feat(simulation): implement economics integration sprint — #810 #821 #822 #823

Implements the full D-180/D-181 economics pipeline:

**#810 — Event input port (D-180)**
- Add EconEvent struct with Target/Effect/Duration/Visibility variants
- Implement EventPort as typed input queue for external disruptions
- Apply events in simulation step; D-179 Test 3 now uses real shock injection

**#821 — Integrate econ-sim into server tick loop**
- Extract econ-sim as library crate (lib.rs + sim.rs, Cargo.toml [lib] section)
- Add Simulation stateful runner; step() advances one economy tick
- Add EconSimResource, EconStateResource (7 D-181 signals), tick_economy_simulation
- Economy loads once at startup; graceful no-op when systems.db absent
- Server advances economy 1 tick per 10 game ticks (D-031)

**#822 — Expose economy state over IPC bridge**
- Protocol version 20 → 21
- Add EconomySnapshot, EconNodeSnapshot wire types
- Add EconStateQuery PlayerAction variant; response in economy_snapshot field
- Add EconQueryBuffer resource + serve_econ_state_query system

**#823 — Economics debug commands**
- Add InjectEconEvent, SetEconParam, GetEconState to DebugCommandKind
- Add EconDebugEffect, EconParamKind enums
- SetEconParam mutates α/β at runtime (α/β promoted to pub const + Simulation fields)
- ALPHA and BETA constants threaded through step_inner/trade_step signatures

All 1147 unit tests pass; zero warnings.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/src/simulation/mod.rs

@@ -8,6 +8,7 @@ pub mod chunk_streaming;
 pub mod contraband;
 pub mod conversation;
 pub mod dialogue;
+pub mod economy;
 pub mod examine;
 pub mod follow;
 pub mod generator;
@@ -166,6 +167,29 @@ impl Plugin for SimulationPlugin {
         // Initialize TickerPool with empty default; populated by ContentPlugin at Startup.
         app.init_resource::<ticker::TickerPool>();
 
+        // Economy simulation (#821, D-031) — loaded once at startup, no-op when DB absent.
+        // Uses seed 0 for now; will be threaded through StartupMessage world seed (#TODO).
+        if let Some((econ_sim, econ_state)) = economy::try_load_economy(0) {
+            app.insert_resource(econ_sim)
+                .insert_resource(econ_state);
+        }
+        // EconQueryBuffer: always registered so EconStateQuery PlayerActions are accepted
+        // even when the economy DB is absent (queries just produce no response).
+        app.init_resource::<economy::EconQueryBuffer>();
+        // tick_economy_simulation + serve_econ_state_query use Option<ResMut<...>> — safe to
+        // register unconditionally. They no-op when EconSimResource / EconStateResource absent.
+        app.add_systems(
+            Update,
+            (
+                economy::tick_economy_simulation
+                    .after(time::advance_tick)
+                    .before(crate::perception::observer::compute_observer_snapshot),
+                economy::serve_econ_state_query
+                    .after(economy::tick_economy_simulation)
+                    .before(crate::perception::observer::compute_observer_snapshot),
+            ),
+        );
+
         tracing::debug!("SimulationPlugin initialized");
     }
 }