frontend: add WarnBanner Preact component, compose ApiErrorPanel from it

mara, on review: "i want each component to import its own css file
itself[;] if you need a bunch of extra css externally, its not a proper
component ... you may need to migrate other components that you would
want to use first".

WarnBanner is the Preact-component successor to the shadow-DOM
<hive-warn> custom element (same three-tier info/warning/error visual
language, colours copied faithfully from hive-warn.css). ApiErrorPanel
now composes it instead of owning a copy of the border/colour/pulse
rules itself — its own CSS is back down to just the layout that's
actually specific to it (heading, copy button, detail text).

Re-verified with a fresh mock-server screenshot: same rendered output as
before, now via composition instead of a duplicated banner shape.

frontend/packages/shared/package.json

@@ -34,7 +34,9 @@
     "./jobq-rollup.css": "./src/jobq-rollup/jobq-rollup.css",
     "./api-error.js": "./src/api-error.ts",
     "./api-error-panel.js": "./src/api-error-panel/ApiErrorPanel.tsx",
-    "./api-error-panel.css": "./src/api-error-panel/api-error-panel.css"
+    "./api-error-panel.css": "./src/api-error-panel/api-error-panel.css",
+    "./warn-banner.js": "./src/warn-banner/WarnBanner.tsx",
+    "./warn-banner.css": "./src/warn-banner/WarnBanner.css"
   },
   "files": [
     "src/"

frontend/packages/shared/src/api-error-panel/ApiErrorPanel.tsx

@@ -8,22 +8,20 @@
 // *that string was the entire diagnosis* — truncating it defeats the
 // point) — plus a copy button for pasting straight into a bug report.
 //
-// Deliberately NOT built on `<hive-warn>`, despite matching its visual
-// language, because that custom element's CSS-as-text import only
-// resolves under a build with `loader: 'text'` for `.css` (dashboard's);
-// swarm-ui's default `css` loader leaves its shadow `<style>` empty,
-// rendering unstyled with no build error (filed separately as a forge
-// issue against swarm-ui's build config). This component
-// is self-contained light-DOM instead, so it needs nothing beyond a
-// normal `.css` import either build already handles, matching
-// `JobqRollup`'s pattern. Colour semantics are still copied from
-// `hive-warn.css`'s `level="error"` rule on purpose — same look, no
-// shared shadow root.
+// Composed from `WarnBanner` (../warn-banner/WarnBanner.js) rather than
+// owning the border/colour/pulse styling itself — mara, on review: "i
+// want each component to import its own css file itself[;] if you need
+// a bunch of extra css externally, its not a proper component". This
+// file's own `.css` only lays out what's specific to it (heading, copy
+// button, detail text); the banner "shape" belongs to `WarnBanner` and
+// stays there so any future error/warning surface reuses it too, rather
+// than every caller growing its own copy of the same rules.
 //
 // Same shared-component shape as `JobqRollup`/`JobqGraph`:
 // `render(h(ApiErrorPanel, { problem }), container)` from vanilla JS, or
 // `<ApiErrorPanel problem={...} />` from swarm-ui's JSX.
 import { useState } from 'preact/hooks';
+import { WarnBanner } from '../warn-banner/WarnBanner.js';
 import type { ProblemDetails } from '../api-error.js';
 import './api-error-panel.css';
 
@@ -61,7 +59,7 @@ export function ApiErrorPanel({ problem, context }: ApiErrorPanelProps) {
   }
 
   return (
-    <div class="api-error-panel" role="alert">
+    <WarnBanner level="error" class="api-error-panel">
       <div class="api-error-heading">
         <span class="api-error-title">
           {context ? `${context}: ` : ''}
@@ -72,6 +70,6 @@ export function ApiErrorPanel({ problem, context }: ApiErrorPanelProps) {
         </button>
       </div>
       {problem.detail ? <p class="api-error-detail">{problem.detail}</p> : null}
-    </div>
+    </WarnBanner>
   );
 }

frontend/packages/shared/src/api-error-panel/api-error-panel.css

@@ -1,27 +1,12 @@
-/* api-error-panel.css — `<ApiErrorPanel>`'s own styling, colour + layout
-   both. Not slotted into `<hive-warn>` (see the component's own header
-   for why) — the border/background/pulse below are deliberately copied
-   from `hive-warn.css`'s `level="error"` rule rather than invented fresh,
-   so this still reads as "the same error banner" everywhere it appears,
-   just declared locally instead of shared through a shadow root. Reuses
-   theme.css's own documented semantics (`--red` = "errors, fail state"),
-   same as `hive-warn.css` does. */
+/* api-error-panel.css — layout for `<ApiErrorPanel>`'s content, plus the
+   one spacing concern that's genuinely this component's own (the top
+   margin — `WarnBanner` only sets `margin-bottom`, tuned for a banner
+   that's the first thing in a page, not a panel that usually follows a
+   form or a table). Colour/border/pulse belong to `WarnBanner`
+   (../warn-banner/WarnBanner.css) — not duplicated here. */
 
