diff --git a/CHANGELOG.md b/CHANGELOG.md
index 15b9ada6..2f79aadf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - **Mermaid diagrams export as PNG, with Copy/Download in the zoom lightbox** (`docs/src/integrations/diagram-png.mjs` (new), `docs/src/components/MermaidZoom.astro`, `docs/astro.config.mjs`, `docs/src/content/docs/development.md`): diagrams render as inline SVG (great for reading — selectable text, screen-reader semantics, theme-reactive colors) but can't be right-click-copied or dropped into a slide deck. A new `astro:build:done` integration now also rasterizes every diagram to `dist/diagrams/<slug>/<index>-<theme>[-transparent].png` — light **and** dark, 2× DPI, in two variants per theme (a WYSIWYG surface card and a transparent-background version for slide decks) — reusing the Playwright Chromium `rehype-mermaid` already needs, with a content-hash cache (`node_modules/.cache/wh-diagram-png`) so unchanged diagrams skip Chromium and the whole pass is wrapped so it can never fail the build. The zoom lightbox (open by clicking any diagram) gains **Copy** (async-clipboard image, falling back to download where unsupported) and **Download** buttons that act on the PNG for the current theme, plus a **background toggle** (checkerboard icon) that flips Copy/Download between the solid and transparent variant and previews transparency as a checkerboard on the zoom stage; inline diagrams stay button-free. The upstream `@wave-rf/astro-themed-mermaid` plugin is intentionally untouched — it's color-agnostic (CSS-var placeholders resolved at runtime), so a WYSIWYG light/dark PNG must be rasterized post-build where `global.css` + a theme apply. PNGs are gitignored build artifacts, regenerated in CI/deploy.
 
+- **Site header override — a top-level "Docs" nav link, the search box kept expanded, and a splash-width header** (`docs/src/components/Header.astro` (new), `docs/src/config/sidebar.ts`, `docs/src/env.d.ts`, `docs/astro.config.mjs`): Starlight has no config hook for header links, so we override its `Header` component through the sanctioned `components` map. The custom header re-renders every built-in control (SiteTitle, Search, ThemeSelect, SocialIcons, LanguageSelect) through its `virtual:starlight/components/*` import — so their overrides and Pagefind search keep working untouched — and adds a `<nav>` with a single top-level **Docs** link (→ `/getting-started`), the way into the doc tree from the sidebar-less splash homepage. The link target lives in a new `headerNav` in `sidebar.ts`, colocated with the sidebar as one navigation source of truth, and the nav is hidden below the `md` (50rem) breakpoint where the sidebar drawer already carries navigation. Search keeps Starlight's expanded "Search … ⌘K" box on every page at ≥50rem (including the splash) so the keyboard shortcut stays discoverable, and its primary-nav link sits on the WaveHouse wordmark's baseline. On the splash homepage the header's inner content is held in a centered content-width column matching the hero, while doc pages stay full-bleed. `env.d.ts` gains type declarations for the built-in component modules the override re-renders so `astro check` passes.
