feat: establish simulation scaling baseline

docs/ARCHITECTURE_OVERVIEW.md

@@ -57,6 +57,10 @@ would otherwise obscure that lifecycle:
 - `simulation/definitions/` owns stable IDs and immutable action/profession
   definitions.
 
+Outside the runtime lifecycle, `simulation/benchmark/` owns reusable,
+schema-valid workload fixtures. CLI tools and headless scenarios consume those
+fixtures; production simulation does not depend on benchmark code.
+
 The manager deliberately remains a façade instead of being split into a
 collection of scene-tree manager nodes. A new collaborator is justified when
 one cohesive rule set has several real consumers or makes the tick lifecycle
@@ -76,6 +80,7 @@ hard to read.
 | `simulation/state/` | Versioned, serializable mutable records |
 | `simulation/definitions/` | Stable IDs and immutable gameplay definitions |
 | `simulation/persistence/` | Validated local save-file storage |
+| `simulation/benchmark/` | Reproducible full-fidelity headless workloads and metrics |
 | `world/` | Loaded-world interaction geometry and presentation adapters |
 | `world/resource_nodes/` | Finite resource presentation bound by stable ID |
 | `world/storage/` | Storage interaction geometry, never stored quantities |
@@ -110,6 +115,9 @@ improving ownership.
 - New mutable features define serialization and deterministic continuation at
   the same time as their first gameplay use. Cross-record causes use stable
   event IDs rather than object references or prose.
+- Benchmark fixtures use ordinary simulation records and must round-trip
+  through the current state schema. They may control workload setup, but must
+  not add benchmark-only fields or branches to production saves and ticks.
 - Opportunity records reference stable NPC, storage, resource, trigger-event,
   and resolution-event IDs. Their generator may observe authoritative state
   and history, but it does not mutate the economy or command NPC behavior. The