frontend: hive-btn — drop the is= customized-built-in, use an autonomous element instead

Per review: don't use is=, it reads as a hack (and it is one — is=-upgraded
built-ins can never host a shadow root, which is what caused the crash this PR
fixes in the first place). <hive-btn> is now a normal autonomous custom element
wrapping a real <button> inside its own shadow root, so it gets its shadow
encapsulation back (matching hive-dialog/hive-toast) instead of the document-
level stylesheet workaround from the previous commit.

delegatesFocus: true on the shadow root means .focus() on the host (what
modal.js calls for autofocus) reaches the inner button directly. The inner
button's native click is a composed event, so host-level click listeners
(what modal.js/themedPrompt already use) keep working unchanged.

modal.js: el('button', { is: 'hive-btn', ... }) -> el('hive-btn', { ... }) at
the one call site. dom.js: removed the is= special case from el() entirely —
it existed only to support this one now-gone usage. Build clean.

frontend/packages/shared/src/dom.js

@@ -5,18 +5,15 @@
 // used).
 //
 // `el(tag, attrs, ...children)` creates an element, applying `attrs` as
-// either the `class`/`html`/`is` special cases or plain attributes, and
+// either the `class`/`html` special cases or plain attributes, and
 // appending `children` (strings become text nodes, `null`/`undefined`
 // entries are skipped so callers can inline conditional children).
-// `is: 'custom-name'` creates a customized built-in element (e.g.
-// `el('button', { is: 'hive-btn' }, 'label')` → `<button is="hive-btn">`)
-// — passed to `document.createElement` itself, since a customized
-// built-in has to be created with its `is` option up front, not upgraded
-// after the fact via `setAttribute`.
+// `tag` can be any custom element's tag name too (e.g. `el('hive-btn',
+// { variant: 'danger' }, 'label')`) — `document.createElement` upgrades
+// it automatically if the tag is already registered.
 export const el = (tag, attrs = {}, ...children) => {
-  const e = attrs.is ? document.createElement(tag, { is: attrs.is }) : document.createElement(tag);
+  const e = document.createElement(tag);
   for (const [k, v] of Object.entries(attrs)) {
-    if (k === 'is') continue;
     if (k === 'class') e.className = v;
     else if (k === 'html') e.innerHTML = v;
     else e.setAttribute(k, v);

frontend/packages/shared/src/hive-btn.css

@@ -1,15 +1,24 @@
-/* hive-btn.css — scoped stylesheet for the <hive-btn> customized built-in
-   button element (hive-btn.js). Loaded as raw text at build time
-   (esbuild's `text` loader) and turned into a `CSSStyleSheet` adopted by
-   the element's own shadow root. `:host` styles the button itself (the
-   element *is* a real `<button is="hive-btn">`, so `:host(:hover)` /
-   `:host(:disabled)` select genuine native pseudo-classes, not
-   hand-rolled state tracking) — this is the base look every `<hive-btn>`
-   gets; `variant` is an attribute (not a class) since it's a semantic
-   property of the component, not an arbitrary styling hook. */
+/* hive-btn.css — shadow-DOM stylesheet for the <hive-btn> autonomous
+   custom element (hive-btn.js). Loaded as raw text at build time
+   (esbuild's `text` loader) and adopted into each instance's own shadow
+   root. `:host` is an invisible wrapper (`display: contents`) — the
+   real box is the plain `button` selector below, targeting the actual
+   `<button>` the shadow root wraps (scope-isolated by the shadow
+   boundary already, no clash risk with anything outside). `variant` is
+   an attribute on the HOST (how callers set it, and where hive-dialog's
+   own selectors read it back); `:host([variant="…"])` sets `color`,
+   which then inherits down into the shadow tree the normal way. */
 
 :host {
+  display: contents;
+}
+:host([variant="cancel"]) { color: var(--subtext0); }
+:host([variant="confirm"]) { color: var(--green); }
+:host([variant="danger"]) { color: var(--red); }
+
+button {
   font-family: inherit;
+  font-size: inherit;
   font-weight: bold;
   text-transform: uppercase;
   letter-spacing: 0.1em;
@@ -24,17 +33,14 @@
   box-shadow: 0 0 0 0 currentColor;
   transition: box-shadow 0.15s ease;
 }
-:host(:hover) {
+button:hover {
   background: color-mix(in srgb, var(--fg) 6%, transparent);
   text-shadow: 0 0 10px currentColor;
   box-shadow: 0 0 10px -2px currentColor;
 }
-:host(:disabled) {
+button:disabled {
   opacity: 0.32;
   cursor: not-allowed;
   text-shadow: none;
   box-shadow: none;
 }
-:host([variant="cancel"]) { color: var(--subtext0); }
-:host([variant="confirm"]) { color: var(--green); }
-:host([variant="danger"]) { color: var(--red); }

