design-md-consolidation 2.2: condense Decision 9 narrative-of-changes opener + drop pre-Decision-9 history paragraphs

docs/DESIGN.md

@@ -649,11 +649,7 @@ without a source-level rewrite.
 
 ## Decision 9: dual allocator — RC canonical, Boehm parity oracle
 
-Originally framed
-as "transitional Boehm until the RC pipeline lands and the default flips"; then re-framed
-as a symmetric dual-allocator policy with Boehm as
-the CLI default. The revision flips the asymmetry to
-match Decision 10:
+AILang ships two allocator backends with an asymmetric role:
 
 - **RC is canonical.** `--alloc=rc` is the CLI default for
   `ail build` and `ail run`. The runtime AILang's memory model
@@ -679,17 +675,6 @@ diagnostic leverage. Decision 10 (RC + uniqueness) holds as the
 specification of the canonical runtime; the rest of this section
 documents the Boehm half, retained as the oracle.
 
-The `--alloc=bump` mode introduced for the bench is a
-measurement tool, not a production target.
-
-Originally, every ADT box, lambda env, and closure pair was
-allocated with bare `malloc` and never freed. That worked for the
-17 test fixtures (all small, all short-lived) but is incompatible
-with any real workload — a stdlib `fold` over a million-element
-list would leak a million boxes. The "Goal" section's "no GC for
-the MVP" framing predates the parameterised-ADT pipeline and the
-explicit-recursion expectation; both make a collector necessary.
-
 **Choice: Boehm-Demers-Weiser conservative GC.** The simplest
 working option: