feat(producer): default-off router for verified parallel drawElement

Promotes the opt-in HF_DE_PARALLEL_STREAM mechanism (#2056) into the
auto-routing decision, gated behind its own default-off flag
(HF_DE_PARALLEL_ROUTER). This is the next step from the 2026-07-08
parallel-DE benchmark verdict: par3/single 1.16-1.36x on real-work
comps >=2,000 frames, no comp anywhere losing to single-worker.

shouldPreferParallelDrawElement mirrors shouldPreferSingleWorkerDrawElement
(#2026) but takes priority over it when both are eligible — its higher
default threshold (HF_DE_PARALLEL_MIN_FRAMES=2000 vs the inversion's 900)
means it only ever picks up the long tail the inversion's own benchmark
didn't cover. Fixed at 3 workers (benchmark-validated; not calibration-
derived), same shape as the inversion pinning to a fixed 1.

resolveParallelRouterRetryPlan mirrors resolveInversionRetryPlan for the
self-verify-failure rollback path: falls back to the ordinary (non-DE)
parallel-disk path at the pre-router worker count. The caller must clear
HF_DE_PARALLEL_STREAM before recomputing useStreamingEncode or the retry
would keep resolving to the parallel-streaming shape.

New telemetry (de_parallel_router, de_pre_router_workers) tags which
render used the router, separate from de_worker_inversion — needed
before the planned telemetry soak can segment revert-rate and
de_verify_min_db to the parallel cohort specifically; today there's no
way to tell those apart from ordinary single-worker DE renders.

Verified end-to-end: HF_DE_PARALLEL_ROUTER=true on a 2,381-frame comp
resolves to 3 workers with 3 separate drawElement sessions and renders
successfully; without the flag, behavior is unchanged (falls through to
the existing single-worker inversion, workerCount=1) — no regression to
current production routing. 114 orchestrator tests pass (15 new).

packages/cli/src/commands/render.ts

@@ -1688,6 +1688,8 @@ function trackRenderMetrics(
     deClampReason: perf?.drawElement?.clampReason,
     deWorkerInversion: perf?.drawElement?.workerInversion,
     dePreInversionWorkers: perf?.drawElement?.preInversionWorkers,
+    deParallelRouter: perf?.drawElement?.parallelRouter,
+    dePreRouterWorkers: perf?.drawElement?.preRouterWorkers,
     deGateReason: perf?.drawElement?.gateReason,
     deWorkerEncode: perf?.drawElement?.workerEncode,
     deVerifyArmed: perf?.drawElement?.verifyArmed,

packages/cli/src/telemetry/events.ts

@@ -126,6 +126,8 @@ export function trackRenderComplete(
     deClampReason?: string;
     deWorkerInversion?: string;
     dePreInversionWorkers?: number;
+    deParallelRouter?: string;
+    dePreRouterWorkers?: number;
     deGateReason?: string;
     deWorkerEncode?: boolean;
     deVerifyArmed?: number;
@@ -204,6 +206,8 @@ export function trackRenderComplete(
       de_clamp_reason: props.deClampReason,
       de_worker_inversion: props.deWorkerInversion,
       de_pre_inversion_workers: props.dePreInversionWorkers,
+      de_parallel_router: props.deParallelRouter,
+      de_pre_router_workers: props.dePreRouterWorkers,
       de_gate_reason: props.deGateReason,
       de_worker_encode: props.deWorkerEncode,
       de_verify_armed: props.deVerifyArmed,