fix(simulation): PR #176 review round — all 12 findings + 2 recommendations addressed

H1 demux: ShapeProbe defensive multi-shape rejection (union frames now Err, not first-match; +2 tests) and doc claim made honest. H2/T1 SystemIndex.reset_test_state() folded into SimBridge.reset_test_state() (load() inline per autoload rule) + has_pending_request() accessor. H3 no-op tests now assert the replay flag both directions. H4 retry test actually ingests a failure and asserts the retry semantic. H5 error fixture uses the normalized status string. H6 bridge_tcp e2e sends all five frame shapes over real TCP (star-map + city-names buffers asserted). H7 positive replay-on-CONNECTED test via the test_local_bridge test-mode-flip precedent (stub bridge captures + decodes the request bytes). H8/T2 stale PLACEHOLDER doc replaced with the confirmed contract. H9 is_capital doc matches the COALESCE reality. T-r1 demux ceiling written down (next shape = tagged envelope). T-r2 AtlasLayerResponse governance ceiling comment. Lead item: the four cargo-fmt-formatted files from the gate round are now committed (layer_proxy/plugin/bridge-mod/main). H10 note for the record: the 13 snapshot_*.msgpack fixtures in commit 845737617 were regenerated because they were stale against their own generator (pre-existing version-key removal) — verified harmless, no client reads that key.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server/src/atlas/layer_proxy.rs

@@ -72,6 +72,11 @@ pub struct DistrictGridLayer {
 /// A layer response: the computed `Layer1Output` + the coarse district grid
 /// (D-225, T-1046) + the road-graph and settlement overlays (T-960 §1/§2), or
 /// a non-ready status.
+///
+/// Growth ceiling (governance-bounded): the one-`Option`-field-per-layer
+/// pattern tops out around six fields — D-226's 2026-07-13 amendment (d)
+/// rules out any L5/tile Atlas layer ever, leaving T-1112 (quarter
+/// footprints) and T-1113 (region climate) as the only remaining candidates.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct AtlasLayerResponse {
     pub body_id: String,
@@ -726,8 +731,13 @@ mod tests {
         assert_eq!(decoded.body_id, "GJ1c");
         let rg = decoded.road_graph.expect("road_graph survives round trip");
         assert_eq!(rg.nodes[0].position, (12, 58));
-        assert_eq!(rg.edges[0].maintenance, MaintenanceAuthority::Administrative);
-        let settlements = decoded.settlements.expect("settlements survives round trip");
+        assert_eq!(
+            rg.edges[0].maintenance,
+            MaintenanceAuthority::Administrative
+        );
+        let settlements = decoded
+            .settlements
+            .expect("settlements survives round trip");
         assert_eq!(settlements.settlements[0].name, "Port Aldren");
         assert_eq!(
             settlements.settlements[0].size_class,