCMOST_PASSWORD=
 # FAILS CLOSED if Redis is unavailable (default: 1,000,000 tokens per workspace
 # per rolling day).
 # SHARE_AI_WORKSPACE_TOKEN_BUDGET_PER_DAY=1000000
+
+# --- Observability / perf metrics (#355) ---
+#
+# Two INDEPENDENT toggles, both OFF by default:
+#
+# 1) METRICS_PORT — the server-side Prometheus scrape endpoint.
+#    UNSET (default) => the whole prom subsystem is OFF: no registry, no
+#    collectors, and NOTHING is exposed on the main app port. There is NO
+#    default port — leaving it blank disables it. When set to a port (e.g.
+#    9464), a SEPARATE bare node:http listener serves GET /metrics on that port
+#    only (never on the main :3000 app listener), for a scraper such as
+#    VictoriaMetrics/Prometheus reaching it as <host>:<port>/metrics.
+# METRICS_PORT=9464
+#
+# 2) CLIENT_TELEMETRY_ENABLED — the public client perf-telemetry sink.
+#    OFF by default. When true, the unauthenticated POST /api/telemetry/vitals
+#    endpoint is registered and browsers collect + send web-vitals / editor
+#    metrics into the `client_metrics` table (read directly by Grafana, separate
+#    from METRICS_PORT). Leave OFF unless you actually consume this data: the
+#    endpoint is public and the table has NO app-side retention, so enabling it
+#    requires an EXTERNAL pruner to bound `client_metrics` growth (the deployed
+#    infra prunes rows >90d via a maintenance container). When off, the endpoint
+#    does not exist and the client installs no observers.
+# CLIENT_TELEMETRY_ENABLED=false

.github/workflows/develop.yml

@@ -18,12 +18,48 @@ env:
   IMAGE: ghcr.io/vvzvlad/gitmost
 
 jobs:
-  # Run the reusable test suite first so a failing test blocks the image build.
+  # Run the reusable test suite. Together with the e2e jobs below it gates the
+  # publish job (the image push), not the build itself — build runs in parallel.
   test:
     uses: ./.github/workflows/test.yml
 
+  # Runs in parallel with the test/e2e jobs and only warms the buildx cache
+  # (GHA cache, scope develop-amd64). No push happens here — the publish job
+  # below is the only one that pushes the image.
   build:
-    needs: test
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Resolve version
+        id: version
+        run: echo "value=$(git describe --tags --always)" >> "$GITHUB_OUTPUT"
+
+      - name: Build develop image (warm cache, no push)
+        uses: docker/build-push-action@v6
+        with:
+          context: .
+          platforms: linux/amd64
+          build-args: |
+            APP_VERSION=${{ steps.version.outputs.value }}
+            AI_AGENT_ROLES_CATALOG_URL=https://raw.githubusercontent.com/vvzvlad/gitmost/develop/agent-roles-catalog
+          push: false
+          cache-from: type=gha,scope=develop-amd64
+          cache-to: type=gha,scope=develop-amd64,mode=max,ignore-error=true
+
+  # The gate: rebuilds from the cache the build job just wrote (near-instant on
+  # a cache hit; worst case — cache eviction — a full rebuild, which matches the
+  # old sequential timing) and pushes :develop only when unit tests AND both
+  # e2e suites AND the build are green.
+  publish:
+    needs: [test, e2e-server, e2e-mcp, build]
     runs-on: ubuntu-latest
     timeout-minutes: 30
     steps:
@@ -57,13 +93,10 @@ jobs:
           push: true
           tags: ${{ env.IMAGE }}:develop
           cache-from: type=gha,scope=develop-amd64
-          cache-to: type=gha,scope=develop-amd64,mode=max,ignore-error=true
 
-  # e2e jobs run on every develop push but DO NOT gate the build/publish above:
-  # `build` stays `needs: test` only, so the :develop image still ships even if
-  # e2e fails. A failing e2e job turns the run red and triggers GitHub's email
-  # to the pusher — that red run + email is the intended notification, not a
-  # deploy block.
+  # e2e jobs gate the publish (image push), not the build: the :develop image
+  # is pushed only when unit tests AND both e2e suites pass (publish.needs
+  # lists them all).
   e2e-server:
     runs-on: ubuntu-latest
     # Hard cap: the full-AppModule e2e leaks open handles and hung jest to the 6h max.
@@ -124,9 +157,7 @@ jobs:
       - name: Run server e2e
         run: pnpm --filter ./apps/server test:e2e
 
-  # Same rationale as e2e-server: this job is intentionally NOT in
-  # `build.needs`. Deploy of the :develop image must not be blocked by e2e;
-  # a red run plus GitHub's email to the pusher is the notification mechanism.
+  # Gates the publish too — see the comment above e2e-server.
   e2e-mcp:
     runs-on: ubuntu-latest
     timeout-minutes: 20

Dockerfile

@@ -5,6 +5,13 @@ RUN npm install -g pnpm@10.4.0
 
 FROM base AS builder
 
+# re2 (packages/mcp) always compiles from source under pnpm (the prebuilt-binary
+# download cannot identify the GitHub repo), so node-gyp needs python3/make/g++.
+# This stage is discarded, so the toolchain can stay installed.
+RUN apt-get update \
+  && apt-get install -y --no-install-recommends python3 make g++ \
+  && rm -rf /var/lib/apt/lists/*
+
 WORKDIR /app
 
 COPY . .
@@ -57,9 +64,16 @@ COPY --from=builder /app/patches /app/patches
 
 RUN chown -R node:node /app
 
-USER node
+# Toolchain is needed transiently to compile re2 during the prod install; install
+# and purge it in one layer to keep the final image slim. The install itself runs
+# as the node user via su to keep node_modules ownership without a costly chown layer.
+RUN apt-get update \
+  && apt-get install -y --no-install-recommends python3 make g++ \
+  && su node -c "pnpm install --frozen-lockfile --prod" \
+  && apt-get purge -y --auto-remove python3 make g++ \
+  && rm -rf /var/lib/apt/lists/*
 
-RUN pnpm install --frozen-lockfile --prod
+USER node
 
 RUN mkdir -p /app/data/storage
 

apps/client/package.json

@@ -61,6 +61,7 @@
     "react-clear-modal": "^2.0.18",
     "react-dom": "^18.3.1",
     "react-drawio": "1.0.7",
+    "web-vitals": "^5.1.0",
     "react-error-boundary": "6.1.1",
     "react-helmet-async": "3.0.0",
     "react-i18next": "16.5.8",

apps/client/src/features/comment/components/comment-content-view.test.tsx

@@ -0,0 +1,250 @@
+import { describe, it, expect, vi } from "vitest";
+import { render, screen } from "@testing-library/react";
+import { MantineProvider } from "@mantine/core";
+import { MemoryRouter } from "react-router-dom";
+
+// matchMedia (read by MantineProvider) is stubbed globally in vitest.setup.ts.
+
+// The fallback path renders the full TipTap editor; stub it so we can assert the
+// safety valve fired without pulling in the editor stack.
+vi.mock("@/features/comment/components/comment-editor", () => ({
+  default: () => <div data-testid="comment-editor-fallback" />,
+}));
+
+// Mention rendering hits react-query; stub the page/share queries so the mention
+// case renders in isolation.
+vi.mock("@/features/page/queries/page-query.ts", () => ({
+  usePageQuery: () => ({ data: undefined, isLoading: false, isError: false }),
+}));
+vi.mock("@/features/share/queries/share-query.ts", () => ({
+  useSharePageQuery: () => ({ data: undefined }),
+}));
+
+import { CommentContentView } from "./comment-content-view";
+
+function renderView(content: string | object) {
+  return render(
+    <MantineProvider>
+      <MemoryRouter>
+        <CommentContentView content={content} />
+      </MemoryRouter>
+    </MantineProvider>,
+  );
+}
+
+const doc = (content: any[]) => JSON.stringify({ type: "doc", content });
+const para = (content: any[]) => ({ type: "paragraph", content });
+const text = (t: string, marks?: any[]) => ({ type: "text", text: t, marks });
+
+describe("CommentContentView", () => {
+  it("renders paragraphs as <p> with text", () => {
+    const { container } = renderView(doc([para([text("Hello world")])]));
+    expect(screen.getByText("Hello world")).toBeDefined();
+    expect(container.querySelector("p")).not.toBeNull();
+  });
+
+  it("reproduces the read-only CommentEditor DOM nesting for CSS parity", () => {
+    const { container } = renderView(doc([para([text("x")])]));
+    // outer .commentEditor > .ProseMirror (module) > .ProseMirror (global) > p
+    const globalPm = container.querySelector("div.ProseMirror > p");
+    expect(globalPm).not.toBeNull();
+  });
+
+  it("renders the bold mark as <strong>", () => {
+    const { container } = renderView(
+      doc([para([text("bold", [{ type: "bold" }])])]),
+    );
+    const el = container.querySelector("strong");
+    expect(el?.textContent).toBe("bold");
+  });
+
+  it("renders the italic mark as <em>", () => {
+    const { container } = renderView(
+      doc([para([text("it", [{ type: "italic" }])])]),
+    );
+    expect(container.querySelector("em")?.textContent).toBe("it");
+  });
+
+  it("renders the strike mark as <s>", () => {
+    const { container } = renderView(
+      doc([para([text("st", [{ type: "strike" }])])]),
+    );
+    expect(container.querySelector("s")?.textContent).toBe("st");
+  });
+
+  it("renders the underline mark as <u> (not the editor fallback)", () => {
+    const { container } = renderView(
+      doc([para([text("un", [{ type: "underline" }])])]),
+    );
+    expect(container.querySelector("u")?.textContent).toBe("un");
+    // Underline is a supported mark, so no degrade to the editor fallback.
+    expect(screen.queryByTestId("comment-editor-fallback")).toBeNull();
+  });
+
+  it("renders the code mark as <code>", () => {
+    const { container } = renderView(
+      doc([para([text("co", [{ type: "code" }])])]),
+    );
+    expect(container.querySelector("code")?.textContent).toBe("co");
+  });
+
+  it("renders the link mark as an anchor with safe rel/target", () => {
+    const { container } = renderView(
+      doc([
+        para([
+          text("click", [
+            { type: "link", attrs: { href: "https://example.com" } },
+          ]),
+        ]),
+      ]),
+    );
+    const a = container.querySelector("a");
+    expect(a?.getAttribute("href")).toBe("https://example.com");
+    expect(a?.getAttribute("target")).toBe("_blank");
+    expect(a?.getAttribute("rel")).toBe("noopener noreferrer nofollow");
+    expect(a?.textContent).toBe("click");
+  });
+
+  it("neutralizes a javascript: link href (stored XSS) while keeping the text", () => {
+    const { container } = renderView(
+      doc([
+        para([
+          text("click", [
+            { type: "link", attrs: { href: "javascript:alert(1)" } },
+          ]),
+        ]),
+      ]),
+    );
+    const a = container.querySelector("a");
+    expect(a).not.toBeNull();
+    // No navigable javascript: href — attribute is absent (or empty).
+    expect(a?.getAttribute("href")).toBeFalsy();
+    // The link text is still rendered.
+    expect(a?.textContent).toBe("click");
+  });
+
+  it("neutralizes a control-char-obfuscated javascript: href", () => {
+    const { container } = renderView(
+      doc([
+        para([
+          text("x", [
+            { type: "link", attrs: { href: "java\tscript:alert(1)" } },
+          ]),
+        ]),
+      ]),
+    );
+    expect(container.querySelector("a")?.getAttribute("href")).toBeFalsy();
+  });
+
+  it("neutralizes a data: link href", () => {
+    const { container } = renderView(
+      doc([
+        para([
+          text("x", [
+            {
+              type: "link",
+              attrs: { href: "data:text/html,<script>alert(1)</script>" },
+            },
+          ]),
+        ]),
+      ]),
+    );
+    expect(container.querySelector("a")?.getAttribute("href")).toBeFalsy();
+  });
+
+  it("preserves a mailto: link href (allowlisted scheme)", () => {
+    const { container } = renderView(
+      doc([
+        para([
+          text("mail", [
+            { type: "link", attrs: { href: "mailto:a@b.com" } },
+          ]),
+        ]),
+      ]),
+    );
+    expect(container.querySelector("a")?.getAttribute("href")).toBe(
+      "mailto:a@b.com",
+    );
+  });
+
+  it("preserves a relative link href (no scheme, not a script vector)", () => {
+    const { container } = renderView(
+      doc([
+        para([
+          text("rel", [{ type: "link", attrs: { href: "/some/path" } }]),
+        ]),
+      ]),
+    );
+    expect(container.querySelector("a")?.getAttribute("href")).toBe(
+      "/some/path",
+    );
+  });
+
+  it("nests multiple marks on one text node", () => {
+    const { container } = renderView(
+      doc([para([text("x", [{ type: "bold" }, { type: "italic" }])])]),
+    );
+    // bold wraps italic (or vice versa) — both elements exist around the text.
+    expect(container.querySelector("strong")).not.toBeNull();
+    expect(container.querySelector("em")).not.toBeNull();
+    expect(screen.getByText("x")).toBeDefined();
+  });
+
+  it("renders hardBreak as <br/>", () => {
+    const { container } = renderView(
+      doc([para([text("a"), { type: "hardBreak" }, text("b")])]),
+    );
+    expect(container.querySelector("br")).not.toBeNull();
+  });
+
+  it("renders a user mention as a styled span", () => {
+    const { container } = renderView(
+      doc([
+        para([
+          {
+            type: "mention",
+            attrs: { label: "Alice", entityType: "user", entityId: "u1" },
+          },
+        ]),
+      ]),
+    );
+    expect(screen.getByText("@Alice")).toBeDefined();
+    // No fallback to the editor.
+    expect(screen.queryByTestId("comment-editor-fallback")).toBeNull();
+  });
+
+  it("renders a page mention as a link", () => {
+    const { container } = renderView(
+      doc([
+        para([
+          {
+            type: "mention",
+            attrs: {
+              label: "Some Page",
+              entityType: "page",
+              slugId: "pg1",
+            },
+          },
+        ]),
+      ]),
+    );
+    expect(container.querySelector("a")).not.toBeNull();
+    expect(screen.getByText("Some Page")).toBeDefined();
+  });
+
+  it("renders a legacy plain-text (non-JSON) string as plain text", () => {
+    renderView("just a legacy string");
+    expect(screen.getByText("just a legacy string")).toBeDefined();
+    expect(screen.queryByTestId("comment-editor-fallback")).toBeNull();
+  });
+
+  it("falls back to CommentEditor for an unknown node type", () => {
+    renderView(doc([{ type: "codeBlock", content: [text("x")] }]));
+    expect(screen.getByTestId("comment-editor-fallback")).toBeDefined();
+  });
+
+  it("falls back to CommentEditor for malformed JSON", () => {
+    renderView('{"type":"doc","content":[');
+    expect(screen.getByTestId("comment-editor-fallback")).toBeDefined();
+  });
+});

apps/client/src/features/comment/components/comment-content-view.tsx

@@ -0,0 +1,199 @@
+import React from "react";
+import classes from "./comment.module.css";
+import { MentionContent } from "@/features/editor/components/mention/mention-view";
+import CommentEditor from "@/features/comment/components/comment-editor";
+
+// Static, editor-free renderer of a comment body (ProseMirror JSON). It walks the
+// document and emits plain DOM, avoiding the cost of a full TipTap/ProseMirror
+// instance per comment (the panel used to spin up 400+ editors on mount).
+//
+// The supported node/mark set MUST mirror what CommentEditor enables
+// (StarterKit + Mention + LinkExtension). Anything outside that set makes the
+// whole comment degrade to the read-only CommentEditor via the fallback below,
+// so we never show a half-rendered comment.
+
+// Sentinel thrown when we hit a node/mark we don't know how to render statically.
+// Caught at the top level to trigger the CommentEditor fallback for the whole comment.
+class UnknownNodeError extends Error {}
+
+// Protocol allowlist mirroring @tiptap/extension-link's default (the read-only
+// CommentEditor path relies on it to blank javascript:/data: hrefs). The static
+// renderer must apply the SAME sanitization because the backend stores comment
+// content verbatim and React does not neutralize javascript: in an href.
+const ALLOWED_URI_SCHEMES = /^(?:https?|ftps?|mailto|tel|callto|sms|cid|xmpp):/i;
+
+function safeHref(href: unknown): string | undefined {
+  if (typeof href !== "string") return undefined;
+  // Strip control chars/whitespace that could smuggle a scheme past the test
+  // (e.g. "java\tscript:").
+  const cleaned = href.replace(/[\u0000-\u0020]/g, "").trim();
+  // Allow relative/anchor/protocol-relative links (no scheme) — not script vectors.
+  if (!/^[a-z][a-z0-9+.-]*:/i.test(cleaned)) return href;
+  return ALLOWED_URI_SCHEMES.test(cleaned) ? href : undefined;
+}
+
+interface PMMark {
+  type: string;
+  attrs?: Record<string, any>;
+}
+
+interface PMNode {
+  type: string;
+  attrs?: Record<string, any>;
+  content?: PMNode[];
+  text?: string;
+  marks?: PMMark[];
+}
+
+// Wrap a text node's string in its marks (marks nest, e.g. bold + italic).
+function renderMarks(
+  text: React.ReactNode,
+  marks: PMMark[] | undefined,
+  keyPrefix: string,
+): React.ReactNode {
+  if (!marks || marks.length === 0) return text;
+
+  return marks.reduce<React.ReactNode>((acc, mark, i) => {
+    const key = `${keyPrefix}-m${i}`;
+    switch (mark.type) {
+      case "bold":
+        return <strong key={key}>{acc}</strong>;
+      case "italic":
+        return <em key={key}>{acc}</em>;
+      case "strike":
+        return <s key={key}>{acc}</s>;
+      case "underline":
+        // StarterKit enables the Underline extension by default (Mod-u) and
+        // CommentEditor does not disable it, so real comments can carry this
+        // mark. Render it here rather than degrading the whole comment.
+        return <u key={key}>{acc}</u>;
+      case "code":
+        return <code key={key}>{acc}</code>;
+      case "link": {
+        // LinkExtension (TiptapLink) opens links in a new tab; keep the same
+        // safe rel semantics the editor produces. Sanitize the href against the
+        // extension's protocol allowlist — a disallowed scheme (javascript:,
+        // data:) yields undefined so the anchor is non-navigable but still shows
+        // its text, matching how extension-link blanks a bad href.
+        const href = safeHref(mark.attrs?.href);
+        return (
+          <a
+            key={key}
+            href={href}
+            target="_blank"
+            rel="noopener noreferrer nofollow"
+          >
+            {acc}
+          </a>
+        );
+      }
+      default:
+        throw new UnknownNodeError(`Unknown mark type: ${mark.type}`);
+    }
+  }, text);
+}
+
+function renderNode(node: PMNode, key: string): React.ReactNode {
+  switch (node.type) {
+    case "paragraph":
+      return <p key={key}>{renderChildren(node.content, key)}</p>;
+    case "text":
+      return (
+        <React.Fragment key={key}>
+          {renderMarks(node.text ?? "", node.marks, key)}
+        </React.Fragment>
+      );
+    case "hardBreak":
+      return <br key={key} />;
+    case "mention":
+      return (
+        <span key={key} style={{ display: "inline" }}>
+          <MentionContent attrs={node.attrs as any} />
+        </span>
+      );
+    default:
+      throw new UnknownNodeError(`Unknown node type: ${node.type}`);
+  }
+}
+
+function renderChildren(
+  content: PMNode[] | undefined,
+  keyPrefix: string,
+): React.ReactNode {
+  if (!content) return null;
+  return content.map((child, i) => renderNode(child, `${keyPrefix}-${i}`));
+}
+
+// Reproduce the exact DOM nesting the read-only CommentEditor renders so the
+// scoped CSS in comment.module.css (which targets
+// `.commentEditor .ProseMirror :global(.ProseMirror)` and `.ProseMirror p`)
+// applies pixel-for-pixel. Read-only => no data-editable / data-surface attrs.
+function Shell({ children }: { children: React.ReactNode }) {
+  return (
+    <div className={classes.commentEditor}>
+      <div className={classes.ProseMirror}>
+        <div className="ProseMirror">{children}</div>
+      </div>
+    </div>
+  );
+}
+
+interface CommentContentViewProps {
+  content: string | object;
+}
+
+export function CommentContentView({ content }: CommentContentViewProps) {
+  // Degrade this single comment to the old editor-based render (safety valve).
+  const fallback = () => {
+    if (import.meta.env.DEV) {
+      console.warn(
+        "CommentContentView: unsupported comment content, falling back to editor",
+      );
+    }
+    return <CommentEditor defaultContent={content} editable={false} />;
+  };
+
+  let doc: unknown = content;
+
+  if (typeof content === "string") {
+    try {
+      doc = JSON.parse(content);
+    } catch {
+      const trimmed = content.trim();
+      // Looks like it was meant to be JSON but is malformed -> safety-valve fallback.
+      if (trimmed.startsWith("{") || trimmed.startsWith("[")) {
+        return fallback();
+      }
+      // Otherwise it's a legacy plain-text comment: render as a single paragraph.
+      return (
+        <Shell>
+          <p>{content}</p>
+        </Shell>
+      );
+    }
+  }
+
+  // Double-stringified / legacy plain-text stored as a JSON string.
+  if (typeof doc === "string") {
+    return (
+      <Shell>
+        <p>{doc}</p>
+      </Shell>
+    );
+  }
+
+  try {
+    const pmDoc = doc as PMNode;
+    if (!pmDoc || typeof pmDoc !== "object" || pmDoc.type !== "doc") {
+      throw new UnknownNodeError("Not a ProseMirror doc");
+    }
+    return <Shell>{renderChildren(pmDoc.content, "n")}</Shell>;
+  } catch (err) {
+    if (err instanceof UnknownNodeError) {
+      return fallback();
+    }
+    throw err;
+  }
+}
+
+export default CommentContentView;

