diff --git a/blog/sexp/header.sexpr b/blog/sexp/header.sexpr
index 3ab3654..6debebe 100644
--- a/blog/sexp/header.sexpr
+++ b/blog/sexp/header.sexpr
@@ -1,22 +1,8 @@
 ;; Blog header components
 
-(defcomp ~blog-oob-header (&key parent-id child-id row-html)
-  (div :id parent-id :hx-swap-oob "outerHTML" :class "w-full"
-    (div :class "w-full" (raw! row-html)
-      (div :id child-id))))
-
 (defcomp ~blog-header-label ()
   (div))
 
-(defcomp ~blog-post-label (&key feature-image title)
-  (<> (when feature-image (img :src feature-image :class "h-8 w-8 rounded-full object-cover border border-stone-300 flex-shrink-0"))
-    (span title)))
-
-(defcomp ~blog-post-cart-link (&key href count)
-  (a :href href :class "relative inline-flex items-center gap-1.5 px-3 py-1.5 text-sm rounded-full border border-emerald-300 bg-emerald-50 text-emerald-800 hover:bg-emerald-100 transition"
-    (i :class "fa fa-shopping-cart" :aria-hidden "true")
-    (span count)))
-
 (defcomp ~blog-container-nav (&key container-nav-html)
   (div :class "flex flex-col sm:flex-row sm:items-center gap-2 border-r border-stone-200 mr-2 sm:max-w-2xl"
     :id "entries-calendars-nav-wrapper" (raw! container-nav-html)))
diff --git a/blog/sexp/sexp_components.py b/blog/sexp/sexp_components.py
index 8c3a3c2..7b85bb9 100644
--- a/blog/sexp/sexp_components.py
+++ b/blog/sexp/sexp_components.py
@@ -15,6 +15,8 @@ from markupsafe import escape
 from shared.sexp.jinja_bridge import render, load_service_components
 from shared.sexp.helpers import (
     call_url, get_asset_url, root_header_html,
+    post_header_html as _shared_post_header_html,
+    oob_header_html,
     search_mobile_html, search_desktop_html,
     full_page, oob_page,
 )
@@ -24,14 +26,10 @@ load_service_components(os.path.dirname(os.path.dirname(__file__)))
 
 
 # ---------------------------------------------------------------------------
-# OOB header helper
+# OOB header helper — delegates to shared
 # ---------------------------------------------------------------------------
 
-def _oob_header_html(parent_id: str, child_id: str, row_html: str) -> str:
-    """Wrap a header row in OOB div with child placeholder."""
-    return render("blog-oob-header",
-        parent_id=parent_id, child_id=child_id, row_html=row_html,
-    )
+_oob_header_html = oob_header_html
 
 
 # ---------------------------------------------------------------------------
@@ -48,59 +46,40 @@ def _blog_header_html(ctx: dict, *, oob: bool = False) -> str:
 
 
 # ---------------------------------------------------------------------------
-# Post header helpers
+# Post header helpers — thin wrapper over shared post_header_html
 # ---------------------------------------------------------------------------
 
 def _post_header_html(ctx: dict, *, oob: bool = False) -> str:
-    """Build the post-level header row."""
-    post = ctx.get("post") or {}
-    slug = post.get("slug", "")
-    title = (post.get("title") or "")[:160]
-    feature_image = post.get("feature_image")
+    """Build the post-level header row (blog-specific: container-nav wrapping + admin cog)."""
+    overrides: dict = {}
 
-    label_html = render("blog-post-label",
-        feature_image=feature_image, title=title,
-    )
-
-    nav_parts = []
-    page_cart_count = ctx.get("page_cart_count", 0)
-    if page_cart_count and page_cart_count > 0:
-        cart_href = call_url(ctx, "cart_url", f"/{slug}/")
-        nav_parts.append(render("blog-post-cart-link",
-            href=cart_href, count=str(page_cart_count),
-        ))
-
-    # Container nav fragments (calendars, markets)
+    # Blog wraps container_nav_html in border styling
     container_nav = ctx.get("container_nav_html", "")
     if container_nav:
-        nav_parts.append(render("blog-container-nav",
+        overrides["container_nav_html"] = render("blog-container-nav",
             container_nav_html=container_nav,
-        ))
+        )
 
