diff --git a/frontend/packages/agent/src/agent.css b/frontend/packages/agent/src/agent.css
index 28519eb4..2b9d7007 100644
--- a/frontend/packages/agent/src/agent.css
+++ b/frontend/packages/agent/src/agent.css
@@ -891,83 +891,34 @@ pre.diff {
 /* Row + pill + details styling moved to hive-fr0nt::TERMINAL_CSS. */
 
 /* ─── side panel (singleton drawer) ────────────────────────────────
-   Inbox + loose-ends details open here instead of expanding inline.
-   Copy of the dashboard's side-panel pattern — candidate for
-   extraction into @hive/shared once both surfaces stabilize. */
-.side-panel {
-  position: fixed;
-  inset: 0;
-  z-index: 50;
-  /* Closed: ignore pointer events so the agent page underneath stays
-     interactive; `.open` flips it back on. */
-  pointer-events: none;
-}
-.side-panel-backdrop {
-  position: absolute;
-  inset: 0;
-  background: rgba(0, 0, 0, 0.55);
-  opacity: 0;
-  transition: opacity 0.2s ease;
-}
-.side-panel-drawer {
-  position: absolute;
-  top: 0;
-  right: 0;
-  bottom: 0;
-  width: min(640px, 92vw);
-  display: flex;
-  flex-direction: column;
-  background: var(--bg-elev);
-  border-left: 2px solid var(--purple);
-  box-shadow: -10px 0 30px rgba(0, 0, 0, 0.45);
-  transform: translateX(100%);
-  transition: transform 0.25s ease;
-}
-.side-panel.open { pointer-events: auto; }
-.side-panel.open .side-panel-backdrop { opacity: 1; }
-.side-panel.open .side-panel-drawer { transform: translateX(0); }
-.side-panel-head {
-  flex: 0 0 auto;
-  display: flex;
-  align-items: center;
-  justify-content: space-between;
-  gap: 1em;
-  padding: 0.7em 1em;
-  border-bottom: 1px solid var(--border);
-}
-.side-panel-title {
-  color: var(--purple);
-  font-weight: bold;
-  letter-spacing: 0.05em;
-  word-break: break-all;
-}
-.side-panel-close {
-  flex: 0 0 auto;
-  background: var(--bg);
-  color: var(--fg);
-  border: 1px solid var(--border);
-  font-family: inherit;
-  font-size: 1em;
-  line-height: 1;
-  padding: 0.25em 0.55em;
-  cursor: pointer;
-}
-.side-panel-close:hover { border-color: var(--red); color: var(--red); }
-.side-panel-body {
-  flex: 1 1 auto;
-  overflow: auto;
-  padding: 0.8em 1em;
+   Inbox + loose-ends details open here instead of expanding inline. The
+   drawer chrome itself (backdrop, drawer, resize handle, header, title,
+   close button) is now the shared `<hive-side-panel>` element
+   (@hive/shared/side-panel.js — this also picks up drag-to-resize,
+   which this page didn't have before); what's left here is the drag
+   cursor-override escape hatch (has to be a global, light-DOM rule — it
+   reaches every element on the page during a drag, not just the shared
+   element's own shadow tree) and the styling for the panel's own
+   content types, which the shared element's shadow tree can never
+   reach (see @hive/shared/side-panel/hive-side-panel.css's header
+   comment). The `hive-side-panel .agent-inbox …` rules below use the
+   element's own tag name as the selector root — no compatibility class
+   needed, the tag name already uniquely identifies the light-DOM
+   instance app.js's `sidePanel` creates. */
+body.side-panel-resizing {
+  user-select: none;
 }
+body.side-panel-resizing * { cursor: ew-resize !important; }
 /* Inbox / loose-ends lists rendered into the side-panel body. The
    legacy <details>-collapsible variant of .agent-inbox is gone, so
    here we strip the inbox-only chrome (background, border-left) and
    let the panel body's own padding own the framing. */
-.side-panel-body .agent-inbox {
+hive-side-panel .agent-inbox {
   margin: 0;
   font-size: inherit;
   color: var(--fg);
 }
-.side-panel-body .agent-inbox ul {
+hive-side-panel .agent-inbox ul {
   background: transparent;
   border-left: 0;
   padding: 0;
diff --git a/frontend/packages/agent/src/app.js b/frontend/packages/agent/src/app.js
index c650910e..729e4b06 100644
--- a/frontend/packages/agent/src/app.js
+++ b/frontend/packages/agent/src/app.js
@@ -6,6 +6,7 @@ import { create as termCreate, linkify as termLinkify } from '@hive/shared/termi
 import { asyncBtn, bindAsyncForms } from '@hive/shared/forms.js';
 import { themedConfirm } from '@hive/shared/modal.js';
 import { el } from '@hive/shared/dom.js';
+import '@hive/shared/side-panel.js'; // registers <hive-side-panel> — side-effect import
 import { marked } from 'marked';
 import DOMPurify from 'dompurify';
 
@@ -37,43 +38,17 @@ window.marked = marked;
   bindAsyncForms(() => refreshState());
 
