diff --git a/src/simulator/crates/mc-trade/tests/courier_lifecycle.rs b/src/simulator/crates/mc-trade/tests/courier_lifecycle.rs
new file mode 100644
index 00000000..44d4770b
--- /dev/null
+++ b/src/simulator/crates/mc-trade/tests/courier_lifecycle.rs
@@ -0,0 +1,236 @@
+//! Courier route resolver lifecycle tests (p3-01 c4).
+//!
+//! Tests cover:
+//! - OpenBorders decrement + expiry
+//! - SharedMap with zero-intercept map: courier reaches destination, fires SharedMapDelivered
+//! - SharedMap with 100% intercept map: courier intercepted on first step
+
+use mc_trade::{
+    CourierMapView, CourierRoute, DiplomacyEvent, DiplomaticAgreement, OpenBordersAgreement,
+    SharedMapAgreement, TradeLedger, step_shared_map_agreements,
+};
+
+// ── Mock map view ────────────────────────────────────────────────────────────
+
+struct MockMap {
+    /// Capital positions indexed by player.
+    capitals: Vec<Option<(i32, i32)>>,
+    /// Fixed intercept probability returned for every tile.
+    intercept_chance: f32,
+}
+
+impl CourierMapView for MockMap {
+    fn capital_position(&self, player: u8) -> Option<(i32, i32)> {
+        self.capitals.get(player as usize).copied().flatten()
+    }
+
+    fn intercept_chance_at(&self, _pos: (i32, i32), _courier_owner: u8) -> f32 {
+        self.intercept_chance
+    }
+
+    fn route_intact(&self, _route: &CourierRoute) -> bool {
+        true
+    }
+}
+
+// ── Deterministic RNG (xorshift64 — no rand crate dependency in tests) ──────
+
+/// Returns a deterministic pseudo-random f32 in [0.0, 1.0) and the next state.
+fn xorshift64(mut state: u64) -> (f32, u64) {
+    state ^= state << 13;
+    state ^= state >> 7;
+    state ^= state << 17;
+    let bits = 0x3f80_0000u32 | ((state >> 41) as u32 & 0x007f_ffff);
+    (f32::from_bits(bits) - 1.0, state)
+}
+
+/// A minimal `impl Rng`-compatible adapter wrapping xorshift64 so we can
+/// pass a deterministic RNG to `step_shared_map_agreements` without pulling
+/// the full `rand` crate into the test file.
+struct XorRng(u64);
+
+impl rand::RngCore for XorRng {
+    fn next_u32(&mut self) -> u32 {
+        let (_, next) = xorshift64(self.0);
+        self.0 = next;
+        next as u32
+    }
+    fn next_u64(&mut self) -> u64 {
+        let (_, next) = xorshift64(self.0);
+        self.0 = next;
+        next
+    }
+    fn fill_bytes(&mut self, dest: &mut [u8]) {
+        for chunk in dest.chunks_mut(8) {
+            let (_, next) = xorshift64(self.0);
+            self.0 = next;
+            let bytes = next.to_le_bytes();
+            chunk.copy_from_slice(&bytes[..chunk.len()]);
+        }
+    }
+}
+
+// ── Helpers ──────────────────────────────────────────────────────────────────
+
+fn open_borders(agreement_id: u64, turns_remaining: u32) -> DiplomaticAgreement {
+    DiplomaticAgreement::OpenBorders(OpenBordersAgreement {
+        agreement_id,
+        partners: (0, 1),
+        turn_started: 1,
+        turns_remaining,
+        payment_gold: 20,
+        payment_luxury: None,
+    })
+}
+
+fn shared_map_agreement(
+    agreement_id: u64,
+    sender_pos: (i32, i32),
+    duration: u32,
+) -> DiplomaticAgreement {
+    DiplomaticAgreement::SharedMap(SharedMapAgreement {
+        agreement_id,
+        partners: (0, 1),
+        turn_started: 1,
+        duration,
+        share_turns_remaining: 0,
+        payment_gold: 30,
+        payment_luxury: None,
+        courier_route: Some(CourierRoute {
+            sender: 0,
+            receiver: 1,
+            courier_era_tier: 2,
+            dispatched_turn: 1,
+            position: sender_pos,
+            eta_turn: None,
+            delivered: false,
+            intercepted: false,
+        }),
+    })
+}
+
+// ── Tests ────────────────────────────────────────────────────────────────────
+
+/// OpenBorders decrements each turn and emits OpenBordersExpired at zero.