+
 ### Changed
 
 - **Live SSE events are now projected and serialized once per role instead of once per subscriber** (`internal/stream/hub.go` (new), `internal/stream/{subscriber,bucket,heartbeat,metrics,doc}.go`, `internal/api/stream.go`, `internal/api/hub.go` + `internal/api/transform.go` (both removed — the broadcast hub moves to `internal/stream`, and the orphaned test-only `transformForClient` is dropped), `cmd/wavehouse/main.go`, `docs/src/content/docs/architecture.md`, `AGENTS.md`, plus tests in `internal/stream/{hub,filter,subscriber,bucket,heartbeat}_test.go` and `internal/api/{stream,transform,router,errors}_test.go`): the first PR of the SSE delivery-path throughput epic ([#294](https://github.com/Wave-RF/WaveHouse/issues/294)), building on the `internal/stream` primitives from #346. The broadcast hub moves into `internal/stream` as `Hub`: subscribers register under `(topic, role)`, and `Broadcast` decodes each event **once**, applies each subscribed role's column policy **once**, builds one SSE frame per role, and fans it to every member of that role's `Bucket`. Previously every connection independently ran `json.Unmarshal → policy.Evaluate → filterEventColumns → json.Marshal` (plus a second unmarshal just to read the `id:` timestamp) on the *same* event in its own read loop — byte-identical work repeated N times. For a single-role audience (the public dashboard, every viewer `public`) that collapses N re-projections to 1, moving the measured ~2 270 deliveries/s ceiling toward an events/s ceiling. The `(topic, role)` key is sufficient and claims-independent: column visibility derives only from the role+table policy entry, and the stream path applies no row-level filter (a documented invariant — if row-level filtering is ever added to streaming, the key must take claims into account). The handler's two `select` cases (keepalive vs. per-subscriber event) collapse into one byte-pump over a single `Subscriber.Frames()` queue carrying typed `Frame`s; the subscriber queue grows from cap 1 (keepalive-only) to 64 so live events buffer while the handler is mid-write. Gap-fill replay and `Last-Event-ID`/`?since=` resumption are unchanged (replay stays per-connection via the shared `stream.ReplayFrame`; live frames carry the same `id: <received_timestamp>`). Slow-consumer drops, silent before, now increment `wavehouse_sse_dropped_frames_total`; an inert `Subscriber.Evicted()` seam is wired for the eviction follow-up. The per-delivery OpenTelemetry span (another #294 item) was already removed in #346. **Deferred to follow-ups:** active slow-consumer eviction (#94) and right-sizing the subscriber buffer + broadcast lock cost (#152).
diff --git a/docs/astro.config.mjs b/docs/astro.config.mjs
index b9b71ad1..afe007bc 100644
--- a/docs/astro.config.mjs
+++ b/docs/astro.config.mjs
@@ -146,6 +146,7 @@ export default defineConfig({
         },
       },
       components: {
+        Header: "./src/components/Header.astro",
         Hero: "./src/components/Hero.astro",
         SiteTitle: "./src/components/SiteTitle.astro",
         Footer: "./src/components/Footer.astro",
diff --git a/docs/src/components/Header.astro b/docs/src/components/Header.astro
new file mode 100644
index 00000000..1ba56fc2
--- /dev/null
+++ b/docs/src/components/Header.astro
@@ -0,0 +1,204 @@
+---
+// Custom header overriding Starlight's default. The layout is our own: brand +
+// primary nav pinned left, controls (search, social, theme, language) pinned
+// right. On doc pages the bar is full-bleed to the edges; on the splash homepage
+// (the only page with a hero) the inner content is held in a centered max-width
+// column matching the hero, à la ClickHouse/Supabase. Search shows Starlight's
+// expanded "Search … ⌘K" box on every page (≥50rem), so the keyboard shortcut
+// stays discoverable. Every control is still Starlight's own built-in, pulled in
+// through its `virtual:starlight/components/*` import, so the SiteTitle/Search/
+// Theme overrides and the Pagefind-search logic keep working untouched. The
+// outer <header class="header"> (PageFrame — fixed position + full-width glass
+// background) is not ours and stays as-is; only our inner content is
+// column-constrained on the splash, so the bar itself still spans the page.
+//
+// Because the controls are Starlight built-ins re-rendered here, env.d.ts
+// declares their virtual modules so `astro check` can resolve them. On
+// @astrojs/starlight upgrades, re-check those component module paths.
+//
+// The left nav and the controls/CTA are hidden below Starlight's `md` (50rem):
+// under 50rem the sidebar (a hamburger drawer) already carries navigation on
+// doc pages, leaving the logo + the (always-visible) search button.
+import config from "virtual:starlight/user-config";
+
+import LanguageSelect from "virtual:starlight/components/LanguageSelect";
+import Search from "virtual:starlight/components/Search";
+import SiteTitle from "virtual:starlight/components/SiteTitle";
+import SocialIcons from "virtual:starlight/components/SocialIcons";
+import ThemeSelect from "virtual:starlight/components/ThemeSelect";
+import { headerNav } from "../config/sidebar.ts";
+
+// Mirror of the package default: only render Search when Pagefind is enabled or
+// the Search component has been overridden.
+const shouldRenderSearch =
+  config.pagefind ||
+  config.components.Search !== "@astrojs/starlight/components/Search.astro";
+
+// Highlight the active destination — exact match, or any nested page beneath it
+// (so a "/guides" link stays current on "/guides/foo"). trailingSlash is
+// "never", so strip a stray trailing slash before comparing, just in case.