-    # Admin link
-    from quart import url_for as qurl, g, request
+    # Admin cog link
+    from quart import url_for as qurl, request
+    post = ctx.get("post") or {}
+    slug = post.get("slug", "")
     rights = ctx.get("rights") or {}
     has_admin = rights.get("admin") if isinstance(rights, dict) else getattr(rights, "admin", False)
-    if has_admin:
+    if has_admin and slug:
         select_colours = ctx.get("select_colours", "")
         styles = ctx.get("styles") or {}
         nav_btn = styles.get("nav_button", "") if isinstance(styles, dict) else getattr(styles, "nav_button", "")
         admin_href = qurl("blog.post.admin.admin", slug=slug)
         is_admin_page = "/admin" in request.path
-        nav_parts.append(render("nav-link",
+        overrides["post_admin_nav_html"] = render("nav-link",
             href=admin_href, hx_select="#main-panel", icon="fa fa-cog",
             aclass=f"{nav_btn} {select_colours}",
             select_colours=select_colours, is_selected=is_admin_page,
-        ))
+        )
 
-    nav_html = "".join(nav_parts)
-    link_href = call_url(ctx, "blog_url", f"/{slug}/")
-
-    return render("menu-row",
-        id="post-row", level=1,
-        link_href=link_href, link_label_html=label_html,
-        nav_html=nav_html, child_id="post-header-child", oob=oob,
-    )
+    effective_ctx = {**ctx, **overrides} if overrides else ctx
+    return _shared_post_header_html(effective_ctx, oob=oob)
 
 
 # ---------------------------------------------------------------------------
diff --git a/events/sexp/header.sexpr b/events/sexp/header.sexpr
index 84d6990..69ba3dd 100644
--- a/events/sexp/header.sexpr
+++ b/events/sexp/header.sexpr
@@ -1,20 +1,5 @@
 ;; Events header components
 
-(defcomp ~events-oob-header (&key parent-id child-id row-html)
-  (div :id parent-id :hx-swap-oob "outerHTML" :class "w-full"
-    (div :class "w-full"
-      (raw! row-html)
-      (div :id child-id))))
-
-(defcomp ~events-post-label (&key feature-image title)
-  (<> (when feature-image (img :src feature-image :class "h-8 w-8 rounded-full object-cover border border-stone-300 flex-shrink-0"))
-      (span title)))
-
-(defcomp ~events-post-cart-link (&key href count)
-  (a :href href :class "relative inline-flex items-center gap-1.5 px-3 py-1.5 text-sm rounded-full border border-emerald-300 bg-emerald-50 text-emerald-800 hover:bg-emerald-100 transition"
-    (i :class "fa fa-shopping-cart" :aria-hidden "true")
-    (span count)))
-
 (defcomp ~events-calendars-label ()
   (<> (i :class "fa fa-calendar" :aria-hidden "true") (div "Calendars")))
 
@@ -39,5 +24,3 @@
   (div :id (str "entry-title-" entry-id) :class "flex gap-1 items-center"
     (raw! title-html) (raw! times-html)))
 
-(defcomp ~events-header-child (&key inner-html)
-  (div :id "root-header-child" :class "w-full" (raw! inner-html)))
diff --git a/events/sexp/sexp_components.py b/events/sexp/sexp_components.py
index d0039d5..093e9d2 100644
--- a/events/sexp/sexp_components.py
+++ b/events/sexp/sexp_components.py
@@ -14,6 +14,8 @@ from markupsafe import escape
 from shared.sexp.jinja_bridge import render, load_service_components
 from shared.sexp.helpers import (
     call_url, get_asset_url, root_header_html,
+    post_header_html as _shared_post_header_html,
+    oob_header_html,
     search_mobile_html, search_desktop_html,
     full_page, oob_page,
 )
@@ -23,46 +25,21 @@ load_service_components(os.path.dirname(os.path.dirname(__file__)))
 
 
 # ---------------------------------------------------------------------------
-# OOB header helper (same pattern as market)
+# OOB header helper — delegates to shared
 # ---------------------------------------------------------------------------
 
-def _oob_header_html(parent_id: str, child_id: str, row_html: str) -> str:
-    """Wrap a header row in OOB div with child placeholder."""
-    return render("events-oob-header",
-                  parent_id=parent_id, child_id=child_id, row_html=row_html)
+_oob_header_html = oob_header_html
 
