The MC half of #170 (World/C21): `aura mc <closed blueprint.json> --seeds N`
builds a FamilyKind::MonteCarlo family from a loaded CLOSED blueprint. Each seed
draws a distinct synthetic price walk (synthetic_walk_sources, the mc_family
pattern), so members differ in the DATA (not just a manifest label) — the sim is
deterministic (C1), so MC variation must come from re-drawing the input. Draws
run disjointly in parallel via the shared monte_carlo helper (invariant 1). The
canonical blueprint is stored once keyed by the shared topology_hash (the 0094
hook), and reproduce_family_in gains a MonteCarlo realization branch that
reconstructs each member's seed-driven walk from manifest.seed — so a persisted
mc family 'aura reproduce's bit-identically (the store-hook proof).
Closed-blueprint only: MC binds no axis, so a free knob has no binder; an open
blueprint yields a named Err (rendered to stderr + exit 2 at the run_blueprint_mc
boundary, mirroring blueprint_sweep_family — no hidden process exit in the pure
builder), pre-empting the compile_with_params arity panic.
Two quality-gate-driven improvements over the ratified plan, both applied and
verified: (1) delegate the disjoint draws to the engine monte_carlo seam instead
of a hand-rolled loop (my plan's 'closure-shape mismatch' rationale was wrong —
the Fn(u64,&[Scalar]) closure ignores the unused base_point, exactly as mc_family
does); (2) the closed-blueprint guard returns Result rather than exiting inside
the builder, matching the sweep sibling's contract and making the rejection
unit-testable. Engine + registry untouched (invariants 8/9).
Verified: cargo build --workspace clean; cargo clippy --workspace --all-targets
-- -D warnings clean; cargo test --workspace green (5 new tests: the parser,
anti-degenerate family, MC reproduce round-trip, and two E2Es incl. the open
rejection; no regressions).
refs #170
Brummel
14e27a978b