+const currentPath = Astro.url.pathname.replace(/(.)\/$/, "$1");
+---
+
+<div class="header">
+  <div class="wh-lead">
+    <div class="title-wrapper sl-flex">
+      <SiteTitle />
+    </div>
+    <nav
+      class="wh-header-nav sl-hidden md:sl-flex print:hidden"
+      aria-label="Primary"
+    >
+      {
+        headerNav.map(({ label, href }) => (
+          <a
+            href={href}
+            class="wh-header-nav__link"
+            aria-current={
+              currentPath === href || currentPath.startsWith(`${href}/`)
+                ? "page"
+                : undefined
+            }
+          >
+            {label}
+          </a>
+        ))
+      }
+    </nav>
+  </div>
+
+  <div class="wh-right">
+    {
+      shouldRenderSearch && (
+        <div class="wh-search sl-flex print:hidden">
+          <Search />
+        </div>
+      )
+    }
+    <div class="wh-controls sl-hidden md:sl-flex print:hidden">
+      <div class="sl-flex social-icons">
+        <SocialIcons />
+      </div>
+      <ThemeSelect />
+      <LanguageSelect />
+    </div>
+  </div>
+</div>
+
+<style>
+  /* Our own header layout. Unlayered so it authoritatively styles this
+     component's inner .header row (Starlight's own rules are @layer'd and would
+     otherwise win). Base case — doc pages — is full-bleed to the bar edges, like
+     Supabase/ClickHouse docs; the splash override below holds the inner content
+     in a centered content-width column instead. The outer PageFrame bar always
+     spans full width; only this inner content is ever capped + centered. */
+  .header {
+    display: flex;
+    align-items: center;
+    justify-content: space-between;
+    gap: 1rem;
+    height: 100%;
+  }
+  /* Splash homepage (the only page with a hero): hold the header in a centered
+     content-width column instead. Keyed off the hero's presence in the body —
+     the same signal global.css uses — rather than an SSR class/attribute on the
+     header, because vtbot's <ReplacementSwap/> PRESERVES the header element
+     across view-transitions while swapping the body content: a baked-in
+     attribute would go stale, but this `:has()` selector re-evaluates live. */
+  :global(body:has(.wh-hero)) .header {
+    max-width: 68rem;
+    margin-inline: auto;
+  }
+
+  .wh-lead {
+    display: flex;
+    align-items: center;
+    gap: 1.75rem;
+    min-width: 0;
+  }
+  .title-wrapper {
+    /* Avoid clipping the focus ring around the title link. */
+    padding: 0.25rem;
+    margin: -0.25rem;
+    min-width: 0;
+  }
+
+  .wh-right {
+    display: flex;
+    align-items: center;
+    gap: 1rem;
+  }
+  /* No `display` here on purpose — let the `sl-hidden md:sl-flex` utilities
+     govern visibility so the controls collapse under 50rem (an unlayered
+     `display: flex` would override Starlight's layered `sl-hidden`). This only
+     styles the flex row they become at >=50rem. */
+  .wh-controls {
+    align-items: center;
+    gap: 1rem;
+  }
+  .social-icons {
+    align-items: center;
+    gap: 1rem;
+  }
+  /* Hairline divider before the theme/lang controls, matching the default. */
+  .social-icons::after {
+    content: "";
+    height: 1.5rem;
+    border-inline-end: 1px solid var(--sl-color-gray-5);
+  }
+
+  /* Search. Starlight's expanded "Search … ⌘K" box on every page (≥50rem) so the
+     keyboard shortcut stays discoverable; below 50rem it sizes down to its icon. */
+  .wh-search {
+    align-items: center;
+  }
+  /* Expand to the box only from 50rem up — the same breakpoint that reveals the
+     controls. Below it the label + ⌘K are already hidden (md:-only), so forcing
+     a width would leave a wide, near-empty button overflowing the narrow header
+     beside the logo; letting it size to its icon keeps it compact there.
