docs(devops): add Nginx caching investigation task for app version pickup issue

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

documentation/TODO__Agents.md

@@ -494,6 +494,23 @@ Firefox unaffected. Production unaffected (public IPs only).
   ago and regressed. Check Nginx site config and FastAPI `CORSMiddleware` settings.
   Low urgency (dev-only, Firefox workaround available), but blocks home-network iframe testing.
 
+### [DevOps] Nginx caching — app version pickup issue
+- [ ] **Investigate Nginx reverse proxy caching so users pick up new app deploys.**
+  Some users are not getting the updated app after a deploy. SvelteKit hashes JS/CSS bundle
+  filenames (cache-busting is automatic), but if Nginx or the browser caches `index.html`
+  itself, users get stale HTML pointing to old (possibly deleted) hashed assets.
+
+  **Check:**
+  - `proxy_cache` / `expires` directives in Nginx config for the SvelteKit app location
+  - Actual `Cache-Control` header on `/` — `curl -I https://<host>/` to verify
+  - Any service worker registration that might add another caching layer
+
+  **Expected fix:** Serve `index.html` with `Cache-Control: no-cache` (or `no-store`).
+  Hashed static assets (`/_app/immutable/`) can stay aggressively cached (`max-age=31536000,
+  immutable`). Root page must always be fresh so users pick up the new bundle references.
+
+  **Task ID:** #182928308 (shared Kanban)
+
 ### [DevOps] Remaining deployment items
 
 - [ ] **Simplify Dockerfile env file selection** — Currently the Dockerfile uses a `BUILD_MODE` arg to