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

@@ -1,5 +1,5 @@
-import { describe, it, expect, vi } from "vitest";
-import { render, screen, fireEvent } from "@testing-library/react";
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { render, screen, fireEvent, waitFor } from "@testing-library/react";
 import { MantineProvider } from "@mantine/core";
 import { IComment } from "@/features/comment/types/comment.types";
 
@@ -9,10 +9,11 @@ import { IComment } from "@/features/comment/types/comment.types";
 // component renders in isolation. We only assert the AI-badge rendering branch.
 const applyMutateAsync = vi.fn();
 const dismissMutateAsync = vi.fn();
+const updateMutateAsync = vi.fn();
 vi.mock("@/features/comment/queries/comment-query", () => ({
   useDeleteCommentMutation: () => ({ mutateAsync: vi.fn() }),
   useResolveCommentMutation: () => ({ mutateAsync: vi.fn() }),
-  useUpdateCommentMutation: () => ({ mutateAsync: vi.fn() }),
+  useUpdateCommentMutation: () => ({ mutateAsync: updateMutateAsync }),
   useApplySuggestionMutation: () => ({
     mutateAsync: applyMutateAsync,
     isPending: false,
@@ -23,9 +24,51 @@ vi.mock("@/features/comment/queries/comment-query", () => ({
   }),
 }));
 
+// The document the mocked editor emits via onUpdate when the edit form is open.
+// Duplicated inside the mock factory (below) to keep the factory self-contained.
+const EDITED_DOC = {
+  type: "doc",
+  content: [
+    { type: "paragraph", content: [{ type: "text", text: "edited via editor" }] },
+  ],
+};
+
 // CommentEditor pulls in the full TipTap editor stack; replace it with a stub.
-vi.mock("@/features/comment/components/comment-editor", () => ({
-  default: () => <div data-testid="comment-editor" />,
+// In edit mode the stub exposes buttons that fire the real onUpdate/onSave props
+// so the edit->save/cancel flow can be driven without a live editor.
+vi.mock("@/features/comment/components/comment-editor", () => {
+  const doc = {
+    type: "doc",
+    content: [
+      { type: "paragraph", content: [{ type: "text", text: "edited via editor" }] },
+    ],
+  };
+  return {
+    default: ({ onUpdate, onSave }: any) => (
+      <div data-testid="comment-editor">
+        <button
+          type="button"
+          data-testid="editor-emit-update"
+          onClick={() => onUpdate?.(doc)}
+        />
+        <button
+          type="button"
+          data-testid="editor-emit-save"
+          onClick={() => onSave?.()}
+        />
+      </div>
+    ),
+  };
+});
+
+// CommentContentView (used for the read-only body) imports the mention view,
+// which pulls page-query -> main.tsx (createRoot). Stub the queries so the item
+// renders in isolation without the app entry side-effect.
+vi.mock("@/features/page/queries/page-query.ts", () => ({
+  usePageQuery: () => ({ data: undefined, isLoading: false, isError: false }),
+}));
+vi.mock("@/features/share/queries/share-query.ts", () => ({
+  useSharePageQuery: () => ({ data: undefined }),
 }));
 
 import CommentListItem from "./comment-list-item";
@@ -286,3 +329,132 @@ describe("canShowDismiss predicate", () => {
     expect(canShowDismiss(c({ parentCommentId: "p" }), true, true)).toBe(false);
   });
 });
+
+describe("CommentListItem — edit -> save/cancel flow (#340 F3)", () => {
+  const body = (t: string) =>
+    JSON.stringify({
+      type: "doc",
+      content: [{ type: "paragraph", content: [{ type: "text", text: t }] }],
+    });
+
+  // The edit menu item is gated on the viewer owning the comment
+  // (currentUser.id === creatorId). currentUserAtom is atomWithStorage-backed,
+  // so seed localStorage to make the viewer the owner (creatorId "user-1").
+  beforeEach(() => {
+    updateMutateAsync.mockClear();
+    localStorage.setItem(
+      "currentUser",
+      JSON.stringify({ user: { id: "user-1", name: "Owner" } }),
+    );
+  });
+  afterEach(() => {
+    localStorage.clear();
+  });
+
+  async function openEditor() {
+    // Open the comment menu, then click "Edit comment" to toggle into edit mode.
+    fireEvent.click(screen.getByLabelText("Comment menu"));
+    fireEvent.click(await screen.findByText("Edit comment"));
+    // Edit form (mocked editor + actions) is now mounted.
+    await screen.findByTestId("comment-editor");
+  }
+
+  it("saves the edited content and, on cache update, shows the new body", async () => {
+    const { rerender } = renderItem(
+      baseComment({ content: body("original body") }),
+    );
+    // Static body first.
+    expect(screen.getByText("original body")).toBeDefined();
+
+    await openEditor();
+
+    // Editor emits an update (populates editContentRef), then Save is clicked.
+    fireEvent.click(screen.getByTestId("editor-emit-update"));
+    fireEvent.click(screen.getByRole("button", { name: "Save" }));
+
+    // mutateAsync is called with the stringified edited doc.
+    expect(updateMutateAsync).toHaveBeenCalledWith({
+      commentId: "c-1",
+      content: JSON.stringify(EDITED_DOC),
+    });
+
+    // On success the form closes (isEditing -> false); the static body renders
+    // from the comment.content prop again.
+    await waitFor(() =>
+      expect(screen.queryByTestId("comment-editor")).toBeNull(),
+    );
+
+    // Simulate the cache invalidation swapping in a new comment object with the
+    // updated content — the static body reflects it.
+    rerender(
+      <MantineProvider>
+        <CommentListItem
+          comment={baseComment({ content: body("updated body after save") })}
+          pageId="page-1"
+          canComment={true}
+          canEdit={true}
+        />
+      </MantineProvider>,
+    );
+    expect(screen.getByText("updated body after save")).toBeDefined();
+    expect(screen.queryByText("original body")).toBeNull();
+  });
+
+  it("cancel restores the static body and does not call the update mutation", async () => {
+    renderItem(baseComment({ content: body("original body") }));
+    await openEditor();
+
+    // Type something (editContentRef set), then cancel.
+    fireEvent.click(screen.getByTestId("editor-emit-update"));
+    fireEvent.click(screen.getByRole("button", { name: "Cancel" }));
+
+    // Editor unmounts, static body restored, no save happened.
+    await waitFor(() =>
+      expect(screen.queryByTestId("comment-editor")).toBeNull(),
+    );
+    expect(screen.getByText("original body")).toBeDefined();
+    expect(updateMutateAsync).not.toHaveBeenCalled();
+  });
+
+  it("saving without editing sends the existing content (editContentRef cleared after cancel)", async () => {
+    renderItem(baseComment({ content: body("original body") }));
+
+    // Cancel path clears editContentRef...
+    await openEditor();
+    fireEvent.click(screen.getByTestId("editor-emit-update"));
+    fireEvent.click(screen.getByRole("button", { name: "Cancel" }));
+    await waitFor(() =>
+      expect(screen.queryByTestId("comment-editor")).toBeNull(),
+    );
+
+    // ...so re-opening and saving WITHOUT an update falls back to comment.content.
+    await openEditor();
+    fireEvent.click(screen.getByRole("button", { name: "Save" }));
+    expect(updateMutateAsync).toHaveBeenCalledWith({
+      commentId: "c-1",
+      content: JSON.stringify(body("original body")),
+    });
+  });
+});
+
+describe("CommentListItem — read-only body renders statically", () => {
+  it("renders the comment body as static text without a TipTap editor", () => {
+    renderItem(
+      baseComment({
+        content: JSON.stringify({
+          type: "doc",
+          content: [
+            {
+              type: "paragraph",
+              content: [{ type: "text", text: "Hello static world" }],
+            },
+          ],
+        }),
+      }),
+    );
+    // Body text is present...
+    expect(screen.getByText("Hello static world")).toBeDefined();
+    // ...and it did NOT go through the (mocked) CommentEditor instance.
+    expect(screen.queryByTestId("comment-editor")).toBeNull();
+  });
+});

apps/client/src/features/comment/components/comment-list-item.tsx

@@ -1,10 +1,11 @@
 import { Group, Text, Box, Badge, Button } from "@mantine/core";
 import { AgentAvatarStack } from "@/components/ui/agent-avatar-stack.tsx";
-import React, { useEffect, useMemo, useRef, useState } from "react";
+import React, { useMemo, useRef, useState } from "react";
 import classes from "./comment.module.css";
 import { useAtom, useAtomValue } from "jotai";
 import { useTimeAgo } from "@/hooks/use-time-ago";
 import CommentEditor from "@/features/comment/components/comment-editor";
+import CommentContentView from "@/features/comment/components/comment-content-view";
 import { pageEditorAtom } from "@/features/editor/atoms/editor-atoms";
 import CommentActions from "@/features/comment/components/comment-actions";
 import CommentMenu from "@/features/comment/components/comment-menu";
@@ -50,7 +51,6 @@ function CommentListItem({
   const [isEditing, setIsEditing] = useState(false);
   const [isLoading, setIsLoading] = useState(false);
   const editor = useAtomValue(pageEditorAtom);
-  const [content, setContent] = useState<string>(comment.content);
   const editContentRef = useRef<any>(null);
   const updateCommentMutation = useUpdateCommentMutation();
   const deleteCommentMutation = useDeleteCommentMutation(comment.pageId);
@@ -78,22 +78,16 @@ function CommentListItem({
   const isOwnerOrAdmin =
     currentUser?.user?.id === comment.creatorId || userSpaceRole === "admin";
 
-  useEffect(() => {
-    setContent(comment.content);
-  }, [comment]);
 
   async function handleUpdateComment() {
     try {
       setIsLoading(true);
       const commentToUpdate = {
         commentId: comment.id,
-        content: JSON.stringify(editContentRef.current ?? content),
+        content: JSON.stringify(editContentRef.current ?? comment.content),
       };
       await updateCommentMutation.mutateAsync(commentToUpdate);
-      if (editContentRef.current) {
-        setContent(editContentRef.current);
-        editContentRef.current = null;
-      }
+      editContentRef.current = null;
       setIsEditing(false);
     } catch (error) {
       console.error("Failed to update comment:", error);
@@ -350,11 +344,11 @@ function CommentListItem({
         )}
 
         {!isEditing ? (
-          <CommentEditor defaultContent={content} editable={false} />
+          <CommentContentView content={comment.content} />
         ) : (
           <>
             <CommentEditor
-              defaultContent={content}
+              defaultContent={comment.content}
               editable={true}
               onUpdate={(newContent: any) => { editContentRef.current = newContent; }}
               onSave={handleUpdateComment}
@@ -374,4 +368,6 @@ function CommentListItem({
   );
 }
 
-export default CommentListItem;
+// Memoized so a resolve/apply/reply cache update (which only replaces the touched
+// comment's object identity) re-renders that one thread, not all ~356 items.
+export default React.memo(CommentListItem);

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

@@ -0,0 +1,108 @@
+import { describe, it, expect, vi } from "vitest";
+import { render, screen, fireEvent } from "@testing-library/react";
+import { MantineProvider } from "@mantine/core";
+import { IComment } from "@/features/comment/types/comment.types";
+
+// matchMedia (read by MantineProvider) is stubbed globally in vitest.setup.ts.
+
+// CommentEditor pulls in the full TipTap editor stack; replace it with a stub so
+// the lazy reply editor's mount transition can be observed without the editor.
+vi.mock("@/features/comment/components/comment-editor", () => ({
+  default: () => <div data-testid="comment-editor" />,
+}));
+
+// page-query -> main.tsx (createRoot) is a module side effect; stub the queries
+// pulled in transitively so importing the module is side-effect free.
+vi.mock("@/features/page/queries/page-query.ts", () => ({
+  usePageQuery: () => ({ data: undefined, isLoading: false, isError: false }),
+}));
+vi.mock("@/features/share/queries/share-query.ts", () => ({
+  useSharePageQuery: () => ({ data: undefined }),
+}));
+// space-query -> main.tsx (createRoot) is another module side effect; stub it.
+vi.mock("@/features/space/queries/space-query.ts", () => ({
+  useGetSpaceBySlugQuery: () => ({ data: undefined }),
+}));
+
+import {
+  buildChildrenByParent,
+  CommentEditorWithActions,
+} from "./comment-list-with-tabs";
+
+const c = (id: string, parentCommentId: string | null = null): IComment =>
+  ({ id, parentCommentId }) as IComment;
+
+describe("buildChildrenByParent (childrenByParent grouping)", () => {
+  it("returns an empty map for undefined or empty input", () => {
+    expect(buildChildrenByParent(undefined).size).toBe(0);
+    expect(buildChildrenByParent([]).size).toBe(0);
+  });
+
+  it("does not index a top-level comment (parentCommentId null)", () => {
+    const map = buildChildrenByParent([c("p1", null)]);
+    expect(map.size).toBe(0);
+    expect(map.has("p1")).toBe(false);
+  });
+
+  it("groups replies under the correct parent, including reply-to-reply nesting", () => {
+    const p1 = c("p1", null);
+    const r1 = c("r1", "p1");
+    const r2 = c("r2", "r1"); // a reply to a reply
+    const map = buildChildrenByParent([p1, r1, r2]);
+    expect(map.get("p1")).toEqual([r1]);
+    expect(map.get("r1")).toEqual([r2]);
+    // The top-level comment itself is never a key.
+    expect(map.has("p1") && map.get("p1")?.length).toBe(1);
+  });
+
+  it("still groups a reply whose parent is not present in items", () => {
+    const orphan = c("o1", "missing-parent");
+    const map = buildChildrenByParent([orphan]);
+    expect(map.get("missing-parent")).toEqual([orphan]);
+  });
+
+  it("preserves insertion order among sibling replies", () => {
+    const map = buildChildrenByParent([
+      c("a", "p1"),
+      c("b", "p1"),
+      c("d", "p1"),
+    ]);
+    expect(map.get("p1")?.map((x) => x.id)).toEqual(["a", "b", "d"]);
+  });
+});
+
+function renderReplyEditor() {
+  return render(
+    <MantineProvider>
+      <CommentEditorWithActions commentId="c-1" onSave={vi.fn()} />
+    </MantineProvider>,
+  );
+}
+
+describe("CommentEditorWithActions — lazy reply editor activation", () => {
+  it("shows only the stub initially (no editor instance mounted)", () => {
+    renderReplyEditor();
+    expect(screen.getByRole("button")).toBeDefined();
+    expect(screen.queryByTestId("comment-editor")).toBeNull();
+  });
+
+  it("mounts the real editor when the stub is clicked and keeps it mounted", () => {
+    renderReplyEditor();
+    fireEvent.click(screen.getByRole("button"));
+    expect(screen.getByTestId("comment-editor")).toBeDefined();
+    // The stub button is replaced by the editor subtree.
+    expect(screen.queryByRole("button")).toBeNull();
+  });
+
+  it("mounts the editor when the stub receives focus", () => {
+    renderReplyEditor();
+    fireEvent.focus(screen.getByRole("button"));
+    expect(screen.getByTestId("comment-editor")).toBeDefined();
+  });
+
+  it("mounts the editor on Enter keydown of the stub", () => {
+    renderReplyEditor();
+    fireEvent.keyDown(screen.getByRole("button"), { key: "Enter" });
+    expect(screen.getByTestId("comment-editor")).toBeDefined();
+  });
+});

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

@@ -23,7 +23,6 @@ import CommentActions from "@/features/comment/components/comment-actions";
 import { useFocusWithin } from "@mantine/hooks";
 import { IComment } from "@/features/comment/types/comment.types.ts";
 import { usePageQuery } from "@/features/page/queries/page-query.ts";
-import { IPagination } from "@/lib/types.ts";
 import { extractPageSlugId } from "@/lib";
 import { useTranslation } from "react-i18next";
 import { useGetSpaceBySlugQuery } from "@/features/space/queries/space-query.ts";
@@ -36,6 +35,24 @@ interface CommentListWithTabsProps {
   onClose?: () => void;
 }
 
+// Index replies by their parent id once (O(n)), instead of an O(n^2) filter per
+// thread. Replies whose parent is not in `items` are still grouped under their
+// parentCommentId (they simply won't be reached by the top-level walk).
+// Exported for unit testing.
+export function buildChildrenByParent(
+  items: IComment[] | undefined,
+): Map<string, IComment[]> {
+  const m = new Map<string, IComment[]>();
+  for (const c of items ?? []) {
+    if (c.parentCommentId) {
+      const arr = m.get(c.parentCommentId);
+      if (arr) arr.push(c);
+      else m.set(c.parentCommentId, [c]);
+    }
+  }
+  return m;
+}
+
 function CommentListWithTabs({ onClose }: CommentListWithTabsProps) {
   const { t } = useTranslation();
   const { pageSlug } = useParams();
@@ -46,7 +63,9 @@ function CommentListWithTabs({ onClose }: CommentListWithTabsProps) {
     isError,
   } = useCommentsQuery({ pageId: page?.id });
   const createCommentMutation = useCreateCommentMutation();
-  const [isLoading, setIsLoading] = useState(false);
+  // mutateAsync is a stable reference across renders; depend on it (not the
+  // mutation object) so the reply/comment callbacks stay stable.
+  const createCommentAsync = createCommentMutation.mutateAsync;
   const { data: space } = useGetSpaceBySlugQuery(page?.space?.slug);
 
   const canEdit = page?.permissions?.canEdit ?? false;
@@ -75,13 +94,21 @@ function CommentListWithTabs({ onClose }: CommentListWithTabsProps) {
     return { activeComments: active, resolvedComments: resolved };
   }, [comments]);
 
+  // Index replies by their parent once, instead of an O(n^2) filter per thread.
+  // The map ref changes on any comments update, so MemoizedChildComments re-runs
+  // (cheap) and re-looks-up, while memoized CommentListItems skip unchanged items.
+  const childrenByParent = useMemo(
+    () => buildChildrenByParent(comments?.items),
+    [comments?.items],
+  );
+
   const [isPageCommentLoading, setIsPageCommentLoading] = useState(false);
 
   const handleAddPageComment = useCallback(
     async (_commentId: string, content: string) => {
       try {
         setIsPageCommentLoading(true);
-        const createdComment = await createCommentMutation.mutateAsync({
+        const createdComment = await createCommentAsync({
           pageId: page?.id,
           content: JSON.stringify(content),
         });
@@ -100,27 +127,26 @@ function CommentListWithTabs({ onClose }: CommentListWithTabsProps) {
         setIsPageCommentLoading(false);
       }
     },
-    [createCommentMutation, page?.id],
+    [createCommentAsync, page?.id],
   );
 
   const handleAddReply = useCallback(
     async (commentId: string, content: string) => {
+      // Pending state lives inside CommentEditorWithActions so sending a reply
+      // does not churn renderComments and re-render the whole list.
       try {
-        setIsLoading(true);
         const commentData = {
           pageId: page?.id,
           parentCommentId: commentId,
           content: JSON.stringify(content),
         };
 
