diff --git a/server/src/main.rs b/server/src/main.rs
index 3a4574b45..7182c49e9 100644
--- a/server/src/main.rs
+++ b/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);
diff --git a/server/src/simulation/economy.rs b/server/src/simulation/economy.rs
index 5cdad056a..928bf0134 100644
--- a/server/src/simulation/economy.rs
+++ b/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()))
         }
diff --git a/server/src/simulation/economy_plugin.rs b/server/src/simulation/economy_plugin.rs
index 9076e864f..23ab02f5f 100644
--- a/server/src/simulation/economy_plugin.rs
+++ b/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
diff --git a/server/src/simulation/mod.rs b/server/src/simulation/mod.rs
index 0956ccd74..944e65e78 100644
--- a/server/src/simulation/mod.rs
+++ b/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(
diff --git a/server/src/test_world/mod.rs b/server/src/test_world/mod.rs
index 9916aae9a..b70705d0a 100644
--- a/server/src/test_world/mod.rs
+++ b/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);
 
diff --git a/server/tests/archetype_monologue.rs b/server/tests/archetype_monologue.rs
index b5b1e6fe2..b1fb8669a 100644
--- a/server/tests/archetype_monologue.rs
+++ b/server/tests/archetype_monologue.rs
@@ -78,7 +78,7 @@ mod gauntlet_integration {
     /// Build a minimal Gauntlet app with the given archetype and run one tick.
     fn boot_gauntlet(archetype: CharacterArchetype) -> App {
         let mut app = App::new();
-        app.add_plugins(SimulationPlugin);
+        app.add_plugins(SimulationPlugin { seed: 0 });
         test_world::setup_gauntlet(&mut app, archetype);
         app.update();
         app
diff --git a/server/tests/cross_room_transitions.rs b/server/tests/cross_room_transitions.rs
index c4b086a40..92cdd1f95 100644
--- a/server/tests/cross_room_transitions.rs
+++ b/server/tests/cross_room_transitions.rs
@@ -221,7 +221,7 @@ fn t3_pause_mid_corridor_discards_movement_and_resumes() {
     use settled_reach_server::simulation::SimulationPlugin;
 
     let mut app = App::new();
-    app.add_plugins(SimulationPlugin);
+    app.add_plugins(SimulationPlugin { seed: 0 });
     // 200×200 walkability map covers the full gauntlet coordinate space.
     app.insert_resource(WalkabilityMap::new(200, 200, 1));
 
diff --git a/server/tests/determinism.rs b/server/tests/determinism.rs
index 78320afb3..b8ad0285e 100644
--- a/server/tests/determinism.rs
+++ b/server/tests/determinism.rs
@@ -38,7 +38,7 @@ use settled_reach_server::simulation::SimulationPlugin;
 /// Snapshots are written to SnapshotBuffer for direct inspection.
 fn build_deterministic_app(seed: u64) -> App {
     let mut app = App::new();
-    app.add_plugins(SimulationPlugin);
+    app.add_plugins(SimulationPlugin { seed });
     app.add_plugins(BridgePlugin);
     app.add_plugins(KnowledgePlugin);
     app.add_plugins(NpcPlugin);
diff --git a/server/tests/error_handling.rs b/server/tests/error_handling.rs
index 96ebbecc2..7db6a3a55 100644
--- a/server/tests/error_handling.rs
+++ b/server/tests/error_handling.rs
@@ -46,7 +46,7 @@ fn malformed_input_produces_sim_error_and_server_continues() {
         let bridge = TcpBridge::accept_on(listener).expect("accept connection");
 
         let mut app = App::new();
-        app.add_plugins(SimulationPlugin);
+        app.add_plugins(SimulationPlugin { seed: 0 });
         app.add_plugins(BridgePlugin);
         app.add_plugins(KnowledgePlugin);
         app.init_resource::<TrustEventQueue>();
@@ -177,7 +177,7 @@ fn state_hash_populated_in_snapshot() {
         let bridge = TcpBridge::accept_on(listener).expect("accept connection");
 
         let mut app = App::new();
-        app.add_plugins(SimulationPlugin);
+        app.add_plugins(SimulationPlugin { seed: 0 });
         app.add_plugins(BridgePlugin);
         app.add_plugins(KnowledgePlugin);
         app.init_resource::<TrustEventQueue>();
diff --git a/server/tests/game_loop.rs b/server/tests/game_loop.rs
index 8e10fcf81..61e903de2 100644
--- a/server/tests/game_loop.rs
+++ b/server/tests/game_loop.rs
@@ -28,7 +28,7 @@ fn player_moves_north_through_full_pipeline() {
 
