feat: support precompiled ES modules as template implementations

[maartenbreddels]

Lets a VueTemplate use a precompiled ES module export as its implementation, so .vue files can be built ahead of time instead of compiled in the browser.

Problem

Today every ipyvue template ships its .vue source to the browser, and the browser compiles it at runtime with vue/compiler-sfc.
Authors cannot use npm dependencies in a template without window-global hacks.
Template errors only show up when a user opens the page.
ipyreact already solves this for React with define_module; ipyvue (and Solara apps on Vue 3) had no equivalent.

Change

• ipyvue.define_module(name, module: Path=None, *, code=None, url=None, dependencies=None) ships an ES module once per kernel through es-module-shims and the import map.
  It has the same interface and default as ipyreact: without dependencies=, a module waits for every module defined before it whose widget is still open.
  Defining a name again updates its existing widget and keeps the name's first dependency list, the way Solara's esm_vue.py does.
• Template(esm_module=..., esm_export=...) uses one export as the template's implementation.
  The export's options are mixins[0] under the ipyvue model mixin, so Python traits override data() and Python event handlers override methods, the same precedence as compiled templates.
• components={"x": {"esm_module": ..., "esm_export": ...}} uses an export as a tag with its own props and events.
• A module whose default export is a Vue plugin ({ install(app) }) is installed on every app, current and future.
• Mounted views refresh through the existing change:template hot-reload path when a module is defined again, when esm_module, esm_export, components or events change, when a module that failed to load is fixed, and when a plugin loads after its tags already rendered (string templates, components strings, ESM templates and Html(tag=...)).
• The JS module registry keeps waiters alive across a reload and drops a load that a newer load replaced.

Validation

• CI is green on 575cb42, including 19 UI tests in tests/ui/test_esm_module.py and 6 unit tests in tests/unit/test_esm.py.
• The UI tests cover: module as template and as tag, plugin registration, a late plugin (string template, precompiled resolveComponent, Html tag), unrelated input text kept across a plugin load, module reload at the root, inside an ipyvuetify container, inside another template, and for a root plus embedded copy, components/esm_export changes, a failed import that is fixed later, dependency-only recovery, and a reload while a consumer waits.
• Workers ran these suites locally on each fix round; CI ran them on every push.

Gaps

• The VueTemplate data, methods and css traits are not applied to an ESM template.
• The module registry is global to the page, so two kernels in one JupyterLab page that define the same name share it.
• A refresh of a nested template remounts its whole view root, like the existing template hot reload does.
• A nested child that is hidden with v-if during a module reload shows the old export when it is shown again.
• A plugin tag inside another component's slot, or inside a globally registered VueComponent, is not refreshed after a late plugin load.
• A plugin that a module no longer exports after a reload stays installed. Blob URLs from reloads are not revoked.
• Precompiled <script setup> exports do not see Python traits.

Align results

Caution

/align was not run on this change: the design questions were settled with the maintainer in the session instead. They chose ipyreact parity for define_module (same interface and default, plus an explicit dependencies=), fixing the review findings in impact order, and then a simplification pass with Opus workers and astra and sol reviewers.

Crossreview results

• Rounds: 5. Rounds 1 to 3 used astra, sol and opus on c805c09, 27f8f61 and 2257752. The maintainer then asked for a simplification and for astra and sol only; rounds 4 and 5 reviewed 4c63437 and 575cb42.
• Final verdict: astra APPROVE, sol APPROVE on 575cb42.
• No CRITICAL or HIGH finding stands. The HIGH findings raised along the way, and their fixes:
  • define_module made every module depend on every name defined earlier in the Python process, so a second session or test deadlocked (a waits for b, b waits for a). This also made CI red. Fixed: the default skips closed modules, a redefinition updates the live widget, and a name keeps its first dependency list.
  • A late plugin load re-rendered every app and remounted unrelated widgets, losing typed text. Fixed by the simplification: only affected templates refresh.
  • A template whose first import failed never recovered. Fixed: the loading and error placeholders carry the refresh listener.
• Why these defects got in: the dependency default was copied from ipyreact without considering several sessions in one process; the first refresh design assumed a root re-render reaches nested children, which is wrong in Vue 3; listeners lived only in the resolved async component.
• Small fixes and confirmers: the redefinition fix (Solara parity) was confirmed by the reviewer who raised it on the Vue 2 PR, then ported here.
• Constitution changes that could have prevented them: a brief that copies a design from a sibling library names that library's assumptions to check (here: one session per process); a refresh design for a component tree names the nesting cases it must cover before implementation.

🤖 Generated with Claude Code

[maartenbreddels]

API update on the branch: define_module now takes exactly one of module (a Path), code= or url= — nothing is guessed from a plain str (also mirrored in ipyreact#80 and solara#1169).