-        await createCommentMutation.mutateAsync(commentData);
+        await createCommentAsync(commentData);
       } catch (error) {
         console.error("Failed to post comment:", error);
-      } finally {
-        setIsLoading(false);
       }
     },
-    [createCommentMutation, page?.id],
+    [createCommentAsync, page?.id],
   );
 
   const renderComments = useCallback(
@@ -143,7 +169,7 @@ function CommentListWithTabs({ onClose }: CommentListWithTabsProps) {
             userSpaceRole={space?.membership?.role}
           />
           <MemoizedChildComments
-            comments={comments}
+            childrenByParent={childrenByParent}
             parentId={comment.id}
             pageId={page?.id}
             canComment={canComment}
@@ -158,16 +184,15 @@ function CommentListWithTabs({ onClose }: CommentListWithTabsProps) {
             <CommentEditorWithActions
               commentId={comment.id}
               onSave={handleAddReply}
-              isLoading={isLoading}
             />
           </>
         )}
       </Paper>
     ),
     [
-      comments,
+      childrenByParent,
       handleAddReply,
-      isLoading,
+      page?.id,
       space?.membership?.role,
       canComment,
       canEdit,
@@ -203,6 +228,11 @@ function CommentListWithTabs({ onClose }: CommentListWithTabsProps) {
       <Tabs
         defaultValue="open"
         variant="default"
+        // Default to not mounting an inactive tab (the heavy Resolved list stays
+        // unmounted while Open is shown). The Open panel overrides this with its
+        // own keepMounted (below) so an in-progress reply/edit draft survives an
+        // Open -> Resolved -> Open switch.
+        keepMounted={false}
         style={{
           flex: "1 1 auto",
           display: "flex",
@@ -261,7 +291,10 @@ function CommentListWithTabs({ onClose }: CommentListWithTabsProps) {
           type="scroll"
         >
           <div style={{ paddingBottom: "8px" }}>
-            <Tabs.Panel value="open" pt="xs">
+            {/* keepMounted keeps the Open panel alive even while Resolved is
+                active, so a lazily-mounted reply editor's draft (and an
+                in-progress edit) is not discarded on tab switch. */}
+            <Tabs.Panel value="open" pt="xs" keepMounted>
               {activeComments.length === 0 ? (
                 <Center py="xl">
                   <Stack align="center" gap="xs">
@@ -307,7 +340,7 @@ function CommentListWithTabs({ onClose }: CommentListWithTabsProps) {
 }
 
 interface ChildCommentsProps {
-  comments: IPagination<IComment>;
+  childrenByParent: Map<string, IComment[]>;
   parentId: string;
   pageId: string;
   canComment: boolean;
@@ -315,24 +348,18 @@ interface ChildCommentsProps {
   userSpaceRole?: string;
 }
 const ChildComments = ({
-  comments,
+  childrenByParent,
   parentId,
   pageId,
   canComment,
   canEdit,
   userSpaceRole,
 }: ChildCommentsProps) => {
-  const getChildComments = useCallback(
-    (parentId: string) =>
-      comments.items.filter(
-        (comment: IComment) => comment.parentCommentId === parentId,
-      ),
-    [comments.items],
-  );
+  const children = childrenByParent.get(parentId) ?? [];
 
   return (
     <div>
-      {getChildComments(parentId).map((childComment) => (
+      {children.map((childComment) => (
         <div key={childComment.id}>
           <CommentListItem
             comment={childComment}
@@ -342,7 +369,7 @@ const ChildComments = ({
             userSpaceRole={userSpaceRole}
           />
           <MemoizedChildComments
-            comments={comments}
+            childrenByParent={childrenByParent}
             parentId={childComment.id}
             pageId={pageId}
             canComment={canComment}
@@ -357,22 +384,61 @@ const ChildComments = ({
 
 const MemoizedChildComments = memo(ChildComments);
 
-const CommentEditorWithActions = ({
+export const CommentEditorWithActions = ({
   commentId,
   onSave,
-  isLoading,
   placeholder = undefined,
 }) => {
+  const { t } = useTranslation();
+  // Lazily mount the TipTap reply editor: until the user interacts with the
+  // stub, no editor instance is created for this thread. Once mounted it stays
+  // mounted so the draft is preserved.
+  const [mounted, setMounted] = useState(false);
   const [content, setContent] = useState("");
+  const [isSending, setIsSending] = useState(false);
   const { ref, focused } = useFocusWithin();
   const commentEditorRef = useRef(null);
 
-  const handleSave = useCallback(() => {
-    onSave(commentId, content);
-    setContent("");
-    commentEditorRef.current?.clearContent();
+  const activate = useCallback(() => setMounted(true), []);
+
+  const handleSave = useCallback(async () => {
+    try {
+      setIsSending(true);
+      await onSave(commentId, content);
+      setContent("");
+      commentEditorRef.current?.clearContent();
+    } finally {
+      setIsSending(false);
+    }
   }, [commentId, content, onSave]);
 
+  if (!mounted) {
+    return (
+      <div
+        role="button"
+        tabIndex={0}
+        onClick={activate}
+        onFocus={activate}
+        onKeyDown={(e) => {
+          if (e.key === "Enter" || e.key === " ") {
+            e.preventDefault();
+            activate();
+          }
+        }}
+        style={{
+          padding: "6px",
+          fontSize: "var(--mantine-font-size-sm)",
+          lineHeight: 1.4,
+          color: "var(--mantine-color-placeholder)",
+          cursor: "text",
+          borderRadius: "var(--mantine-radius-sm)",
+        }}
+      >
+        {placeholder || t("Reply...")}
+      </div>
+    );
+  }
+
   return (
     <div ref={ref}>
       <CommentEditor
@@ -381,8 +447,9 @@ const CommentEditorWithActions = ({
         onSave={handleSave}
         editable={true}
         placeholder={placeholder}
+        autofocus={true}
       />
-      {focused && <CommentActions onSave={handleSave} isLoading={isLoading} />}
+      {focused && <CommentActions onSave={handleSave} isLoading={isSending} />}
     </div>
   );
 };

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

@@ -53,7 +53,10 @@ export function useCommentsQuery(params: ICommentParams) {
 
   return {
     data,
-    isLoading: query.isLoading || query.hasNextPage,
+    // Paint the first page as soon as it arrives instead of blocking until every
+    // page has loaded; the background effect above keeps streaming the rest
+    // (tab counts grow as pages arrive).
+    isLoading: query.isLoading,
     isError: query.isError,
   };
 }

apps/client/src/features/editor/components/mention/mention-view.tsx

@@ -11,9 +11,19 @@ import {
 import { extractPageSlugId } from "@/lib";
 import classes from "./mention.module.css";
 
-export default function MentionView(props: NodeViewProps) {
-  const { node } = props;
-  const { label, entityType, entityId, slugId, anchorId } = node.attrs;
+interface MentionAttrs {
+  label?: string;
+  entityType?: string;
+  entityId?: string;
+  slugId?: string;
+  anchorId?: string;
+}
+
+// Presentational mention renderer (no NodeViewWrapper). Shared by the editor
+// NodeView (MentionView) and the static comment renderer (CommentContentView)
+// so mention click/nav/icon behavior stays identical outside of an editor.
+export function MentionContent({ attrs }: { attrs: MentionAttrs }) {
+  const { label, entityType, slugId, anchorId } = attrs;
   const isPageMention = entityType === "page";
   const { spaceSlug, pageSlug } = useParams();
   const { shareId } = useParams();
@@ -56,7 +66,7 @@ export default function MentionView(props: NodeViewProps) {
   });
 
   return (
-    <NodeViewWrapper style={{ display: "inline" }} data-drag-handle>
+    <>
       {entityType === "user" && (
         <Text className={classes.userMention} component="span">
           @{label}
@@ -139,6 +149,14 @@ export default function MentionView(props: NodeViewProps) {
           </span>
         </Anchor>
       )}
+    </>
+  );
+}
+
+export default function MentionView(props: NodeViewProps) {
+  return (
+    <NodeViewWrapper style={{ display: "inline" }} data-drag-handle>
+      <MentionContent attrs={props.node.attrs} />
     </NodeViewWrapper>
   );
 }

apps/client/src/features/editor/page-editor.tsx

@@ -93,6 +93,11 @@ import {
   isBodyEditable,
   isCollabSynced,
 } from "@/features/editor/editor-sync-state";
+import {
+  isVitalsActive,
+  measurePageOpen,
+  reportEditorTx,
+} from "@/lib/telemetry/vitals";
 
 interface PageEditorProps {
   pageId: string;
@@ -351,6 +356,40 @@ export default function PageEditor({
           editor.storage.pageId = pageId;
           handleScrollTo(editor);
           editorRef.current = editor;
+
+          // #355 — perf instrumentation. Skip ALL of it when telemetry is
+          // disabled (F1 flag off) or this session isn't sampled: no page-open
+          // measure, and crucially NO dispatch wrapping, so a non-collecting
+          // session pays zero per-transaction cost.
+          if (isVitalsActive()) {
+            // page_open_ms: this is the first editor-content render, so measure
+            // against any page-open mark set on the tree-row/link click.
+            measurePageOpen();
+
+            // editor_tx_ms: time the SYNCHRONOUS part of applying each
+            // transaction (state.apply + updateState) by wrapping the view's
+            // dispatch. Only slow syncs (>8ms) are reported (see reportEditorTx),
+            // so the common path adds just one performance.now() pair. Passive:
+            // the original dispatch still runs unchanged.
+            try {
+              const view = editor.view as unknown as {
+                dispatch: (tr: unknown) => void;
+              };
+              const originalDispatch = view.dispatch.bind(view);
+              view.dispatch = (tr: unknown) => {
+                const started = performance.now();
+                originalDispatch(tr);
+                const elapsed = performance.now() - started;
+                try {
+                  reportEditorTx(elapsed, editor.state.doc.content.size);
+                } catch {
+                  // never let telemetry break editing
+                }
+              };
+            } catch {
+              // if the view shape changes, skip editor_tx instrumentation
+            }
+          }
         }
       },
       onUpdate({ editor }) {

apps/client/src/lib/config.ts

@@ -47,6 +47,13 @@ export function isCompactPageTreeEnabled(): boolean {
   return castToBoolean(getConfigValue("COMPACT_PAGE_TREE", "true"));
 }
 
+// #355 — operator toggle for client perf-telemetry. DEFAULT OFF: the server
+// mirrors CLIENT_TELEMETRY_ENABLED into window.CONFIG; when off the client
+// installs no observers and sends nothing (the sink endpoint doesn't exist).
+export function isClientTelemetryEnabled(): boolean {
+  return castToBoolean(getConfigValue("CLIENT_TELEMETRY_ENABLED", "false"));
+}
+
 export function getAvatarUrl(
   avatarUrl: string,
   type: AvatarIconType = AvatarIconType.AVATAR,

apps/client/src/lib/telemetry/route-template.test.ts

@@ -0,0 +1,35 @@
+import { describe, it, expect } from "vitest";
+import { templateRoute } from "./route-template";
+
+describe("templateRoute", () => {
+  it("templates a space page path (never leaks slugs)", () => {
+    const t = templateRoute("/s/engineering/p/design-doc-abc123");
+    expect(t).toBe("/s/:space/p/:slug");
+    expect(t).not.toContain("engineering");
+    expect(t).not.toContain("design-doc");
+  });
+
+  it("templates share, redirect and space paths", () => {
+    expect(templateRoute("/share/abc/p/xyz")).toBe("/share/:shareId/p/:slug");
+    expect(templateRoute("/share/p/xyz")).toBe("/share/p/:slug");
+    expect(templateRoute("/p/some-slug")).toBe("/p/:slug");
+    expect(templateRoute("/s/team")).toBe("/s/:space");
+    expect(templateRoute("/s/team/trash")).toBe("/s/:space/trash");
+    expect(templateRoute("/labels/urgent")).toBe("/labels/:label");
+  });
+
+  it("keeps known static routes verbatim", () => {
+    expect(templateRoute("/home")).toBe("/home");
+    expect(templateRoute("/settings/members")).toBe("/settings/members");
+    expect(templateRoute("/")).toBe("/");
+  });
+
+  it("normalises a trailing slash", () => {
+    expect(templateRoute("/s/team/p/slug/")).toBe("/s/:space/p/:slug");
+  });
+
+  it("collapses unknown paths to 'other' (bounded cardinality)", () => {
+    expect(templateRoute("/weird/unknown/thing")).toBe("other");
+    expect(templateRoute("/s/team/p/slug/extra/segments")).toBe("other");
+  });
+});

apps/client/src/lib/telemetry/route-template.ts

@@ -0,0 +1,70 @@
+/**
+ * Map a raw pathname to a BOUNDED route TEMPLATE (#355).
+ *
+ * Perf metrics must be labelled by route template only — never a raw path with
+ * slugs/ids — so the server-side `route` column and any downstream aggregation
+ * stay low-cardinality and carry NO page slugs/titles (privacy). Anything that
+ * does not match a known pattern collapses to `other`.
+ *
+ * The template vocabulary mirrors the issue's example (`/s/:space/p/:slug`).
+ */
+const ROUTE_PATTERNS: { re: RegExp; template: string }[] = [
+  // Share pages (public).
+  { re: /^\/share\/[^/]+\/p\/[^/]+$/, template: '/share/:shareId/p/:slug' },
+  { re: /^\/share\/p\/[^/]+$/, template: '/share/p/:slug' },
+  { re: /^\/share\/[^/]+$/, template: '/share/:shareId' },
+  // Page redirect.
+  { re: /^\/p\/[^/]+$/, template: '/p/:slug' },
+  // Space + page.
+  { re: /^\/s\/[^/]+\/p\/[^/]+$/, template: '/s/:space/p/:slug' },
+  { re: /^\/s\/[^/]+\/trash$/, template: '/s/:space/trash' },
+  { re: /^\/s\/[^/]+$/, template: '/s/:space' },
+  // Misc dynamic.
+  { re: /^\/labels\/[^/]+$/, template: '/labels/:label' },
+  { re: /^\/invites\/[^/]+$/, template: '/invites/:invitationId' },
+  { re: /^\/settings\/groups\/[^/]+$/, template: '/settings/groups/:groupId' },
+];
+
+// Static routes we accept verbatim (finite set).
+const STATIC_ROUTES = new Set<string>([
+  '/home',
+  '/spaces',
+  '/favorites',
+  '/login',
+  '/forgot-password',
+  '/password-reset',
+  '/setup/register',
+  '/settings/account/profile',
+  '/settings/account/preferences',
+  '/settings/workspace',
+  '/settings/ai',
+  '/settings/members',
+  '/settings/groups',
+  '/settings/spaces',
+  '/settings/sharing',
+]);
+
+export function templateRoute(pathname: string): string {
+  // Normalise a trailing slash (except root).
+  const path =
+    pathname.length > 1 && pathname.endsWith('/')
+      ? pathname.slice(0, -1)
+      : pathname;
+
+  if (path === '' || path === '/') return '/';
+  if (STATIC_ROUTES.has(path)) return path;
+
+  for (const { re, template } of ROUTE_PATTERNS) {
+    if (re.test(path)) return template;
+  }
+  return 'other';
+}
+
+/** Template for the current window location. */
+export function currentRouteTemplate(): string {
+  try {
+    return templateRoute(window.location.pathname);
+  } catch {
+    return 'other';
+  }
+}

