Every card instance attached its summary-panel runtime through
import().then(), even when the chunk had loaded long ago. The first render
therefore measured a header without summary controls; the controls arrived
a beat later, the stage shrank, the deferred refit opened a `stage-resize`
continuity candidate and the first HA tick paid three extra render passes
(Full Performance: blend stateUpdate1 50 → 130 ms, overlay 217 → 809 ms;
locally 4 performUpdate per tick instead of 1).
summary-runtime-loader.ts separates the summary code from its state: the
loaded factory is cached per page, every host builds its own runtime from
it (no shared preferences, drafts, subscriptions, timers or DOM). A warm
factory yields the runtime synchronously in connectedCallback, before the
first Lit render; a cold mount still pays one lazy import, concurrent cold
mounts share the pending import, a failed import is forgotten so the next
connection retries, and a disconnect cancels the pending attachment of that
connection. SummaryRuntimeSlot owns the per-host lifecycle so the card core
stays under its line ceiling.
Witnesses: loader unit tests (distinct instances, shared pending import,
cancelled attachment, retry after failure); demo/smoke_summary_warm_attach
(warm replacement and cold-key instance on a warm page own the runtime
before the first render, header/stage stable from the first frame, no
stage-resize, one performUpdate per geometry-neutral tick, a real viewport
resize still opens stage-resize); mutant summary-runtime-attaches-after-
first-render. smoke_summary_panel waited for `_summary` as a readiness
proxy; it now waits for the server config load, which stays asynchronous.
Local paired glow benchmarks (4× CPU throttle): blend 159.7 → 49.9 ms and
overlay 326.7 → 120.4 ms at stateUpdate1 with renders 4 → 1; the isometric
load loses the three summary-owned long tasks.
Docs screenshots: all 11 frames decode pixel-identical to the committed
ones; the manifest carries only the new source fingerprint. Initial View
ceiling recentred 299 100 → 299 600 for the +299 B loader.
Issue: #506
User-Visible: yes
