C12 axis 4: Monte-Carlo as a sweep over seeds. `monte_carlo(base_point, seeds,
closure) -> McFamily`, the analog of SweepFamily, reusing the disjoint-parallel
executor (extracted into a shared `run_indexed` core) rather than forking a new
run loop. Each realization is a disjoint C1 unit; parallelism is across draws.
The aggregate (V1) covers all three run metrics with mean + p5/p25/p50/p75/p95,
a pure post-run reduction over the retained raw draws.
Eager-agnostic firewall (#71): the API takes seeds + a per-draw closure, never a
materialized stream Vec; seed->Source construction stays a closure-body concern.
Signed under the /boss spec auto-sign gate: objective gates green (precondition,
self-review, grounding-check PASS) and a unanimous five-lens spec-skeptic panel
(criterion, grounding, scope-fork, ambiguity, plan-readiness) returned SOUND.
The aggregate fork was settled to V1 by the user (issue #68 reconciliation
comment, verbatim "ja, wir machen v1", 2026-06-15).
refs #68
Brummel
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