 
 # ---------------------------------------------------------------------------
-# Post header helpers (mirrors events/templates/_types/post/header/_header.html)
+# Post header helpers — thin wrapper over shared post_header_html
 # ---------------------------------------------------------------------------
 
 def _post_header_html(ctx: dict, *, oob: bool = False) -> str:
-    """Build the post-level header row."""
-    post = ctx.get("post") or {}
-    slug = post.get("slug", "")
-    title = (post.get("title") or "")[:160]
-    feature_image = post.get("feature_image")
-
-    label_html = render("events-post-label",
-                        feature_image=feature_image, title=title)
-
-    nav_parts = []
-    page_cart_count = ctx.get("page_cart_count", 0)
-    if page_cart_count and page_cart_count > 0:
-        cart_href = call_url(ctx, "cart_url", f"/{slug}/")
-        nav_parts.append(render("events-post-cart-link",
-                                href=cart_href, count=str(page_cart_count)))
-
-    # Post nav: calendar links + admin
-    nav_parts.append(_post_nav_html(ctx))
-
-    nav_html = "".join(nav_parts)
-    link_href = call_url(ctx, "blog_url", f"/{slug}/")
-
-    return render("menu-row", id="post-row", level=1,
-                  link_href=link_href, link_label_html=label_html,
-                  nav_html=nav_html, child_id="post-header-child", oob=oob,
-                  external=True)
+    """Build the post-level header row (events-specific: calendar links + admin cog)."""
+    admin_nav = _post_nav_html(ctx)
+    effective_ctx = {**ctx, "post_admin_nav_html": admin_nav} if admin_nav else ctx
+    return _shared_post_header_html(effective_ctx, oob=oob)
 
 
 def _post_nav_html(ctx: dict) -> str:
@@ -1235,7 +1212,7 @@ async def render_page_summary_page(ctx: dict, entries, has_more, pending_tickets
     )
 
     hdr = root_header_html(ctx)
-    hdr += render("events-header-child",
+    hdr += render("header-child",
                   inner_html=_post_header_html(ctx))
     return full_page(ctx, header_rows_html=hdr, content_html=content)
 
@@ -1289,7 +1266,7 @@ async def render_calendars_page(ctx: dict) -> str:
     content = _calendars_main_panel_html(ctx)
     hdr = root_header_html(ctx)
     child = _post_header_html(ctx) + _calendars_header_html(ctx)
-    hdr += render("events-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     return full_page(ctx, header_rows_html=hdr, content_html=content)
 
 
@@ -1311,7 +1288,7 @@ async def render_calendar_page(ctx: dict) -> str:
     content = _calendar_main_panel_html(ctx)
     hdr = root_header_html(ctx)
     child = _post_header_html(ctx) + _calendar_header_html(ctx)
-    hdr += render("events-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     return full_page(ctx, header_rows_html=hdr, content_html=content)
 
 
@@ -1334,7 +1311,7 @@ async def render_day_page(ctx: dict) -> str:
     hdr = root_header_html(ctx)
     child = (_post_header_html(ctx)
              + _calendar_header_html(ctx) + _day_header_html(ctx))
-    hdr += render("events-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     return full_page(ctx, header_rows_html=hdr, content_html=content)
 
 
@@ -1358,7 +1335,7 @@ async def render_day_admin_page(ctx: dict) -> str:
     child = (_post_header_html(ctx)
              + _calendar_header_html(ctx) + _day_header_html(ctx)
              + _day_admin_header_html(ctx))
-    hdr += render("events-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     return full_page(ctx, header_rows_html=hdr, content_html=content)
 
 
@@ -1381,7 +1358,7 @@ async def render_calendar_admin_page(ctx: dict) -> str:
     hdr = root_header_html(ctx)
     child = (_post_header_html(ctx)
              + _calendar_header_html(ctx) + _calendar_admin_header_html(ctx))
-    hdr += render("events-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     return full_page(ctx, header_rows_html=hdr, content_html=content)
 
 
@@ -1407,7 +1384,7 @@ async def render_slots_page(ctx: dict) -> str:
     hdr = root_header_html(ctx)
     child = (_post_header_html(ctx)
              + _calendar_header_html(ctx) + _calendar_admin_header_html(ctx))
-    hdr += render("events-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     return full_page(ctx, header_rows_html=hdr, content_html=content)
 
