diff --git a/apps/client/package.json b/apps/client/package.json
index 76d617da..b922efe9 100644
--- a/apps/client/package.json
+++ b/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",
diff --git a/apps/client/src/features/editor/page-editor.tsx b/apps/client/src/features/editor/page-editor.tsx
index 9953d6c5..8b2f2fc9 100644
--- a/apps/client/src/features/editor/page-editor.tsx
+++ b/apps/client/src/features/editor/page-editor.tsx
@@ -93,6 +93,10 @@ import {
   isBodyEditable,
   isCollabSynced,
 } from "@/features/editor/editor-sync-state";
+import {
+  measurePageOpen,
+  reportEditorTx,
+} from "@/lib/telemetry/vitals";
 
 interface PageEditorProps {
   pageId: string;
@@ -351,6 +355,34 @@ export default function PageEditor({
           editor.storage.pageId = pageId;
           handleScrollTo(editor);
           editorRef.current = editor;
+
+          // #355 — 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();
+
+          // #355 — 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 }) {
diff --git a/apps/client/src/lib/telemetry/route-template.test.ts b/apps/client/src/lib/telemetry/route-template.test.ts
new file mode 100644
index 00000000..aa798a3d
--- /dev/null
+++ b/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");
+  });
+});
diff --git a/apps/client/src/lib/telemetry/route-template.ts b/apps/client/src/lib/telemetry/route-template.ts
new file mode 100644
index 00000000..45fe4855
--- /dev/null
+++ b/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';
+  }
+}
diff --git a/apps/client/src/lib/telemetry/vitals.ts b/apps/client/src/lib/telemetry/vitals.ts
new file mode 100644
index 00000000..b18bcba0
--- /dev/null
+++ b/apps/client/src/lib/telemetry/vitals.ts
@@ -0,0 +1,275 @@
+import {
+  onCLS,
+  onINP,
+  onLCP,
+  onTTFB,
+  type CLSMetricWithAttribution,
+  type INPMetricWithAttribution,
+  type LCPMetricWithAttribution,
+  type TTFBMetricWithAttribution,
+} from "web-vitals/attribution";
+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);
+  }
+}
+
+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 (!isVitalsSampled()) 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;
+
+  // 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);
+}
diff --git a/apps/client/src/main.tsx b/apps/client/src/main.tsx
index 5dbf6b81..0c19fe28 100644
--- a/apps/client/src/main.tsx
+++ b/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);
 
diff --git a/apps/server/package.json b/apps/server/package.json
index 4e566d9d..517f1b3d 100644
--- a/apps/server/package.json
+++ b/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",
diff --git a/apps/server/src/app.module.ts b/apps/server/src/app.module.ts
index e257fe9b..381970fa 100644
--- a/apps/server/src/app.module.ts
+++ b/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 +95,8 @@ try {
     SandboxModule,
     AiModule,
     AiChatModule,
+    MetricsModule,
+    ClientTelemetryModule,
     ...enterpriseModules,
   ],
   controllers: [AppController],
diff --git a/apps/server/src/collaboration/extensions/persistence.extension.ts b/apps/server/src/collaboration/extensions/persistence.extension.ts
index 18eb99e6..35310cf4 100644
--- a/apps/server/src/collaboration/extensions/persistence.extension.ts
+++ b/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);
diff --git a/apps/server/src/core/telemetry/client-metrics.constants.ts b/apps/server/src/core/telemetry/client-metrics.constants.ts
new file mode 100644
index 00000000..4f4cc70f
--- /dev/null
+++ b/apps/server/src/core/telemetry/client-metrics.constants.ts
@@ -0,0 +1,93 @@
+/**
+ * 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;
+
+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);
+  }
+
+  return { name, value, rating, route, attr, docSize, workspaceId };
+}
diff --git a/apps/server/src/core/telemetry/client-telemetry.module.ts b/apps/server/src/core/telemetry/client-telemetry.module.ts
new file mode 100644
index 00000000..cf94efc0
--- /dev/null
+++ b/apps/server/src/core/telemetry/client-telemetry.module.ts
@@ -0,0 +1,15 @@
+import { 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.
+ */
+@Module({
+  controllers: [VitalsController],
+  providers: [VitalsService],
+})
+export class ClientTelemetryModule {}
diff --git a/apps/server/src/core/telemetry/vitals.controller.ts b/apps/server/src/core/telemetry/vitals.controller.ts
new file mode 100644
index 00000000..62812671
--- /dev/null
+++ b/apps/server/src/core/telemetry/vitals.controller.ts
@@ -0,0 +1,47 @@
+import {
+  Body,
+  Controller,
+  HttpCode,
+  Post,
+  Req,
+  UseGuards,
+} from '@nestjs/common';
+import { Throttle, ThrottlerGuard } from '@nestjs/throttler';
+import { FastifyRequest } from 'fastify';
+import { Public } from '../../common/decorators/public.decorator';
+import { 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)
+  @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 };
+  }
+}
diff --git a/apps/server/src/core/telemetry/vitals.service.spec.ts b/apps/server/src/core/telemetry/vitals.service.spec.ts
new file mode 100644
index 00000000..2fca1228
--- /dev/null
+++ b/apps/server/src/core/telemetry/vitals.service.spec.ts
@@ -0,0 +1,122 @@
+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();
+  });
+});
diff --git a/apps/server/src/core/telemetry/vitals.service.ts b/apps/server/src/core/telemetry/vitals.service.ts
new file mode 100644
index 00000000..076a2506
--- /dev/null
+++ b/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);
+  }
+}
diff --git a/apps/server/src/database/database.module.ts b/apps/server/src/database/database.module.ts
index 4e9c5d13..ea56ed11 100644
--- a/apps/server/src/database/database.module.ts
+++ b/apps/server/src/database/database.module.ts
@@ -40,6 +40,8 @@ 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 } from '../integrations/metrics/metrics.registry';
+import { firstSqlToken } from '../integrations/metrics/metrics.constants';
 
