v0.7.12

A code-review pass: four real bugs, one per-frame layout read, and a round of
deduplication across the shared helpers. No API changes — every fix below either
restores documented behaviour or is invisible to consumers.

Fixed

• typed: true no longer destroys every --const-meta-* value. A source's
  undeclared value was always registered with the <number> default — but the
  meta plugin writes strings (#3367d6, /cover.jpg, dark light) under
  property names it only learns from the page at runtime, so it can't declare
  them. A <number>-registered property rejects a string at computed-value time,
  so every meta value computed to 0. Undeclared strings are now left
  untyped; numbers, and any value whose source declares a props syntax, are
  registered exactly as before.
• img-color no longer re-decodes on every scroll-back. The swatch cache
  lived inside start, which the viewport gate re-runs on each re-entry — so the
  cache it was written for could never survive one, and every pass over a gallery
  re-ran createImageBitmap + getImageData per image. It's now a module-scoped
  WeakMap, keyed by the rendered source.
• video-color no longer pins a core on a tainted canvas. The sample
  throttle only advanced on a successful read, so a cross-origin video with no
  CORS grant re-drew and re-threw on every presented frame, forever. Taint is now
  latched: it gives up after the first failure, and still writes nothing.
• select's --live-value-num no longer goes stale. It was written only for
  a numeric value and never cleared, so picking "3" and then a non-numeric
  option left 3 behind — and the documented var(--live-value-num, …) fallback
  could never apply again. It's now removed when the value isn't numeric.
• battery no longer leaves an unhandled promise rejection when getBattery
  exists but rejects (insecure context, or disabled by policy).

Changed

• scroll-velocity reads the scroll position in its scroll handler, not
  inside the frame. Reading window.scrollY from a per-frame sampler forced a
  style+layout recalc every frame, since the previous frame's writes left style
  dirty — the one place the library broke its own read/write split. Behaviour is
  unchanged in a browser (scroll events fire before rAF in the same frame).
• pointer-local, motion, and orientation now seed zeros, like every
  other source, so their properties resolve on frame one instead of needing a
  var(…, 0) fallback. One thing to know: a var(--live-local-pointer-x-ratio)
  with no fallback used to invalidate its whole declaration until the first
  event, and now resolves to 0 — so gate on --live-local-pointer-inside
  rather than letting a highlight sit in the top-left corner on load. Global
  pointer still doesn't seed: the position genuinely isn't knowable before the
  first event.
• ctx.write(name, '') removes a property, for a value that stops being
  meaningful. Verified across Chromium, Firefox, and WebKit.
• visual-viewport and keyboard share one set of visual-viewport
  listeners via the new ref-counted onVisualViewport, instead of attaching
  their own. battery and network listeners are now passive, like every other
  source's.
• form-state's post-reset recompute rides the shared frame loop, replacing
  the library's only stray requestAnimationFrame.

Internal

• core/window-events.ts + core/document-events.ts collapse into
  core/events.ts — one ref-counted hub factory per target (onWindow,
  onDocument, onVisualViewport), plus an onAll helper for the per-element
  case. observeResize / observeIntersection likewise share one hub factory.
  Shared noop and slug replace ~15 and 2 copies respectively.
• The per-target queue maps in the writer are pooled and reused rather than
  reallocated every frame.