   // ─── side panel (singleton drawer for inbox + loose-ends flyouts) ──────
-  // Shared shape with the dashboard's panel. Candidate for extraction
-  // into @hive/shared once both surfaces stabilise.
-  const Panel = (() => {
-    const root = $('side-panel');
-    const titleEl = $('side-panel-title');
-    const bodyEl = $('side-panel-body');
-    /** Owner key (e.g. 'inbox', 'loose-ends'). Refresh hooks check
-     *  against this so a live event only re-renders the panel when
-     *  the matching view is actually visible. null when closed. */
-    let owner = null;
-    function open(name, title, content) {
-      owner = name;
-      titleEl.textContent = title;
-      bodyEl.replaceChildren(...(content ? [content] : []));
-      root.classList.add('open');
-      root.setAttribute('aria-hidden', 'false');
-    }
-    function close() {
-      owner = null;
-      root.classList.remove('open');
-      root.setAttribute('aria-hidden', 'true');
-    }
-    function refresh(name, title, content) {
-      if (owner !== name) return;
-      titleEl.textContent = title;
-      bodyEl.replaceChildren(...(content ? [content] : []));
-    }
-    function bind() {
-      $('side-panel-close').addEventListener('click', close);
-      $('side-panel-backdrop').addEventListener('click', close);
-      document.addEventListener('keydown', (e) => {
-        if (e.key === 'Escape' && root.classList.contains('open')) close();
-      });
-    }
-    return { open, close, refresh, bind, currentOwner: () => owner };
-  })();
-  Panel.bind();
+  // The shared `<hive-side-panel>` element (see @hive/shared/side-panel.js
+  // for the chrome/behavior it owns), created once, eagerly, when this
+  // module's IIFE runs (ES modules execute after the document is
+  // parsed, so `document.body` already exists). Used directly — this
+  // UI's opens always take an owner name, so call sites use the
+  // element's own `openNamed(name, title, content)` rather than the
+  // untyped `open`. `agent.css` reaches the slotted content via a plain
+  // `hive-side-panel .agent-inbox …` tag-name selector (no compat class
+  // needed — the element's own tag name already identifies it).
+  const sidePanel = document.createElement('hive-side-panel');
+  document.body.append(sidePanel);
 
   // Wire the header pills to open the side panel. Pre-built (vs
   // re-building per-click) so the freshest snapshot already lives
@@ -83,14 +58,14 @@ window.marked = marked;
     const inboxPill = $('inbox-pill');
     if (inboxPill) {
       inboxPill.addEventListener('click', () => {
-        Panel.open('inbox', 'inbox · ' + lastInbox.length,
+        sidePanel.openNamed('inbox', 'inbox · ' + lastInbox.length,
           buildInboxList(lastInbox));
       });
     }
     const todosPill = $('todos-pill');
     if (todosPill) {
       todosPill.addEventListener('click', () => {
-        Panel.open('todos', 'todos · ' + lastTodos.length,
+        sidePanel.openNamed('todos', 'todos · ' + lastTodos.length,
           buildTodosList(lastTodos));
       });
     }
@@ -352,7 +327,7 @@ window.marked = marked;
     else closeOverflowMenu();
   }
   // Wire once on boot. The trigger itself + click-outside + Escape
-  // dismissal pattern matches the side-panel flyout (Panel).
+  // dismissal pattern matches the side-panel flyout (sidePanel).
   (function bindOverflowMenu() {
     const btn = $('overflow-btn');
     if (!btn) return;
@@ -823,7 +798,7 @@ window.marked = marked;
   function buildLooseEndsList(threads) {
     // Returns the <div> the side panel renders. The structural shape
     // mirrors the legacy <details>-collapsible block — same CSS rules
-    // apply via `.side-panel-body .agent-inbox`.
+    // apply via `hive-side-panel .agent-inbox`.
     const wrap = el('div', { class: 'agent-inbox' });
     if (!threads.length) {
       wrap.append(el('p', { class: 'side-panel-empty' },
@@ -923,7 +898,7 @@ window.marked = marked;
     const count = $('todos-count');
     if (count) count.textContent = todos.length;
     if (pill) pill.hidden = todos.length === 0;
-    Panel.refresh('todos', 'todos · ' + todos.length,
+    sidePanel.refresh('todos', 'todos · ' + todos.length,
       buildTodosList(todos));
   }
 
@@ -1089,7 +1064,7 @@ window.marked = marked;
     const count = $('inbox-count');
     if (count) count.textContent = rows.length;
     if (pill) pill.hidden = rows.length === 0;
-    Panel.refresh('inbox', 'inbox · ' + rows.length, buildInboxList(rows));
+    sidePanel.refresh('inbox', 'inbox · ' + rows.length, buildInboxList(rows));
   }
   // Harness reachability badge: derived from the same `s.status` the
   // status block reads. Each status maps to a glyph + label + colour
diff --git a/frontend/packages/agent/src/index.html b/frontend/packages/agent/src/index.html
index 0e1c1d68..86686717 100644
--- a/frontend/packages/agent/src/index.html
+++ b/frontend/packages/agent/src/index.html
@@ -93,21 +93,10 @@
     <div id="term-input" class="term-input"></div>
   </footer>
 
