feat(media-use): core infrastructure — manifest, cache, adopt, probe (#1682)

* feat(media-use): core infrastructure — manifest, cache, adopt, probe

Foundation for media-use — the media resolution layer for HyperFrames.

- manifest.mjs: JSONL read/write/find for .media/manifest.jsonl
- index-gen.mjs: regenerate agent-readable index.md from manifest
- cache.mjs: content-addressed global cache at ~/.media/ (SHA-256, sentinel)
- freeze.mjs: download URL or copy local file to .media/
- probe.mjs: extract duration/dimensions via ffprobe
- adopt.mjs: scan assets/ directory, register existing files with metadata
- 19 passing tests (manifest round-trip, cache, promote, index generation)

* fix(media-use): oxfmt formatting + cap freeze download size

Format adopt/cache/probe/manifest.test (CI oxfmt --check gate).
Cap freezeUrl downloads at 256MB so a hostile/runaway URL can't fill
the disk (addresses CodeQL #670: network data written to file).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

skills/media-use/scripts/lib/index-gen.mjs

@@ -0,0 +1,63 @@
+import { writeFileSync, mkdirSync } from "node:fs";
+import { dirname } from "node:path";
+import { readManifest, indexPath } from "./manifest.mjs";
+
+function pad(str, len) {
+  return String(str ?? "").padEnd(len);
+}
+
+function formatDur(record) {
+  if (record.duration == null) return "—";
+  return `${record.duration}s`;
+}
+
+function formatDims(record) {
+  if (record.width && record.height) return `${record.width}×${record.height}`;
+  if (record.type === "icon" && record.transparent) return "svg";
+  return "—";
+}
+
+export function generateIndexContent(records) {
+  const count = records.length;
+  const header = `# .media · ${count} asset${count === 1 ? "" : "s"}\n`;
+  if (count === 0) return header;
+
+  const cols = { id: 4, type: 5, dur: 4, dims: 5, path: 5, desc: 11 };
+  for (const r of records) {
+    cols.id = Math.max(cols.id, (r.id ?? "").length);
+    cols.type = Math.max(cols.type, (r.type ?? "").length);
+    cols.dur = Math.max(cols.dur, formatDur(r).length);
+    cols.dims = Math.max(cols.dims, formatDims(r).length);
+    cols.path = Math.max(cols.path, (r.path ?? "").length);
+  }
+
+  const heading =
+    pad("id", cols.id + 2) +
+    pad("type", cols.type + 2) +
+    pad("dur", cols.dur + 2) +
+    pad("dims", cols.dims + 2) +
+    pad("path", cols.path + 2) +
+    "description";
+
+  const lines = [header, heading];
+  for (const r of records) {
+    lines.push(
+      pad(r.id, cols.id + 2) +
+        pad(r.type, cols.type + 2) +
+        pad(formatDur(r), cols.dur + 2) +
+        pad(formatDims(r), cols.dims + 2) +
+        pad(r.path, cols.path + 2) +
+        (r.description ?? ""),
+    );
+  }
+  return lines.join("\n") + "\n";
+}
+
+export function regenerateIndex(projectDir) {
+  const records = readManifest(projectDir);
+  const content = generateIndexContent(records);
+  const p = indexPath(projectDir);
+  mkdirSync(dirname(p), { recursive: true });
+  writeFileSync(p, content);
+  return content;
+}