feat(ui): add decorative style primitives

src/lib/ui/components/CornerBracketFrame.svelte

@@ -0,0 +1,97 @@
+<script lang="ts">
+  let {
+    density = "regular",
+    size = "md",
+    tone = "neutral",
+  }: {
+    density?: "regular" | "tight";
+    size?: "sm" | "md" | "lg";
+    tone?: "neutral" | "accent" | "danger";
+  } = $props();
+</script>
+
+<div
+  class="corner-bracket-frame"
+  data-density={density}
+  data-size={size}
+  data-tone={tone}
+  aria-hidden="true"
+>
+  <span data-corner="top-left"></span>
+  <span data-corner="top-right"></span>
+  <span data-corner="bottom-left"></span>
+  <span data-corner="bottom-right"></span>
+</div>
+
+<style>
+  .corner-bracket-frame {
+    --corner-color: var(--ui-color-line-strong);
+    --corner-offset: 0.5rem;
+    --corner-size: 1.45rem;
+    position: relative;
+    min-height: 5rem;
+    border: 1px solid transparent;
+    background:
+      linear-gradient(90deg, color-mix(in srgb, var(--corner-color), transparent 78%) 1px, transparent 1px),
+      linear-gradient(color-mix(in srgb, var(--corner-color), transparent 84%) 1px, transparent 1px),
+      rgba(2, 3, 2, 0.64);
+    background-size: 2rem 2rem, 2rem 2rem, auto;
+  }
+
+  span {
+    position: absolute;
+    width: var(--corner-size);
+    height: var(--corner-size);
+    border-color: var(--corner-color);
+  }
+
+  [data-corner="top-left"] {
+    top: var(--corner-offset);
+    left: var(--corner-offset);
+    border-top: 1px solid;
+    border-left: 1px solid;
+  }
+
+  [data-corner="top-right"] {
+    top: var(--corner-offset);
+    right: var(--corner-offset);
+    border-top: 1px solid;
+    border-right: 1px solid;
+  }
+
+  [data-corner="bottom-left"] {
+    bottom: var(--corner-offset);
+    left: var(--corner-offset);
+    border-bottom: 1px solid;
+    border-left: 1px solid;
+  }
+
+  [data-corner="bottom-right"] {
+    right: var(--corner-offset);
+    bottom: var(--corner-offset);
+    border-right: 1px solid;
+    border-bottom: 1px solid;
+  }
+
+  .corner-bracket-frame[data-density="tight"] {
+    --corner-offset: 0.28rem;
+  }
+
+  .corner-bracket-frame[data-size="sm"] {
+    --corner-size: 0.95rem;
+    min-height: 3rem;
+  }
+
+  .corner-bracket-frame[data-size="lg"] {
+    --corner-size: 2.25rem;
+    min-height: 8rem;
+  }
+
+  .corner-bracket-frame[data-tone="accent"] {
+    --corner-color: var(--ui-color-accent);
+  }
+
+  .corner-bracket-frame[data-tone="danger"] {
+    --corner-color: var(--ui-color-danger);
+  }
+</style>