         // Build app
         let mut app = App::new();
-        app.add_plugins(SimulationPlugin);
+        app.add_plugins(SimulationPlugin { seed: 0 });
         app.add_plugins(BridgePlugin);
         app.add_plugins(KnowledgePlugin);
         app.init_resource::<TrustEventQueue>();
diff --git a/server/tests/gen_gauntlet_fixtures.rs b/server/tests/gen_gauntlet_fixtures.rs
index beb59243f..aa6cb05d1 100644
--- a/server/tests/gen_gauntlet_fixtures.rs
+++ b/server/tests/gen_gauntlet_fixtures.rs
@@ -39,7 +39,7 @@ const FIXTURE_DIR: &str = "../tests/fixtures/gauntlet";
 /// Identical to what the server runs in --test-mode.
 fn build_gauntlet(seed: u64) -> App {
     let mut app = App::new();
-    app.add_plugins(SimulationPlugin);
+    app.add_plugins(SimulationPlugin { seed: 0 });
     app.add_plugins(BridgePlugin);
     app.add_plugins(KnowledgePlugin);
     app.add_plugins(NpcPlugin);
diff --git a/server/tests/golden_suite.rs b/server/tests/golden_suite.rs
index ea4afba00..9b025f575 100644
--- a/server/tests/golden_suite.rs
+++ b/server/tests/golden_suite.rs
@@ -46,7 +46,7 @@ const NUM_TICKS: usize = 10;
 /// Mirrors the setup in determinism.rs / main.rs.
 fn build_app(seed: u64) -> App {
     let mut app = App::new();
-    app.add_plugins(SimulationPlugin);
+    app.add_plugins(SimulationPlugin { seed: 0 });
     app.add_plugins(BridgePlugin);
     app.add_plugins(KnowledgePlugin);
     app.add_plugins(NpcPlugin);
diff --git a/server/tests/movement.rs b/server/tests/movement.rs
index 27c11fe57..f6b0766d1 100644
--- a/server/tests/movement.rs
+++ b/server/tests/movement.rs
@@ -6,7 +6,7 @@ use settled_reach_server::simulation::SimulationPlugin;
 #[test]
 fn movement_validated_within_app() {
     let mut app = App::new();
-    app.add_plugins(SimulationPlugin);
+    app.add_plugins(SimulationPlugin { seed: 0 });
 
     // Insert a walkability map with one blocked tile
     let mut map = WalkabilityMap::new(10, 10, 1);
@@ -56,7 +56,7 @@ fn movement_validated_within_app() {
 #[test]
 fn entity_collision_blocks_movement() {
     let mut app = App::new();
-    app.add_plugins(SimulationPlugin);
+    app.add_plugins(SimulationPlugin { seed: 0 });
     app.insert_resource(WalkabilityMap::new(10, 10, 1));
 
     // Stationary entity at (5,4)
diff --git a/server/tests/perf_bench.rs b/server/tests/perf_bench.rs
index b0e440035..6cdfd0247 100644
--- a/server/tests/perf_bench.rs
+++ b/server/tests/perf_bench.rs
@@ -66,7 +66,7 @@ fn perf_tick_timing() {
         let bridge = TcpBridge::accept_on(listener).expect("accept connection");
 
         let mut app = App::new();
-        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);
diff --git a/server/tests/smoke.rs b/server/tests/smoke.rs
index 9420d4216..96d32cbd6 100644
--- a/server/tests/smoke.rs
+++ b/server/tests/smoke.rs
@@ -7,7 +7,7 @@ use settled_reach_server::simulation::SimulationPlugin;
 #[test]
 fn world_boots_and_ticks() {
     let mut app = App::new();
-    app.add_plugins(SimulationPlugin);
+    app.add_plugins(SimulationPlugin { seed: 0 });
 
     // Verify initial state
     let time = app.world().resource::<SimulationTime>();
diff --git a/server/tests/tell_escalation.rs b/server/tests/tell_escalation.rs
index 1f41b93f6..a30f75555 100644
--- a/server/tests/tell_escalation.rs
+++ b/server/tests/tell_escalation.rs
@@ -112,7 +112,7 @@ fn build_storyteller_app() -> App {
         bridge::types::CharacterArchetype, simulation::SimulationPlugin, test_world,
     };
     let mut app = App::new();
-    app.add_plugins(SimulationPlugin);
+    app.add_plugins(SimulationPlugin { seed: 0 });
     test_world::setup_gauntlet(&mut app, CharacterArchetype::default());
     app
 }