+     min-width:0 + max-width let it shrink rather than overflow if the desktop
+     row gets tight. */
+  @media (min-width: 50rem) {
+    .wh-search {
+      min-width: 0;
+    }
+    .wh-search :global(button[data-open-modal]) {
+      width: 22rem;
+      max-width: 100%;
+    }
+  }
+
+  /* Primary nav links — present but subordinate to the wordmark, brand accent on
+     hover and when current. */
+  .wh-header-nav {
+    align-items: center;
+    gap: 1.5rem;
+  }
+  .wh-header-nav__link {
+    /* A step up from muted secondary text so it reads as an interactive nav link
+       at rest (plain muted looked like a static label), but held just under the
+       wordmark's full ink so the brand stays dominant. */
+    color: color-mix(in oklab, var(--wh-ink) 80%, var(--wh-ink-muted));
+    /* Smaller than the "WaveHouse" wordmark (1.0625rem). Flex-centering leaves
+       the link's baseline ~1.25px ABOVE the wordmark's, so nudge it down to sit
+       their bottoms flush. Value gauged against the rendered wordmark baseline
+       (canvas font metrics disagree with the browser's actual placement here). */
+    font-size: 0.875rem;
+    transform: translateY(1.25px);
+    font-weight: 500;
+    line-height: 1;
+    text-decoration: none;
+    white-space: nowrap;
+    transition: color 0.15s ease;
+  }
+  /* Brand accent on hover, matching the footer links (a clearer "this is a link"
+     cue than the earlier brighten-to-ink, which is now near-invisible from the
+     lifted resting colour). */
+  .wh-header-nav__link:hover {
+    color: var(--wh-accent-hi);
+  }
+  .wh-header-nav__link[aria-current="page"] {
+    color: var(--wh-accent-text);
+    font-weight: 600;
+  }
+</style>
diff --git a/docs/src/config/sidebar.ts b/docs/src/config/sidebar.ts
index ab113d2a..22c041ae 100644
--- a/docs/src/config/sidebar.ts
+++ b/docs/src/config/sidebar.ts
@@ -83,3 +83,13 @@ export const sidebar: StarlightUserConfig["sidebar"] = [
     ],
   },
 ];
+
+// Top-level link(s) for the site header (src/components/Header.astro), colocated
+// with the sidebar so header and sidebar share one file as the single source of
+// truth for navigation. A single "Docs" entry into the doc tree: the splash
+// homepage hides the sidebar, so this is the way in from there; every doc page
+// already carries the full sidebar. Root-absolute href matches the internal link
+// convention used across the docs (index.mdx hero, LinkCards).
+export const headerNav: { label: string; href: string }[] = [
+  { label: "Docs", href: "/getting-started" },
+];
diff --git a/docs/src/env.d.ts b/docs/src/env.d.ts
index 740490d2..d5372f61 100644
--- a/docs/src/env.d.ts
+++ b/docs/src/env.d.ts
@@ -3,8 +3,8 @@
 // Starlight exposes its built-in components to overrides through these virtual
 // modules (Vite resolves them at build time), but only ships their TYPES in an
 // internal declaration file that isn't visible to user code — so `astro check`
-// can't find them. Declare the ones the Footer override re-renders. See
-// node_modules/@astrojs/starlight/virtual-internal.d.ts for the canonical list.
+// can't find them. Declare the ones the Footer and Header overrides re-render.
+// See node_modules/@astrojs/starlight/virtual-internal.d.ts for the canonical list.
 declare module "virtual:starlight/components/EditLink" {
   const Component: import("astro").AstroComponentFactory;
   export default Component;
@@ -17,3 +17,23 @@ declare module "virtual:starlight/components/Pagination" {
   const Component: import("astro").AstroComponentFactory;
   export default Component;
 }
+declare module "virtual:starlight/components/LanguageSelect" {
+  const Component: import("astro").AstroComponentFactory;
+  export default Component;
+}
+declare module "virtual:starlight/components/Search" {
+  const Component: import("astro").AstroComponentFactory;
+  export default Component;
+}
+declare module "virtual:starlight/components/SiteTitle" {
+  const Component: import("astro").AstroComponentFactory;
+  export default Component;
+}
+declare module "virtual:starlight/components/SocialIcons" {
+  const Component: import("astro").AstroComponentFactory;
+  export default Component;
+}
+declare module "virtual:starlight/components/ThemeSelect" {
+  const Component: import("astro").AstroComponentFactory;
+  export default Component;
+}