 
@@ -1476,7 +1453,7 @@ async def render_markets_page(ctx: dict) -> str:
     content = _markets_main_panel_html(ctx)
     hdr = root_header_html(ctx)
     child = _post_header_html(ctx) + _markets_header_html(ctx)
-    hdr += render("events-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     return full_page(ctx, header_rows_html=hdr, content_html=content)
 
 
@@ -1860,7 +1837,7 @@ async def render_entry_page(ctx: dict) -> str:
     child = (_post_header_html(ctx)
              + _calendar_header_html(ctx) + _day_header_html(ctx)
              + _entry_header_html(ctx))
-    hdr += render("events-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     nav_html = _entry_nav_html(ctx)
     return full_page(ctx, header_rows_html=hdr, content_html=content, menu_html=nav_html)
 
@@ -2873,7 +2850,7 @@ async def render_entry_admin_page(ctx: dict) -> str:
     child = (_post_header_html(ctx)
              + _calendar_header_html(ctx) + _day_header_html(ctx)
              + _entry_header_html(ctx) + _entry_admin_header_html(ctx))
-    hdr += render("events-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     nav_html = render("events-admin-placeholder-nav")
     return full_page(ctx, header_rows_html=hdr, content_html=content, menu_html=nav_html)
 
@@ -2932,7 +2909,7 @@ async def render_slot_page(ctx: dict) -> str:
     child = (_post_header_html(ctx)
              + _calendar_header_html(ctx) + _calendar_admin_header_html(ctx)
              + _slot_header_html(ctx))
-    hdr += render("events-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     return full_page(ctx, header_rows_html=hdr, content_html=content)
 
 
@@ -3140,7 +3117,7 @@ async def render_ticket_types_page(ctx: dict) -> str:
              + _calendar_header_html(ctx) + _day_header_html(ctx)
              + _entry_header_html(ctx) + _entry_admin_header_html(ctx)
              + _ticket_types_header_html(ctx))
-    hdr += render("events-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     nav_html = render("events-admin-placeholder-nav")
     return full_page(ctx, header_rows_html=hdr, content_html=content, menu_html=nav_html)
 
@@ -3214,7 +3191,7 @@ async def render_ticket_type_page(ctx: dict) -> str:
              + _calendar_header_html(ctx) + _day_header_html(ctx)
              + _entry_header_html(ctx) + _entry_admin_header_html(ctx)
              + _ticket_types_header_html(ctx) + _ticket_type_header_html(ctx))
-    hdr += render("events-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     nav_html = render("events-admin-placeholder-nav")
     return full_page(ctx, header_rows_html=hdr, content_html=content, menu_html=nav_html)
 
diff --git a/market/sexp/headers.sexpr b/market/sexp/headers.sexpr
index 1bbfe7c..57e7633 100644
--- a/market/sexp/headers.sexpr
+++ b/market/sexp/headers.sexpr
@@ -1,16 +1,5 @@
 ;; Market header components
 
-(defcomp ~market-post-label-image (&key src)
-  (img :src src :class "h-8 w-8 rounded-full object-cover border border-stone-300 flex-shrink-0"))
-
-(defcomp ~market-post-label-title (&key title)
-  (span title))
-
-(defcomp ~market-post-cart-badge (&key href count)
-  (a :href href :class "relative inline-flex items-center gap-1.5 px-3 py-1.5 text-sm rounded-full border border-emerald-300 bg-emerald-50 text-emerald-800 hover:bg-emerald-100 transition"
-    (i :class "fa fa-shopping-cart" :aria-hidden "true")
-    (span count)))
-
 (defcomp ~market-shop-label (&key title top-slug sub-div-html)
   (div :class "font-bold text-xl flex-shrink-0 flex gap-2 items-center"
     (div (i :class "fa fa-shop") " " title)
@@ -29,10 +18,3 @@
      :class "px-2 py-1 text-stone-500 hover:text-stone-700"
      (i :class "fa fa-cog" :aria-hidden "true")))
 