apps/client/src/lib/telemetry/vitals.ts

@@ -0,0 +1,290 @@
+import {
+  onCLS,
+  onINP,
+  onLCP,
+  onTTFB,
+  type CLSMetricWithAttribution,
+  type INPMetricWithAttribution,
+  type LCPMetricWithAttribution,
+  type TTFBMetricWithAttribution,
+} from "web-vitals/attribution";
+import { isClientTelemetryEnabled } from "@/lib/config";
+import { currentRouteTemplate } from "./route-template";
+
+/**
+ * Client perf-telemetry (#355): web-vitals + custom metrics buffered and posted
+ * to POST /api/telemetry/vitals via sendBeacon.
+ *
+ * Design constraints from the issue:
+ *  - Sampling is decided ONCE per session (25%), cached in sessionStorage,
+ *    BEFORE any observer is subscribed. Non-sampled sessions send nothing.
+ *  - Route labels are TEMPLATES only; attr is truncated to 120 chars; no page
+ *    titles/slugs/text ever leave the browser.
+ *  - Observers are passive and reporting is best-effort — telemetry must not
+ *    degrade the perf it measures.
+ */
+
+const ENDPOINT = "/api/telemetry/vitals";
+const SAMPLE_RATE = 0.25;
+const SAMPLE_KEY = "gm_vitals_sampled";
+const FLUSH_INTERVAL_MS = 15_000;
+const MAX_BUFFER = 40; // flush early if the buffer fills between timers
+const MAX_ATTR_LENGTH = 120;
+const EDITOR_TX_MIN_MS = 8; // only report editor transactions slower than this
+
+const ALLOWED_NAMES = new Set([
+  "INP",
+  "LCP",
+  "CLS",
+  "TTFB",
+  "editor_tx_ms",
+  "page_open_ms",
+  "longtask_ms",
+]);
+
+interface VitalEvent {
+  name: string;
+  value: number;
+  rating?: string;
+  route?: string;
+  attr?: string;
+  docSize?: number;
+}
+
+let sampledCache: boolean | null = null;
+let initialised = false;
+let buffer: VitalEvent[] = [];
+let longtaskSum = 0; // accumulated longtask duration (ms) for the current window
+
+/**
+ * Decide once per session whether this session is sampled. Cached in
+ * sessionStorage so the choice is stable across reloads within the session and
+ * identical for every observer/custom-metric caller.
+ */
+export function isVitalsSampled(): boolean {
+  if (sampledCache !== null) return sampledCache;
+  try {
+    const stored = sessionStorage.getItem(SAMPLE_KEY);
+    if (stored === "1") return (sampledCache = true);
+    if (stored === "0") return (sampledCache = false);
+    const sampled = Math.random() < SAMPLE_RATE;
+    sessionStorage.setItem(SAMPLE_KEY, sampled ? "1" : "0");
+    return (sampledCache = sampled);
+  } catch {
+    // sessionStorage unavailable (private mode / SSR): default to not sampled.
+    return (sampledCache = false);
+  }
+}
+
+/**
+ * True only when telemetry is BOTH enabled by the operator (F1 flag) AND this
+ * session is sampled. Callers outside initVitals (e.g. the editor dispatch
+ * wrapper) use this to skip ALL instrumentation cost on disabled/non-sampled
+ * sessions — no observers, no per-transaction timing.
+ */
+export function isVitalsActive(): boolean {
+  return isClientTelemetryEnabled() && isVitalsSampled();
+}
+
+function truncateAttr(value: unknown): string | undefined {
+  if (typeof value !== "string" || value.length === 0) return undefined;
+  return value.slice(0, MAX_ATTR_LENGTH);
+}
+
+function enqueue(event: VitalEvent): void {
+  if (!ALLOWED_NAMES.has(event.name)) return;
+  if (!Number.isFinite(event.value)) return;
+  buffer.push(event);
+  if (buffer.length >= MAX_BUFFER) flush();
+}
+
+function flush(): void {
+  // Fold any pending longtask total into the batch first.
+  if (longtaskSum > 0) {
+    buffer.push({
+      name: "longtask_ms",
+      value: Math.round(longtaskSum),
+      route: currentRouteTemplate(),
+    });
+    longtaskSum = 0;
+  }
+  if (buffer.length === 0) return;
+
+  const payload = JSON.stringify({ events: buffer });
+  buffer = [];
+
+  try {
+    const blob = new Blob([payload], { type: "application/json" });
+    if (navigator.sendBeacon && navigator.sendBeacon(ENDPOINT, blob)) return;
+    // Fallback for browsers without sendBeacon: keepalive fetch.
+    void fetch(ENDPOINT, {
+      method: "POST",
+      body: payload,
+      headers: { "Content-Type": "application/json" },
+      keepalive: true,
+    }).catch(() => undefined);
+  } catch {
+    // Best-effort: never throw out of telemetry.
+  }
+}
+
+/**
+ * Report a custom client metric (editor_tx_ms, page_open_ms). No-op unless the
+ * session is sampled. Route is always the current TEMPLATE.
+ */
+export function reportClientMetric(
+  name: "editor_tx_ms" | "page_open_ms",
+  value: number,
+  extra?: { docSize?: number },
+): void {
+  if (!isVitalsActive()) return;
+  if (!Number.isFinite(value)) return;
+  enqueue({
+    name,
+    value,
+    route: currentRouteTemplate(),
+    docSize: extra?.docSize,
+  });
+}
+
+/** Threshold-gated editor transaction reporter (only reports slow syncs). */
+export function reportEditorTx(ms: number, docSize: number): void {
+  if (ms <= EDITOR_TX_MIN_MS) return;
+  reportClientMetric("editor_tx_ms", ms, { docSize });
+}
+
+const PAGE_OPEN_MARK = "gm_page_open_start";
+
+/** Mark the start of a page-open interaction (tree-row / link click). */
+export function markPageOpenStart(): void {
+  try {
+    performance.clearMarks(PAGE_OPEN_MARK);
+    performance.mark(PAGE_OPEN_MARK);
+  } catch {
+    // ignore
+  }
+}
+
+/**
+ * Measure page_open_ms at first editor-content render, if a start mark exists.
+ * Consumes the mark so a later render doesn't double-count.
+ */
+export function measurePageOpen(): void {
+  try {
+    const marks = performance.getEntriesByName(PAGE_OPEN_MARK, "mark");
+    if (marks.length === 0) return;
+    const started = marks[0].startTime;
+    const elapsed = performance.now() - started;
+    performance.clearMarks(PAGE_OPEN_MARK);
+    if (elapsed > 0 && Number.isFinite(elapsed)) {
+      reportClientMetric("page_open_ms", elapsed);
+    }
+  } catch {
+    // ignore
+  }
+}
+
+function attrTarget(
+  metric:
+    | INPMetricWithAttribution
+    | LCPMetricWithAttribution
+    | CLSMetricWithAttribution,
+): string | undefined {
+  const a = metric.attribution as Record<string, unknown> | undefined;
+  if (!a) return undefined;
+  // Different vitals expose their culprit element under different keys; only a
+  // CSS-selector-ish target string is taken (no text content / titles).
+  return (
+    truncateAttr(a.interactionTarget) ??
+    truncateAttr(a.element) ??
+    truncateAttr(a.largestShiftTarget) ??
+    undefined
+  );
+}
+
+/**
+ * Initialise client telemetry. Safe to call multiple times (idempotent). Returns
+ * immediately without subscribing when the session is not sampled — so a
+ * non-sampled session subscribes to NO observers and sends nothing.
+ */
+export function initVitals(): void {
+  if (initialised) return;
+  initialised = true;
+
+  // Operator flag gate (F1, default OFF): when telemetry is disabled the sink
+  // endpoint does not even exist server-side, so install ZERO observers.
+  if (!isClientTelemetryEnabled()) return;
+
+  // Sampling gate is evaluated BEFORE any observer subscription.
+  if (!isVitalsSampled()) return;
+
+  const report = (
+    metric:
+      | INPMetricWithAttribution
+      | LCPMetricWithAttribution
+      | CLSMetricWithAttribution
+      | TTFBMetricWithAttribution,
+  ) => {
+    enqueue({
+      name: metric.name,
+      value: metric.value,
+      rating: metric.rating,
+      route: currentRouteTemplate(),
+      attr:
+        metric.name === "TTFB"
+          ? undefined
+          : attrTarget(
+              metric as
+                | INPMetricWithAttribution
+                | LCPMetricWithAttribution
+                | CLSMetricWithAttribution,
+            ),
+    });
+  };
+
+  onINP(report);
+  onLCP(report);
+  onCLS(report);
+  onTTFB(report);
+
+  // Long tasks: aggregate the total blocking time per flush window (a passive
+  // observer; individual entries are summed, never stored/sent individually).
+  try {
+    if (typeof PerformanceObserver !== "undefined") {
+      const observer = new PerformanceObserver((list) => {
+        for (const entry of list.getEntries()) {
+          longtaskSum += entry.duration;
+        }
+      });
+      observer.observe({ type: "longtask", buffered: true });
+    }
+  } catch {
+    // longtask entry type unsupported: skip silently.
+  }
+
+  // page_open_ms start: mark when the user clicks a page link/tree-row (any
+  // anchor navigating to a page URL). Passive capture listener; the matching
+  // measure fires at first editor-content render (measurePageOpen). No page
+  // titles/slugs are read — only the click timing is marked.
+  document.addEventListener(
+    "click",
+    (event) => {
+      const target = event.target as Element | null;
+      const anchor = target?.closest?.("a[href]") as HTMLAnchorElement | null;
+      if (!anchor) return;
+      const href = anchor.getAttribute("href") ?? "";
+      // A page link is `/s/:space/p/:slug`, `/p/:slug` or a share page path.
+      if (/\/p\//.test(href)) markPageOpenStart();
+    },
+    { capture: true, passive: true },
+  );
+
+  // Flush on tab hide (most reliable delivery point) and periodically.
+  const onHidden = () => {
+    if (document.visibilityState === "hidden") flush();
+  };
+  document.addEventListener("visibilitychange", onHidden);
+  window.addEventListener("pagehide", flush);
+
+  setInterval(flush, FLUSH_INTERVAL_MS);
+}

apps/client/src/main.tsx

@@ -22,6 +22,7 @@ import {
   isPostHogEnabled,
 } from "@/lib/config.ts";
 import posthog from "posthog-js";
+import { initVitals } from "@/lib/telemetry/vitals";
 
 export const queryClient = new QueryClient({
   defaultOptions: {
@@ -43,6 +44,10 @@ if (isCloud() && isPostHogEnabled) {
   });
 }
 
+// #355 — client perf-telemetry. Decides sampling ONCE (25%/session) before
+// subscribing to any observer; non-sampled sessions send nothing.
+initVitals();
+
 const container = document.getElementById("root") as HTMLElement;
 const root = (container as any).__reactRoot ??= ReactDOM.createRoot(container);
 

apps/server/package.json

@@ -111,6 +111,7 @@
     "pino-pretty": "^13.1.3",
     "postgres": "^3.4.8",
     "postmark": "^4.0.7",
+    "prom-client": "^15.1.3",
     "react": "^18.3.1",
     "react-email": "6.0.8",
     "reflect-metadata": "^0.2.2",

apps/server/src/app.module.ts

@@ -31,6 +31,8 @@ import { McpModule } from './integrations/mcp/mcp.module';
 import { SandboxModule } from './integrations/sandbox/sandbox.module';
 import { AiModule } from './integrations/ai/ai.module';
 import { AiChatModule } from './core/ai-chat/ai-chat.module';
+import { MetricsModule } from './integrations/metrics/metrics.module';
+import { ClientTelemetryModule } from './core/telemetry/client-telemetry.module';
 
 const enterpriseModules = [];
 try {
@@ -93,6 +95,10 @@ try {
     SandboxModule,
     AiModule,
     AiChatModule,
+    MetricsModule,
+    // Gated OFF by default: only registers the public vitals sink controller
+    // when CLIENT_TELEMETRY_ENABLED=true (maintainer decision E1=B).
+    ClientTelemetryModule.register(),
     ...enterpriseModules,
   ],
   controllers: [AppController],

apps/server/src/collaboration/extensions/persistence.extension.ts

@@ -41,6 +41,7 @@ import {
   HISTORY_INTERVAL,
 } from '../constants';
 import { TransclusionService } from '../../core/page/transclusion/transclusion.service';
+import { observeCollabStore } from '../../integrations/metrics/metrics.registry';
 
 /**
  * #251 — wire format of the client→server stateless message that signals a
@@ -192,6 +193,17 @@ export class PersistenceExtension implements Extension {
   }
 
   async onStoreDocument(data: onStoreDocumentPayload) {
+    // #355 — time the full store (persist + post-store side effects) into
+    // collab_store_duration_seconds. No-op when METRICS_PORT is unset.
+    const startedAt = performance.now();
+    try {
+      await this.storeDocument(data);
+    } finally {
+      observeCollabStore((performance.now() - startedAt) / 1000);
+    }
+  }
+
+  private async storeDocument(data: onStoreDocumentPayload) {
     const { documentName, document, context } = data;
 
     const pageId = getPageId(documentName);

apps/server/src/core/auth/auth.controller.ts

@@ -16,6 +16,7 @@ import {
   AUTH_THROTTLER,
   PAGE_TEMPLATE_THROTTLER,
   PUBLIC_SHARE_AI_THROTTLER,
+  VITALS_THROTTLER,
 } from '../../integrations/throttle/throttler-names';
 import { LoginDto } from './dto/login.dto';
 import { AuthService } from './services/auth.service';
@@ -184,16 +185,21 @@ export class AuthController {
   }
 
   // The global ThrottlerGuard applies ALL named throttlers to every route by
-  // default, so each non-AUTH bucket (AI chat, page template, public-share AI)
-  // is explicitly skipped here. collab-token is auth-guarded (JwtAuthGuard),
-  // per-user and client-cached, so those feature buckets are irrelevant to it;
-  // skipping them avoids spurious 429s when a user opens many pages in a short
-  // window. The AUTH bucket is skipped too for the same per-user, cached reason.
+  // default, so each non-AUTH bucket (AI chat, page template, public-share AI,
+  // client vitals) is explicitly skipped here. collab-token is auth-guarded
+  // (JwtAuthGuard), per-user and client-cached, so those feature buckets are
+  // irrelevant to it; skipping them avoids spurious 429s when a user opens many
+  // pages in a short window. The VITALS bucket must be skipped too: it is a
+  // process-wide named throttler, so without this skip its per-IP limit would
+  // silently cap collab-token (the one route that opts out of every other
+  // bucket) and break editing behind shared/NAT IPs. The AUTH bucket is skipped
+  // for the same per-user, cached reason.
   @SkipThrottle({
     [AUTH_THROTTLER]: true,
     [AI_CHAT_THROTTLER]: true,
     [PAGE_TEMPLATE_THROTTLER]: true,
     [PUBLIC_SHARE_AI_THROTTLER]: true,
+    [VITALS_THROTTLER]: true,
   })
   @UseGuards(JwtAuthGuard)
   @HttpCode(HttpStatus.OK)

apps/server/src/core/telemetry/client-metrics.constants.ts

@@ -0,0 +1,105 @@
+/**
+ * Server-side whitelist + limits for POST /api/telemetry/vitals (#355).
+ *
+ * The endpoint is PUBLIC (browsers post it, no auth) so it is a privacy and
+ * abuse surface: everything not on these lists is silently DROPPED and the
+ * request still returns 200 (never 400 — a 400 would make browsers retry).
+ */
+
+// The only metric names accepted. Anything else is dropped.
+export const ALLOWED_METRIC_NAMES = new Set<string>([
+  'INP',
+  'LCP',
+  'CLS',
+  'TTFB',
+  'editor_tx_ms',
+  'page_open_ms',
+  'longtask_ms',
+]);
+
+// The only rating values accepted (web-vitals). Anything else -> null.
+export const ALLOWED_RATINGS = new Set<string>([
+  'good',
+  'needs-improvement',
+  'poor',
+]);
+
+// Max events accepted per batch; the rest are ignored.
+export const MAX_EVENTS_PER_BATCH = 50;
+
+// Defence-in-depth body cap (~16KB). Fastify's global bodyLimit is far larger,
+// so we re-check the parsed payload size here and drop oversized batches.
+export const MAX_BODY_BYTES = 16 * 1024;
+
+// attr is truncated to this many characters (attribution target only, no PII).
+export const MAX_ATTR_LENGTH = 120;
+
+// route label sanity cap (client sends a template like /s/:space/p/:slug).
+export const MAX_ROUTE_LENGTH = 200;
+
+// `client_metrics.doc_size` is a Postgres `int` (int4). A garbage/huge docSize
+// on a single event would overflow int4 and make Postgres reject the WHOLE
+// batch INSERT, losing every event in it. Values outside this range are DROPPED
+// to null (the event is still kept) so one bad field never loses the batch.
+export const DOC_SIZE_MAX = 2147483647; // 2^31 - 1 (int4 max)
+
+export interface ClientMetricRow {
+  name: string;
+  value: number;
+  rating: string | null;
+  route: string | null;
+  attr: string | null;
+  docSize: number | null;
+  workspaceId: string | null;
+}
+
+/**
+ * Validate + normalise a single incoming event into a DB row, or return null to
+ * DROP it. Pure so it is directly unit-testable. Enforces the name whitelist,
+ * numeric value, rating whitelist, attr truncation and doc_size (int) coercion.
+ */
+export function sanitizeVitalEvent(
+  raw: unknown,
+  workspaceId: string | null,
+): ClientMetricRow | null {
+  if (!raw || typeof raw !== 'object') return null;
+  const e = raw as Record<string, unknown>;
+
+  const name = e.name;
+  if (typeof name !== 'string' || !ALLOWED_METRIC_NAMES.has(name)) return null;
+
+  const value =
+    typeof e.value === 'number' && Number.isFinite(e.value) ? e.value : null;
+  if (value === null) return null;
+
+  const rating =
+    typeof e.rating === 'string' && ALLOWED_RATINGS.has(e.rating)
+      ? e.rating
+      : null;
+
+  let route: string | null = null;
+  if (typeof e.route === 'string' && e.route.length > 0) {
+    route = e.route.slice(0, MAX_ROUTE_LENGTH);
+  }
+
+  let attr: string | null = null;
+  if (typeof e.attr === 'string' && e.attr.length > 0) {
+    attr = e.attr.slice(0, MAX_ATTR_LENGTH);
+  }
+
+  let docSize: number | null = null;
+  if (typeof e.docSize === 'number' && Number.isFinite(e.docSize)) {
+    docSize = Math.trunc(e.docSize);
+  } else if (typeof e.doc_size === 'number' && Number.isFinite(e.doc_size)) {
+    // Accept snake_case too, in case a client sends the raw column name.
+    docSize = Math.trunc(e.doc_size as number);
+  }
+  // Guard the int4 column: an out-of-range docSize would overflow int4 and make
+  // Postgres reject the whole batch INSERT. Drop the field (keep the event)
+  // rather than lose every other event in the batch.
+  if (docSize !== null && (docSize < 0 || docSize > DOC_SIZE_MAX)) {
+    docSize = null;
+  }
+
+  return { name, value, rating, route, attr, docSize, workspaceId };
+}

apps/server/src/core/telemetry/client-telemetry.module.spec.ts

@@ -0,0 +1,47 @@
+import { ClientTelemetryModule } from './client-telemetry.module';
+import { VitalsController } from './vitals.controller';
+import { VitalsService } from './vitals.service';
+
+// The register() gate is the CORE of the maintainer's E1=B decision: the public,
+// unauthenticated /api/telemetry/vitals endpoint must be OFF by default, so a
+// self-host deploy has no anonymous disk-fill surface into `client_metrics`. A
+// regression that inverts the flag (or a truthiness bug where "" / "false"
+// registers the route) would silently reopen that surface — pin it here.
+describe('ClientTelemetryModule.register (E1=B gate)', () => {
+  const original = process.env.CLIENT_TELEMETRY_ENABLED;
+  afterEach(() => {
+    if (original === undefined) delete process.env.CLIENT_TELEMETRY_ENABLED;
+    else process.env.CLIENT_TELEMETRY_ENABLED = original;
+  });
+
+  it('OFF by default (flag unset) — no controller, no provider (endpoint absent)', () => {
+    delete process.env.CLIENT_TELEMETRY_ENABLED;
+    const mod = ClientTelemetryModule.register();
+    expect(mod.controllers).toEqual([]);
+    expect(mod.providers).toEqual([]);
+  });
+
+  it.each(['false', 'False', '0', '', 'yes', '1'])(
+    'stays OFF for non-"true" value %p (no route)',
+    (val) => {
+      process.env.CLIENT_TELEMETRY_ENABLED = val;
+      const mod = ClientTelemetryModule.register();
+      expect(mod.controllers).toEqual([]);
+      expect(mod.providers).toEqual([]);
+    },
+  );
+
+  it('ON only for "true" — registers VitalsController + VitalsService', () => {
+    process.env.CLIENT_TELEMETRY_ENABLED = 'true';
+    const mod = ClientTelemetryModule.register();
+    expect(mod.controllers).toContain(VitalsController);
+    expect(mod.providers).toContain(VitalsService);
+  });
+
+  it('ON is case-insensitive ("TRUE")', () => {
+    process.env.CLIENT_TELEMETRY_ENABLED = 'TRUE';
+    const mod = ClientTelemetryModule.register();
+    expect(mod.controllers).toContain(VitalsController);
+    expect(mod.providers).toContain(VitalsService);
+  });
+});

apps/server/src/core/telemetry/client-telemetry.module.ts

@@ -0,0 +1,32 @@
+import { DynamicModule, Module } from '@nestjs/common';
+import { VitalsController } from './vitals.controller';
+import { VitalsService } from './vitals.service';
+
+/**
+ * Client perf-telemetry (#355): the public /api/telemetry/vitals sink that
+ * persists web-vitals + custom client metrics into `client_metrics`.
+ * Named ClientTelemetryModule to avoid confusion with the unrelated
+ * integrations/telemetry (product usage ping) module.
+ *
+ * GATED OFF BY DEFAULT (maintainer decision E1=B). The public, unauthenticated
+ * endpoint is only registered when CLIENT_TELEMETRY_ENABLED=true — otherwise the
+ * route does NOT exist at all (no anonymous disk-fill surface, and no unbounded
+ * `client_metrics` growth on a self-host deploy without an external pruner). The
+ * client is told the same flag via window.CONFIG and skips sending when off.
+ */
+@Module({})
+export class ClientTelemetryModule {
+  static register(): DynamicModule {
+    // Read process.env directly (not EnvironmentService) so the toggle is
+    // resolved at module-registration time, identical to how the metrics
+    // subsystem reads METRICS_PORT. Absent/anything-but-"true" => OFF.
+    const enabled =
+      (process.env.CLIENT_TELEMETRY_ENABLED ?? '').toLowerCase() === 'true';
+
+    return {
+      module: ClientTelemetryModule,
+      controllers: enabled ? [VitalsController] : [],
+      providers: enabled ? [VitalsService] : [],
+    };
+  }
+}

apps/server/src/core/telemetry/vitals.controller.ts

@@ -0,0 +1,64 @@
+import {
+  Body,
+  Controller,
+  HttpCode,
+  Post,
+  Req,
+  UseGuards,
+} from '@nestjs/common';
+import { SkipThrottle, Throttle, ThrottlerGuard } from '@nestjs/throttler';
+import { FastifyRequest } from 'fastify';
+import { Public } from '../../common/decorators/public.decorator';
+import {
+  AI_CHAT_THROTTLER,
+  AUTH_THROTTLER,
+  PAGE_TEMPLATE_THROTTLER,
+  PUBLIC_SHARE_AI_THROTTLER,
+  VITALS_THROTTLER,
+} from '../../integrations/throttle/throttler-names';
+import { VitalsService } from './vitals.service';
+
+/**
+ * POST /api/telemetry/vitals (#355) — public client perf-metrics sink.
+ *
+ * PUBLIC (browsers post via sendBeacon, no session) but IP-throttled. Always
+ * returns 200 with no body of interest: invalid/foreign/oversized payloads are
+ * silently dropped by the service rather than 400'd, so browsers never retry.
+ */
+@Controller('telemetry')
+export class VitalsController {
+  constructor(private readonly vitalsService: VitalsService) {}
+
+  @Public()
+  @UseGuards(ThrottlerGuard)
+  // The global ThrottlerGuard applies ALL named throttlers to every route, so
+  // every OTHER bucket must be skipped here — otherwise the strictest of them
+  // (public-share AI at 5/min) would override the intended vitals limit and cap
+  // this route at 5/min instead of 120/min. Skip them all so ONLY the VITALS
+  // bucket below applies.
+  @SkipThrottle({
+    [AUTH_THROTTLER]: true,
+    [AI_CHAT_THROTTLER]: true,
+    [PAGE_TEMPLATE_THROTTLER]: true,
+    [PUBLIC_SHARE_AI_THROTTLER]: true,
+  })
+  @Throttle({ [VITALS_THROTTLER]: { limit: 120, ttl: 60_000 } })
+  @Post('vitals')
+  @HttpCode(200)
+  async vitals(
+    @Body() body: unknown,
+    @Req() req: FastifyRequest,
+  ): Promise<{ ok: true }> {
+    // workspaceId is resolved by the workspace-host middleware onto req.raw when
+    // the browser posts from a workspace host; null otherwise. No other PII.
+    const workspaceId =
+      ((req.raw as unknown as { workspaceId?: string })?.workspaceId ?? null) ||
+      null;
+    try {
+      await this.vitalsService.ingest(body, workspaceId);
+    } catch {
+      // Never surface storage errors to the browser; telemetry is best-effort.
+    }
+    return { ok: true };
+  }
+}

