feat: kernel-aware ES module support for ipyvue

[maartenbreddels]

Summary

Companion to widgetti/ipyvue#106 (ipyvue's vue3 branch gains define_module for precompiled ESM bundles). This gives those modules the same server-side handling ipyreact modules get in solara/server/esm.py:

• definitions recorded once (module level), Module widgets materialized per kernel inside the kernel context
• widgets recreated when context.restart() closed them, so in-place hot reload works (same fix as fix: make ES module (define_module) hot reload survive in-place app reload #1168)
• define_module(Path) registered with the reloader — rebuilding a bundle (vite build --watch) triggers a normal in-place reload
• per-kernel bookkeeping dropped on kernel close; _modules mutation locked

Everything is hasattr(ipyvue, "define_module")-gated, so it is a no-op on current ipyvue releases; the unit tests skip likewise until an ipyvue release ships the feature (verified 5/5 passing locally against the ipyvue#106 branch).

Url modules: preload + content-hash caching

define_module takes exactly one of module (a Path), code= or url= (nothing is guessed from a plain str); url= serves the bundle from the app's static dir. For urls solara serves itself (/static/public/...):

• the page emits <link rel="modulepreload" href=".../bundle.mjs?v=<content-hash>">, so the browser fetches the bundle in parallel with kernel startup instead of waiting for the Module widget over the websocket (es-module-shims honors modulepreload in shim mode);
• the same versioned url is used for the hint and the widget (one helper, esm_vue.versioned_url), so the preload is always a cache hit;
• StaticPublic serves the file with Cache-Control: max-age=1y, immutable only when the requested ?v matches the current content hash — rebuilds change the hash and therefore the url (automatic cache busting), stale hashes get normal headers (no poisoning). External urls and urls with their own query string pass through untouched.

This generalizes the existing nbextension-hash mechanism (nbextensions_hashes + requirejs urlArgs) to app-served ES modules.

Documentation

Includes a website howto page (documentation/advanced/howto/vue-esm-components) with a complete runnable example (verified end to end locally against the ipyvue#106 branch: renders, click events reach Python, trait updates re-render) plus the vite workflow and the tag form.

Usage (once ipyvue#106 is released)

solara.component_vue gains esm_module/esm_export as an alternative to vue_path:

import ipyvue
import solara

# build .vue SFCs ahead of time with vite (vue external, npm deps bundled);
# solara watches the file, so `vite build --watch` gives in-place hot reload
ipyvue.define_module("my-components", Path(__file__).parent / "dist/my-components.mjs")


@solara.component_vue(esm_module="my-components", esm_export="Counter")
def Counter(count: int = 0, event_bump: Callable[[int], None] = None):
    pass

Same contract as a .vue-file component: arguments become Vue data (overriding the component's own data() placeholders), event_* arguments become callable methods. The howto page in this PR contains a complete no-build-step runnable example (verified end to end against the ipyvue#106 branch: renders, clicks reach Python, state re-renders) plus the vite workflow and the tag form.

No template source goes over the wire and vue/compiler-sfc is not needed at runtime for these components. Coexists with ipyreact modules on the same page (verified; registries are separate, the import-map namespace is shared so module names must be unique across libraries).