 @Global()
 @Module({
@@ -67,6 +69,14 @@ import { normalizePostgresUrl } from '../common/helpers';
         }),
         plugins: [new CamelCasePlugin()],
         log: (event: LogEvent) => {
+          // #355 — db_query_duration_seconds, labelled by the leading SQL token
+          // (bounded cardinality). No-op when METRICS_PORT is unset. Runs for
+          // every query, independent of the dev-only debug logging below.
+          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') {
diff --git a/apps/server/src/database/migrations/20260704T120000-client-metrics.ts b/apps/server/src/database/migrations/20260704T120000-client-metrics.ts
new file mode 100644
index 00000000..92c42334
--- /dev/null
+++ b/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);
+}
diff --git a/apps/server/src/database/types/db.d.ts b/apps/server/src/database/types/db.d.ts
index dab98b3d..d5ec8d5e 100644
--- a/apps/server/src/database/types/db.d.ts
+++ b/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;
diff --git a/apps/server/src/integrations/metrics/http-metrics.hook.ts b/apps/server/src/integrations/metrics/http-metrics.hook.ts
new file mode 100644
index 00000000..a01a7d1a
--- /dev/null
+++ b/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.
+  }
+}
diff --git a/apps/server/src/integrations/metrics/metrics-bull.service.ts b/apps/server/src/integrations/metrics/metrics-bull.service.ts
new file mode 100644
index 00000000..04722cd1
--- /dev/null
+++ b/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();
+  }
+}
diff --git a/apps/server/src/integrations/metrics/metrics.constants.ts b/apps/server/src/integrations/metrics/metrics.constants.ts
new file mode 100644
index 00000000..16ad4950
--- /dev/null
+++ b/apps/server/src/integrations/metrics/metrics.constants.ts
@@ -0,0 +1,80 @@
+/**
+ * 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`.
+ */
+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();
+  const known = new Set([
+    'select',
+    'insert',
+    'update',
+    'delete',
+    'with',
+    'begin',
+    'commit',
+    'rollback',
+    'alter',
+    'create',
+    'drop',
+    'truncate',
+    'explain',
+  ]);
+  return known.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;
+}
diff --git a/apps/server/src/integrations/metrics/metrics.module.ts b/apps/server/src/integrations/metrics/metrics.module.ts
new file mode 100644
index 00000000..a89bdff0
--- /dev/null
+++ b/apps/server/src/integrations/metrics/metrics.module.ts
@@ -0,0 +1,13 @@
+import { Module } from '@nestjs/common';
+import { MetricsBullService } from './metrics-bull.service';
+
+/**
+ * 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.
+ */
+@Module({
+  providers: [MetricsBullService],
+})
+export class MetricsModule {}
diff --git a/apps/server/src/integrations/metrics/metrics.registry.ts b/apps/server/src/integrations/metrics/metrics.registry.ts
new file mode 100644
index 00000000..d62be165
--- /dev/null
+++ b/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);
+}
diff --git a/apps/server/src/integrations/metrics/metrics.server.ts b/apps/server/src/integrations/metrics/metrics.server.ts
new file mode 100644
index 00000000..f1b90b15
--- /dev/null
+++ b/apps/server/src/integrations/metrics/metrics.server.ts
@@ -0,0 +1,56 @@
+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 (default 9464,
+ * overridable via `METRICS_PORT`). 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.
+ */
+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}`);
+  });
+
+  return server;
+}
diff --git a/apps/server/src/integrations/metrics/metrics.spec.ts b/apps/server/src/integrations/metrics/metrics.spec.ts
new file mode 100644
index 00000000..ffcc11e6
--- /dev/null
+++ b/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');
+  });
+});
diff --git a/apps/server/src/integrations/throttle/throttle.module.ts b/apps/server/src/integrations/throttle/throttle.module.ts
index db197015..4ad0f9c4 100644
--- a/apps/server/src/integrations/throttle/throttle.module.ts
+++ b/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
diff --git a/apps/server/src/integrations/throttle/throttler-names.ts b/apps/server/src/integrations/throttle/throttler-names.ts
index f1ab971e..c54b0898 100644
--- a/apps/server/src/integrations/throttle/throttler-names.ts
+++ b/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';
diff --git a/apps/server/src/main.ts b/apps/server/src/main.ts
index b5fa0027..e31f2ddc 100644
--- a/apps/server/src/main.ts
+++ b/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 +194,10 @@ 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, default
+  // 9464), started after the app is up. No-op when METRICS_PORT is unset.
+  startMetricsServer();
 }
 
 bootstrap();
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 299f5e51..0d99a612 100644
--- a/pnpm-lock.yaml
+++ b/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