apps/server/src/core/telemetry/vitals.service.spec.ts

@@ -0,0 +1,149 @@
+import { VitalsService } from './vitals.service';
+import { MAX_ATTR_LENGTH } from './client-metrics.constants';
+
+// buildRows is pure (no DB access), so a null db is fine here.
+const svc = new VitalsService(null as any);
+
+describe('VitalsService.buildRows', () => {
+  const WS = 'ws-uuid';
+
+  it('accepts a valid batch and maps whitelisted fields to rows', () => {
+    const body = {
+      events: [
+        { name: 'INP', value: 123.4, rating: 'good', route: '/s/:space/p/:slug' },
+        { name: 'editor_tx_ms', value: 12, route: '/s/:space/p/:slug', docSize: 4096 },
+      ],
+    };
+    const rows = svc.buildRows(body, WS);
+    expect(rows).toHaveLength(2);
+    expect(rows[0]).toEqual({
+      name: 'INP',
+      value: 123.4,
+      rating: 'good',
+      route: '/s/:space/p/:slug',
+      attr: null,
+      docSize: null,
+      workspaceId: WS,
+    });
+    expect(rows[1].name).toBe('editor_tx_ms');
+    expect(rows[1].docSize).toBe(4096);
+    expect(rows[1].workspaceId).toBe(WS);
+  });
+
+  it('accepts a bare array body', () => {
+    const rows = svc.buildRows([{ name: 'LCP', value: 1 }], WS);
+    expect(rows).toHaveLength(1);
+    expect(rows[0].name).toBe('LCP');
+  });
+
+  it('drops events with foreign metric names', () => {
+    const rows = svc.buildRows(
+      { events: [{ name: 'evil_metric', value: 1 }, { name: 'LCP', value: 2 }] },
+      WS,
+    );
+    expect(rows).toHaveLength(1);
+    expect(rows[0].name).toBe('LCP');
+  });
+
+  it('drops events with a non-numeric or missing value', () => {
+    const rows = svc.buildRows(
+      {
+        events: [
+          { name: 'CLS', value: 'nan' },
+          { name: 'CLS' },
+          { name: 'CLS', value: 0.1 },
+        ],
+      },
+      WS,
+    );
+    expect(rows).toHaveLength(1);
+    expect(rows[0].value).toBe(0.1);
+  });
+
+  it('strips foreign fields and only keeps whitelisted columns', () => {
+    const rows = svc.buildRows(
+      { events: [{ name: 'TTFB', value: 5, secret: 'drop-me', title: 'my page' }] },
+      WS,
+    );
+    expect(rows).toHaveLength(1);
+    expect(Object.keys(rows[0]).sort()).toEqual(
+      ['attr', 'docSize', 'name', 'rating', 'route', 'value', 'workspaceId'].sort(),
+    );
+    expect((rows[0] as any).secret).toBeUndefined();
+    expect((rows[0] as any).title).toBeUndefined();
+  });
+
+  it('rejects a rating outside the allowed set (-> null)', () => {
+    const rows = svc.buildRows(
+      { events: [{ name: 'INP', value: 1, rating: 'terrible' }] },
+      WS,
+    );
+    expect(rows[0].rating).toBeNull();
+  });
+
+  it('truncates attr to 120 chars', () => {
+    const longAttr = 'a'.repeat(500);
+    const rows = svc.buildRows(
+      { events: [{ name: 'INP', value: 1, attr: longAttr }] },
+      WS,
+    );
+    expect(rows[0].attr).toHaveLength(MAX_ATTR_LENGTH);
+  });
+
+  it('caps the batch at 50 events', () => {
+    const events = Array.from({ length: 200 }, () => ({ name: 'CLS', value: 1 }));
+    const rows = svc.buildRows({ events }, WS);
+    expect(rows).toHaveLength(50);
+  });
+
+  it('drops an oversized (>16KB) payload wholesale', () => {
+    const events = Array.from({ length: 50 }, () => ({
+      name: 'INP',
+      value: 1,
+      attr: 'x'.repeat(400),
+      route: '/s/:space/p/:slug',
+    }));
+    // Serialised body far exceeds 16KB.
+    const rows = svc.buildRows({ events }, WS);
+    expect(rows).toHaveLength(0);
+  });
+
+  it('returns [] for malformed bodies', () => {
+    expect(svc.buildRows(null, WS)).toEqual([]);
+    expect(svc.buildRows('nope', WS)).toEqual([]);
+    expect(svc.buildRows({ notEvents: 1 }, WS)).toEqual([]);
+    expect(svc.buildRows(42, WS)).toEqual([]);
+  });
+
+  it('carries a null workspaceId through', () => {
+    const rows = svc.buildRows({ events: [{ name: 'LCP', value: 1 }] }, null);
+    expect(rows[0].workspaceId).toBeNull();
+  });
+
+  it('drops an out-of-int4-range docSize to null without losing the batch', () => {
+    const rows = svc.buildRows(
+      {
+        events: [
+          // Garbage docSize overflowing int4 must NOT reject the whole batch:
+          // the field is dropped to null and the event is kept.
+          { name: 'editor_tx_ms', value: 10, docSize: 9_999_999_999 },
+          { name: 'editor_tx_ms', value: 20, docSize: -5 },
+          { name: 'editor_tx_ms', value: 30, docSize: 4096 },
+        ],
+      },
+      WS,
+    );
+    expect(rows).toHaveLength(3);
+    expect(rows[0].docSize).toBeNull();
+    expect(rows[1].docSize).toBeNull();
+    expect(rows[2].docSize).toBe(4096);
+  });
+
+  it('keeps a docSize exactly at the int4 max', () => {
+    const rows = svc.buildRows(
+      { events: [{ name: 'editor_tx_ms', value: 1, docSize: 2147483647 }] },
+      WS,
+    );
+    expect(rows[0].docSize).toBe(2147483647);
+  });
+});

apps/server/src/core/telemetry/vitals.service.ts

@@ -0,0 +1,70 @@
+import { Injectable } from '@nestjs/common';
+import { InjectKysely } from 'nestjs-kysely';
+import { KyselyDB } from '@docmost/db/types/kysely.types';
+import {
+  ClientMetricRow,
+  MAX_BODY_BYTES,
+  MAX_EVENTS_PER_BATCH,
+  sanitizeVitalEvent,
+} from './client-metrics.constants';
+
+@Injectable()
+export class VitalsService {
+  constructor(@InjectKysely() private readonly db: KyselyDB) {}
+
+  /**
+   * Turn a raw request body into the (bounded, whitelisted) rows to persist.
+   * Pure/synchronous so it is unit-testable without a DB. Returns [] for any
+   * malformed / oversized / foreign input — the caller still responds 200.
+   */
+  buildRows(body: unknown, workspaceId: string | null): ClientMetricRow[] {
+    if (!body || typeof body !== 'object') return [];
+
+    // Defence-in-depth body cap (~16KB): drop oversized batches wholesale.
+    try {
+      if (JSON.stringify(body).length > MAX_BODY_BYTES) return [];
+    } catch {
+      return [];
+    }
+
+    // Accept either a bare array or `{ events: [...] }`.
+    const events = Array.isArray(body)
+      ? body
+      : Array.isArray((body as { events?: unknown }).events)
+        ? ((body as { events: unknown[] }).events as unknown[])
+        : null;
+    if (!events) return [];
+
+    const rows: ClientMetricRow[] = [];
+    for (const event of events) {
+      if (rows.length >= MAX_EVENTS_PER_BATCH) break;
+      const row = sanitizeVitalEvent(event, workspaceId);
+      if (row) rows.push(row);
+    }
+    return rows;
+  }
+
+  /** Batch-insert the sanitised rows in a single statement. No-op on []. */
+  async insertRows(rows: ClientMetricRow[]): Promise<void> {
+    if (rows.length === 0) return;
+    await this.db
+      .insertInto('clientMetrics')
+      .values(
+        rows.map((r) => ({
+          name: r.name,
+          value: r.value,
+          rating: r.rating,
+          route: r.route,
+          attr: r.attr,
+          docSize: r.docSize,
+          workspaceId: r.workspaceId,
+        })),
+      )
+      .execute();
+  }
+
+  async ingest(body: unknown, workspaceId: string | null): Promise<void> {
+    const rows = this.buildRows(body, workspaceId);
+    await this.insertRows(rows);
+  }
+}

apps/server/src/database/database.module.ts

@@ -40,6 +40,11 @@ import { PageListener } from '@docmost/db/listeners/page.listener';
 import { PostgresJSDialect } from 'kysely-postgres-js';
 import * as postgres from 'postgres';
 import { normalizePostgresUrl } from '../common/helpers';
+import {
+  observeDbQuery,
+  isMetricsEnabled,
+} from '../integrations/metrics/metrics.registry';
+import { firstSqlToken } from '../integrations/metrics/metrics.constants';
 
 @Global()
 @Module({
@@ -67,6 +72,18 @@ import { normalizePostgresUrl } from '../common/helpers';
         }),
         plugins: [new CamelCasePlugin()],
         log: (event: LogEvent) => {
+          // #355 — db_query_duration_seconds, labelled by the leading SQL token
+          // (bounded cardinality). Gated on isMetricsEnabled() so the token work
+          // (regex + Set lookup) is skipped entirely when metrics are OFF — not
+          // just observeDbQuery no-op'd — so a non-metrics deployment pays nothing
+          // per query. Runs independent of the dev-only debug logging below.
+          if (isMetricsEnabled()) {
+            observeDbQuery(
+              firstSqlToken(event.query.sql),
+              event.queryDurationMillis / 1000,
+            );
+          }
+
           if (environmentService.getNodeEnv() !== 'development') return;
           const logger = new Logger(DatabaseModule.name);
           if (process.env.DEBUG_DB?.toLowerCase() === 'true') {

apps/server/src/database/migrations/20260704T120000-client-metrics.ts

@@ -0,0 +1,52 @@
+import { type Kysely, sql } from 'kysely';
+
+/**
+ * #355 — `client_metrics`: raw sink for client-side perf telemetry (web-vitals
+ * + custom editor/page metrics) posted to /api/telemetry/vitals.
+ *
+ * The table/columns/indexes here are a FIXED contract shared with the deployed
+ * Grafana infra (the `grafana_ro` role reads this table; a separate maintenance
+ * container prunes rows >90d and re-GRANTs daily). No app-side retention is
+ * added on purpose. Written as raw SQL to match that contract 1:1 (identity PK,
+ * conditional GRANT).
+ */
+export async function up(db: Kysely<any>): Promise<void> {
+  await sql`
+    CREATE TABLE client_metrics (
+      id bigint GENERATED ALWAYS AS IDENTITY PRIMARY KEY,
+      created_at timestamptz NOT NULL DEFAULT now(),
+      name text NOT NULL,          -- INP|LCP|CLS|TTFB|editor_tx_ms|page_open_ms|longtask_ms
+      value double precision NOT NULL,
+      rating text,                 -- good|needs-improvement|poor (web-vitals only)
+      route text,                  -- templated: /s/:space/p/:slug — never raw slugs
+      attr text,                   -- attribution target, truncated to 120 chars
+      doc_size int,                -- editor_tx_ms only
+      workspace_id uuid
+    )
+  `.execute(db);
+
+  await sql`
+    CREATE INDEX idx_client_metrics_name_created
+      ON client_metrics (name, created_at)
+  `.execute(db);
+
+  await sql`
+    CREATE INDEX idx_client_metrics_created
+      ON client_metrics (created_at)
+  `.execute(db);
+
+  // The read-only Grafana role only exists in the deployed environment; guard so
+  // the migration still applies cleanly in dev/CI where the role is absent.
+  await sql`
+    DO $$
+    BEGIN
+      IF EXISTS (SELECT FROM pg_roles WHERE rolname = 'grafana_ro') THEN
+        GRANT SELECT ON client_metrics TO grafana_ro;
+      END IF;
+    END $$;
+  `.execute(db);
+}
+
+export async function down(db: Kysely<any>): Promise<void> {
+  await sql`DROP TABLE IF EXISTS client_metrics`.execute(db);
+}

apps/server/src/database/types/db.d.ts

@@ -156,6 +156,18 @@ export interface Billing {
   workspaceId: string;
 }
 
+export interface ClientMetrics {
+  id: Generated<Int8>;
+  createdAt: Generated<Timestamp>;
+  name: string;
+  value: number;
+  rating: string | null;
+  route: string | null;
+  attr: string | null;
+  docSize: number | null;
+  workspaceId: string | null;
+}
+
 export interface Comments {
   aiChatId: string | null;
   content: Json | null;
@@ -691,6 +703,7 @@ export interface DB {
   authProviders: AuthProviders;
   backlinks: Backlinks;
   billing: Billing;
+  clientMetrics: ClientMetrics;
   comments: Comments;
   favorites: Favorites;
   fileTasks: FileTasks;

apps/server/src/integrations/environment/environment.service.ts

@@ -227,6 +227,22 @@ export class EnvironmentService {
     return compactTree === 'true';
   }
 
+  /**
+   * Operator toggle for the public client-telemetry sink (#355). DEFAULT OFF:
+   * the unauthenticated POST /api/telemetry/vitals endpoint + client vitals
+   * collection are only wired when this is explicitly true. Kept SEPARATE from
+   * METRICS_PORT (the server Prometheus half) because Grafana reads the
+   * `client_metrics` table directly, independent of the scrape port — and
+   * because `client_metrics` has no app-side retention, so an operator must opt
+   * in and run an external pruner.
+   */
+  isClientTelemetryEnabled(): boolean {
+    const enabled = this.configService
+      .get<string>('CLIENT_TELEMETRY_ENABLED', 'false')
+      .toLowerCase();
+    return enabled === 'true';
+  }
+
   getStripePublishableKey(): string {
     return this.configService.get<string>('STRIPE_PUBLISHABLE_KEY');
   }

apps/server/src/integrations/metrics/http-metrics.hook.ts

@@ -0,0 +1,46 @@
+import { FastifyReply, FastifyRequest } from 'fastify';
+import { isStreamingResponse } from './metrics.constants';
+import { observeHttp } from './metrics.registry';
+
+/**
+ * Resolve the BOUNDED route label for an HTTP response.
+ *
+ * HARD REQUIREMENT (#355): use the ROUTE TEMPLATE (`/pages/:id`), NEVER the raw
+ * URL (`/pages/abc-123`), so label cardinality stays finite. Fastify exposes the
+ * matched template on `req.routeOptions.url`. On 404s (no route matched) that is
+ * missing → collapse to the literal `unknown`.
+ */
+export function resolveRouteLabel(req: FastifyRequest): string {
+  const url = req.routeOptions?.url;
+  return typeof url === 'string' && url.length > 0 ? url : 'unknown';
+}
+
+/**
+ * Fastify onResponse handler that records http_request_duration_seconds.
+ * No-op when metrics are disabled (the hook is only registered when enabled,
+ * but the observe helpers are also guarded). Never throws into the response
+ * pipeline — telemetry must not break request handling.
+ */
+export function recordHttpResponse(
+  req: FastifyRequest,
+  reply: FastifyReply,
+): void {
+  try {
+    const route = resolveRouteLabel(req);
+
+    // Exclude SSE/streaming responses: onResponse fires at connection close for
+    // those, so it would record the stream lifetime and poison p95/p99.
+    const contentType = reply.getHeader('content-type');
+    if (isStreamingResponse(contentType, route)) return;
+
+    observeHttp(
+      req.method,
+      route,
+      reply.statusCode,
+      // Fastify measures elapsed time in ms; the metric is in seconds.
+      reply.elapsedTime / 1000,
+    );
+  } catch {
+    // Swallow: a telemetry failure must never affect the served response.
+  }
+}

apps/server/src/integrations/metrics/metrics-bull.service.ts

@@ -0,0 +1,146 @@
+import {
+  Injectable,
+  Logger,
+  OnModuleDestroy,
+  OnModuleInit,
+} from '@nestjs/common';
+import { InjectQueue } from '@nestjs/bullmq';
+import { Queue, QueueEvents } from 'bullmq';
+import { QueueName } from '../queue/constants';
+import { EnvironmentService } from '../environment/environment.service';
+import { parseRedisUrl } from '../../common/helpers';
+import {
+  isMetricsEnabled,
+  observeJobDuration,
+  setQueueDepth,
+} from './metrics.registry';
+
+const POLL_INTERVAL_MS = 15_000;
+// Cap the in-flight start-time map so a job that never emits completed/failed
+// (worker crash) cannot leak memory unbounded. Well above realistic concurrency.
+const MAX_INFLIGHT = 10_000;
+
+/**
+ * BullMQ instrumentation for #355:
+ *  - `bullmq_queue_depth{queue}`: polled from getJobCounts() every 15s.
+ *  - `bullmq_job_duration_seconds{queue}`: wall-clock time between a job going
+ *    `active` and `completed`/`failed`, observed via per-queue QueueEvents.
+ *
+ * Queue names are a FINITE list (the QueueName enum), so labels are bounded — no
+ * job ids ever enter a label. Everything is gated on METRICS_PORT: when metrics
+ * are off, onModuleInit does nothing (no interval, no QueueEvents connections).
+ */
+@Injectable()
+export class MetricsBullService implements OnModuleInit, OnModuleDestroy {
+  private readonly logger = new Logger(MetricsBullService.name);
+  private readonly queues: { label: string; queue: Queue }[];
+  private timer: NodeJS.Timeout | null = null;
+  private queueEvents: QueueEvents[] = [];
+  // jobId -> start timestamp (ms). Bounded by MAX_INFLIGHT.
+  private readonly inflight = new Map<string, number>();
+
+  constructor(
+    private readonly environmentService: EnvironmentService,
+    @InjectQueue(QueueName.EMAIL_QUEUE) emailQueue: Queue,
+    @InjectQueue(QueueName.ATTACHMENT_QUEUE) attachmentQueue: Queue,
+    @InjectQueue(QueueName.GENERAL_QUEUE) generalQueue: Queue,
+    @InjectQueue(QueueName.BILLING_QUEUE) billingQueue: Queue,
+    @InjectQueue(QueueName.FILE_TASK_QUEUE) fileTaskQueue: Queue,
+    @InjectQueue(QueueName.SEARCH_QUEUE) searchQueue: Queue,
+    @InjectQueue(QueueName.AI_QUEUE) aiQueue: Queue,
+    @InjectQueue(QueueName.HISTORY_QUEUE) historyQueue: Queue,
+    @InjectQueue(QueueName.NOTIFICATION_QUEUE) notificationQueue: Queue,
+    @InjectQueue(QueueName.AUDIT_QUEUE) auditQueue: Queue,
+  ) {
+    this.queues = [
+      { label: 'email', queue: emailQueue },
+      { label: 'attachment', queue: attachmentQueue },
+      { label: 'general', queue: generalQueue },
+      { label: 'billing', queue: billingQueue },
+      { label: 'file-task', queue: fileTaskQueue },
+      { label: 'search', queue: searchQueue },
+      { label: 'ai', queue: aiQueue },
+      { label: 'history', queue: historyQueue },
+      { label: 'notification', queue: notificationQueue },
+      { label: 'audit', queue: auditQueue },
+    ];
+  }
+
+  onModuleInit(): void {
+    if (!isMetricsEnabled()) return;
+
+    // Poll queue depth.
+    this.timer = setInterval(() => {
+      void this.pollDepths();
+    }, POLL_INTERVAL_MS);
+    // Do not keep the event loop alive solely for polling.
+    this.timer.unref?.();
+    void this.pollDepths();
+
+    // Wire per-queue job-duration events.
+    const redisConfig = parseRedisUrl(this.environmentService.getRedisUrl());
+    const connection = {
+      host: redisConfig.host,
+      port: redisConfig.port,
+      password: redisConfig.password,
+      db: redisConfig.db,
+      family: redisConfig.family,
+    };
+
+    for (const { label, queue } of this.queues) {
+      const events = new QueueEvents(queue.name, { connection });
+      events.on('active', ({ jobId }) => {
+        if (this.inflight.size >= MAX_INFLIGHT) {
+          // Drop the oldest tracked start to keep the map bounded.
+          const oldest = this.inflight.keys().next().value;
+          if (oldest !== undefined) this.inflight.delete(oldest);
+        }
+        this.inflight.set(jobId, Date.now());
+      });
+      const finalize = ({ jobId }: { jobId: string }) => {
+        const start = this.inflight.get(jobId);
+        if (start === undefined) return;
+        this.inflight.delete(jobId);
+        observeJobDuration(label, (Date.now() - start) / 1000);
+      };
+      events.on('completed', finalize);
+      events.on('failed', finalize);
+      events.on('error', (err) => {
+        this.logger.debug(`QueueEvents error (${label}): ${err?.message}`);
+      });
+      this.queueEvents.push(events);
+    }
+  }
+
+  private async pollDepths(): Promise<void> {
+    for (const { label, queue } of this.queues) {
+      try {
+        const counts = await queue.getJobCounts();
+        // "Depth" = jobs not yet finished (backlog + in-flight).
+        const depth =
+          (counts.waiting ?? 0) +
+          (counts.active ?? 0) +
+          (counts.delayed ?? 0) +
+          (counts.prioritized ?? 0) +
+          (counts.paused ?? 0);
+        setQueueDepth(label, depth);
+      } catch (err) {
+        this.logger.debug(
+          `Failed to read job counts for ${label}: ${(err as Error)?.message}`,
+        );
+      }
+    }
+  }
+
+  async onModuleDestroy(): Promise<void> {
+    if (this.timer) {
+      clearInterval(this.timer);
+      this.timer = null;
+    }
+    await Promise.all(
+      this.queueEvents.map((e) => e.close().catch(() => undefined)),
+    );
+    this.queueEvents = [];
+    this.inflight.clear();
+  }
+}