-  <!-- Slide-in side panel. Singleton — JS swaps the title + body
-       and toggles `.open`. Shared shape with the dashboard's panel
-       (candidate for extraction into @hive/shared in a follow-up). -->
-  <div id="side-panel" class="side-panel" aria-hidden="true">
-    <div class="side-panel-backdrop" id="side-panel-backdrop"></div>
-    <aside class="side-panel-drawer" role="dialog" aria-modal="true"
-           aria-labelledby="side-panel-title">
-      <header class="side-panel-head">
-        <span class="side-panel-title" id="side-panel-title"></span>
-        <button type="button" class="side-panel-close" id="side-panel-close"
-                title="close (esc)">✕</button>
-      </header>
-      <div class="side-panel-body" id="side-panel-body"></div>
-    </aside>
-  </div>
+  <!-- Slide-in side panel (inbox / todos flyouts) is a <hive-side-panel>
+       element (@hive/shared/side-panel.js) — the Panel singleton in
+       app.js creates + appends it to <body> lazily on first use, so
+       nothing needs to be pre-declared here. -->
 
   <!-- Single bundled entry. esbuild folds @hive/shared/terminal.js and
        the marked npm package into app.js. -->
diff --git a/frontend/packages/dashboard/src/call.js b/frontend/packages/dashboard/src/call.js
index 9e8df3a6..34902847 100644
--- a/frontend/packages/dashboard/src/call.js
+++ b/frontend/packages/dashboard/src/call.js
@@ -14,7 +14,7 @@
 // live-mutation paths call an injected `onCountsChanged` callback the entry
 // registers once via `initCall`.
 
-import { $, form, Panel, appendLinkified } from './common.js';
+import { $, form, appendLinkified } from './common.js';
 import { el } from '@hive/shared/dom.js';
 import { themedToast } from '@hive/shared/modal.js';
 import { epochSec, fmtAgo, fmtDuration } from './util.js';
diff --git a/frontend/packages/dashboard/src/common.css b/frontend/packages/dashboard/src/common.css
index 8922df45..d8746d73 100644
--- a/frontend/packages/dashboard/src/common.css
+++ b/frontend/packages/dashboard/src/common.css
@@ -366,134 +366,59 @@ code {
 }
 
 /* ─── side panel ─────────────────────────────────────────────────
-   Long content (file previews, diffs, journald, applied config)
-   opens in a drawer that swipes in from the right — used by both
-   /flow.html and the dashboard. */
-.side-panel {
-  position: fixed;
-  inset: 0;
-  z-index: 200;
-  pointer-events: none;
-}
-.side-panel-backdrop {
-  position: absolute;
-  inset: 0;
-  background: color-mix(in srgb, var(--crust) 55%, transparent);
-  opacity: 0;
-  transition: opacity 200ms ease;
-}
-.side-panel-drawer {
-  position: absolute;
-  top: 0;
-  right: 0;
-  bottom: 0;
-  width: min(42em, 95vw);
-  background: var(--bg-elev);
-  border-left: 1px solid var(--purple-dim);
-  display: flex;
-  flex-direction: column;
-  transform: translateX(100%);
-  transition: transform 220ms ease;
-  overflow: hidden;
-}
-.side-panel.open { pointer-events: auto; }
-.side-panel.open .side-panel-backdrop { opacity: 1; }
-.side-panel.open .side-panel-drawer { transform: translateX(0); }
-.side-panel-resize {
-  position: absolute;
-  left: 0;
-  top: 0;
-  bottom: 0;
-  width: 6px;
-  cursor: ew-resize;
-  opacity: 0;
-  transition: opacity 120ms;
-  background: var(--purple-dim);
-}
-.side-panel-resize:hover,
-body.side-panel-resizing .side-panel-resize {
-  opacity: 1;
-}
-body.side-panel-resizing .side-panel-resize {
-  background: var(--purple);
-}
+   Long content (file previews, diffs, journald, applied config) opens in
+   a drawer that swipes in from the right — used by both /flow.html and
+   the dashboard. The drawer chrome itself (backdrop, drawer, resize
+   handle, header, title, close button) is now the shared
+   `<hive-side-panel>` element (@hive/shared/side-panel.js); what's left
+   here is the drag cursor-override escape hatch (has to be a global,