-(defcomp ~market-oob-header (&key parent-id child-id row-html)
-  (div :id parent-id :hx-swap-oob "outerHTML" :class "w-full"
-    (div :class "w-full" (raw! row-html)
-      (div :id child-id))))
-
-(defcomp ~market-header-child (&key inner-html)
-  (div :id "root-header-child" :class "w-full" (raw! inner-html)))
diff --git a/market/sexp/sexp_components.py b/market/sexp/sexp_components.py
index fcf6616..3131aa7 100644
--- a/market/sexp/sexp_components.py
+++ b/market/sexp/sexp_components.py
@@ -14,6 +14,8 @@ from markupsafe import escape
 from shared.sexp.jinja_bridge import render, load_service_components
 from shared.sexp.helpers import (
     call_url, get_asset_url, root_header_html,
+    post_header_html as _post_header_html,
+    oob_header_html as _oob_header_html,
     search_mobile_html, search_desktop_html,
     full_page, oob_page,
 )
@@ -66,42 +68,9 @@ def _card_price_html(p: dict) -> str:
 
 
 # ---------------------------------------------------------------------------
-# Header helpers
+# Header helpers — _post_header_html and _oob_header_html imported from shared
 # ---------------------------------------------------------------------------
 
-def _post_header_html(ctx: dict, *, oob: bool = False) -> str:
-    """Build the post-level header row (feature image + title + page cart count)."""
-    post = ctx.get("post") or {}
-    slug = post.get("slug", "")
-    title = (post.get("title") or "")[:160]
-    feature_image = post.get("feature_image")
-
-    label_html = ""
-    if feature_image:
-        label_html += render("market-post-label-image", src=feature_image)
-    label_html += render("market-post-label-title", title=title)
-
-    nav_html = ""
-    page_cart_count = ctx.get("page_cart_count", 0)
-    if page_cart_count and page_cart_count > 0:
-        cart_href = call_url(ctx, "cart_url", f"/{slug}/")
-        nav_html += render("market-post-cart-badge", href=cart_href, count=str(page_cart_count))
-
-    # Container nav
-    container_nav = ctx.get("container_nav_html", "")
-    if container_nav:
-        nav_html += container_nav
-
-    link_href = call_url(ctx, "blog_url", f"/{slug}/")
-
-    return render(
-        "menu-row",
-        id="post-row", level=1,
-        link_href=link_href, link_label_html=label_html,
-        nav_html=nav_html, child_id="post-header-child", oob=oob,
-        external=True,
-    )
-
 
 def _market_header_html(ctx: dict, *, oob: bool = False) -> str:
     """Build the market-level header row (shop icon + market title + category slugs + nav)."""
@@ -1153,16 +1122,9 @@ def _market_cards_html(markets: list, page_info: dict, page: int, has_more: bool
 
 
 # ---------------------------------------------------------------------------
-# OOB header helpers
+# OOB header helpers — _oob_header_html imported from shared
 # ---------------------------------------------------------------------------
 
-def _oob_header_html(parent_id: str, child_id: str, row_html: str) -> str:
-    """Wrap a header row in OOB div with child placeholder."""
-    return render(
-        "market-oob-header",
-        parent_id=parent_id, child_id=child_id, row_html=row_html,
-    )
-
 
 # ===========================================================================
 # PUBLIC API
@@ -1258,7 +1220,7 @@ async def render_page_markets_page(ctx: dict, markets: list, has_more: bool,
     content += render("market-bottom-spacer")
 
     hdr = root_header_html(ctx)
-    hdr += render("market-header-child", inner_html=_post_header_html(ctx))
+    hdr += render("header-child", inner_html=_post_header_html(ctx))
     return full_page(ctx, header_rows_html=hdr, content_html=content)
 
 
@@ -1309,7 +1271,7 @@ async def render_market_home_page(ctx: dict) -> str:
 
     hdr = root_header_html(ctx)
     child = _post_header_html(ctx) + _market_header_html(ctx)
-    hdr += render("market-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     menu = _mobile_nav_panel_html(ctx)
     return full_page(ctx, header_rows_html=hdr, content_html=content, menu_html=menu)
 