src/lib/ui/components/DiagonalStripeField.svelte

@@ -0,0 +1,77 @@
+<script lang="ts">
+  let {
+    density = "regular",
+    direction = "forward",
+    size = "md",
+    tone = "accent",
+  }: {
+    density?: "open" | "regular" | "tight";
+    direction?: "forward" | "backward";
+    size?: "sm" | "md" | "lg";
+    tone?: "neutral" | "accent" | "warning" | "danger";
+  } = $props();
+</script>
+
+<div
+  class="diagonal-stripe-field"
+  data-density={density}
+  data-direction={direction}
+  data-size={size}
+  data-tone={tone}
+  aria-hidden="true"
+></div>
+
+<style>
+  .diagonal-stripe-field {
+    --stripe-angle: 135deg;
+    --stripe-color: var(--ui-color-line-strong);
+    --stripe-gap: 1.1rem;
+    --stripe-width: 0.18rem;
+    display: block;
+    min-height: 3rem;
+    border: var(--ui-border);
+    background:
+      repeating-linear-gradient(
+        var(--stripe-angle),
+        transparent 0 var(--stripe-gap),
+        color-mix(in srgb, var(--stripe-color), transparent 26%) var(--stripe-gap)
+          calc(var(--stripe-gap) + var(--stripe-width))
+      ),
+      linear-gradient(90deg, rgba(255, 255, 255, 0.05), transparent 42%),
+      rgba(2, 3, 2, 0.82);
+  }
+
+  .diagonal-stripe-field[data-direction="backward"] {
+    --stripe-angle: 45deg;
+  }
+
+  .diagonal-stripe-field[data-density="open"] {
+    --stripe-gap: 1.65rem;
+    --stripe-width: 0.16rem;
+  }
+
+  .diagonal-stripe-field[data-density="tight"] {
+    --stripe-gap: 0.72rem;
+    --stripe-width: 0.14rem;
+  }
+
+  .diagonal-stripe-field[data-size="sm"] {
+    min-height: 1.75rem;
+  }
+
+  .diagonal-stripe-field[data-size="lg"] {
+    min-height: 5.5rem;
+  }
+
+  .diagonal-stripe-field[data-tone="accent"] {
+    --stripe-color: var(--ui-color-accent);
+  }
+
+  .diagonal-stripe-field[data-tone="warning"] {
+    --stripe-color: var(--ui-color-warning);
+  }
+
+  .diagonal-stripe-field[data-tone="danger"] {
+    --stripe-color: var(--ui-color-danger);
+  }
+</style>

src/lib/ui/components/ScanlineField.svelte

@@ -0,0 +1,66 @@
+<script lang="ts">
+  let {
+    intensity = "medium",
+    size = "md",
+    tone = "neutral",
+  }: {
+    intensity?: "soft" | "medium" | "hard";
+    size?: "sm" | "md" | "lg";
+    tone?: "neutral" | "accent" | "warning";
+  } = $props();
+</script>
+
+<div
+  class="scanline-field"
+  data-intensity={intensity}
+  data-size={size}
+  data-tone={tone}
+  aria-hidden="true"
+></div>
+
+<style>
+  .scanline-field {
+    --scan-color: rgba(243, 244, 237, 0.12);
+    --scan-gap: 0.48rem;
+    --scan-weight: 1px;
+    display: block;
+    min-height: 4rem;
+    border: var(--ui-border);
+    background:
+      radial-gradient(circle at 18% 24%, color-mix(in srgb, var(--scan-color), transparent 35%) 0 1px, transparent 2px),
+      radial-gradient(circle at 76% 62%, color-mix(in srgb, var(--scan-color), transparent 44%) 0 1px, transparent 2px),
+      repeating-linear-gradient(
+        180deg,
+        transparent 0 calc(var(--scan-gap) - var(--scan-weight)),
+        var(--scan-color) calc(var(--scan-gap) - var(--scan-weight)) var(--scan-gap)
+      ),
+      rgba(6, 7, 6, 0.78);
+    background-size: 3.1rem 3.1rem, 4.7rem 4.7rem, auto, auto;
+  }
+
+  .scanline-field[data-intensity="soft"] {
+    --scan-color: rgba(243, 244, 237, 0.07);
+    --scan-gap: 0.62rem;
+  }
+
+  .scanline-field[data-intensity="hard"] {
+    --scan-color: rgba(215, 255, 0, 0.2);
+    --scan-gap: 0.36rem;
+  }
+
+  .scanline-field[data-size="sm"] {
+    min-height: 2rem;
+  }
+
+  .scanline-field[data-size="lg"] {
+    min-height: 6.25rem;
+  }
+
+  .scanline-field[data-tone="accent"] {
+    --scan-color: rgba(215, 255, 0, 0.16);
+  }
+
+  .scanline-field[data-tone="warning"] {
+    --scan-color: rgba(255, 176, 32, 0.16);
+  }
+</style>