+   light-DOM rule — it reaches every element on the page during a drag,
+   not just the shared element's own shadow tree) and the styling for
+   the panel's own content types, which the shared element's shadow tree
+   can never reach (see @hive/shared/side-panel/hive-side-panel.css's
+   header comment). The `hive-side-panel .md …` rules below use the
+   element's own tag name as the selector root — no compatibility class
+   needed, the tag name already uniquely identifies the light-DOM
+   instance `common.js`'s `sidePanel` creates. */
 body.side-panel-resizing {
   user-select: none;
 }
 body.side-panel-resizing * { cursor: ew-resize !important; }
-.side-panel-head {
-  display: flex;
-  align-items: center;
-  gap: 0.6em;
-  padding: 0.6em 1em;
-  border-bottom: 1px solid var(--border);
-  flex: none;
-}
-.side-panel-title {
-  flex: 1;
-  font-size: 0.88em;
-  color: var(--muted);
-  letter-spacing: 0.04em;
-  overflow: hidden;
-  text-overflow: ellipsis;
-  white-space: nowrap;
-}
-.side-panel-close {
-  display: flex;
-  align-items: center;
-  justify-content: center;
-  background: none;
-  border: 1px solid var(--border);
-  border-radius: 3px;
-  color: var(--muted);
-  font-size: 1em;
-  line-height: 1;
-  padding: 0.15em 0.4em;
-  cursor: pointer;
-  transition: border-color 0.15s ease, color 0.15s ease;
-}
-.side-panel-close:hover { border-color: var(--red); color: var(--red); }
-.side-panel-body {
-  flex: 1;
-  overflow-y: auto;
-  padding: 0.8em 1em;
-  font-size: 0.88em;
-}
-.side-panel-body .md { color: var(--fg); line-height: 1.5; }
-.side-panel-body .md > :first-child { margin-top: 0; }
-.side-panel-body .md > :last-child { margin-bottom: 0; }
-.side-panel-body .md p { margin: 0.5em 0; }
-.side-panel-body .md h1,
-.side-panel-body .md h2,
-.side-panel-body .md h3,
-.side-panel-body .md h4 { color: var(--purple); margin: 0.9em 0 0.4em; }
-.side-panel-body .md code {
+hive-side-panel .md { color: var(--fg); line-height: 1.5; }
+hive-side-panel .md > :first-child { margin-top: 0; }
+hive-side-panel .md > :last-child { margin-bottom: 0; }
+hive-side-panel .md p { margin: 0.5em 0; }
+hive-side-panel .md h1,
+hive-side-panel .md h2,
+hive-side-panel .md h3,
+hive-side-panel .md h4 { color: var(--purple); margin: 0.9em 0 0.4em; }
+hive-side-panel .md code {
   background: var(--bg);
   border: 1px solid var(--border);
   border-radius: 2px;
   padding: 0.1em 0.3em;
   font-size: 0.9em;
 }
-.side-panel-body .md pre {
+hive-side-panel .md pre {
   background: var(--crust);
   border: 1px solid var(--border);
   padding: 0.5em 0.7em;
   overflow-x: auto;
   margin: 0.5em 0;
 }
-.side-panel-body .md pre code { background: none; border: none; padding: 0; }
-.side-panel-body .md a { color: var(--cyan); }
-.side-panel-body .md ul,
-.side-panel-body .md ol { margin: 0.4em 0; padding-left: 1.5em; }
-.side-panel-body .md blockquote {
+hive-side-panel .md pre code { background: none; border: none; padding: 0; }
+hive-side-panel .md a { color: var(--cyan); }
+hive-side-panel .md ul,
+hive-side-panel .md ol { margin: 0.4em 0; padding-left: 1.5em; }
+hive-side-panel .md blockquote {
   border-left: 3px solid var(--purple-dim);
   padding-left: 0.8em;
   margin: 0.4em 0;
   color: var(--muted);
 }
-.side-panel-body .md table { border-collapse: collapse; margin: 0.5em 0; }
-.side-panel-body .md th,
-.side-panel-body .md td {
+hive-side-panel .md table { border-collapse: collapse; margin: 0.5em 0; }
+hive-side-panel .md th,
+hive-side-panel .md td {
   border: 1px solid var(--border);
   padding: 0.2em 0.5em;
 }
diff --git a/frontend/packages/dashboard/src/common.js b/frontend/packages/dashboard/src/common.js
index 44d6a56d..6d34c7a7 100644
--- a/frontend/packages/dashboard/src/common.js
+++ b/frontend/packages/dashboard/src/common.js
@@ -5,6 +5,7 @@
 
