feat(simulation): thread world seed from StartupMessage into economy (#826)

Replaces the hardcoded seed=0 with the seed received in StartupMessage,
threading it through SimulationPlugin -> EconomyPlugin / SimRng. Integration
test fixtures updated for the new SimulationPlugin { seed } signature.

server/src/main.rs

@@ -147,7 +147,7 @@ fn main() {
 
     let mut app = App::new();
     settled_reach_server::tick_phases::TickPhase::configure(&mut app);
-    app.add_plugins(SimulationPlugin);
+    app.add_plugins(SimulationPlugin { seed });
     app.add_plugins(BridgePlugin);
     app.add_plugins(settled_reach_server::knowledge::KnowledgePlugin);
     app.add_plugins(settled_reach_server::npc::NpcPlugin);
@@ -176,7 +176,8 @@ fn main() {
     app.insert_resource(BridgeResource::new(bridge));
     app.insert_resource(HandshakeState::Complete);
 
-    // Override SimRng with the chosen seed (SimulationPlugin defaults to seed 0)
+    // SimulationPlugin { seed } already inserts SimRng with the correct seed.
+    // Re-insert here as a defensive override in case plugin ordering shifts.
     app.insert_resource(settled_reach_server::simulation::rng::SimRng::new(seed));
 
     // Initialize empty line pool index (populated by generator pipeline in v0.2).
@@ -359,7 +360,7 @@ fn dump_schedule_graph() {
 
     let mut app = App::new();
     settled_reach_server::tick_phases::TickPhase::configure(&mut app);
-    app.add_plugins(SimulationPlugin);
+    app.add_plugins(SimulationPlugin { seed: 0 });
     app.add_plugins(BridgePlugin);
     app.add_plugins(settled_reach_server::knowledge::KnowledgePlugin);
     app.add_plugins(settled_reach_server::npc::NpcPlugin);

server/src/simulation/economy.rs

@@ -358,9 +358,10 @@ pub fn try_load_economy(run_seed: u64) -> Option<(EconSimResource, EconStateReso
     match Simulation::load_auto(run_seed) {
         Ok(sim) => {
             tracing::info!(
+                econ_seed = run_seed,
                 commodities = sim.economy().commodities.len(),
                 active_nodes = sim.nodes.len(),
-                "Economy simulation loaded"
+                "Economy simulation loaded with seed"
             );
             Some((EconSimResource::new(sim), EconStateResource::default()))
         }

server/src/simulation/economy_plugin.rs

@@ -8,13 +8,17 @@ use bevy_ecs::schedule::IntoScheduleConfigs;
 
 use crate::tick_phases::TickPhase;
 
-pub struct EconomyPlugin;
+pub struct EconomyPlugin {
+    /// World seed from `StartupMessage` (#826). Passed to `try_load_economy` so the
+    /// tâtonnement simulation is seeded deterministically from the client's world seed.
+    pub seed: u64,
+}
 
 impl Plugin for EconomyPlugin {
     fn build(&self, app: &mut App) {
         // 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 (#826).
-        if let Some((econ_sim, econ_state)) = super::economy::try_load_economy(0) {
+        // Seed comes from StartupMessage.world_seed, threaded via SimulationPlugin (#826).
+        if let Some((econ_sim, econ_state)) = super::economy::try_load_economy(self.seed) {
             app.insert_resource(econ_sim).insert_resource(econ_state);
         }
         // EconQueryBuffer: always registered so EconStateQuery PlayerActions are accepted

server/src/simulation/mod.rs

@@ -50,7 +50,12 @@ pub mod zone;
 /// Each sub-plugin owns its domain's systems, resources, and phase assignment.
 /// No system registration happens here — only sub-plugin composition and
 /// shared resources needed by multiple sub-plugins.
-pub struct SimulationPlugin;
+///
+/// `seed` is threaded through to [`economy_plugin::EconomyPlugin`] so the
+/// economy simulation uses the world seed from `StartupMessage` (#826).
+pub struct SimulationPlugin {
+    pub seed: u64,
+}
 
 impl Plugin for SimulationPlugin {
     fn build(&self, app: &mut App) {
@@ -59,7 +64,7 @@ impl Plugin for SimulationPlugin {
 
         // Shared resources needed by multiple sub-plugins.
         // Each sub-plugin inits its own domain-specific resources.
-        app.insert_resource(rng::SimRng::new(0))
+        app.insert_resource(rng::SimRng::new(self.seed))
             .init_resource::<save_io::SaveLoadPending>()
             .init_resource::<crate::knowledge::EntityRegistry>()
             // Triangle escalation event queue (#250) — consumed by storyteller + npc plugins
@@ -81,7 +86,7 @@ impl Plugin for SimulationPlugin {
         app.add_plugins(input_plugin::InputPlugin);
         app.add_plugins(movement_plugin::MovementPlugin);
         app.add_plugins(social_plugin::SocialPlugin);
-        app.add_plugins(economy_plugin::EconomyPlugin);
+        app.add_plugins(economy_plugin::EconomyPlugin { seed: self.seed });
 
         // Background worker tick integration (#843 Part C)
         app.add_systems(

server/src/test_world/mod.rs

@@ -695,7 +695,7 @@ mod tests {
     #[test]
     fn gauntlet_setup_creates_expected_entities() {
         let mut app = App::new();
-        app.add_plugins(crate::simulation::SimulationPlugin);
+        app.add_plugins(crate::simulation::SimulationPlugin { seed: 0 });
         app.add_plugins(crate::knowledge::KnowledgePlugin);
         app.add_plugins(crate::npc::NpcPlugin);
 
@@ -718,7 +718,7 @@ mod tests {
     #[test]
     fn hub_center_is_walkable() {
         let mut app = App::new();
-        app.add_plugins(crate::simulation::SimulationPlugin);
+        app.add_plugins(crate::simulation::SimulationPlugin { seed: 0 });
         app.add_plugins(crate::knowledge::KnowledgePlugin);
         app.add_plugins(crate::npc::NpcPlugin);
 
@@ -735,7 +735,7 @@ mod tests {
     #[test]
     fn occlusion_north_wall_blocks() {
         let mut app = App::new();
-        app.add_plugins(crate::simulation::SimulationPlugin);
+        app.add_plugins(crate::simulation::SimulationPlugin { seed: 0 });
         app.add_plugins(crate::knowledge::KnowledgePlugin);
         app.add_plugins(crate::npc::NpcPlugin);
 
@@ -754,7 +754,7 @@ mod tests {
     #[test]
     fn corridor_connects_hub_to_occlusion() {
         let mut app = App::new();
-        app.add_plugins(crate::simulation::SimulationPlugin);
+        app.add_plugins(crate::simulation::SimulationPlugin { seed: 0 });
         app.add_plugins(crate::knowledge::KnowledgePlugin);
         app.add_plugins(crate::npc::NpcPlugin);
 
@@ -771,7 +771,7 @@ mod tests {
     #[test]
     fn stable_id_ranges_match_spec() {
         let mut app = App::new();
-        app.add_plugins(crate::simulation::SimulationPlugin);
+        app.add_plugins(crate::simulation::SimulationPlugin { seed: 0 });
         app.add_plugins(crate::knowledge::KnowledgePlugin);
         app.add_plugins(crate::npc::NpcPlugin);