@@ -1354,7 +1316,7 @@ async def render_browse_page(ctx: dict) -> str:
 
     hdr = root_header_html(ctx)
     child = _post_header_html(ctx) + _market_header_html(ctx)
-    hdr += render("market-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     menu = _mobile_nav_panel_html(ctx)
     filter_html = _mobile_filter_summary_html(ctx)
     aside_html = _desktop_filter_html(ctx)
@@ -1395,7 +1357,7 @@ async def render_product_page(ctx: dict, d: dict) -> str:
 
     hdr = root_header_html(ctx)
     child = _post_header_html(ctx) + _market_header_html(ctx) + _product_header_html(ctx, d)
-    hdr += render("market-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     return full_page(ctx, header_rows_html=hdr, content_html=content, meta_html=meta)
 
 
@@ -1421,7 +1383,7 @@ async def render_product_admin_page(ctx: dict, d: dict) -> str:
     hdr = root_header_html(ctx)
     child = (_post_header_html(ctx) + _market_header_html(ctx)
              + _product_header_html(ctx, d) + _product_admin_header_html(ctx, d))
-    hdr += render("market-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     return full_page(ctx, header_rows_html=hdr, content_html=content)
 
 
@@ -1459,7 +1421,7 @@ async def render_market_admin_page(ctx: dict) -> str:
 
     hdr = root_header_html(ctx)
     child = _post_header_html(ctx) + _market_header_html(ctx) + _market_admin_header_html(ctx)
-    hdr += render("market-header-child", inner_html=child)
+    hdr += render("header-child", inner_html=child)
     return full_page(ctx, header_rows_html=hdr, content_html=content)
 
 
diff --git a/shared/browser/app/errors.py b/shared/browser/app/errors.py
index 7cb2c3a..4a0d751 100644
--- a/shared/browser/app/errors.py
+++ b/shared/browser/app/errors.py
@@ -83,8 +83,7 @@ async def _rich_error_page(errnum: str, message: str, image: str | None = None)
         return None
 
     try:
-        from shared.sexp.jinja_bridge import render
-        from shared.sexp.helpers import full_page, call_url
+        from shared.sexp.helpers import full_page
 
         # Build a minimal context — avoid get_template_context() which
         # calls cross-service fragment fetches that may fail.
@@ -150,44 +149,22 @@ async def _rich_error_page(errnum: str, message: str, image: str | None = None)
                 pass
 
         # Root header (site nav bar)
-        from shared.sexp.helpers import root_header_html
+        from shared.sexp.helpers import (
+            root_header_html, post_header_html,
+            header_child_html, error_content_html,
+        )
         hdr = root_header_html(ctx)
 
         # Post breadcrumb if we resolved a post
         post = (post_data or {}).get("post") or ctx.get("post") or {}
         if post.get("slug"):
-            title = (post.get("title") or "")[:160]
-            feature_image = post.get("feature_image")
-            label_html = ""
-            if feature_image:
-                label_html += (
-                    f'<img src="{feature_image}" '
-                    f'class="h-8 w-8 rounded-full object-cover border border-stone-300 flex-shrink-0">'
-                )
-            label_html += f"<span>{escape(title)}</span>"
-            post_row = render(
-                "menu-row",
-                id="post-row", level=1,
-                link_href=call_url(ctx, "blog_url", f"/{post['slug']}/"),
-                link_label_html=label_html,
-                child_id="post-header-child",
-                external=True,
-            )
-            hdr += (
-                f'<div id="root-header-child" class="w-full">'
-                f'{post_row}'
-                f'</div>'
-            )
+            ctx["post"] = post
+            post_row = post_header_html(ctx)
+            if post_row:
+                hdr += header_child_html(post_row)
 
         # Error content
-        error_html = (
-            '<div class="text-center p-8 max-w-lg mx-auto">'
-            f'<div class="font-bold text-2xl md:text-4xl text-red-500 mb-4">{errnum}</div>'
-            f'<div class="text-stone-600 mb-4">{escape(message)}</div>'
-        )
-        if image:
-            error_html += f'<div class="flex justify-center"><img src="{image}" width="300" height="300"></div>'
-        error_html += "</div>"
+        error_html = error_content_html(errnum, message, image)
 
         return full_page(ctx, header_rows_html=hdr, content_html=error_html)
     except Exception:
diff --git a/shared/sexp/helpers.py b/shared/sexp/helpers.py
index 9533692..59f17aa 100644
--- a/shared/sexp/helpers.py
+++ b/shared/sexp/helpers.py
@@ -67,6 +67,59 @@ def search_desktop_html(ctx: dict) -> str:
     )
 