apps/server/src/integrations/metrics/metrics-server.lifecycle.ts

@@ -0,0 +1,16 @@
+import { Injectable, OnModuleDestroy } from '@nestjs/common';
+import { closeMetricsServer } from './metrics.server';
+
+/**
+ * Ties the bare node:http metrics scrape server (started in main.ts after the
+ * Fastify app is up, outside the DI container) into Nest's shutdown lifecycle.
+ * With `app.enableShutdownHooks()`, onModuleDestroy fires on SIGTERM/SIGINT and
+ * closes the listener so it is not left dangling (jest/e2e never exits, and a
+ * prod restart doesn't leak the port). No-op when metrics are disabled.
+ */
+@Injectable()
+export class MetricsServerLifecycle implements OnModuleDestroy {
+  async onModuleDestroy(): Promise<void> {
+    await closeMetricsServer();
+  }
+}

apps/server/src/integrations/metrics/metrics.constants.ts

@@ -0,0 +1,84 @@
+/**
+ * Perf-metrics contract (#355). These names/labels are FIXED by the already
+ * deployed scrape+dashboard infra (VictoriaMetrics scraping docmost:9464,
+ * Grafana dashboards, alerts). Do NOT rename them.
+ */
+export const METRIC_HTTP_REQUEST_DURATION = 'http_request_duration_seconds';
+export const METRIC_DB_QUERY_DURATION = 'db_query_duration_seconds';
+export const METRIC_BULLMQ_QUEUE_DEPTH = 'bullmq_queue_depth';
+export const METRIC_BULLMQ_JOB_DURATION = 'bullmq_job_duration_seconds';
+export const METRIC_COLLAB_STORE_DURATION = 'collab_store_duration_seconds';
+
+// Histogram buckets (seconds). Chosen to give useful p50/p95/p99 resolution
+// for typical web/DB latencies without exploding series cardinality.
+export const HTTP_BUCKETS = [
+  0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10,
+];
+export const DB_BUCKETS = [
+  0.001, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5,
+];
+export const COLLAB_BUCKETS = [
+  0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5,
+];
+export const JOB_BUCKETS = [
+  0.01, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10, 30, 60, 120,
+];
+
+/**
+ * Extract the first SQL token (select/insert/update/delete/...) from a query,
+ * lower-cased, to use as a BOUNDED label for db_query_duration_seconds. Using
+ * the full query text would blow up label cardinality; the leading keyword is a
+ * finite set. Unknown/empty queries collapse to `other`.
+ */
+// The bounded set of SQL leading keywords used as db_query_duration_seconds
+// labels. Module-const so it is built ONCE, not per query (this runs on every DB
+// query when metrics are enabled).
+const KNOWN_SQL_TOKENS = new Set([
+  'select',
+  'insert',
+  'update',
+  'delete',
+  'with',
+  'begin',
+  'commit',
+  'rollback',
+  'alter',
+  'create',
+  'drop',
+  'truncate',
+  'explain',
+]);
+
+export function firstSqlToken(sql: string | undefined): string {
+  if (!sql) return 'other';
+  // Skip leading whitespace / comments and grab the first word.
+  const match = /^[\s(]*([a-zA-Z]+)/.exec(sql);
+  if (!match) return 'other';
+  const token = match[1].toLowerCase();
+  return KNOWN_SQL_TOKENS.has(token) ? token : 'other';
+}
+
+/**
+ * Whether an HTTP response must be EXCLUDED from http_request_duration_seconds.
+ *
+ * SSE/streaming responses (the AI-chat `text/event-stream`) keep the connection
+ * open for the whole conversation, so Fastify's onResponse fires only when the
+ * client disconnects — recording the connection lifetime, not a response time,
+ * which would poison p95/p99. We skip by content-type (authoritative) with a
+ * route-suffix fallback for the two known stream endpoints.
+ */
+export function isStreamingResponse(
+  contentType: unknown,
+  route: string | undefined,
+): boolean {
+  if (
+    typeof contentType === 'string' &&
+    contentType.toLowerCase().includes('text/event-stream')
+  ) {
+    return true;
+  }
+  // Fallback: the AI-chat stream routes (/api/ai-chat/stream,
+  // /api/shares/ai/stream) both end in `/stream`.
+  if (route && route.endsWith('/stream')) return true;
+  return false;
+}

apps/server/src/integrations/metrics/metrics.module.ts

@@ -0,0 +1,15 @@
+import { Module } from '@nestjs/common';
+import { MetricsBullService } from './metrics-bull.service';
+import { MetricsServerLifecycle } from './metrics-server.lifecycle';
+
+/**
+ * Wires the BullMQ collectors (#355). The queues are provided by the @Global
+ * QueueModule (which exports BullModule), so no re-registration is needed here.
+ * The HTTP histogram, DB-query and collab-store collectors live in module-level
+ * singletons (metrics.registry) and are wired directly at their call sites.
+ * MetricsServerLifecycle closes the scrape server on shutdown.
+ */
+@Module({
+  providers: [MetricsBullService, MetricsServerLifecycle],
+})
+export class MetricsModule {}

apps/server/src/integrations/metrics/metrics.registry.ts

@@ -0,0 +1,126 @@
+import {
+  collectDefaultMetrics,
+  Histogram,
+  Gauge,
+  Registry,
+} from 'prom-client';
+import {
+  COLLAB_BUCKETS,
+  DB_BUCKETS,
+  HTTP_BUCKETS,
+  JOB_BUCKETS,
+  METRIC_BULLMQ_JOB_DURATION,
+  METRIC_BULLMQ_QUEUE_DEPTH,
+  METRIC_COLLAB_STORE_DURATION,
+  METRIC_DB_QUERY_DURATION,
+  METRIC_HTTP_REQUEST_DURATION,
+} from './metrics.constants';
+
+/**
+ * Process-wide perf-metrics registry (#355).
+ *
+ * This is a plain module singleton (NOT a Nest provider) because the collectors
+ * are cross-cutting: the Kysely `log` callback (built in a DI factory), the
+ * Fastify onResponse hook (main.ts, before the Nest container hands out
+ * providers) and the collab persistence extension all need the SAME instruments
+ * without threading DI through them.
+ *
+ * HARD CONTRACT: when `METRICS_PORT` is unset the whole subsystem is OFF — the
+ * registry is never created, `collectDefaultMetrics` never runs, and every
+ * observe/set helper is a cheap no-op. Nothing is exposed on :3000.
+ */
+
+// Decided once at process start. Deliberately read here (not via
+// EnvironmentService) so the toggle is identical for the DI and non-DI callers.
+const enabled = Boolean(process.env.METRICS_PORT);
+
+let registry: Registry | null = null;
+let httpHist: Histogram<'method' | 'route' | 'status'> | null = null;
+let dbHist: Histogram<'op'> | null = null;
+let queueDepthGauge: Gauge<'queue'> | null = null;
+let jobHist: Histogram<'queue'> | null = null;
+let collabHist: Histogram | null = null;
+
+function init(): void {
+  if (registry || !enabled) return;
+
+  registry = new Registry();
+
+  // Node/runtime metrics: gives nodejs_eventloop_lag_p99_seconds, GC, heap, etc.
+  collectDefaultMetrics({ register: registry });
+
+  httpHist = new Histogram({
+    name: METRIC_HTTP_REQUEST_DURATION,
+    help: 'HTTP request duration in seconds, by method, route template and status',
+    labelNames: ['method', 'route', 'status'],
+    buckets: HTTP_BUCKETS,
+    registers: [registry],
+  });
+
+  dbHist = new Histogram({
+    name: METRIC_DB_QUERY_DURATION,
+    help: 'Database query duration in seconds, by leading SQL keyword',
+    labelNames: ['op'],
+    buckets: DB_BUCKETS,
+    registers: [registry],
+  });
+
+  queueDepthGauge = new Gauge({
+    name: METRIC_BULLMQ_QUEUE_DEPTH,
+    help: 'Number of not-yet-finished BullMQ jobs per queue',
+    labelNames: ['queue'],
+    registers: [registry],
+  });
+
+  jobHist = new Histogram({
+    name: METRIC_BULLMQ_JOB_DURATION,
+    help: 'BullMQ job processing duration in seconds, per queue',
+    labelNames: ['queue'],
+    buckets: JOB_BUCKETS,
+    registers: [registry],
+  });
+
+  collabHist = new Histogram({
+    name: METRIC_COLLAB_STORE_DURATION,
+    help: 'Collaboration onStoreDocument duration in seconds',
+    buckets: COLLAB_BUCKETS,
+    registers: [registry],
+  });
+}
+
+// Runs once when this module is first imported. Safe to call again (idempotent).
+init();
+
+export function isMetricsEnabled(): boolean {
+  return enabled;
+}
+
+/** The prom-client registry, or null when metrics are disabled. */
+export function getMetricsRegistry(): Registry | null {
+  return registry;
+}
+
+export function observeHttp(
+  method: string,
+  route: string,
+  status: number,
+  seconds: number,
+): void {
+  httpHist?.observe({ method, route, status }, seconds);
+}
+
+export function observeDbQuery(op: string, seconds: number): void {
+  dbHist?.observe({ op }, seconds);
+}
+
+export function setQueueDepth(queue: string, depth: number): void {
+  queueDepthGauge?.set({ queue }, depth);
+}
+
+export function observeJobDuration(queue: string, seconds: number): void {
+  jobHist?.observe({ queue }, seconds);
+}
+
+export function observeCollabStore(seconds: number): void {
+  collabHist?.observe(seconds);
+}

apps/server/src/integrations/metrics/metrics.server.ts

@@ -0,0 +1,86 @@
+import { createServer, Server } from 'node:http';
+import { Logger } from '@nestjs/common';
+import { getMetricsRegistry, isMetricsEnabled } from './metrics.registry';
+
+/**
+ * Start the Prometheus scrape endpoint on a SEPARATE port, taken from
+ * `METRICS_PORT`. There is NO default port: when `METRICS_PORT` is unset the
+ * whole metrics subsystem is OFF and this returns null. This is a bare node:http
+ * server, NOT part of the Fastify app, so `/metrics` never exists on the public
+ * :3000 listener.
+ *
+ * Returns the http.Server (so callers can close it on shutdown) or null when
+ * metrics are disabled. The reference is also kept module-side so the Nest
+ * lifecycle (see MetricsModule) can close it on application shutdown without
+ * threading the handle back through the non-DI bootstrap.
+ */
+let metricsServer: Server | null = null;
+
+export function startMetricsServer(): Server | null {
+  if (!isMetricsEnabled()) return null;
+
+  const logger = new Logger('MetricsServer');
+  const register = getMetricsRegistry();
+  if (!register) return null;
+
+  const port = Number(process.env.METRICS_PORT);
+  if (!Number.isInteger(port) || port <= 0) {
+    logger.warn(
+      `Invalid METRICS_PORT="${process.env.METRICS_PORT}", metrics endpoint not started`,
+    );
+    return null;
+  }
+
+  const server = createServer(async (req, res) => {
+    if (req.method === 'GET' && req.url === '/metrics') {
+      try {
+        const body = await register.metrics();
+        res.setHeader('Content-Type', register.contentType);
+        res.statusCode = 200;
+        res.end(body);
+      } catch (err) {
+        res.statusCode = 500;
+        res.end(String((err as Error)?.message ?? 'error'));
+      }
+      return;
+    }
+    res.statusCode = 404;
+    res.end();
+  });
+
+  // Bind on all interfaces: the scraper (VictoriaMetrics) reaches this from
+  // another container as docmost:9464. The port is not published to the host.
+  server.listen(port, '0.0.0.0', () => {
+    logger.log(`Metrics endpoint listening on :${port}/metrics`);
+  });
+
+  server.on('error', (err) => {
+    logger.error(`Metrics server error: ${err?.message}`);
+  });
+
+  metricsServer = server;
+  return server;
+}
+
+/**
+ * Close the metrics scrape server if one is running. Idempotent and safe to call
+ * when metrics are disabled (no server was ever started). Wired into Nest's
+ * shutdown lifecycle so the listener is not left dangling on shutdown.
+ */
+export function closeMetricsServer(): Promise<void> {
+  const server = metricsServer;
+  metricsServer = null;
+  if (!server) return Promise.resolve();
+  return new Promise((resolve) => {
+    server.close(() => resolve());
+    // server.close() stops accepting NEW connections but its callback does not
+    // fire until existing keep-alive sockets drain. The scraper (VictoriaMetrics/
+    // vmagent) holds an idle HTTP keep-alive socket, so without this the callback
+    // — and thus shutdown — would hang until the scraper disconnects or the
+    // orchestrator escalates to SIGKILL on the kill-grace window. Force-close idle
+    // keep-alive sockets so close() completes immediately, and unref so this
+    // server never keeps the event loop alive on its own.
+    server.closeIdleConnections();
+    server.unref();
+  });
+}

apps/server/src/integrations/metrics/metrics.spec.ts

@@ -0,0 +1,70 @@
+import { FastifyRequest } from 'fastify';
+import { resolveRouteLabel } from './http-metrics.hook';
+import { firstSqlToken, isStreamingResponse } from './metrics.constants';
+
+describe('resolveRouteLabel (histogram route label)', () => {
+  it('uses the ROUTE TEMPLATE, never the raw URL', () => {
+    // routeOptions.url is the matched template; url is the raw path with the id.
+    const req = {
+      url: '/api/pages/abc-123-def',
+      routeOptions: { url: '/api/pages/:id' },
+    } as unknown as FastifyRequest;
+    expect(resolveRouteLabel(req)).toBe('/api/pages/:id');
+    expect(resolveRouteLabel(req)).not.toContain('abc-123-def');
+  });
+
+  it('falls back to "unknown" on a 404 (no matched route template)', () => {
+    const req = {
+      url: '/totally/unmatched/path',
+      routeOptions: {},
+    } as unknown as FastifyRequest;
+    expect(resolveRouteLabel(req)).toBe('unknown');
+  });
+
+  it('falls back to "unknown" when routeOptions is missing', () => {
+    const req = { url: '/x' } as unknown as FastifyRequest;
+    expect(resolveRouteLabel(req)).toBe('unknown');
+  });
+});
+
+describe('isStreamingResponse (SSE exclusion)', () => {
+  it('excludes text/event-stream responses by content-type', () => {
+    expect(isStreamingResponse('text/event-stream', '/api/ai-chat/stream')).toBe(
+      true,
+    );
+    expect(isStreamingResponse('text/event-stream; charset=utf-8', '/x')).toBe(
+      true,
+    );
+  });
+
+  it('excludes known /stream routes by suffix as a fallback', () => {
+    expect(isStreamingResponse('application/json', '/api/ai-chat/stream')).toBe(
+      true,
+    );
+    expect(isStreamingResponse(undefined, '/api/shares/ai/stream')).toBe(true);
+  });
+
+  it('does not exclude ordinary JSON responses', () => {
+    expect(isStreamingResponse('application/json', '/api/pages/:id')).toBe(
+      false,
+    );
+    expect(isStreamingResponse(undefined, '/api/pages/:id')).toBe(false);
+  });
+});
+
+describe('firstSqlToken (bounded db label)', () => {
+  it('returns the lower-cased leading keyword', () => {
+    expect(firstSqlToken('SELECT * FROM pages')).toBe('select');
+    expect(firstSqlToken('  insert into x values (1)')).toBe('insert');
+    expect(firstSqlToken('UPDATE pages SET a=1')).toBe('update');
+    expect(firstSqlToken('delete from pages')).toBe('delete');
+    expect(firstSqlToken('(SELECT 1)')).toBe('select');
+  });
+
+  it('collapses unknown/empty queries to "other"', () => {
+    expect(firstSqlToken('')).toBe('other');
+    expect(firstSqlToken(undefined)).toBe('other');
+    expect(firstSqlToken('123 not sql')).toBe('other');
+    expect(firstSqlToken('vacuum analyze')).toBe('other');
+  });
+});

apps/server/src/integrations/static/static.module.ts

@@ -50,6 +50,10 @@ export class StaticModule implements OnModuleInit {
           : undefined,
         POSTHOG_HOST: this.environmentService.getPostHogHost(),
         POSTHOG_KEY: this.environmentService.getPostHogKey(),
+        // #355 — mirrors the server-side CLIENT_TELEMETRY_ENABLED gate so the
+        // client only collects/sends vitals when the operator opts in.
+        CLIENT_TELEMETRY_ENABLED:
+          this.environmentService.isClientTelemetryEnabled(),
       };
 
       const windowScriptContent = `<script>window.CONFIG=${JSON.stringify(configString)};</script>`;

apps/server/src/integrations/throttle/throttle.module.ts

@@ -9,6 +9,7 @@ import {
   AI_CHAT_THROTTLER,
   PAGE_TEMPLATE_THROTTLER,
   PUBLIC_SHARE_AI_THROTTLER,
+  VITALS_THROTTLER,
 } from './throttler-names';
 