src/lib/ui/components/SignalTrace.svelte

@@ -0,0 +1,112 @@
+<script lang="ts">
+  let {
+    density = "regular",
+    orientation = "horizontal",
+    tone = "accent",
+  }: {
+    density?: "regular" | "tight";
+    orientation?: "horizontal" | "vertical";
+    tone?: "neutral" | "accent" | "warning";
+  } = $props();
+</script>
+
+<div
+  class="signal-trace"
+  data-density={density}
+  data-orientation={orientation}
+  data-tone={tone}
+  aria-hidden="true"
+>
+  <span class="signal-trace__rail"></span>
+  <span class="signal-trace__node" data-node="start"></span>
+  <span class="signal-trace__node" data-node="middle"></span>
+  <span class="signal-trace__node" data-node="end"></span>
+</div>
+
+<style>
+  .signal-trace {
+    --trace-color: var(--ui-color-accent);
+    --trace-track: min(100%, 20rem);
+    position: relative;
+    display: block;
+    width: 100%;
+    min-height: 1.5rem;
+  }
+
+  .signal-trace__rail {
+    position: absolute;
+    inset: 50% 0 auto;
+    height: 1px;
+    background:
+      linear-gradient(90deg, transparent, var(--trace-color) 18%, var(--trace-color) 82%, transparent),
+      linear-gradient(90deg, transparent 0 35%, rgba(255, 255, 255, 0.42) 35% 38%, transparent 38%);
+  }
+
+  .signal-trace__node {
+    position: absolute;
+    top: 50%;
+    width: 0.55rem;
+    height: 0.55rem;
+    border: 1px solid var(--trace-color);
+    background: var(--ui-color-canvas);
+    transform: translate(-50%, -50%) rotate(45deg);
+  }
+
+  .signal-trace__node[data-node="start"] {
+    left: 18%;
+  }
+
+  .signal-trace__node[data-node="middle"] {
+    left: 50%;
+  }
+
+  .signal-trace__node[data-node="end"] {
+    left: 82%;
+  }
+
+  .signal-trace[data-density="tight"] {
+    min-height: 0.95rem;
+  }
+
+  .signal-trace[data-density="tight"] .signal-trace__node {
+    width: 0.38rem;
+    height: 0.38rem;
+  }
+
+  .signal-trace[data-orientation="vertical"] {
+    width: 1.5rem;
+    min-height: 12rem;
+  }
+
+  .signal-trace[data-orientation="vertical"] .signal-trace__rail {
+    inset: 0 auto 0 50%;
+    width: 1px;
+    height: auto;
+    background:
+      linear-gradient(180deg, transparent, var(--trace-color) 18%, var(--trace-color) 82%, transparent),
+      linear-gradient(180deg, transparent 0 35%, rgba(255, 255, 255, 0.42) 35% 38%, transparent 38%);
+  }
+
+  .signal-trace[data-orientation="vertical"] .signal-trace__node[data-node="start"] {
+    top: 18%;
+    left: 50%;
+  }
+
+  .signal-trace[data-orientation="vertical"] .signal-trace__node[data-node="middle"] {
+    top: 50%;
+    left: 50%;
+  }
+
+  .signal-trace[data-orientation="vertical"] .signal-trace__node[data-node="end"] {
+    top: 82%;
+    left: 50%;
+  }
+
+  .signal-trace[data-tone="neutral"] {
+    --trace-color: var(--ui-color-line-strong);
+  }
+
+  .signal-trace[data-tone="warning"] {
+    --trace-color: var(--ui-color-warning);
+  }
+</style>