+#[test]
+fn open_borders_decrements_and_expires() {
+    let map = MockMap {
+        capitals: vec![Some((0, 0)), Some((3, 0))],
+        intercept_chance: 0.0,
+    };
+    let mut rng = XorRng(12345);
+
+    let mut ledger = TradeLedger::default();
+    let id = ledger.alloc_agreement_id();
+    ledger.agreements.push(open_borders(id, 3));
+
+    // Turn 1: 3 → 2
+    let events = step_shared_map_agreements(&mut ledger, &map, &mut rng);
+    assert!(events.is_empty(), "no expiry yet");
+    assert_eq!(ledger.agreements.len(), 1);
+    if let DiplomaticAgreement::OpenBorders(ob) = &ledger.agreements[0] {
+        assert_eq!(ob.turns_remaining, 2);
+    }
+
+    // Turn 2: 2 → 1
+    let events = step_shared_map_agreements(&mut ledger, &map, &mut rng);
+    assert!(events.is_empty());
+    assert_eq!(ledger.agreements.len(), 1);
+    if let DiplomaticAgreement::OpenBorders(ob) = &ledger.agreements[0] {
+        assert_eq!(ob.turns_remaining, 1);
+    }
+
+    // Turn 3: 1 → 0 → expired, removed
+    let events = step_shared_map_agreements(&mut ledger, &map, &mut rng);
+    assert_eq!(events.len(), 1, "expiry event expected");
+    assert!(
+        matches!(&events[0], DiplomacyEvent::OpenBordersExpired(e) if e.agreement_id == id),
+        "wrong event: {events:?}"
+    );
+    assert!(ledger.agreements.is_empty(), "agreement must be removed after expiry");
+}
+
+/// SharedMap with intercept_chance=0.0: courier starts adjacent to destination
+/// and delivers on the first step, emitting SharedMapDelivered.
+#[test]
+fn shared_map_delivers_with_zero_intercept() {
+    // Sender at (2, 0), capital of receiver at (3, 0) — one step away.
+    let map = MockMap {
+        capitals: vec![Some((0, 0)), Some((3, 0))],
+        intercept_chance: 0.0,
+    };
+    let mut rng = XorRng(99);
+    let duration = 4;
+
+    let mut ledger = TradeLedger::default();
+    let id = ledger.alloc_agreement_id();
+    ledger.agreements.push(shared_map_agreement(id, (2, 0), duration));
+
+    // First step: courier at (2,0) → no intercept → moves to (3,0) → delivered.
+    let events = step_shared_map_agreements(&mut ledger, &map, &mut rng);
+    assert_eq!(events.len(), 1, "expected SharedMapDelivered event");
+    assert!(
+        matches!(&events[0], DiplomacyEvent::SharedMapDelivered(e)
+            if e.agreement_id == id && e.turns_remaining == duration),
+        "wrong event: {events:?}"
+    );
+
+    // Agreement still present (share window ticking).
+    assert_eq!(ledger.agreements.len(), 1);
+    if let DiplomaticAgreement::SharedMap(sm) = &ledger.agreements[0] {
+        assert_eq!(sm.share_turns_remaining, duration);
+        let route = sm.courier_route.as_ref().expect("route present");
+        assert!(route.delivered);
+    }
+
+    // Tick the share window down to zero — should emit SharedMapExpired.
+    for _ in 0..duration {
+        step_shared_map_agreements(&mut ledger, &map, &mut rng);
+    }
+    // On the turn share_turns_remaining hits zero:
+    let events = step_shared_map_agreements(&mut ledger, &map, &mut rng);
+    // The expiry may have fired in the loop above; check ledger is empty.
+    // (exact timing: share_turns_remaining starts at `duration`, decrements
+    // each tick, fires when it reaches 0 — that's after `duration` ticks.)
+    assert!(
+        ledger.agreements.is_empty(),
+        "SharedMap agreement must be removed after share window expires"
+    );
+    let _ = events; // expiry event already consumed or in final tick
+}
+
+/// SharedMap with intercept_chance=1.0: courier is intercepted on the first
+/// step, emitting CourierIntercepted. Agreement is NOT removed (caller decides).
+#[test]
+fn shared_map_intercepted_on_first_step() {
+    // Sender at (0, 0), far from receiver capital at (10, 0).
+    let map = MockMap {
+        capitals: vec![Some((0, 0)), Some((10, 0))],
+        intercept_chance: 1.0,
+    };
+    let mut rng = XorRng(42);
+
+    let mut ledger = TradeLedger::default();
+    let id = ledger.alloc_agreement_id();
+    ledger.agreements.push(shared_map_agreement(id, (0, 0), 5));
+
+    let events = step_shared_map_agreements(&mut ledger, &map, &mut rng);
+    assert_eq!(events.len(), 1, "expected CourierIntercepted event");
+    assert!(
+        matches!(&events[0], DiplomacyEvent::CourierIntercepted(e)
+            if e.agreement_id == id && e.at_position == (0, 0)),
+        "wrong event: {events:?}"
+    );
+
+    // Courier state is intercepted; agreement stays for caller inspection.
+    assert_eq!(ledger.agreements.len(), 1);
+    if let DiplomaticAgreement::SharedMap(sm) = &ledger.agreements[0] {
+        let route = sm.courier_route.as_ref().expect("route present");
+        assert!(route.intercepted);
+        assert!(!route.delivered);
+    }
+
+    // Subsequent steps do nothing (terminal state).
+    let events2 = step_shared_map_agreements(&mut ledger, &map, &mut rng);
+    assert!(events2.is_empty(), "no events after intercept");
+}