 @Module({
@@ -29,6 +30,8 @@ import {
             { name: PAGE_TEMPLATE_THROTTLER, ttl: 60_000, limit: 30 },
             // Anonymous public-share assistant: ~5 req/min per IP.
             { name: PUBLIC_SHARE_AI_THROTTLER, ttl: 60_000, limit: 5 },
+            // Anonymous client perf-telemetry sink: 120 batched posts/min per IP.
+            { name: VITALS_THROTTLER, ttl: 60_000, limit: 120 },
           ],
           errorMessage: 'Too many requests',
           // Pass ioredis options (not a pre-built Redis instance) so

apps/server/src/integrations/throttle/throttler-names.ts

@@ -6,3 +6,7 @@ export const PAGE_TEMPLATE_THROTTLER = 'page-template';
 // ThrottlerGuard tracker) to bound anonymous abuse — the workspace owner pays
 // for the tokens.
 export const PUBLIC_SHARE_AI_THROTTLER = 'public-share-ai';
+// IP-keyed throttler for the anonymous client perf-telemetry sink
+// (POST /api/telemetry/vitals). Browsers batch metrics, so the limit is
+// generous; it only exists to bound abuse of the public, unauthenticated route.
+export const VITALS_THROTTLER = 'vitals';

apps/server/src/main.ts

@@ -16,6 +16,9 @@ import { EnvironmentService } from './integrations/environment/environment.servi
 import { SANDBOX_API_PATH } from './integrations/sandbox/sandbox.constants';
 import { resolveFrameHeader } from './common/helpers';
 import { resolveTrustProxy } from './integrations/environment/trust-proxy.util';
+import { isMetricsEnabled } from './integrations/metrics/metrics.registry';
+import { recordHttpResponse } from './integrations/metrics/http-metrics.hook';
+import { startMetricsServer } from './integrations/metrics/metrics.server';
 
 async function bootstrap() {
   const app = await NestFactory.create<NestFastifyApplication>(
@@ -91,6 +94,19 @@ async function bootstrap() {
       done();
     });
 
+  // #355 — HTTP request-duration histogram. Registered ONLY when METRICS_PORT is
+  // set (otherwise no collector runs at all). Uses the bounded route template
+  // label and excludes SSE/streaming responses (see recordHttpResponse).
+  if (isMetricsEnabled()) {
+    app
+      .getHttpAdapter()
+      .getInstance()
+      .addHook('onResponse', (req, reply, done) => {
+        recordHttpResponse(req, reply);
+        done();
+      });
+  }
+
   app
     .getHttpAdapter()
     .getInstance()
@@ -127,6 +143,9 @@ async function bootstrap() {
         '/api/workspace/create',
         '/api/workspace/joined',
         '/api/workspace/find-by-email',
+        // Public client perf-telemetry sink: browsers post it without a
+        // resolved workspace host, so the workspace-resolution gate must not 404 it.
+        '/api/telemetry/vitals',
         // Anonymous in-RAM blob sandbox: a remote consumer fetches blobs by an
         // unguessable UUID without any workspace host context, so the
         // workspace-resolution gate must not apply.
@@ -175,6 +194,11 @@ async function bootstrap() {
       `Listening on http://127.0.0.1:${port} / ${process.env.APP_URL}`,
     );
   });
+
+  // #355 — Prometheus scrape endpoint on a SEPARATE port (METRICS_PORT),
+  // started after the app is up. No default port: a no-op when METRICS_PORT is
+  // unset. Closed on shutdown by MetricsServerLifecycle (MetricsModule).
+  startMetricsServer();
 }
 
 bootstrap();

packages/mcp/test-e2e.mjs

@@ -450,7 +450,7 @@ async function main() {
     // 8. get_page markdown round-trip sanity (table separator present)
     const md = await client.getPage(pageId);
     check("get_page md: table separator emitted", md.data.content.includes("| --- |"), "");
-    check("get_page md: callout exported as :::", md.data.content.includes(":::info"));
+    check("get_page md: callout exported as Obsidian '> [!info]'", md.data.content.includes("> [!info]"));
 
     // 9. comments: create / list / reply / update / check_new / delete
     const beforeComments = new Date(Date.now() - 1000).toISOString();

packages/prosemirror-markdown/src/lib/docmost-schema.ts

@@ -635,13 +635,17 @@ const Attachment = Node.create({
       },
       name: {
         default: null,
-        parseHTML: (el: HTMLElement) => el.getAttribute("data-attachment-name"),
+        // Empty-string-vs-absent idempotency (GS-EDIT-REVERT class): "" -> default.
+        parseHTML: (el: HTMLElement) =>
+          el.getAttribute("data-attachment-name") || null,
         renderHTML: (attrs: Record<string, any>) =>
           attrs.name ? { "data-attachment-name": attrs.name } : {},
       },
       mime: {
         default: null,
-        parseHTML: (el: HTMLElement) => el.getAttribute("data-attachment-mime"),
+        // Empty-string-vs-absent idempotency (GS-EDIT-REVERT class): "" -> default.
+        parseHTML: (el: HTMLElement) =>
+          el.getAttribute("data-attachment-mime") || null,
         renderHTML: (attrs: Record<string, any>) =>
           attrs.mime ? { "data-attachment-mime": attrs.mime } : {},
       },
@@ -689,7 +693,10 @@ const Video = Node.create({
       },
       alt: {
         default: null,
-        parseHTML: (el: HTMLElement) => el.getAttribute("aria-label"),
+        // Empty-string-vs-absent idempotency: coerce "" back to the default so a
+        // stray empty `aria-label` never materializes `alt: ""` on a video stored
+        // with no alt (same GS-EDIT-REVERT class as the image `alt` fix).
+        parseHTML: (el: HTMLElement) => el.getAttribute("aria-label") || null,
         renderHTML: (attrs: Record<string, any>) =>
           attrs.alt ? { "aria-label": attrs.alt } : {},
       },
@@ -864,13 +871,15 @@ const diagramAttributes = () => ({
   },
   title: {
     default: null,
-    parseHTML: (el: HTMLElement) => el.getAttribute("data-title"),
+    // Empty-string-vs-absent idempotency (GS-EDIT-REVERT class): "" -> default.
+    parseHTML: (el: HTMLElement) => el.getAttribute("data-title") || null,
     renderHTML: (attrs: Record<string, any>) =>
       attrs.title ? { "data-title": attrs.title } : {},
   },
   alt: {
     default: null,
-    parseHTML: (el: HTMLElement) => el.getAttribute("data-alt"),
+    // Empty-string-vs-absent idempotency (GS-EDIT-REVERT class): "" -> default.
+    parseHTML: (el: HTMLElement) => el.getAttribute("data-alt") || null,
     renderHTML: (attrs: Record<string, any>) =>
       attrs.alt ? { "data-alt": attrs.alt } : {},
   },
@@ -1106,7 +1115,8 @@ const Pdf = Node.create({
       },
       name: {
         default: null,
-        parseHTML: (el: HTMLElement) => el.getAttribute("data-name"),
+        // Empty-string-vs-absent idempotency (GS-EDIT-REVERT class): "" -> default.
+        parseHTML: (el: HTMLElement) => el.getAttribute("data-name") || null,
         renderHTML: (attrs: Record<string, any>) =>
           attrs.name ? { "data-name": attrs.name } : {},
       },
@@ -1491,6 +1501,29 @@ export const docmostExtensions = [
           ...parent.height,
           parseHTML: (el: HTMLElement) => el.getAttribute("height"),
         },
+        // Empty-string-vs-absent idempotency (GS-EDIT-REVERT class). `marked`
+        // renders `![](src)` as `<img alt="">`, so the stock Image `alt`
+        // parseHTML (`getAttribute("alt")`) materializes `alt: ""` on an image
+        // that was stored with NO alt (attr absent). That is a false diff against
+        // the editor-stored form (a no-alt image has alt ABSENT, not ""), so a
+        // git-sync / ai-chat touch of a page with a plain image produced phantom
+        // churn. Coerce an empty string back to the attr's default (null) so the
+        // import is idempotent. A real alt survives verbatim (`|| undefined` keeps
+        // the truthy value; the default fills the empty case). `title` is coerced
+        // the same way for the whole class, even though `marked` does not
+        // currently emit `title=""` — defence in depth against any path that does.
+        // NOTE: this DIVERGES from editor-ext's literal image `alt` parseHTML
+        // (`getAttribute("alt")`, which returns "" verbatim), but CONVERGES on
+        // editor-ext's real STORED shape: an editor image inserted without alt
+        // renders with no `alt` attribute and re-parses as absent, never "".
+        alt: {
+          ...parent.alt,
+          parseHTML: (el: HTMLElement) => el.getAttribute("alt") || null,
+        },
+        title: {
+          ...parent.title,
+          parseHTML: (el: HTMLElement) => el.getAttribute("title") || null,
+        },
       };
     },
   }).configure({ inline: false }),

packages/prosemirror-markdown/test/roundtrip-stability.helper.ts

@@ -0,0 +1,443 @@
+/**
+ * Reusable round-trip-STABILITY matrix helper (fixtures-first).
+ *
+ * A single stored node authored WITHOUT a given string attribute (attr
+ * absent / undefined) must not gain a phantom EMPTY-STRING value after a
+ * markdown round-trip — the "empty-string-vs-absent" churn class. This helper,
+ * given a node spec, drives a matrix of attribute combinations through the REAL
+ * converter (`convertProseMirrorToMarkdown` -> `markdownToProseMirror`) and
+ * asserts byte-stability on two contours:
+ *
+ *   1. RAW round-trip: for the node under test, every attribute the round-trip
+ *      materializes must equal what the INPUT authored — an authored attr keeps
+ *      its value, an ABSENT attr may only reappear at its SCHEMA DEFAULT. If an
+ *      absent attr comes back as a NON-default value (e.g. `alt: ""` where the
+ *      default is `null`), that is an instability and is reported precisely as
+ *      `type.attr: absent -> "<got>"`. This is the contour git-sync / stored
+ *      JSON diffs on, so masking it only in `canonicalize` would leave the noise.
+ *
+ *   2. CANONICAL round-trip: `canonicalizeContent(original)` must deep-equal
+ *      `canonicalizeContent(roundtrip)` (a second, semantic contour).
+ *
+ * The ONLY normalization the helper treats as allowed (not an instability) is
+ * the DOCUMENTED numeric width/height/size/aspectRatio -> string coercion the
+ * converter performs on purpose (a stored numeric `640` re-parses via
+ * `getAttribute` as the string `"640"`). It is encoded here as an explicit
+ * per-spec `numericStringAttrs` set applied to BOTH contours, NOT a silent skip.
+ *
+ * The helper is node-type agnostic: image and the whole media family share the
+ * `align !== "center"` predicate + `<!--name {…}-->` comment machinery, so one
+ * matrix guards the shared class.
+ */
+import { getSchema } from "@tiptap/core";
+import {
+  convertProseMirrorToMarkdown,
+  markdownToProseMirror,
+  canonicalizeContent,
+  docmostExtensions,
+} from "../src/lib/index.js";
+import { firstDivergence } from "./roundtrip-helpers.js";
+
+/** One attribute's two probe values. */
+export interface AttrMatrixEntry {
+  /** Attribute name on the node. */
+  attr: string;
+  /**
+   * The "default" pick. `undefined` means the attribute is OMITTED entirely
+   * (the absent case — the one that can materialize an empty string on import).
+   * A concrete value is authored verbatim.
+   */
+  default: unknown;
+  /** A representative NON-default value to exercise (must survive verbatim). */
+  nonDefault: unknown;
+  /**
+   * Marks the attr as a member of the EMPTY-STRING class the fix targets: a
+   * string attr whose schema default is `null`/absent and whose parseHTML
+   * coerces `"" -> default` (image/drawio `alt`+`title`, video `alt` via
+   * aria-label, pdf/attachment `name`, attachment `mime`). Set true to also
+   * drive the THIRD-STATE convergence case (see runConvergenceCase) for this
+   * attr. Attrs whose default is NOT null (e.g. embed `provider`, default "")
+   * or that are not `""`-coerced (control attrs) are left unset.
+   */
+  emptyStringClass?: boolean;
+}
+
+/** A node type + the attribute matrix to sweep for it. */
+export interface NodeStabilitySpec {
+  /** Node type (e.g. "image", "video"). */
+  type: string;
+  /** Attributes always present on the node (e.g. `{ src: "/i.png" }`). */
+  baseAttrs?: Record<string, unknown>;
+  /** Attributes to sweep at default and non-default. */
+  attrMatrix: AttrMatrixEntry[];
+  /**
+   * Attributes whose numeric -> string coercion on round-trip is DOCUMENTED and
+   * intentional; compared modulo `String(x)` on both sides. Defaults to the
+   * converter's known sizing set.
+   */
+  numericStringAttrs?: string[];
+}
+
+/** A single unstable finding, legible enough to tie a gate-lock to. */
+export interface Instability {
+  type: string;
+  attr: string;
+  /** What the input authored: the literal value, or the ABSENT sentinel. */
+  authored: unknown | typeof ABSENT;
+  /** What the round-trip produced. */
+  got: unknown;
+  /** What a stable round-trip should have produced (authored value or default). */
+  expected: unknown;
+}
+
+/** One matrix cell's result. */
+export interface ComboResult {
+  label: string;
+  authored: Record<string, unknown>;
+  /** RAW-contour instabilities on the node under test. */
+  raw: Instability[];
+  /** CANONICAL-contour divergence (path + values) or null when equal. */
+  canonical: { path: string; a: unknown; b: unknown } | null;
+  /** True when the node type failed to round-trip at all (structural loss). */
+  missing: boolean;
+  md: string;
+}
+
+/** Whole-matrix report for one node spec. */
+export interface MatrixReport {
+  type: string;
+  combos: ComboResult[];
+}
+
+/** Sentinel marking an attribute the input did NOT author. */
+export const ABSENT = Symbol("ABSENT");
+
+const DEFAULT_NUMERIC_STRING_ATTRS = [
+  "width",
+  "height",
+  "size",
+  "aspectRatio",
+];
+
+// The ProseMirror schema the converter targets — its attribute `default`s are
+// the authoritative "what an absent attr should re-materialize as" oracle.
+const schema = getSchema(docmostExtensions);
+
+/** Read the schema default for every attribute of a node type. */
+function schemaDefaults(type: string): Record<string, unknown> {
+  const specAttrs = (schema.nodes[type]?.spec?.attrs ?? {}) as Record<
+    string,
+    { default: unknown }
+  >;
+  const out: Record<string, unknown> = {};
+  for (const [k, v] of Object.entries(specAttrs)) out[k] = v.default;
+  return out;
+}
+
+/** Find the first node of a given type anywhere in a PM doc tree. */
+function findFirst(node: any, type: string): any {
+  if (node && node.type === type) return node;
+  for (const child of node?.content ?? []) {
+    const hit = findFirst(child, type);
+    if (hit) return hit;
+  }
+  return null;
+}
+
+/** Coerce a scalar for the documented numeric->string comparison. */
+const numStr = (x: unknown): unknown => (x == null ? x : String(x));
+
+/**
+ * Enumerate the cartesian product of the matrix: every attribute independently
+ * at its default (index 0) or non-default (index 1) pick. The all-default
+ * corner is included (the baseline). Small by construction (2^N over a handful
+ * of at-risk string attrs).
+ */
+function enumerateCombos(matrix: AttrMatrixEntry[]): number[][] {
+  let combos: number[][] = [[]];
+  for (let i = 0; i < matrix.length; i++) {
+    const next: number[][] = [];
+    for (const c of combos) {
+      next.push([...c, 0]);
+      next.push([...c, 1]);
+    }
+    combos = next;
+  }
+  return combos;
+}
+
+/** Build the authored attrs for one combo pick vector. */
+function authoredAttrs(
+  spec: NodeStabilitySpec,
+  picks: number[],
+): Record<string, unknown> {
+  const attrs: Record<string, unknown> = { ...(spec.baseAttrs ?? {}) };
+  spec.attrMatrix.forEach((entry, i) => {
+    if (picks[i] === 1) {
+      attrs[entry.attr] = entry.nonDefault;
+    } else if (entry.default !== undefined) {
+      attrs[entry.attr] = entry.default;
+    }
+    // default === undefined -> OMIT the attr entirely (the absent case).
+  });
+  return attrs;
+}
+
+/** Human-readable label for a combo (which attrs are at non-default). */
+function comboLabel(spec: NodeStabilitySpec, picks: number[]): string {
+  const on = spec.attrMatrix
+    .filter((_, i) => picks[i] === 1)
+    .map((e) => e.attr);
+  return on.length === 0 ? "<all-default>" : on.join("+");
+}
+
+/**
+ * Run the full stability matrix for one node spec and return a structured
+ * report (does NOT throw — the caller asserts, so a failure can print the whole
+ * report). Every combo runs the real export->import pipeline once.
+ */
+export async function runStabilityMatrix(
+  spec: NodeStabilitySpec,
+): Promise<MatrixReport> {
+  const numericStringAttrs = new Set(
+    spec.numericStringAttrs ?? DEFAULT_NUMERIC_STRING_ATTRS,
+  );
+  const defaults = schemaDefaults(spec.type);
+  const combos: ComboResult[] = [];
+
+  for (const picks of enumerateCombos(spec.attrMatrix)) {
+    const authored = authoredAttrs(spec, picks);
+    const doc = { type: "doc", content: [{ type: spec.type, attrs: authored }] };
+    const md = convertProseMirrorToMarkdown(doc);
+    const rt = await markdownToProseMirror(md);
+    const node = findFirst(rt, spec.type);
+
+    const result: ComboResult = {
+      label: comboLabel(spec, picks),
+      authored,
+      raw: [],
+      canonical: null,
+      missing: node == null,
+      md,
+    };
+
+    if (node != null) {
+      // RAW contour: every materialized attr must equal the authored value, or
+      // (for an absent attr) the schema default — modulo the documented numeric
+      // string coercion.
+      const rtAttrs = (node.attrs ?? {}) as Record<string, unknown>;
+      for (const key of Object.keys(rtAttrs)) {
+        const authoredHas = Object.prototype.hasOwnProperty.call(authored, key);
+        const expected = authoredHas ? authored[key] : defaults[key];
+        let got = rtAttrs[key];
+        let exp = expected;
+        if (numericStringAttrs.has(key)) {
+          got = numStr(got);
+          exp = numStr(exp);
+        }
+        if (firstDivergence(got, exp) !== null) {
+          result.raw.push({
+            type: spec.type,
+            attr: key,
+            authored: authoredHas ? authored[key] : ABSENT,
+            got: rtAttrs[key],
+            expected,
+          });
+        }
+      }
+
+      // CANONICAL contour: canonical forms deep-equal, modulo the same numeric
+      // string coercion (applied to both trees so a documented coercion is not
+      // counted as a divergence).
+      const ca = normalizeNumeric(canonicalizeContent(doc), numericStringAttrs);
+      const cb = normalizeNumeric(canonicalizeContent(rt), numericStringAttrs);
+      result.canonical = firstDivergence(ca, cb);
+    }
+
+    combos.push(result);
+  }
+
+  return { type: spec.type, combos };
+}
+
+/**
+ * Deep-copy a canonical tree, coercing the documented numeric->string attrs to
+ * their string form so an intentional `640 -> "640"` coercion is not reported
+ * as a canonical divergence. Only touches the listed attribute keys.
+ */
+function normalizeNumeric(node: any, attrs: Set<string>): any {
+  if (Array.isArray(node)) return node.map((n) => normalizeNumeric(n, attrs));
+  if (node === null || typeof node !== "object") return node;
+  const out: Record<string, unknown> = {};
+  for (const key of Object.keys(node)) {
+    if (key === "attrs" && node.attrs && typeof node.attrs === "object") {
+      const a: Record<string, unknown> = {};
+      for (const [k, v] of Object.entries(node.attrs)) {
+        a[k] = attrs.has(k) ? numStr(v) : v;
+      }
+      out.attrs = a;
+    } else {
+      out[key] = normalizeNumeric(node[key], attrs);
+    }
+  }
+  return out;
+}
+
+/** Flatten a report to just its unstable combos (for a terse assertion). */
+export function unstableCombos(report: MatrixReport): ComboResult[] {
+  return report.combos.filter(
+    (c) => c.missing || c.raw.length > 0 || c.canonical !== null,
+  );
+}
+
+// ---------------------------------------------------------------------------
+// THIRD STATE: an EXPLICITLY-STORED empty string on a string attr.
+//
+// The matrix above sweeps TWO states per string attr: absent/default and a
+// non-default value — and asserts FIRST-pass byte-stability for both. There is
+// a third, degenerate state the matrix does NOT cover: the attr stored as a
+// LITERAL `""`. This is DISTINCT from "the node never had the attr": a user
+// types an alt in the editor, then deletes it, and Tiptap's
+// `updateAttributes({ alt: "" })` persists a literal `alt: ""` in the stored
+// JSON. There is no absent-vs-"" distinction in the DOM once serialized, so the
+// fix's `getAttribute("alt") || null` coercion canonicalizes BOTH to the
+// default (`null`).
+//
+// Consequence — and this is CORRECT, not a bug: a doc carrying an explicit `""`
+// converges to the default on the FIRST round-trip (a ONE-TIME diff: `"" ->
+// null`), then is byte-stable from the SECOND round-trip on (idempotent). So
+// this state must be pinned with a DIFFERENT contract than the matrix's:
+//   - do NOT assert first-pass byte-stability (the first pass legitimately
+//     changes `""` -> default), and
+//   - DO assert the first pass converges to the default AND the second pass is
+//     idempotent (rt2 deep-equals rt1).
+//
+// A future sync/QA pass diffing stored pages will see this one-time `"" -> null`
+// normalization exactly once per affected node; it is the converter canon, not
+// corruption, and must not be flagged as data loss.
+// ---------------------------------------------------------------------------
+
+/** Result of the third-state ("explicit empty string") convergence probe. */
+export interface ConvergenceResult {
+  type: string;
+  attr: string;
+  /** The schema default the attr must converge to on pass 1 (null / absent). */
+  expectedDefault: unknown;
+  /** rt1's materialized value for the attr — must equal `expectedDefault`. */
+  firstPassValue: unknown;
+  /** True when the node round-tripped AND rt1 converged the attr to default. */
+  convergedToDefault: boolean;
+  /** rt1-vs-rt2 divergence; MUST be null (idempotent from pass 2 on). */
+  secondPassDivergence: { path: string; a: unknown; b: unknown } | null;
+  /** True when the node type failed to round-trip at all (structural loss). */
+  missing: boolean;
+}
+
+/** Round-trip a full PM doc through the real converter once. */
+async function roundtripDoc(doc: any): Promise<any> {
+  return markdownToProseMirror(convertProseMirrorToMarkdown(doc));
+}
+
+/**
+ * Third-state convergence probe for one string attr of the empty-string class.
+ *
+ * (a) builds a doc with the attr EXPLICITLY set to `""` (baseAttrs + `""`),
+ * (b) rt1 = roundtrip(doc); asserts rt1's attr equals the schema default — the
+ *     documented ONE-TIME `"" -> default` normalization (NOT byte-stable vs the
+ *     `""` input, so first-pass stability is deliberately NOT asserted here),
+ * (c) rt2 = roundtrip(rt1); asserts rt2 deep-equals rt1 — idempotent from the
+ *     second round-trip on.
+ *
+ * Returns a structured result (does NOT throw) so the caller can assert and
+ * print. Reusable across the whole node family: drive it for every attr flagged
+ * `emptyStringClass` on every spec (see convergenceCasesFor / the test driver).
+ */
+export async function runConvergenceCase(
+  spec: NodeStabilitySpec,
+  attr: string,
+): Promise<ConvergenceResult> {
+  const expectedDefault = schemaDefaults(spec.type)[attr];
+
+  // (a) The degenerate third state: attr persisted as a LITERAL "".
+  const authored = { ...(spec.baseAttrs ?? {}), [attr]: "" };
+  const doc = { type: "doc", content: [{ type: spec.type, attrs: authored }] };
+
+  // (b) First round-trip: "" must normalize to the default (a one-time diff).
+  const rt1 = await roundtripDoc(doc);
+  const node1 = findFirst(rt1, spec.type);
+  const firstPassValue = node1?.attrs?.[attr];
+  const convergedToDefault =
+    node1 != null && firstDivergence(firstPassValue, expectedDefault) === null;
+
+  // (c) Second round-trip: must be byte-stable (rt2 deep-equals rt1). We compare
+  // the WHOLE docs — both are converter OUTPUTS already in the same materialized
+  // form (numeric attrs are strings on both sides), so no numeric normalization
+  // is needed here, unlike the raw/canonical contours above.
+  const rt2 = node1 != null ? await roundtripDoc(rt1) : rt1;
+  const secondPassDivergence =
+    node1 != null ? firstDivergence(rt1, rt2) : null;
+
+  return {
+    type: spec.type,
+    attr,
+    expectedDefault,
+    firstPassValue,
+    convergedToDefault,
+    secondPassDivergence,
+    missing: node1 == null,
+  };
+}
+
+/** The attrs of a spec flagged as members of the empty-string class. */
+export function convergenceCasesFor(spec: NodeStabilitySpec): string[] {
+  return spec.attrMatrix
+    .filter((e) => e.emptyStringClass)
+    .map((e) => e.attr);
+}
+
+/** True when a convergence result honours the "converges once, then stable" contract. */
+export function convergenceOk(r: ConvergenceResult): boolean {
+  return !r.missing && r.convergedToDefault && r.secondPassDivergence === null;
+}
+
+/** Render a convergence result as a legible one-liner for a failed assertion. */
+export function formatConvergence(r: ConvergenceResult): string {
+  if (r.missing) return `${r.type}.${r.attr}: DID-NOT-ROUND-TRIP`;
+  const parts: string[] = [];
+  if (!r.convergedToDefault) {
+    parts.push(
+      `pass1 did NOT converge: got ${JSON.stringify(r.firstPassValue)} (expected default ${JSON.stringify(r.expectedDefault)})`,
+    );
+  }
+  if (r.secondPassDivergence) {
+    parts.push(
+      `pass2 NOT idempotent @ ${r.secondPassDivergence.path}: ${JSON.stringify(r.secondPassDivergence.a)} vs ${JSON.stringify(r.secondPassDivergence.b)}`,
+    );
+  }
+  const status = parts.length === 0 ? "converges-once-then-stable" : parts.join("; ");
+  return `${r.type}.${r.attr}: ${status}`;
+}
+
+/** Render a report as a legible multi-line string for a failed assertion. */
+export function formatReport(report: MatrixReport): string {
+  const lines: string[] = [`node "${report.type}":`];
+  for (const c of report.combos) {
+    const flags: string[] = [];
+    if (c.missing) flags.push("DID-NOT-ROUND-TRIP");
+    for (const i of c.raw) {
+      const authored =
+        i.authored === ABSENT ? "absent" : JSON.stringify(i.authored);
+      flags.push(
+        `RAW ${i.type}.${i.attr}: ${authored} -> ${JSON.stringify(i.got)} (expected ${JSON.stringify(i.expected)})`,
+      );
+    }
+    if (c.canonical) {
+      flags.push(
+        `CANON @ ${c.canonical.path}: ${JSON.stringify(c.canonical.a)} vs ${JSON.stringify(c.canonical.b)}`,
+      );
+    }
+    const status = flags.length === 0 ? "stable" : flags.join("; ");
+    lines.push(`  [${c.label}] ${status}`);
+  }
+  return lines.join("\n");
+}

