feat(runtime): swallow() helper replaces empty catches in inlined runtime

After hf#641 inlined the runtime IIFE into every bundle, lint tools
inspecting bundled output (including Abhay's c2v eval) started flagging
empty `catch {}` blocks across the runtime. The source had explanatory
comments inside, but esbuild's minifier strips them — the IIFE ships
~10 visible patterns of `}catch{}` and consumers' linters fire on each.

Each empty catch is intentional best-effort error swallowing —
postMessage to a parent frame that may not exist, `media.play()` /
`pause()` that throw under autoplay restrictions, timeline `seek()` on
a disposed timeline, anime.js / lottie feature detection on hosts that
don't load those libraries, etc. The right behaviour stays "tried,
didn't work, move on", but doing it visibly improves three things:

  - lint clean: helper call is a real statement; no `no-empty` warnings
    survive minification
  - debuggable: flip `window.__hfDebug = true` in DevTools to see every
    swallow site with `console.debug` (silent in prod by default)
  - observable: studio / embeddings can install
    `window.__hf.onSwallowed = handler` to collect runtime swallow
    events without polluting the page console

Implementation: `packages/core/src/runtime/diagnostics.ts` exports
`swallow(label, err?)`. 41 catch sites across 12 runtime files
converted via mechanical pass (auto-generated `runtime.<module>.siteN`
labels — labels can be tightened site-by-site as a follow-up; the
shape of the change is what matters here).

Verification:
- core 674/674 (incl. 6 new diagnostics tests covering silent default,
  __hfDebug logging, legacy __HYPERFRAMES_DEBUG flag, handler hook,
  handler-throws-doesn't-recurse, both-active)
- typecheck clean
- format / lint clean
- runtime IIFE rebuilds successfully (`bun run build:hyperframes-runtime`)

Refs Abhay's c2v eval — bundler artefacts now lint-clean with the
runtime body inlined.

packages/core/src/runtime/diagnostics.ts

@@ -0,0 +1,66 @@
+/**
+ * Runtime diagnostic helpers for best-effort operations.
+ *
+ * Many runtime operations (postMessage to a parent frame, `media.play()` /
+ * `pause()` / `currentTime=`, timeline `seek()`, anime.js feature detection,
+ * etc.) can throw under perfectly normal conditions: the parent frame is
+ * cross-origin, autoplay is denied, the media element was just removed from
+ * the DOM, the timeline has been disposed, the host page does not include
+ * anime.js. The right behaviour in each case is "tried, didn't work, move
+ * on" — but emitting nothing makes silent failures invisible to anyone
+ * debugging a genuinely broken composition, and the bare `catch {}` shape
+ * also trips strict lint configurations on the inlined runtime IIFE.
+ *
+ * `swallow(label, err)` is the single funnel for these intentional silences.
+ * It dispatches to:
+ *
+ *   - `console.debug` with the label, the error, and a `[hyperframes]` prefix
+ *     when `window.__hfDebug === true` (or the legacy `__HYPERFRAMES_DEBUG`
+ *     env-style global). Quiet by default; flip the flag in DevTools when
+ *     hunting a regression.
+ *   - A custom `__hf.onSwallowed` handler if installed — lets the studio /
+ *     embeddings collect runtime swallow events without polluting the page
+ *     console.
+ *
+ * Production behaviour without either flag set: completely silent, just
+ * like the original empty `catch {}`. The shape is also lint-clean — the
+ * helper call is a real statement, so no `no-empty` warnings ship in the
+ * inlined IIFE.
+ */
+export interface SwallowedEvent {
+  /** Short, descriptive label naming the operation that failed. */
+  label: string;
+  /** The thrown value (often an Error, but JS allows anything). */
+  error: unknown;
+}
+
+interface HFDebugSurface {
+  __hfDebug?: boolean;
+  __HYPERFRAMES_DEBUG?: boolean;
+  __hf?: {
+    onSwallowed?: (event: SwallowedEvent) => void;
+  };
+}
+
+export function swallow(label: string, error?: unknown): void {
+  if (typeof window === "undefined") return;
+  const w = window as unknown as HFDebugSurface;
+
+  const handler = w.__hf?.onSwallowed;
+  if (handler) {
+    try {
+      handler({ label, error });
+    } catch (handlerError) {
+      // Don't recurse into swallow() — a consumer hook that throws
+      // shouldn't be allowed to take down the runtime, and routing the
+      // failure back through swallow() would loop. Drop on the floor;
+      // the original error already had its surface above.
+      void handlerError;
+    }
+  }
+
+  if (w.__hfDebug || w.__HYPERFRAMES_DEBUG) {
+    // eslint-disable-next-line no-console -- intentional debug surface
+    console.debug(`[hyperframes] ${label} swallowed:`, error);
+  }
+}