docs(adr): ADR 009 is accepted; Z-set weights are checked i64 and the group is partial (improvise-felo.4)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VdfEGXA7aJ6ftMsCc9PJze

context/adr/009-incremental-evaluation.md

@@ -1,6 +1,6 @@
 # ADR 009 — Incremental evaluation: an in-house DBSP core, plugged in behind a trait
 
-**Status:** proposed. ·
+**Status:** accepted. ·
 **Ticket:** improvise-felo.4 (the record of this ADR; implementation goes to its own
 epic) ·
 **Relates to:** ADR 001 (the basis a write claims), ADR 002 (surrogates on the wire),
@@ -29,7 +29,11 @@ mutation, it says so and names the incremental path that normally applies.
 
 A problem-agnostic workspace crate with no dependencies beyond `std` (so it is
 wasm32-clean and serde-free). It provides:
-- `ZSet<K>`, a map from `K: Ord` to a non-zero `i64` weight, which is an abelian group;
+- `ZSet<K>`, a map from `K: Ord` to a non-zero `i64` weight. Weight arithmetic is checked
+  and panics on overflow, in debug and in release. The group laws are exact wherever no
+  weight, intermediate ones included, leaves `i64`, so the structure is an abelian group
+  that is partial at the `i64` boundary. Weights are validated where deltas enter from
+  the wire (clause 9), so a hostile frame is rejected and never reaches the panic;
 - a synchronous, single-threaded `Circuit` per process, with `delay`, `integrate`,
   `differentiate`, `map`, `filter`, `flat_map`, `index_by`, the bilinear delta join
   `join_indexed`, `distinct` and `aggregate`;