packages/prosemirror-markdown/test/roundtrip-stability.test.ts

@@ -0,0 +1,164 @@
+import { describe, expect, it } from "vitest";
+import {
+  runStabilityMatrix,
+  unstableCombos,
+  formatReport,
+  runConvergenceCase,
+  convergenceCasesFor,
+  convergenceOk,
+  formatConvergence,
+  type NodeStabilitySpec,
+} from "./roundtrip-stability.helper.js";
+
+// ---------------------------------------------------------------------------
+// Round-trip STABILITY matrix for image + the media family.
+//
+// Guards the "empty-string-vs-absent" churn class (GS-EDIT-REVERT family): a
+// stored node authored WITHOUT a string attr (alt/title/caption/aria-label/...)
+// must not gain a phantom `attr: ""` after `markdownToProseMirror(convert…)`.
+// Each spec sweeps the at-risk string attrs at DEFAULT (absent) and at a real
+// NON-default value; the helper asserts both the RAW round-trip (attrs equal the
+// input's, modulo the documented numeric width/height/size/aspectRatio -> string
+// coercion) and the CANONICAL round-trip (canonical forms deep-equal).
+//
+// The image + media family share the `align !== "center"` predicate and the
+// `<!--name {…}-->` comment machinery, so one matrix guards the shared class.
+// align is NOT part of this class (it round-trips correctly) and is not swept.
+// ---------------------------------------------------------------------------
+
+const SPECS: NodeStabilitySpec[] = [
+  {
+    // Image carries the most at-risk string attrs. `alt` is the one marked
+    // materializes as `<img alt="">` on `![](src)` import (the real bug); title
+    // and caption are covered as the same class. attachmentId is a string attr
+    // that must stay absent when unset (control).
+    type: "image",
+    baseAttrs: { src: "/i.png" },
+    attrMatrix: [
+      { attr: "alt", default: undefined, nonDefault: "a real alt text", emptyStringClass: true },
+      { attr: "title", default: undefined, nonDefault: "a real title", emptyStringClass: true },
+      { attr: "caption", default: undefined, nonDefault: "a real caption" },
+      { attr: "attachmentId", default: undefined, nonDefault: "att-42" },
+    ],
+  },
+  {
+    // Video's `alt` rides the `aria-label` attribute (media aria-label at risk).
+    type: "video",
+    baseAttrs: { src: "/v.mp4" },
+    attrMatrix: [
+      { attr: "alt", default: undefined, nonDefault: "a clip", emptyStringClass: true },
+      { attr: "attachmentId", default: undefined, nonDefault: "att-1" },
+    ],
+  },
+  {
+    // Audio carries no alt/title; attachmentId is its only optional string attr.
+    type: "audio",
+    baseAttrs: { src: "/a.mp3" },
+    attrMatrix: [
+      { attr: "attachmentId", default: undefined, nonDefault: "att-2" },
+    ],
+  },
+  {
+    // pdf: link-form media. `name` (filename) is its at-risk string attr.
+    type: "pdf",
+    baseAttrs: { src: "/d.pdf" },
+    attrMatrix: [
+      { attr: "name", default: undefined, nonDefault: "report.pdf", emptyStringClass: true },
+      { attr: "attachmentId", default: undefined, nonDefault: "att-3" },
+    ],
+  },
+  {
+    // attachment: link-form media (file card). `name` + `mime` string attrs.
+    type: "attachment",
+    baseAttrs: { url: "/f.zip" },
+    attrMatrix: [
+      { attr: "name", default: undefined, nonDefault: "bundle.zip", emptyStringClass: true },
+      { attr: "mime", default: undefined, nonDefault: "application/zip", emptyStringClass: true },
+      { attr: "attachmentId", default: undefined, nonDefault: "att-4" },
+    ],
+  },
+  {
+    // embed: link-form media. `provider` is its at-risk string attr (schema
+    // default ""). embed's numeric width/height defaults (800/600) are a SEPARATE,
+    // documented limitation OUTSIDE the empty-string class: they are not in
+    // canonicalize's KNOWN_DEFAULTS, so an ABSENT width/height re-imports as the
+    // 800/600 default and diverges canonically (see the note in canonicalize.ts).
+    // That is canonicalize-owned and out of scope here, so we author the
+    // dimensions at their defaults (as real editor embeds carry them) to keep this
+    // guard focused on the empty-string/provider class.
+    // provider's schema default is "" (NOT null), so a re-imported "" is the
+    // correct value, not a phantom — it is outside the null-default empty-string
+    // class. We author it at its "" default (the default pick) so the sweep still
+    // asserts a non-default provider ("youtube") round-trips, without tripping the
+    // canonicalize KNOWN_DEFAULTS gap for embed's non-null defaults.
+    type: "embed",
+    baseAttrs: { src: "https://example.com/x", width: 800, height: 600 },
+    attrMatrix: [
+      { attr: "provider", default: "", nonDefault: "youtube" },
+    ],
+  },
+  {
+    // drawio: image-form diagram. `title` + `alt` string attrs (data-title/-alt).
+    type: "drawio",
+    baseAttrs: { src: "blob:drawio" },
+    attrMatrix: [
+      { attr: "title", default: undefined, nonDefault: "flow chart", emptyStringClass: true },
+      { attr: "alt", default: undefined, nonDefault: "an alt", emptyStringClass: true },
+      { attr: "attachmentId", default: undefined, nonDefault: "att-5" },
+    ],
+  },
+  {
+    // excalidraw: image-form diagram, same shared diagramAttributes set.
+    type: "excalidraw",
+    baseAttrs: { src: "blob:excalidraw" },
+    attrMatrix: [
+      { attr: "title", default: undefined, nonDefault: "sketch", emptyStringClass: true },
+      { attr: "alt", default: undefined, nonDefault: "an alt", emptyStringClass: true },
+      { attr: "attachmentId", default: undefined, nonDefault: "att-6" },
+    ],
+  },
+];
+
+describe("round-trip stability matrix (image + media family)", () => {
+  for (const spec of SPECS) {
+    it(`${spec.type}: no attr materializes an empty-string / phantom value`, async () => {
+      const report = await runStabilityMatrix(spec);
+      const unstable = unstableCombos(report);
+      // On failure, print the WHOLE matrix so which (attr, value) combos are
+      // unstable is legible.
+      expect(unstable, `\n${formatReport(report)}\n`).toEqual([]);
+    });
+  }
+});
+
+// ---------------------------------------------------------------------------
+// THIRD STATE: an attr EXPLICITLY stored as a literal "" (GS-EDIT-REVERT: a user
+// typed alt/title/name/... then deleted it, so Tiptap persisted `attr: ""` — a
+// value DISTINCT from "attr was never set"). Unlike the absent case above, this
+// state is NOT first-pass byte-stable: the fix's `"" -> default` coercion is a
+// deliberate ONE-TIME normalization on the FIRST sync round-trip, stable
+// thereafter. We therefore assert a DIFFERENT contract — "converges to default
+// on pass 1, then idempotent from pass 2 on" — for every empty-string-class attr
+// across the whole node family (image/video/pdf/attachment/drawio/excalidraw).
+//
+// IMPORTANT for a future sync/QA pass: the pass-1 `"" -> null` diff is the
+// converter canon, not corruption. It appears at most once per affected node and
+// must NOT be flagged as "the converter is losing/corrupting page data".
+// ---------------------------------------------------------------------------
+describe("round-trip third state: explicit empty string converges once, then idempotent", () => {
+  for (const spec of SPECS) {
+    for (const attr of convergenceCasesFor(spec)) {
+      it(`${spec.type}.${attr}: "" normalizes to default on pass 1, byte-stable from pass 2`, async () => {
+        const r = await runConvergenceCase(spec, attr);
+        // Pass 1 must converge "" -> the schema default (the one-time diff) and
+        // pass 2 (roundtrip of pass-1 output) must be byte-stable. formatConvergence
+        // prints exactly which half failed.
+        expect(convergenceOk(r), `\n${formatConvergence(r)}\n`).toBe(true);
+        // Spell the contract out explicitly so the intent is legible in the test:
+        expect(r.convergedToDefault, `\n${formatConvergence(r)}\n`).toBe(true);
+        expect(r.firstPassValue).toEqual(r.expectedDefault);
+        expect(r.secondPassDivergence, `\n${formatConvergence(r)}\n`).toBeNull();
+      });
+    }
+  }
+});

pnpm-lock.yaml

@@ -416,6 +416,9 @@ importers:
       socket.io-client:
         specifier: 4.8.3
         version: 4.8.3
+      web-vitals:
+        specifier: ^5.1.0
+        version: 5.1.0
       zod:
         specifier: 4.3.6
         version: 4.3.6
@@ -744,6 +747,9 @@ importers:
       postmark:
         specifier: ^4.0.7
         version: 4.0.7
+      prom-client:
+        specifier: ^15.1.3
+        version: 15.1.3
       react:
         specifier: ^18.3.1
         version: 18.3.1
@@ -5988,6 +5994,9 @@ packages:
   bind-event-listener@3.0.0:
     resolution: {integrity: sha512-PJvH288AWQhKs2v9zyfYdPzlPqf5bXbGMmhmUIY9x4dAUGIWgomO771oBQNwJnMQSnUIXhKu6sgzpBRXTlvb8Q==}
 
+  bintrees@1.0.2:
+    resolution: {integrity: sha512-VOMgTMwjAaUG580SXn3LacVgjurrbMme7ZZNYGSSV7mmtY6QQRh0Eg3pwIcntQ77DErK1L0NxkbetjcoXzVwKw==}
+
   bl@4.1.0:
     resolution: {integrity: sha512-1W07cM9gS6DcLperZfFSj+bWLtaPGSOHWhPiGzXmvVJbRLdG82sH/Kn8EtW1VqWVA54AKf2h5k5BbnIbwF3h6w==}
 
@@ -9318,6 +9327,10 @@ packages:
   process-warning@5.0.0:
     resolution: {integrity: sha512-a39t9ApHNx2L4+HBnQKqxxHNs1r7KF+Intd8Q/g1bUh6q0WIp9voPXJ/x0j+ZL45KF1pJd9+q2jLIRMfvEshkA==}
 
+  prom-client@15.1.3:
+    resolution: {integrity: sha512-6ZiOBfCywsD4k1BN9IX0uZhF+tJkV8q8llP64G5Hajs4JOeVLPCwpPVcpXy3BwYiUGgyJzsJJQeOIv7+hDSq8g==}
+    engines: {node: ^16 || ^18 || >=20}
+
   prompts@2.4.2:
     resolution: {integrity: sha512-NxNv/kLguCA7p3jE8oL2aEBsrJWgAakBpgmgK6lpPWV+WuOmY6r2/zbAVnP+T8bQlA0nzHXSJSJW0Hq7ylaD2Q==}
     engines: {node: '>= 6'}
@@ -10145,6 +10158,9 @@ packages:
     resolution: {integrity: sha512-4LeEWl96twnS2Q7Bz4MGqgazLqO+hJN63GZxXoIqh1T3VweYD997gbU1ItNsQafqqXTXd5WFyFdReLtwvRBNiw==}
     engines: {node: '>=18'}
 
+  tdigest@0.1.2:
+    resolution: {integrity: sha512-+G0LLgjjo9BZX2MfdvPfH+MKLCrxlXSYec5DaPYP1fe6Iyhf0/fSmJ0bFiZ1F8BT6cGXl2LpltQptzjXKWEkKA==}
+
   terser-webpack-plugin@5.4.0:
     resolution: {integrity: sha512-Bn5vxm48flOIfkdl5CaD2+1CiUVbonWQ3KQPyP7/EuIl9Gbzq/gQFOzaMFUEgVjB1396tcK0SG8XcNJ/2kDH8g==}
     engines: {node: '>= 10.13.0'}
@@ -16153,7 +16169,7 @@ snapshots:
       obug: 2.1.1
       std-env: 4.1.0
       tinyrainbow: 3.1.0
-      vitest: 4.1.6(@opentelemetry/api@1.9.0)(@types/node@25.5.0)(@vitest/coverage-v8@4.1.6)(happy-dom@20.8.9)(jsdom@27.4.0(@noble/hashes@2.0.1))(vite@8.0.5(@types/node@25.5.0)(esbuild@0.28.0)(jiti@2.4.2)(less@4.2.0)(sugarss@5.0.1(postcss@8.5.14))(terser@5.39.0)(tsx@4.21.0)(yaml@2.8.3))
+      vitest: 4.1.6(@opentelemetry/api@1.9.0)(@types/node@22.19.1)(@vitest/coverage-v8@4.1.6)(happy-dom@20.8.9)(jsdom@25.0.0)(vite@8.0.5(@types/node@22.19.1)(esbuild@0.28.0)(jiti@2.4.2)(less@4.2.0)(sugarss@5.0.1(postcss@8.5.14))(terser@5.39.0)(tsx@4.21.0)(yaml@2.8.3))
 
   '@vitest/expect@4.1.6':
     dependencies:
@@ -16665,6 +16681,8 @@ snapshots:
 
   bind-event-listener@3.0.0: {}
 
+  bintrees@1.0.2: {}
+
   bl@4.1.0:
     dependencies:
       buffer: 5.7.1
@@ -20476,6 +20494,11 @@ snapshots:
 
   process-warning@5.0.0: {}
 
+  prom-client@15.1.3:
+    dependencies:
+      '@opentelemetry/api': 1.9.0
+      tdigest: 0.1.2
+
   prompts@2.4.2:
     dependencies:
       kleur: 3.0.3
@@ -21521,6 +21544,10 @@ snapshots:
       minizlib: 3.1.0
       yallist: 5.0.0
 
+  tdigest@0.1.2:
+    dependencies:
+      bintrees: 1.0.2
+
   terser-webpack-plugin@5.4.0(@swc/core@1.5.25(@swc/helpers@0.5.5))(webpack@5.106.0(@swc/core@1.5.25(@swc/helpers@0.5.5))):
     dependencies:
       '@jridgewell/trace-mapping': 0.3.31