docs(design): compilation/compilat reading of composites + C23 optimisation contract

Settle the Construction-layer milestone's design fork before any spec is written:
a composite is a blueprint fragment compiled away by inlining, not a runtime
sub-engine Node.

- C23 (new): the bootstrap is a compilation -- a param-generic, named blueprint
  is lowered to a flat, type-erased compilat wired by raw index; composites
  inline (C9). The compilat is the target of behaviour-preserving optimisation
  (C1 is the correctness invariant) on two levels: intra-compilat (CSE/DCE) and
  across the sweep family (loop-invariant prefix hoisting -- the sweep-invariant
  sub-graph computed once and shared via C11/C12). Passes are deferred follow-on;
  this milestone builds the representation only.
- C9 refined: "a composite is itself a Node" is an authoring-level identity; the
  nested Box<dyn Node> sub-engine reading is explicitly rejected (it keeps the
  interior opaque to the cross-graph optimiser and adds a runtime sub-loop the
  flat model does not need).
- C19 refined: the blueprint->instance binding is a compilation; "no recompile"
  means no Rust/cdylib rebuild -- re-deriving an instance per param-set is a
  cheap graph re-compilation, not a code recompile.
- Names are non-load-bearing debug symbols (as FieldSpec.name already is); the
  wiring resolves by raw index, names survive only for tracing/rendering.
- CLAUDE.md domain-invariant 11 pulled coherent with the compilat reading.

refs #12

CLAUDE.md

@@ -114,6 +114,12 @@ design decision, not a refactor, and belongs in the ledger.
     blueprint). The harness — sources + strategy + broker node(s) + sinks — is
     the root sim graph, itself bootstrapped, and is C1's disjoint unit; its
     structural axes form the experiment matrix, its tuning params the sweep.
+    **The bootstrap is a compilation** to a flat, type-erased *compilat*, wired
+    by raw index (composites inline — a composite is an authoring-level node, not
+    a runtime object; names survive only as non-load-bearing debug symbols, as
+    today). The compilat is the target of **behaviour-preserving** optimisation,
+    C1 the correctness invariant — intra-graph (CSE/DCE) and across a sweep family
+    (sweep-invariant sub-graph computed once, shared via C11/C12). See C9/C19/C23.
 12. **The World is the product; the playground is a trace explorer.** Three
     ontological tiers: a *node* is an open, composable fragment (at most one
     output, C8); a *harness* is the closed root graph that runs (sources +