refactor(edges): use CSS animations for snake/flow edges instead of SVG SMIL

Snake and flow edge animations used SVG SMIL <animate repeatCount="indefinite">.
SMIL keeps running while a tab is hidden (CSS animations pause) and grows memory
in Chrome over long-lived background tabs. Convert both to CSS @keyframes
(homelable-snake / homelable-flow), matching the existing basic-dash pattern.

Identical visuals and timings; bidirectional snake yo-yos via `alternate`.
Adds a regression test asserting animated edges emit zero <animate> nodes and a
CSS animation instead.

ha-relevant: yes

frontend/src/components/canvas/edges/__tests__/HomelableEdge.animation.test.tsx

@@ -0,0 +1,77 @@
+import { describe, it, expect } from 'vitest'
+import { render } from '@testing-library/react'
+import { ReactFlowProvider } from '@xyflow/react'
+import type { EdgeProps, Edge } from '@xyflow/react'
+import { HomelableEdge } from '../index'
+import type { EdgeData } from '@/types'
+
+/**
+ * Regression: edge flow animations must use CSS, never SVG SMIL <animate>.
+ *
+ * SMIL <animate> keeps running while the tab is hidden and leaks memory in
+ * Chrome over time (RAM climbed only when the canvas tab was backgrounded).
+ * CSS animations pause when the tab is hidden and don't leak — so the rendered
+ * output must contain a CSS `animation` on the path and zero <animate> nodes.
+ */
+function renderEdge(data: Partial<EdgeData> = {}) {
+  const props = {
+    id: 'e1',
+    source: 'a',
+    target: 'b',
+    sourceX: 0,
+    sourceY: 0,
+    targetX: 100,
+    targetY: 100,
+    sourcePosition: 'bottom',
+    targetPosition: 'top',
+    data: { type: 'ethernet', ...data } as EdgeData,
+    selected: false,
+  } as unknown as EdgeProps<Edge<EdgeData>>
+
+  return render(
+    <ReactFlowProvider>
+      <svg>
+        <HomelableEdge {...props} />
+      </svg>
+    </ReactFlowProvider>,
+  )
+}
+
+describe('HomelableEdge animation', () => {
+  it('renders snake animation as CSS, not SMIL <animate>', () => {
+    const { container } = renderEdge({ animated: 'snake' })
+    expect(container.querySelector('animate')).toBeNull()
+    const animated = Array.from(container.querySelectorAll('path')).find((p) =>
+      (p.getAttribute('style') ?? '').includes('homelable-snake'),
+    )
+    expect(animated).toBeTruthy()
+  })
+
+  it('renders flow animation as CSS, not SMIL <animate>', () => {
+    const { container } = renderEdge({ animated: 'flow' })
+    expect(container.querySelector('animate')).toBeNull()
+    const animated = Array.from(container.querySelectorAll('path')).find((p) =>
+      (p.getAttribute('style') ?? '').includes('homelable-flow'),
+    )
+    expect(animated).toBeTruthy()
+  })
+
+  it('legacy animated:true maps to snake CSS animation', () => {
+    const { container } = renderEdge({ animated: true })
+    expect(container.querySelector('animate')).toBeNull()
+    const animated = Array.from(container.querySelectorAll('path')).find((p) =>
+      (p.getAttribute('style') ?? '').includes('homelable-snake'),
+    )
+    expect(animated).toBeTruthy()
+  })
+
+  it('non-animated edge has no flow animation and no <animate>', () => {
+    const { container } = renderEdge({ animated: false })
+    expect(container.querySelector('animate')).toBeNull()
+    const animated = Array.from(container.querySelectorAll('path')).find((p) => {
+      const s = p.getAttribute('style') ?? ''
+      return s.includes('homelable-snake') || s.includes('homelable-flow')
+    })
+    expect(animated).toBeUndefined()
+  })
+})

frontend/src/components/canvas/edges/index.tsx

@@ -378,14 +378,14 @@ export function HomelableEdge({ id, source, target, sourceHandleId, targetHandle
           strokeWidth={((style.strokeWidth as number ?? 2) + 1.5) * 2}
           strokeDasharray="20 10000"
           strokeLinecap="round"
-          style={{ pointerEvents: 'none' }}
-        >
-          {isBidirectional ? (
-            <animate attributeName="stroke-dashoffset" values="-10000;0;-10000" keyTimes="0;0.5;1" dur="20s" repeatCount="indefinite" />
-          ) : (
-            <animate attributeName="stroke-dashoffset" from="-10000" to="0" dur="10s" repeatCount="indefinite" />
-          )}
-        </path>
+          style={{
+            pointerEvents: 'none',
+            // CSS (not SMIL) so it pauses when the tab is hidden — see index.css.
+            // Bidirectional yo-yos via `alternate` (10s each way = 20s round trip,
+            // matching the old SMIL keyTimes); unidirectional loops in one direction.
+            animation: `homelable-snake 10s linear infinite${isBidirectional ? ' alternate' : ''}`,
+          }}
+        />
       )}
       {animMode === 'flow' && (
         <path
@@ -396,10 +396,11 @@ export function HomelableEdge({ id, source, target, sourceHandleId, targetHandle
           strokeDasharray="6 12"
           strokeLinecap="round"
           strokeOpacity={0.85}
-          style={{ pointerEvents: 'none' }}
-        >
-          <animate attributeName="stroke-dashoffset" from="0" to="18" dur="1.2s" repeatCount="indefinite" />
-        </path>
+          style={{
+            pointerEvents: 'none',
+            animation: 'homelable-flow 1.2s linear infinite',
+          }}
+        />
       )}
 
       <EdgeLabelRenderer>

frontend/src/index.css

@@ -11,6 +11,18 @@
   to   { stroke-dashoffset: 0; }
 }
 
+/* Edge flow animations — CSS (not SVG SMIL) so the browser pauses them when the
+   tab is hidden. SMIL <animate> keeps running in background tabs and leaks
+   memory in Chrome over time; CSS animations do neither. */
+@keyframes homelable-snake {
+  from { stroke-dashoffset: -10000; }
+  to   { stroke-dashoffset: 0; }
+}
+@keyframes homelable-flow {
+  from { stroke-dashoffset: 0; }
+  to   { stroke-dashoffset: 18; }
+}
+
 /* Disable React Flow's built-in edgeupdater entirely — HomelableEdge renders
    its own interactive endpoint dots in EdgeLabelRenderer (above the node
    layer) so the node Handle DOM cannot steal the reconnection drag. */