 
+def post_header_html(ctx: dict, *, oob: bool = False) -> str:
+    """Build the post-level header row (level 1). Used by all apps + error pages."""
+    post = ctx.get("post") or {}
+    slug = post.get("slug", "")
+    if not slug:
+        return ""
+    title = (post.get("title") or "")[:160]
+    feature_image = post.get("feature_image")
+
+    label_html = render("post-label", feature_image=feature_image, title=title)
+
+    nav_parts: list[str] = []
+    page_cart_count = ctx.get("page_cart_count", 0)
+    if page_cart_count and page_cart_count > 0:
+        cart_href = call_url(ctx, "cart_url", f"/{slug}/")
+        nav_parts.append(render("page-cart-badge", href=cart_href, count=str(page_cart_count)))
+
+    container_nav = ctx.get("container_nav_html", "")
+    if container_nav:
+        nav_parts.append(container_nav)
+
+    admin_nav = ctx.get("post_admin_nav_html", "")
+    if admin_nav:
+        nav_parts.append(admin_nav)
+
+    nav_html = "".join(nav_parts)
+    link_href = call_url(ctx, "blog_url", f"/{slug}/")
+
+    return render("menu-row",
+        id="post-row", level=1,
+        link_href=link_href, link_label_html=label_html,
+        nav_html=nav_html, child_id="post-header-child",
+        oob=oob, external=True,
+    )
+
+
+def oob_header_html(parent_id: str, child_id: str, row_html: str) -> str:
+    """Wrap a header row in an OOB swap div with child placeholder."""
+    return render("oob-header",
+        parent_id=parent_id, child_id=child_id, row_html=row_html,
+    )
+
+
+def header_child_html(inner_html: str, *, id: str = "root-header-child") -> str:
+    """Wrap inner HTML in a header-child div."""
+    return render("header-child", id=id, inner_html=inner_html)
+
+
+def error_content_html(errnum: str, message: str, image: str | None = None) -> str:
+    """Render the error content block."""
+    return render("error-content", errnum=errnum, message=message, image=image)
+
+
 def full_page(ctx: dict, *, header_rows_html: str,
               filter_html: str = "", aside_html: str = "",
               content_html: str = "", menu_html: str = "",
diff --git a/shared/sexp/templates/layout.sexp b/shared/sexp/templates/layout.sexp
index 3877a7f..cc34cf3 100644
--- a/shared/sexp/templates/layout.sexp
+++ b/shared/sexp/templates/layout.sexp
@@ -146,6 +146,32 @@
         (div :id child-id :class "flex flex-col w-full items-center"
           (when child-html (raw! child-html)))))))
 
+(defcomp ~post-label (&key feature-image title)
+  (<> (when feature-image
+        (img :src feature-image :class "h-8 w-8 rounded-full object-cover border border-stone-300 flex-shrink-0"))
+    (span title)))
+
+(defcomp ~page-cart-badge (&key href count)
+  (a :href href :class "relative inline-flex items-center gap-1.5 px-3 py-1.5 text-sm rounded-full border border-emerald-300 bg-emerald-50 text-emerald-800 hover:bg-emerald-100 transition"
+    (i :class "fa fa-shopping-cart" :aria-hidden "true")
+    (span count)))
+
+(defcomp ~oob-header (&key parent-id child-id row-html)
+  (div :id parent-id :hx-swap-oob "outerHTML" :class "w-full"
+    (div :class "w-full" (raw! row-html)
+      (div :id child-id))))
+
+(defcomp ~header-child (&key id inner-html)
+  (div :id (or id "root-header-child") :class "w-full" (raw! inner-html)))
+
+(defcomp ~error-content (&key errnum message image)
+  (div :class "text-center p-8 max-w-lg mx-auto"
+    (div :class "font-bold text-2xl md:text-4xl text-red-500 mb-4" errnum)
+    (div :class "text-stone-600 mb-4" message)
+    (when image
+      (div :class "flex justify-center"
+        (img :src image :width "300" :height "300")))))
+
 (defcomp ~nav-link (&key href hx-select label icon aclass select-colours is-selected)
   (div :class "relative nav-group"
     (a :href href