Design tier-2 vue component delivery via httpVueLoader URL mode

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: maartenbreddels

notes.md

@@ -308,6 +308,40 @@ Measured before building tier-1 — and it would have been the wrong thing:
 - Minor: _remove_buffers/_separate_buffers walk all state values per open (~1.4% process);
   comm-creation machinery ~3.8%.
 
+## Tier-2 template/component delivery design (investigated 2026-06-12, late)
+
+Code reading (ipyvue repo, js/src + python) makes this much cheaper than feared:
+
+Mechanics today:
+- `VueTemplate.template = Union([Instance(Template), Unicode()])` — template-as-widget already
+  exists (used by template_file/get_template via per-kernel template_registry under solara).
+- JS `TemplateModel` is a trivial WidgetModel; `VueTemplateRenderer` reads `template` SYNCHRONOUSLY
+  at component build (async here needs renderer surgery).
+- JS `VueComponentModel` (the register_components path = leasing's ~30 components) feeds
+  `httpVueLoader(componentString)` — and the vendored httpVueLoader RETAINS its original HTTP
+  mode: `httpVueLoader.load(url, name)`, `httpRequest`, parseComponentURL, <style src> fetching.
+  URL mode = Vue ASYNC component factory, natively supported by Vue (no sync problem).
+
+Plan (minimal viable, VueComponent path first — exactly the leasing hot spot):
+1. ipyvue python: `VueComponent.component_url` trait; `register_component_from_string` consults a
+   pluggable module-level `url_provider(content) -> url|None`; if a URL comes back, sync
+   component_url instead of the source (component=None).
+2. ipyvue JS VueComponentModel: if component_url set -> `Vue.component(name, httpVueLoader.load(url))`
+   (existing code path); string mode unchanged.
+3. solara: content-hash store + immutable-cached route (e.g. /_solara/static/vue/<sha256>.vue),
+   installed as the url_provider at server start. Content-addressed URL = browser disk cache
+   across page loads => first load: 30 parallel HTTP/2 fetches off the websocket; repeat loads:
+   zero bytes, zero parse on the ws path.
+4. Phase 2: same treatment for Template widgets (template_url) — needs VueTemplateRenderer to go
+   async (placeholder + re-render on change:template, hot-reload listener machinery already exists).
+5. Compat: provider unset (jupyter/lab, voila) -> exact current behavior; solara pins matching
+   ipyvue python+JS via its bundle, so no runtime negotiation needed.
+Cost: ipyvue py (small), ipyvue JS (small for VueComponent, moderate for Template), solara endpoint
+(small), the real tax is the bundle rebuild chain (jupyter-vue -> solara-vuetify-app -> version bumps).
+
+Also noted: ipyvue get_template re-reads the .vue file from disk on every call even on registry
+hits (to support dev watching) — harmless under OS cache, but could be gated on a dev flag.
+
 ## Stash (possible bugs / questionable behavior found along the way)
 
 - pandas 3.0 re-render on equal DataFrame (see above) — env pin papering over it for now.