frontend/packages/shared/src/hive-btn.js

@@ -1,40 +1,58 @@
-// hive-btn.js — <hive-btn>, a customized built-in `<button>` (`<button
-// is="hive-btn">`) with a shadow root for style encapsulation, replacing
-// the light-DOM `.btn` class as the button primitive for shadow-DOM
-// consumers (starting with modal.js's dialog buttons — see the frontend
-// components-split discussion on the forge issue tracker).
+// hive-btn.js — <hive-btn>, the button primitive for modal.js's dialog
+// buttons. Autonomous custom element (previously a customized built-in,
+// `<button is="hive-btn">` — dropped: `is=` upgrades can't host a shadow
+// root at all, which crashed every themed dialog, and reads as a hack
+// regardless once you know that). A real `<button>` lives inside the
+// shadow root instead, so native click/keyboard activation and
+// `:disabled` still come for free — just one level down from the host.
 //
-// Extending `HTMLButtonElement` (a "customized built-in element", not an
-// autonomous one) keeps every native `<button>` behaviour for free —
-// click/keyboard activation, `:disabled`, form participation/submission —
-// instead of re-implementing them on a generic wrapper. The shadow root
-// holds only a `<style>`-equivalent (adopted stylesheet) plus a `<slot>`
-// so the button's light-DOM content (its label, or asyncBtn's swapped-in
-// spinner span) renders through unchanged — slotted content stays styled
-// by the light-DOM cascade (global `.spinner` etc. still apply), only the
-// host element's own box/text styling is shadow-scoped.
+// `delegatesFocus: true` on the shadow root means `.focus()` on the host
+// (what modal.js calls) focuses the inner button directly, and a click
+// anywhere on the host focuses it too, matching native `<button>` feel.
+// The inner button's native `click` is a composed event, so it bubbles
+// out through the shadow boundary — callers add `click` listeners on the
+// `<hive-btn>` host exactly as they would on a plain `<button>`.
 //
-// Customized built-ins aren't supported in Safari/WebKit (a deliberate
-// WebKit-team stance, unlikely to change) — fine here since the project
-// targets recent Firefox only.
-//
-// Usage: `el('button', { type: 'button', is: 'hive-btn', variant: 'danger' }, 'label')`
-// (dom.js's `el()` passes `is` to `document.createElement` so custom-
-// element upgrade happens at creation, not after). `variant` is one of
-// 'cancel' | 'confirm' | 'danger' | (unset, for the neutral/default look)
-// — a plain attribute, not a class, since it's a semantic prop of the
-// component rather than an arbitrary styling hook.
+// Usage: `el('hive-btn', { type: 'button', variant: 'danger' }, 'label')`.
+// `variant` ∈ 'cancel' | 'confirm' | 'danger' | unset (neutral default) —
+// reflected straight through to the inner button so hive-btn.css's
+// `:host([variant="…"])` selectors keep working unchanged.
+// `disabled`/`type` are likewise plain attributes on the host, mirrored
+// onto the inner button on connect and on every attribute change.
 
 import hiveBtnCss from './hive-btn.css';
 
-class HiveBtn extends HTMLButtonElement {
+const OBSERVED = ['disabled', 'type'];
+
+class HiveBtn extends HTMLElement {
+  static get observedAttributes() {
+    return OBSERVED;
+  }
+
   connectedCallback() {
-    if (this.shadowRoot) return; // guard: connectedCallback can re-fire (e.g. re-parenting)
-    const root = this.attachShadow({ mode: 'open' });
+    if (this._btn) {
+      this._sync();
+      return; // already built (e.g. re-parenting re-fires connectedCallback)
+    }
+    const root = this.attachShadow({ mode: 'open', delegatesFocus: true });
     const sheet = new CSSStyleSheet();
     sheet.replaceSync(hiveBtnCss);
     root.adoptedStyleSheets = [sheet];
-    root.append(document.createElement('slot'));
+    const btn = document.createElement('button');
+    btn.append(document.createElement('slot'));
+    root.append(btn);
+    this._btn = btn;
+    this._sync();
+  }
+
+  attributeChangedCallback() {
+    this._sync();
+  }
+
+  _sync() {
+    if (!this._btn) return;
+    this._btn.disabled = this.hasAttribute('disabled');
+    this._btn.type = this.getAttribute('type') || 'button';
   }
 }
-customElements.define('hive-btn', HiveBtn, { extends: 'button' });
+customElements.define('hive-btn', HiveBtn);

frontend/packages/shared/src/modal.js

@@ -4,15 +4,13 @@
 // actions and prompts match each page's chrome instead of a jarring OS
 // dialog.
 //
-// Implemented as two shadow-DOM custom elements (`<hive-dialog>`,
-// `<hive-toast>`), plus `<hive-btn>` (hive-btn.js) for the dialog's own
-// buttons — real per-component style encapsulation, CSS in real `.css`
-// files imported as raw text (see each component's own header comment
-// for the design rationale: shadow-DOM-vs-light-DOM tradeoffs live atop
-// the `<hive-dialog>`/`<hive-toast>` classes below, the customized-
-// built-in choice lives in hive-btn.js). Other `.btn` consumers across
-// the app stay on the light-DOM `.btn` class for now — migrating them
-// is a separate follow-up.
+// Implemented as three shadow-DOM custom elements (`<hive-dialog>`,
+// `<hive-toast>`, and `<hive-btn>` for the dialog's own buttons) — real
+// per-component style encapsulation, CSS in real `.css` files imported
+// as raw text (see each component's own header comment for the design
+// rationale). Other `.btn` consumers across the app stay on the
+// light-DOM `.btn` class for now — migrating them is a separate
+// follow-up.
 //
 // `openDialog` is the general primitive (any title/message/content + a row of
 // buttons); `themedConfirm` is a thin cancel/confirm wrapper with optional
@@ -78,8 +76,8 @@ class HiveDialog extends HTMLElement {
       // overrides it to the 'danger' look regardless (a destructive
       // confirm button reads as danger, not as a plain confirm).
       const variant = b.danger ? 'danger' : b.class;
-      const btn = el('button', {
-        type: 'button', is: 'hive-btn',
+      const btn = el('hive-btn', {
+        type: 'button',
         ...(variant ? { variant } : {}),
       }, b.label);
       btn.addEventListener('click', () => done(b.value));