src/lib/ui/index.ts

@@ -1,7 +1,9 @@
 export { default as Badge } from "./components/Badge.svelte";
 export { default as Button } from "./components/Button.svelte";
+export { default as CornerBracketFrame } from "./components/CornerBracketFrame.svelte";
 export { default as DashboardHeader } from "./components/DashboardHeader.svelte";
 export { default as DashboardFrame } from "./components/DashboardFrame.svelte";
+export { default as DiagonalStripeField } from "./components/DiagonalStripeField.svelte";
 export { default as FooterCell } from "./components/FooterCell.svelte";
 export { default as FooterStatusCell } from "./components/FooterStatusCell.svelte";
 export { default as GridFrame } from "./components/GridFrame.svelte";
@@ -14,6 +16,8 @@ export { default as Separator } from "./components/Separator.svelte";
 export { default as ServiceGroupPanel } from "./components/ServiceGroupPanel.svelte";
 export { default as ServicePanel } from "./components/ServicePanel.svelte";
 export { default as ServiceRow } from "./components/ServiceRow.svelte";
+export { default as ScanlineField } from "./components/ScanlineField.svelte";
+export { default as SignalTrace } from "./components/SignalTrace.svelte";
 export { default as Sparkline } from "./components/Sparkline.svelte";
 export { default as StatusBadge } from "./components/StatusBadge.svelte";
 export { default as StatusStrip } from "./components/StatusStrip.svelte";

src/lib/ui/stories/CornerBracketFrame.stories.svelte

@@ -0,0 +1,22 @@
+<script module lang="ts">
+  import { defineMeta } from "@storybook/addon-svelte-csf";
+  import CornerBracketFrame from "../components/CornerBracketFrame.svelte";
+  import GridFrame from "../components/GridFrame.svelte";
+
+  const { Story } = defineMeta({
+    title: "Style Primitives/CornerBracketFrame",
+    component: CornerBracketFrame,
+    tags: ["autodocs"],
+  });
+</script>
+
+<Story name="Neutral Medium" args={{ tone: "neutral", size: "md" }} />
+<Story name="Accent Tight" args={{ tone: "accent", density: "tight" }} />
+<Story name="Large Danger" args={{ tone: "danger", size: "lg" }} />
+<Story name="Grid Set" asChild>
+  <GridFrame density="compact">
+    <CornerBracketFrame tone="neutral" size="sm" />
+    <CornerBracketFrame tone="accent" size="sm" />
+    <CornerBracketFrame tone="danger" size="sm" density="tight" />
+  </GridFrame>
+</Story>

src/lib/ui/stories/DiagonalStripeField.stories.svelte

@@ -0,0 +1,23 @@
+<script module lang="ts">
+  import { defineMeta } from "@storybook/addon-svelte-csf";
+  import DiagonalStripeField from "../components/DiagonalStripeField.svelte";
+  import Panel from "../components/Panel.svelte";
+  import SignalTrace from "../components/SignalTrace.svelte";
+
+  const { Story } = defineMeta({
+    title: "Style Primitives/DiagonalStripeField",
+    component: DiagonalStripeField,
+    tags: ["autodocs"],
+  });
+</script>
+
+<Story name="Accent Regular" args={{ density: "regular", tone: "accent", size: "md" }} />
+<Story name="Tight Warning" args={{ density: "tight", tone: "warning", direction: "backward" }} />
+<Story name="Large Danger" args={{ density: "open", tone: "danger", size: "lg" }} />
+<Story name="Composed Divider" asChild>
+  <Panel title="Generic Surface">
+    <DiagonalStripeField density="tight" size="sm" />
+    <SignalTrace tone="accent" />
+    <DiagonalStripeField direction="backward" tone="neutral" />
+  </Panel>
+</Story>

