feat: precompiled ES module support (vue2)

[maartenbreddels]

Brings precompiled ES module support from the Vue 3 line (#106) to the Vue 2 1.x line, so current Solara apps can use .vue files built ahead of time.

Problem

Today every ipyvue template ships its .vue source to the browser, and the browser compiles it at runtime.
Authors cannot use npm dependencies in a template without window-global hacks, and template errors only show up when a user opens the page.
Most production apps still run on Vue 2 (1.x), so they cannot wait for a Vue 3 migration to get this.

Change

• ipyvue.define_module(name, module: Path=None, *, code=None, url=None, dependencies=None) ships a precompiled bundle (for example vite with vue external) through es-module-shims and an import map in which vue is the running Vue 2.
  It has the same interface and default as ipyreact and #106: without dependencies=, a module waits for every module defined before it whose widget is still open.
  Defining a name again updates its widget and keeps the name's first dependency list, like Solara's esm_vue.py.
• Template(esm_module=..., esm_export=...) uses an export as a VueTemplate's implementation, with the export's options as mixins[0] under the model mixin.
• components={"x": {"esm_module": ..., "esm_export": ...}} uses an export as a tag. A module whose default export is a plugin ({ install }) is Vue.used.
• Each ES module is a reactive cell. An ESM template is a functional holder that reads the cell and a per-model version, so it re-renders by itself after a module reload or an esm_module, esm_export, components or events change. Refs, events and slots pass through to the export. Ordinary compiled templates render exactly as on 1.x.
• After a plugin installs, mounted templates and VueWidget tags re-render, so tags that rendered before the plugin resolve without remounting unrelated widgets.
• Model listeners of a template instance are detached when it is destroyed, also for compiled templates.

Validation

• CI is green on the PR, including 27 UI tests in tests/ui/test_esm_module.py and 6 unit tests in tests/unit/test_esm.py.
• The UI tests cover: plugin registration and late plugin loads (string template, precompiled export, Html tag) without losing unrelated input text, module as template and as tag, module reload at the root, inside an ipyvuetify container, and inside another template, components/esm_export changes, refs, slots and events through components, switching esm_module on and off on a mounted Template, 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

• Only precompiled components can use ESM syntax. VueTemplate <script> blocks keep module.exports, because they are evaluated with new Function.
• 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 page that define the same name share it.
• A plugin hot reload that replaces a component already mounted through a VueWidget tag, and a Template replaced while its widget is hidden, keep the old implementation until the next re-render.
• After a mounted Template switches from ESM back to compiled, its $parent is the holder's wrapper until an ancestor re-renders.
• Plugins must be objects with install; function-form Vue 2 plugins are not installed. Blob URLs from reloads are not revoked.

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, a simplification pass with Opus workers and astra and sol reviewers, and no production cost for widgets that do not use ES modules.

Crossreview results

• Rounds: 7. Rounds 1 to 5 used astra, sol and opus on e8edbd8, 36005aa, 8e479d1, c7cd6a8 and 8bdc302. The maintainer then asked for a simplification and for astra and sol only; rounds 6 and 7 reviewed 20aad71 and 61bf824. A last confirmation reviewed bd3c154.
• Final verdict: astra and sol APPROVE on 61bf824. On bd3c154 both confirmed their earlier MEDIUMs fixed and each raised one narrow issue about switching esm_module off on a mounted Template; astra's was fixed in 916db4c, sol's is listed under Gaps.
• 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 process; a second session, a test run, or a re-run cell after a page reload deadlocked (a waits for b, b waits for a). Fixed: the default skips closed modules, a redefinition updates the live widget, and a name keeps its first dependency list.
  • A VueWidget tag such as Html(tag="late-tag") stayed unresolved after its plugin's first load. Fixed: VueModel renderers re-render after a plugin installs.
• Why these defects got in: the dependency default was copied from ipyreact without considering several sessions in one process; refresh fixes were added one review finding at a time, and the accumulated machinery (owner tracking, child-cache edits, wrappers) caused regressions such as lost refs, slots and sibling state until the simplification replaced it with a reactive module cell.
• Small fixes and confirmers: the redefinition fix (b30553f) was confirmed by opus, which raised it; the change:dependencies listener (98303bc) was confirmed by the driver; the stable compiled component (916db4c) by astra, which raised it.
• 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); after two fix rounds on the same mechanism, re-design it before a third fix.

🤖 Generated with Claude Code

[maartenbreddels]

Build artifacts removed from this branch (squashed to one source-only commit). Installable variant lives on feat/esm-modules-1.x-dist = this branch + one prebuilt-frontend commit (never to be merged); GrottoAI/exploration#2424 installs from that.

🤖 Generated with Claude Code

[maartenbreddels]

Same API update as #106: define_module(name, module: Path | None, *, code=..., url=...) — exactly one, nothing guessed from a plain str. The -dist install branch is regenerated on top.