 import { linkify as termLinkify } from '@hive/shared/terminal.js';
 import { el } from '@hive/shared/dom.js';
+import '@hive/shared/side-panel.js'; // registers <hive-side-panel> — side-effect import
 import DOMPurify from 'dompurify';
 
 // ─── helpers ────────────────────────────────────────────────────────────
@@ -280,141 +281,21 @@ export function openBuildLogStream(id, pre, { onDone, onError } = {}) {
 // ─── side panel ─────────────────────────────────────────────────────────
 // Singleton drawer that swipes in from the right. Long content
 // (file previews, approval diffs, journald logs, applied config)
-// opens here via `Panel.open(title, node)` instead of expanding
+// opens here via `sidePanel.open(title, node)` instead of expanding
 // inline. Body is swapped on each open; closing just slides out so
 // the content stays visible through the transition.
-export const Panel = (() => {
-  let root = null;
-  let titleEl = null;
-  let bodyEl = null;
-  let drawer = null;
-  /** Owner key set by `openNamed` (e.g. 'inbox'). `refresh(name, …)`
-   *  is a no-op when the current owner doesn't match, so live
-   *  updates can re-render an open view without grabbing focus
-   *  from a closed one (or from an unrelated open view like a
-   *  diff drill-in). Untyped calls via `open(title, content)`
-   *  clear the owner — the legacy file-preview/diff/log paths
-   *  don't participate in named-refresh semantics. */
-  let owner = null;
-  function ensure() {
-    if (!root) {
-      root = $('side-panel');
-      titleEl = $('side-panel-title');
-      bodyEl = $('side-panel-body');
-      drawer = root && root.querySelector('.side-panel-drawer');
-    }
-    return root != null;
-  }
-  function open(title, content) {
-    if (!ensure()) return;
-    owner = null;
-    titleEl.textContent = title;
-    bodyEl.replaceChildren(...(content ? [content] : []));
-    root.classList.add('open');
-    root.setAttribute('aria-hidden', 'false');
-  }
-  function openNamed(name, title, content) {
-    open(title, content);
-    owner = name;
-  }
-  function refresh(name, title, content) {
-    if (!ensure()) return;
-    if (owner !== name) return;
-    titleEl.textContent = title;
-    bodyEl.replaceChildren(...(content ? [content] : []));
-  }
-  function close() {
-    if (!ensure()) return;
-    owner = null;
-    root.classList.remove('open');
-    root.setAttribute('aria-hidden', 'true');
-  }
-  // Drag-to-resize the drawer's width. See docs/web-ui.md::Side panel
-  // for the hit-strip + pointer-capture + localStorage persistence
-  // model; CSS clamps the stored value to min 320px / max 96vw and
-  // out-of-range stored values are dropped silently.
-  const WIDTH_KEY = 'hyperhive:side-panel-width';
-  const WIDTH_MIN = 320;
-  function clampWidth(w) {
-    // Use document.documentElement.clientWidth rather than window.innerWidth:
-    // clientWidth gives the actual CSS layout viewport width and is not
-    // altered by Firefox's Fingerprinting Protection (which rounds
-    // window.innerWidth/outerWidth to the nearest 200px).
-    const max = Math.floor(document.documentElement.clientWidth * 0.96);
-    return Math.max(WIDTH_MIN, Math.min(max, w));
-  }
-  function applyStoredWidth() {
-    if (!drawer) return;
-    const raw = (() => {
-      try { return localStorage.getItem(WIDTH_KEY); }
-      catch { return null; }
-    })();
-    if (!raw) return;
-    const parsed = parseInt(raw, 10);
-    if (!Number.isFinite(parsed) || parsed <= 0) return;
-    drawer.style.setProperty('--side-panel-w', clampWidth(parsed) + 'px');
-  }
-  function bindResize() {
-    if (!drawer) return;
-    const handle = document.createElement('div');
-    handle.className = 'side-panel-resize';
-    handle.setAttribute('role', 'separator');
-    handle.setAttribute('aria-orientation', 'vertical');
-    handle.setAttribute('aria-label', 'drag to resize side panel');
-    handle.title = 'drag to resize';
-    drawer.prepend(handle);
-    let dragging = false;
-    handle.addEventListener('pointerdown', (e) => {
-      e.preventDefault();
-      dragging = true;
-      document.body.classList.add('side-panel-resizing');
-      // Capture so we keep getting pointermove even when the cursor
-      // outpaces the handle band (drag-fast-then-pause loses the
-      // handle's :hover state otherwise).
-      try { handle.setPointerCapture(e.pointerId); } catch { /* legacy */ }
-    });
-    document.addEventListener('pointermove', (e) => {
-      if (!dragging) return;
-      // Drawer is anchored to the right edge — width = viewport - pointer X.
-      const w = clampWidth(document.documentElement.clientWidth - e.clientX);
-      drawer.style.setProperty('--side-panel-w', w + 'px');
-    });
-    function stopDrag() {
-      if (!dragging) return;
-      dragging = false;
-      document.body.classList.remove('side-panel-resizing');
-      // Persist the final width. Read the actual rendered width
-      // rather than re-deriving so the stored value matches what
-      // the operator saw at mouseup.
-      const w = drawer.getBoundingClientRect().width;
-      try { localStorage.setItem(WIDTH_KEY, String(Math.round(w))); }
-      catch { /* localStorage unavailable — width is session-only */ }
-    }
-    document.addEventListener('pointerup', stopDrag);
-    document.addEventListener('pointercancel', stopDrag);
-    // Re-clamp on viewport resize so a persisted width that exceeds
-    // 96vw doesn't push the drawer off-screen after a window shrink.
-    window.addEventListener('resize', () => {
-      if (dragging) return;
-      const cur = drawer.getBoundingClientRect().width;
-      const clamped = clampWidth(cur);
-      if (clamped !== Math.round(cur)) {
-        drawer.style.setProperty('--side-panel-w', clamped + 'px');
-      }
-    });
-  }
-  function bind() {
-    if (!ensure()) return;
-    $('side-panel-close').addEventListener('click', close);
-    $('side-panel-backdrop').addEventListener('click', close);
-    document.addEventListener('keydown', (e) => {
-      if (e.key === 'Escape' && root.classList.contains('open')) close();
-    });
-    applyStoredWidth();
-    bindResize();
-  }
-  return { open, openNamed, refresh, close, bind };
-})();
+//
+// The instance is created once, eagerly, at module evaluation time — ES
+// modules run after the document is parsed (same timing `defer` scripts
+// get), so `document.body` already exists here. Exported directly (not
+// wrapped in a forwarding object) — callers use the element's own
+// `open`/`openNamed`/`refresh`/`close`/`currentOwner` methods, see
+// @hive/shared/side-panel.js for what they do. `common.css` reaches the
+// slotted content via a plain `hive-side-panel .md …` tag-name selector
+// (no compatibility class needed — the element's own tag name already
+// uniquely identifies it in the light DOM).
+export const sidePanel = document.createElement('hive-side-panel');
+document.body.append(sidePanel);
 
 // ─── path linkification ─────────────────────────────────────────────────
 // Agents constantly drop pointer strings into messages + question
@@ -505,14 +386,14 @@ async function openFilePanel(path) {
         '(could not load image — it may be missing or over the preview size cap)'));
     });
     img.src = '/api/state-file?path=' + encodeURIComponent(path);
-    Panel.open('↳ ' + path, img);
+    sidePanel.open('↳ ' + path, img);
     return;
   }
   const isMd = /\.(md|markdown)$/i.test(path);
   const isSvg = /\.svg$/i.test(path);
   const view = el('div');
   view.textContent = '(fetching…)';
-  Panel.open('↳ ' + path, view);
+  sidePanel.open('↳ ' + path, view);
   try {
     const text = await fetchStateFile(path);
     if (isSvg) {
diff --git a/frontend/packages/dashboard/src/dashboard.html b/frontend/packages/dashboard/src/dashboard.html
index a15a94e3..e3f3007d 100644
--- a/frontend/packages/dashboard/src/dashboard.html
+++ b/frontend/packages/dashboard/src/dashboard.html
@@ -234,23 +234,11 @@
     <p>▲△▲ <a href="https://forge.darkest.space/hyperhive/hyperhive">hyperhive</a> ▲△▲ hive-c0re on this host ▲△▲</p>
   </footer>
 