src/lib/ui/stories/ScanlineField.stories.svelte

@@ -0,0 +1,20 @@
+<script module lang="ts">
+  import { defineMeta } from "@storybook/addon-svelte-csf";
+  import ScanlineField from "../components/ScanlineField.svelte";
+  import Panel from "../components/Panel.svelte";
+
+  const { Story } = defineMeta({
+    title: "Style Primitives/ScanlineField",
+    component: ScanlineField,
+    tags: ["autodocs"],
+  });
+</script>
+
+<Story name="Soft Neutral" args={{ intensity: "soft", tone: "neutral", size: "md" }} />
+<Story name="Medium Accent" args={{ intensity: "medium", tone: "accent", size: "md" }} />
+<Story name="Hard Warning" args={{ intensity: "hard", tone: "warning", size: "lg" }} />
+<Story name="Panel Backdrop" asChild>
+  <Panel title="Signal Surface">
+    <ScanlineField intensity="hard" tone="accent" />
+  </Panel>
+</Story>

src/lib/ui/stories/SignalTrace.stories.svelte

@@ -0,0 +1,21 @@
+<script module lang="ts">
+  import { defineMeta } from "@storybook/addon-svelte-csf";
+  import SignalTrace from "../components/SignalTrace.svelte";
+  import Panel from "../components/Panel.svelte";
+
+  const { Story } = defineMeta({
+    title: "Style Primitives/SignalTrace",
+    component: SignalTrace,
+    tags: ["autodocs"],
+  });
+</script>
+
+<Story name="Horizontal Accent" args={{ tone: "accent", orientation: "horizontal" }} />
+<Story name="Horizontal Warning Tight" args={{ tone: "warning", density: "tight" }} />
+<Story name="Vertical Neutral" args={{ tone: "neutral", orientation: "vertical" }} />
+<Story name="Panel Trace" asChild>
+  <Panel title="Generic Flow">
+    <SignalTrace tone="accent" />
+    <SignalTrace tone="warning" density="tight" />
+  </Panel>
+</Story>

src/lib/ui/storybook.test.ts

@@ -12,6 +12,8 @@ const requiredStoryFiles = [
   "DashboardFrame.stories.svelte",
   "DashboardHeader.stories.svelte",
   "DashboardOnePager.stories.svelte",
+  "CornerBracketFrame.stories.svelte",
+  "DiagonalStripeField.stories.svelte",
   "FooterCell.stories.svelte",
   "FooterStatusCell.stories.svelte",
   "GridFrame.stories.svelte",
@@ -24,10 +26,12 @@ const requiredStoryFiles = [
   "ServiceGroupPanel.stories.svelte",
   "ServicePanel.stories.svelte",
   "ServiceRow.stories.svelte",
+  "SignalTrace.stories.svelte",
   "Sparkline.stories.svelte",
   "StatusBadge.stories.svelte",
   "StatusStrip.stories.svelte",
   "SystemState.stories.svelte",
+  "ScanlineField.stories.svelte",
   "TelemetryCard.stories.svelte",
   "TelemetryGrid.stories.svelte",
   "TelemetryStrip.stories.svelte",
@@ -79,6 +83,36 @@ describe("Storybook inventory", () => {
     }
   });
 
+  test("includes style-only decorative primitives in the reusable UI inventory", () => {
+    for (const component of [
+      "CornerBracketFrame",
+      "DiagonalStripeField",
+      "ScanlineField",
+      "SignalTrace",
+    ]) {
+      expect(existsSync(join(componentsDir, `${component}.svelte`)), `${component} is missing`).toBe(
+        true,
+      );
+      expect(
+        existsSync(join(storiesDir, `${component}.stories.svelte`)),
+        `${component}.stories.svelte is missing`,
+      ).toBe(true);
+    }
+  });
+
+  test("keeps decorative primitives hidden from assistive technology", () => {
+    for (const component of [
+      "CornerBracketFrame",
+      "DiagonalStripeField",
+      "ScanlineField",
+      "SignalTrace",
+    ]) {
+      const source = readFileSync(join(componentsDir, `${component}.svelte`), "utf8");
+
+      expect(source).toContain('aria-hidden="true"');
+    }
+  });
+
   test("does not add deferred form/navigation primitives", () => {
     for (const component of ["Input", "ToggleGroup", "ScrollArea"]) {
       expect(existsSync(join(root, `src/lib/ui/components/${component}.svelte`))).toBe(false);