 .api-error-panel {
-  display: block;
   margin-top: 1em;
-  margin-bottom: 0.6em;
-  border: 1px solid var(--red);
-  border-radius: 4px;
-  padding: 0.5em 0.8em;
-  color: var(--red);
-  background: color-mix(in srgb, var(--red) 8%, transparent);
-  text-shadow: 0 0 6px color-mix(in srgb, currentColor 40%, transparent);
-  animation: api-error-panel-pulse 2.4s ease-in-out infinite;
-}
-@keyframes api-error-panel-pulse {
-  0%, 100% { box-shadow: 0 0 12px -4px color-mix(in srgb, currentColor 55%, transparent); }
-  50%      { box-shadow: 0 0 22px -2px color-mix(in srgb, currentColor 95%, transparent); }
 }
 .api-error-heading {
   display: flex;

frontend/packages/shared/src/warn-banner/WarnBanner.css

@@ -0,0 +1,36 @@
+/* WarnBanner.css — three levels, not an open-ended severity+modifier
+   combination (same rule `hive-warn.css` states, copied faithfully since
+   this is that component's visual language, just reached through a
+   class instead of a `:host([level])` attribute selector). Colours reuse
+   theme.css's own documented semantics: --cyan = "info accents", --amber
+   = "warnings", --red = "errors, fail state". */
+
+.warn-banner {
+  display: block;
+  border: 1px solid var(--amber);
+  border-radius: 4px;
+  padding: 0.5em 0.8em;
+  margin-bottom: 0.6em;
+  color: var(--amber);
+  background: color-mix(in srgb, var(--amber) 8%, transparent);
+}
+.warn-banner-info {
+  border-color: var(--cyan);
+  color: var(--cyan);
+  background: color-mix(in srgb, var(--cyan) 8%, transparent);
+}
+.warn-banner-error {
+  border-color: var(--red);
+  color: var(--red);
+  background: color-mix(in srgb, var(--red) 8%, transparent);
+  /* Only `error` pulses — an active incident, not a standing caveat. */
+  text-shadow: 0 0 6px color-mix(in srgb, currentColor 40%, transparent);
+  animation: warn-banner-pulse 2.4s ease-in-out infinite;
+}
+@keyframes warn-banner-pulse {
+  0%, 100% { box-shadow: 0 0 12px -4px color-mix(in srgb, currentColor 55%, transparent); }
+  50%      { box-shadow: 0 0 22px -2px color-mix(in srgb, currentColor 95%, transparent); }
+}
+.warn-banner strong {
+  color: inherit;
+}

frontend/packages/shared/src/warn-banner/WarnBanner.tsx

@@ -0,0 +1,38 @@
+// WarnBanner.tsx — <WarnBanner>, the Preact-component successor to the
+// shadow-DOM <hive-warn> custom element (../hive-warn/hive-warn.js).
+// Same three-tier visual language (mara, on `hive-warn`'s own review:
+// "there should be distinction between info, warning, error — all
+// warnings should be styled identically") — built as a plain Preact
+// component instead so it composes cleanly wherever this package's other
+// shared components do (JobqRollup, JobqGraph, ApiErrorPanel), rather
+// than needing a shadow root + CSS-as-text build step that only resolves
+// under one of the two consuming packages' esbuild configs. `ApiErrorPanel`
+// is the first consumer — compose from this instead of duplicating the
+// banner's own border/colour/pulse rules locally.
+//
+// `level` defaults to 'warning', matching `hive-warn.js`'s own default.
+// Only `error` pulses — an active incident, not a standing caveat, same
+// rule `hive-warn.css`'s own comment states.
+import type { ComponentChildren } from 'preact';
+import './WarnBanner.css';
+
+export type WarnLevel = 'info' | 'warning' | 'error';
+
+export interface WarnBannerProps {
+  level?: WarnLevel;
+  // Passed straight through to the root element's `class` list —
+  // for a caller-specific concern the banner itself has no opinion on
+  // (e.g. `ApiErrorPanel` adding a top margin for the context it usually
+  // sits in), not for re-styling the banner's own look.
+  class?: string;
+  children?: ComponentChildren;
+}
+
+export function WarnBanner({ level = 'warning', class: extraClass, children }: WarnBannerProps) {
+  const classes = ['warn-banner', `warn-banner-${level}`, extraClass].filter(Boolean).join(' ');
+  return (
+    <div class={classes} role={level === 'error' ? 'alert' : undefined}>
+      {children}
+    </div>
+  );
+}