-  <!-- Slide-in detail panel. Long content (clicked file previews,
-       approval diffs, journald logs, applied config) opens here
-       instead of expanding inline. Singleton — JS swaps the title +
-       body and toggles `.open`. Lives outside the tab panes so it
-       overlays any active tab. -->
-  <div id="side-panel" class="side-panel" aria-hidden="true">
-    <div class="side-panel-backdrop" id="side-panel-backdrop"></div>
-    <aside class="side-panel-drawer" role="dialog" aria-modal="true"
-           aria-labelledby="side-panel-title">
-      <header class="side-panel-head">
-        <span class="side-panel-title" id="side-panel-title"></span>
-        <button type="button" class="side-panel-close" id="side-panel-close"
-                title="close (esc)">✕</button>
-      </header>
-      <div class="side-panel-body" id="side-panel-body"></div>
-    </aside>
-  </div>
+  <!-- Slide-in detail panel (clicked file previews, approval diffs,
+       journald logs, applied config) is a <hive-side-panel> element
+       (@hive/shared/side-panel.js) — the Panel singleton in common.js
+       creates + appends it to <body> lazily on first use, so nothing
+       needs to be pre-declared here. -->
 
   <!-- Selection action bar. Sticky-bottom strip that slides into
        view when one or more agent cards is selected (click the icon
diff --git a/frontend/packages/dashboard/src/tabs.js b/frontend/packages/dashboard/src/tabs.js
index 7989fc1e..9b2af49c 100644
--- a/frontend/packages/dashboard/src/tabs.js
+++ b/frontend/packages/dashboard/src/tabs.js
@@ -14,7 +14,7 @@
 import { marked } from 'marked';
 import {
   $,
-  Panel, NOTIF,
+  NOTIF,
   openStream, renderServerWarnings,
 } from './common.js';
 import { el } from '@hive/shared/dom.js';
@@ -276,8 +276,9 @@ window.marked = marked;
   // NOTIF.bind() (the enable/mute/unmute toggle UI) moved to /settings.html
   // with the S3TT1NGS page. The dashboard keeps NOTIF.show() for approval/
   // question notifications — it reads the browser permission + localStorage
-  // mute flag the settings page sets, so no bind() is needed here.
-  Panel.bind();
+  // mute flag the settings page sets, so no bind() is needed here. The
+  // side panel (<hive-side-panel>) wires its own internals in
+  // connectedCallback — no bind() step needed either.
 
