test(scratch): leak-hunt probes for cava, render loop, decode stream

One-off diagnostics behind the FFTW leak fix: init/destroy x50 RSS
bound, Mach VM region walker, render-churn region growth, ffmpeg
decode-stream region/rss sampling.

tests/scratch-render-leak.tsx

@@ -0,0 +1,27 @@
+/** Minimal opentui app: VM region growth from render loop and/or text churn. */
+import { appendFileSync } from "node:fs"
+import { createSignal } from "solid-js"
+import { render } from "@opentui/solid"
+import { countRegions } from "./scratch-region-count"
+
+const CHURN = Bun.argv.includes("--churn")
+const OUT = Bun.argv.find((a) => a.startsWith("--out="))?.slice(6) ?? "/tmp/render-leak.log"
+const log = (m: string) => Bun.write(Bun.stderr, m + "\n") // stderr may be hijacked too; use fd via file:
+const append = (m: string) => appendFileSync(OUT, m + "\n")
+
+const [s, setS] = createSignal("hello")
+if (CHURN) {
+  let i = 0
+  setInterval(() => setS(`hello ${++i} ${"x".repeat(i % 50)}`), 33)
+}
+
+render(() => <text>{s()}</text>)
+await Bun.sleep(1000)
+const c0 = countRegions()
+append(`start churn=${CHURN}: total=${c0.total}`)
+for (let w = 1; w <= 4; w++) {
+  await Bun.sleep(15_000)
+  const c = countRegions()
+  append(`t=${w * 15}s total=${c.total} (delta ${c.total - c0.total})`)
+}
+process.exit(0)