Root cause of the 404: _trigger_rebuild was firing bincio render (= full astro build), but:

1. The build took minutes → 404 during that window
  2. Even after the build, the output lands in site/dist/ — nginx serves from /var/www/bincio/ which is only updated by the rsync in the post-receive hook, not by the server process

  Fixes applied:

  1. bincio/render/cli.py: Added --no-build flag — merges sidecars and updates manifests but skips astro build. This is fast (~1 second).
  2. bincio/serve/server.py _trigger_rebuild: Now passes --no-build. After an upload, _merged/ and root index.json are updated immediately, so the feed reflects the new activity. The static Astro pages are
  only rebuilt on git push.
  3. site/src/components/ActivityDetailLoader.svelte (new): Svelte component that reads the activity ID from the URL, calls loadIndex to resolve the shard tree, then renders ActivityDetail dynamically — no
  pre-built page needed.
  4. site/src/pages/activity/index.astro (new): Generic Astro shell page that renders ActivityDetailLoader. Gets compiled to dist/activity/index.html.
  5. docs/deployment/vps.md: Added location /activity/ { try_files $uri $uri/ /activity/index.html; } to the nginx config. When a request arrives for /activity/2026-04-06T153345Z/ and no pre-built file
  exists, nginx serves the shell, which loads the data dynamically from /data/ (which nginx already serves live from disk).

bincio/render/cli.py

@@ -168,6 +168,8 @@ def _link_data(site: Path, data: Path) -> None:
               help="Deploy after build. Currently supports: github.")
 @click.option("--handle", default=None,
               help="(Multi-user) Incrementally re-merge one user's shard only.")
+@click.option("--no-build", "no_build", is_flag=True,
+              help="Skip the Astro build step (just merge sidecars and update manifests).")
 def render(
     config_path: Optional[str],
     data_dir: Optional[str],
@@ -176,6 +178,7 @@ def render(
     serve: bool,
     deploy: Optional[str],
     handle: Optional[str],
+    no_build: bool,
 ) -> None:
     """Build (or serve) the BincioActivity static site from a BAS data store."""
 
@@ -185,9 +188,14 @@ def render(
     console.print(f"Site:  [cyan]{site}[/cyan]")
     console.print(f"Data:  [cyan]{data}[/cyan]")
 
-    _ensure_npm(site)
     _merge_edits(data, handle=handle)
     _write_root_manifest(data)
+
+    if no_build:
+        console.print("[green]Data updated.[/green] Skipping Astro build (--no-build).")
+        return
+
+    _ensure_npm(site)
     _link_data(site, data)
 
     env = {**os.environ, "BINCIO_DATA_DIR": str(data)}

bincio/serve/server.py

@@ -175,7 +175,8 @@ def _trigger_rebuild(handle: str) -> None:
             [uv, "run", "bincio", "render",
              "--data-dir", str(data_dir),
              "--site-dir", str(site_dir),
-             "--handle", handle],
+             "--handle", handle,
+             "--no-build"],
             stdout=subprocess.DEVNULL,
             stderr=subprocess.DEVNULL,
         )

docs/deployment/vps.md

@@ -253,6 +253,17 @@ server {
         add_header Cache-Control "no-cache, must-revalidate";
     }
 
+    # Activity detail pages: fall back to the dynamic shell for activities uploaded
+    # after the last site build (avoids 404 while waiting for a rebuild).
+    location /activity/ {
+        try_files $uri $uri/ /activity/index.html;
+    }
+
+    # Per-user profile pages: same fallback for new users.
+    location /u/ {
+        try_files $uri $uri/ =404;
+    }
+
     # Static files
     location / {
         try_files $uri $uri/ $uri.html =404;

site/src/components/ActivityDetailLoader.svelte

@@ -0,0 +1,40 @@
+<script lang="ts">
+  import { onMount } from 'svelte';
+  import { loadIndex } from '../lib/dataloader';
+  import ActivityDetail from './ActivityDetail.svelte';
+  import type { ActivitySummary } from '../lib/types';
+
+  export let base: string = '/';
+
+  let activity: ActivitySummary | null = null;
+  let notFound = false;
+  let loading = true;
+
+  onMount(async () => {
+    // Extract activity ID from the URL path: /activity/{id}/
+    const match = window.location.pathname.match(/\/activity\/([^/]+)/);
+    const id = match?.[1];
+    if (!id) { notFound = true; loading = false; return; }
+
+    try {
+      const index = await loadIndex(base);
+      activity = index.activities.find(a => a.id === id) ?? null;
+      if (!activity) notFound = true;
+    } catch {
+      notFound = true;
+    }
+    loading = false;
+  });
+</script>
+
+{#if loading}
+  <p class="text-zinc-500 text-sm mt-8 text-center">Loading activity…</p>
+{:else if notFound}
+  <div class="text-center mt-16">
+    <p class="text-zinc-400 text-sm mb-2">Activity not found.</p>
+    <p class="text-zinc-600 text-xs">It may still be processing — try refreshing in a moment.</p>
+    <a href={base} class="mt-4 inline-block text-blue-400 hover:text-blue-300 text-sm">← Back to feed</a>
+  </div>
+{:else if activity}
+  <ActivityDetail {activity} {base} />
+{/if}

site/src/pages/activity/index.astro

@@ -0,0 +1,7 @@
+---
+import Base from '../../layouts/Base.astro';
+import ActivityDetailLoader from '../../components/ActivityDetailLoader.svelte';
+---
+<Base title="Activity — BincioActivity">
+  <ActivityDetailLoader base={import.meta.env.BASE_URL} client:only="svelte" />
+</Base>