   // ─── live updates: dashboard event stream ──────────────────────────────
   // The dashboard subscribes to /dashboard/stream for live mutation
diff --git a/frontend/packages/shared/package.json b/frontend/packages/shared/package.json
index 3bdbeeb0..590794a2 100644
--- a/frontend/packages/shared/package.json
+++ b/frontend/packages/shared/package.json
@@ -19,7 +19,8 @@
     "./dom.js": "./src/dom.js",
     "./modal.js": "./src/modal.js",
     "./shadow-css.js": "./src/shadow-css.js",
-    "./hive-menu.js": "./src/hive-menu/hive-menu.js"
+    "./hive-menu.js": "./src/hive-menu/hive-menu.js",
+    "./side-panel.js": "./src/side-panel/hive-side-panel.js"
   },
   "files": [
     "src/"
diff --git a/frontend/packages/shared/src/side-panel/hive-side-panel.css b/frontend/packages/shared/src/side-panel/hive-side-panel.css
new file mode 100644
index 00000000..51048616
--- /dev/null
+++ b/frontend/packages/shared/src/side-panel/hive-side-panel.css
@@ -0,0 +1,111 @@
+/* hive-side-panel.css — scoped stylesheet for the generic <hive-side-panel>
+   shadow-DOM custom element (hive-side-panel.js). Loaded as raw text at
+   build time (esbuild's `text` loader) and appended as a <style> element
+   inside the shadow root — see @hive/shared/shadow-css.js's header comment
+   for why a plain <style> tag and not adoptedStyleSheets.
+
+   Every rule here styles shadow-owned chrome this element builds itself
+   (backdrop, drawer, resize handle, header, title, close button) — none of
+   it is slotted, so this file needs zero `::slotted()`. The one slotted
+   node (the caller's opaque content, passed to open()/openNamed()/
+   refresh()) is intentionally un-styled from in here: each package's own
+   content-type-specific rules (`hive-side-panel .md` in the dashboard,
+   `hive-side-panel .agent-inbox` in the agent UI) live in that package's
+   own global stylesheet and reach the slotted content via the element's
+   own tag name as the selector root — no compatibility class needed,
+   same architecture floor as `<hive-menu>`'s item-row styling, not a
+   scope choice.
+
+   `:host(.open)`/`:host(.resizing)` respond to the two state classes the
+   JS toggles on the host itself (`open`, and `resizing` during a drag) —
+   the shadow-scoped counterparts of the page-global `body.side-panel-
+   resizing` cursor-override class, which stays in each package's own
+   stylesheet since it has to reach light-DOM elements outside this
+   element entirely (see hive-side-panel.js's module header). */
+
+:host {
+  position: fixed;
+  inset: 0;
+  z-index: 200;
+  pointer-events: none;
+}
+.side-panel-backdrop {
+  position: absolute;
+  inset: 0;
+  background: color-mix(in srgb, var(--crust) 55%, transparent);
+  opacity: 0;
+  transition: opacity 200ms ease;
+}
+.side-panel-drawer {
+  position: absolute;
+  top: 0;
+  right: 0;
+  bottom: 0;
+  width: var(--side-panel-w, min(42em, 95vw));
+  background: var(--bg-elev);
+  border-left: 1px solid var(--purple-dim);
+  display: flex;
+  flex-direction: column;
+  transform: translateX(100%);
+  transition: transform 220ms ease;
+  overflow: hidden;
+}
+:host(.open) { pointer-events: auto; }
+:host(.open) .side-panel-backdrop { opacity: 1; }
+:host(.open) .side-panel-drawer { transform: translateX(0); }
+.side-panel-resize {
+  position: absolute;
+  left: 0;
+  top: 0;
+  bottom: 0;
+  width: 6px;
+  cursor: ew-resize;
+  opacity: 0;
+  transition: opacity 120ms;
+  background: var(--purple-dim);
+}
+.side-panel-resize:hover,
+:host(.resizing) .side-panel-resize {
+  opacity: 1;
+}
+:host(.resizing) .side-panel-resize {
+  background: var(--purple);
+}
+.side-panel-head {
+  display: flex;
+  align-items: center;
+  gap: 0.6em;
+  padding: 0.6em 1em;
+  border-bottom: 1px solid var(--border);
+  flex: none;
+}
+.side-panel-title {
+  flex: 1;
+  font-size: 0.88em;
+  color: var(--muted);
+  letter-spacing: 0.04em;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+.side-panel-close {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  background: none;
+  border: 1px solid var(--border);
+  border-radius: 3px;
+  color: var(--muted);
+  font-size: 1em;
+  line-height: 1;
+  padding: 0.15em 0.4em;
+  cursor: pointer;
+  transition: border-color 0.15s ease, color 0.15s ease;
+}
+.side-panel-close:hover { border-color: var(--red); color: var(--red); }
+.side-panel-body {
+  flex: 1;
+  overflow-y: auto;
+  padding: 0.8em 1em;
+  font-size: 0.88em;
+}
diff --git a/frontend/packages/shared/src/side-panel/hive-side-panel.js b/frontend/packages/shared/src/side-panel/hive-side-panel.js
new file mode 100644
index 00000000..01306719
--- /dev/null
+++ b/frontend/packages/shared/src/side-panel/hive-side-panel.js
@@ -0,0 +1,183 @@
+// hive-side-panel.js — <hive-side-panel>, the generic slide-in drawer
+// shadow-DOM custom element behind the dashboard's and the per-agent UI's
+// side panel (file previews, diffs, logs, inbox/todo lists — anything too
+// long to expand inline). One singleton instance per page, created once,
+// eagerly, by each package's own module (dashboard/src/common.js's
+// `sidePanel`, agent/src/app.js's `sidePanel`) and used directly — no
+// wrapper object, no per-call lazy-init guard.
+//
+// Builds all structural chrome itself in `connectedCallback` (backdrop,
+// drawer, resize handle, header, title, close button) — shadow-owned,
+// zero `::slotted()` needed. Only the panel *content* is opaque
+// caller-built DOM, appended as a light-DOM child and picked up by the
+// shadow tree's single default `<slot>`, exactly like `<hive-menu>`'s
+// `content` (see that file's header for why). Each package's own global
+// stylesheet reaches that content via the element's own tag name as the
+// selector root (`hive-side-panel .md`, `hive-side-panel .agent-inbox`)
+// — no compatibility class needed.
+//
+// Public API is instance methods: `open(title, content)`,
+// `openNamed(name, title, content)`, `refresh(name, title, content)`,
+// `close()`, `currentOwner()`. `open` is exactly `openNamed(null, title,
+// content)` — untyped opens clear the owner, matching the dashboard's
+// original semantics.
+//
