Add the construction layer (C9/C19/C23): a named, param-generic graph-as-data
(`Blueprint`) that *compiles* to the flat, type-erased instance the run loop
already runs. The unit of reuse is the `Composite` — a nestable sub-graph
fragment exposing one output port (C8) and named input roles — which
`Blueprint::compile()` **inlines** by raw-index lowering into the flat
`(nodes, sources, edges)` the unchanged `Harness::bootstrap` consumes.
Design (settled in spec 0012, ledger C9/C19/C23): a composite is an
authoring-level node, NOT a runtime `Box<dyn Node>` sub-engine. The chosen
inlining approach keeps the sacrosanct deterministic run loop untouched and
leaves the composite interior fully inspectable for the deferred cross-graph
optimiser; the rejected "runtime sub-engine" reading would have put throwaway
complexity into the run loop and kept the interior opaque. The compilat is
wired by raw index, not by name; names survive only as non-load-bearing debug
symbols (as `FieldSpec.name` already is).
Lowering is recursive index rewriting: interior items append at an offset,
interior edges rewrite by that offset, an edge into a composite fans through
its input roles (one blueprint edge -> several flat edges), an edge out
resolves to the interior output port, and nesting recurses inside-out.
Construction-phase faults are caught as a typed `CompileError`
(BadInteriorIndex / RoleKindMismatch / OutputPortOutOfRange); the lowered flat
compilat is validated by bootstrap's existing kind- and Kahn-cycle-check
(wrapped as `CompileError::Bootstrap`), with no re-implementation.
Non-goals (deferred per C23/C16): no optimisation pass (CSE/DCE,
sweep-invariant hoisting), no external optimisation crate, no named-handle
ergonomic wiring, no `aura graph` render (#13).
Verification: 48 engine tests green (8 blueprint: derived-schema, single +
nested composite inlining, the three CompileError paths, bootstrap-error wrap,
and the headline `composite_sma_cross_runs_bit_identical_to_hand_wired` C1
demonstrator — the SMA-cross composite lowers to a flat graph byte-identical to
the hand-wired sample harness, producing bit-for-bit identical equity +
exposure traces); `cargo clippy --workspace --all-targets -D warnings` clean.
`Node`, `Harness::bootstrap`, the run loop, and `Edge`/`Target`/`SourceSpec`
are unchanged.
closes#12
Brummel
a4fb5d7182