+// Drag-to-resize + localStorage width persistence is ported from the
+// dashboard's original `Panel` (the only one of the two originals that
+// had it) — making it available to every consumer (the agent UI didn't
+// have it before) is a deliberate behavior widening, not incidental.
+
+import { el } from '../dom.js';
+import { attachShadowCss } from '../shadow-css.js';
+import sidePanelCss from './hive-side-panel.css';
+
+// See docs/web-ui.md::Side panel for the hit-strip + pointer-capture +
+// localStorage persistence model; CSS clamps the stored value to min
+// 320px / max 96vw and out-of-range stored values are dropped silently.
+// Shared by both packages deliberately — see module header.
+const WIDTH_KEY = 'hyperhive:side-panel-width';
+const WIDTH_MIN = 320;
+
+class HiveSidePanel extends HTMLElement {
+  connectedCallback() {
+    const root = attachShadowCss(this, sidePanelCss);
+    this.setAttribute('aria-hidden', 'true');
+    this._owner = null;
+
+    this._titleEl = el('span', { class: 'side-panel-title', id: 'side-panel-title' });
+    this._closeBtn = el('button', {
+      type: 'button', class: 'side-panel-close', title: 'close (esc)',
+    }, '✕');
+    const head = el('header', { class: 'side-panel-head' }, this._titleEl, this._closeBtn);
+
+    this._resizeHandle = el('div', {
+      class: 'side-panel-resize',
+      role: 'separator',
+      'aria-orientation': 'vertical',
+      'aria-label': 'drag to resize side panel',
+      title: 'drag to resize',
+    });
+
+    this._bodyEl = el('div', { class: 'side-panel-body' }, el('slot'));
+
+    this._drawer = el('aside', {
+      class: 'side-panel-drawer',
+      role: 'dialog',
+      'aria-modal': 'true',
+      'aria-labelledby': 'side-panel-title',
+    }, this._resizeHandle, head, this._bodyEl);
+
+    this._backdrop = el('div', { class: 'side-panel-backdrop' });
+
+    root.append(this._backdrop, this._drawer);
+
+    this._closeBtn.addEventListener('click', () => this.close());
+    this._backdrop.addEventListener('click', () => this.close());
+    document.addEventListener('keydown', (e) => {
+      if (e.key === 'Escape' && this.classList.contains('open')) this.close();
+    });
+
+    this._applyStoredWidth();
+    this._bindResize();
+  }
+
+  open(title, content) {
+    this.openNamed(null, title, content);
+  }
+
+  openNamed(name, title, content) {
+    this._owner = name;
+    this._titleEl.textContent = title;
+    this.replaceChildren(...(content ? [content] : []));
+    this.classList.add('open');
+    this.setAttribute('aria-hidden', 'false');
+  }
+
+  refresh(name, title, content) {
+    if (this._owner !== name) return;
+    this._titleEl.textContent = title;
+    this.replaceChildren(...(content ? [content] : []));
+  }
+
+  close() {
+    this._owner = null;
+    this.classList.remove('open');
+    this.setAttribute('aria-hidden', 'true');
+  }
+
+  currentOwner() {
+    return this._owner;
+  }
+
+  _clampWidth(w) {
+    // Use document.documentElement.clientWidth rather than window.innerWidth:
+    // clientWidth gives the actual CSS layout viewport width and is not
+    // altered by Firefox's Fingerprinting Protection (which rounds
+    // window.innerWidth/outerWidth to the nearest 200px).
+    const max = Math.floor(document.documentElement.clientWidth * 0.96);
+    return Math.max(WIDTH_MIN, Math.min(max, w));
+  }
+
+  _applyStoredWidth() {
+    const raw = (() => {
+      try { return localStorage.getItem(WIDTH_KEY); }
+      catch { return null; }
+    })();
+    if (!raw) return;
+    const parsed = parseInt(raw, 10);
+    if (!Number.isFinite(parsed) || parsed <= 0) return;
+    this._drawer.style.setProperty('--side-panel-w', this._clampWidth(parsed) + 'px');
+  }
+
+  _bindResize() {
+    const handle = this._resizeHandle;
+    const drawer = this._drawer;
+    let dragging = false;
+    handle.addEventListener('pointerdown', (e) => {
+      e.preventDefault();
+      dragging = true;
+      document.body.classList.add('side-panel-resizing');
+      // Shadow-scoped counterpart of the global `body.side-panel-resizing`
+      // class below — the resize handle's own hover/drag appearance lives
+      // inside this element's shadow tree, which the global class (a
+      // light-DOM-only escape hatch for the page-wide cursor override)
+      // can't reach.
+      this.classList.add('resizing');
+      // Capture so we keep getting pointermove even when the cursor
+      // outpaces the handle band (drag-fast-then-pause loses the
+      // handle's :hover state otherwise).
+      try { handle.setPointerCapture(e.pointerId); } catch { /* legacy */ }
+    });
+    document.addEventListener('pointermove', (e) => {
+      if (!dragging) return;
+      // Drawer is anchored to the right edge — width = viewport - pointer X.
+      const w = this._clampWidth(document.documentElement.clientWidth - e.clientX);
+      drawer.style.setProperty('--side-panel-w', w + 'px');
+    });
+    const stopDrag = () => {
+      if (!dragging) return;
+      dragging = false;
+      document.body.classList.remove('side-panel-resizing');
+      this.classList.remove('resizing');
+      // Persist the final width. Read the actual rendered width
+      // rather than re-deriving so the stored value matches what
+      // the operator saw at mouseup.
+      const w = drawer.getBoundingClientRect().width;
+      try { localStorage.setItem(WIDTH_KEY, String(Math.round(w))); }
+      catch { /* localStorage unavailable — width is session-only */ }
+    };
+    document.addEventListener('pointerup', stopDrag);
+    document.addEventListener('pointercancel', stopDrag);
+    // Re-clamp on viewport resize so a persisted width that exceeds
+    // 96vw doesn't push the drawer off-screen after a window shrink.
+    window.addEventListener('resize', () => {
+      if (dragging) return;
+      const cur = drawer.getBoundingClientRect().width;
+      const clamped = this._clampWidth(cur);
+      if (clamped !== Math.round(cur)) {
+        drawer.style.setProperty('--side-panel-w', clamped + 'px');
+      }
+    });
+  }
+}
+customElements.define('hive-side-panel', HiveSidePanel);