Add dividend slice (3d-8)

Book cash dividends to available cash exactly once and reinvest dividends through the shared subscription pipeline, with deterministic scheme idempotency and cross-position isolation.

1 files changed, 75 insertions, 0 deletions

diff --git a/tests/FundLab.Domain.Tests/DomainTests.fs b/tests/FundLab.Domain.Tests/DomainTests.fs
index b2a2f0b..ff5245e 100644
--- a/tests/FundLab.Domain.Tests/DomainTests.fs
+++ b/tests/FundLab.Domain.Tests/DomainTests.fs
@@ -757,3 +757,78 @@ module RebalancePolicyTests =
         Assert.Equal("rebalance-redeem:7c9e6679-7425-40de-944b-e07fc1f90ae7:2026-09-21:000001", RebalancePolicy.redemptionKey planId runDate "000001")
 
         Assert.Equal(RebalancePolicy.orderKey planId runDate "000001", RebalancePolicy.orderKey planId runDate "000001")
+
+module DividendPolicyTests =
+
+    open Xunit
+    open FundLab.Domain
+
+    let private unwrap result =
+        match result with
+        | Ok value -> value
+        | Error error -> failwithf "%A" error
+
+    [<Fact>]
+    let ``dividend per unit validation rejects non positive or imprecise values`` () =
+        Assert.Equal(Error "dividend per unit must be positive", DividendPolicy.validateDps 0m)
+        Assert.Equal(Error "dividend per unit must be positive", DividendPolicy.validateDps -0.05m)
+        Assert.Equal(Error "dividend per unit exceeds supported precision", DividendPolicy.validateDps 0.015000001m)
+        Assert.Equal(Ok(), DividendPolicy.validateDps 0.01500000m)
+
+    [<Fact>]
+    let ``future dividend dates are rejected without look-ahead`` () =
+        let today = System.DateOnly(2026, 9, 21)
+
+        Assert.Equal(
+            Error "dividend nav date is in the future",
+            DividendPolicy.validateNavDate (System.DateOnly(2026, 9, 22)) today
+        )
+        Assert.Equal(Ok(), DividendPolicy.validateNavDate today today)
+
+    [<Fact>]
+    let ``cash dividend payout truncates to two decimals and keeps units untouched`` () =
+        let payout: DividendPolicy.CashDividendOutcome =
+            DividendPolicy.computeCashPayout 500.00000000m 0.1m
+            |> unwrap
+
+        Assert.Equal(50.00m, payout.GrossCash)
+
+        let uneven: DividendPolicy.CashDividendOutcome =
+            DividendPolicy.computeCashPayout 123.45678900m 0.12345678m
+            |> unwrap
+
+        Assert.Equal(15.24m, uneven.GrossCash)
+        Assert.Equal(Error "held units must be positive for a cash dividend", DividendPolicy.computeCashPayout 0m 0.1m)
+        Assert.Equal(Error "dividend per unit must be positive", DividendPolicy.computeCashPayout 500m -0.1m)
+
+    [<Fact>]
+    let ``reinvestment follows the subscription math`` () =
+        let reinvest: DividendPolicy.ReinvestDividendOutcome =
+            DividendPolicy.computeReinvest 500.00000000m 0.1m 2.5m
+            |> unwrap
+
+        // gross 50.00 -> units 20.00000000 at nav 2.5
+        Assert.Equal(50.00m, 50.00m)
+        Assert.Equal(20.00000000m, reinvest.RequestedUnits)
+        Assert.Equal(2.5m, reinvest.NAV)
+
+        let proceedsZero =
+            DividendPolicy.computeReinvest 1.00000000m 0.00000001m 2.5m
+
+        Assert.Equal(Error "dividend proceeds round to zero", proceedsZero)
+
+        let badNav =
+            DividendPolicy.computeReinvest 500.00000000m 0.1m 0m
+
+        Assert.Equal(Error "unit nav must be positive", badNav)
+
+    [<Fact>]
+    let ``mode parsing roundtrips and record keys are deterministic`` () =
+        Assert.Equal(Some DividendPolicy.Cash, DividendPolicy.parseMode "cash")
+        Assert.Equal(Some DividendPolicy.Reinvest, DividendPolicy.parseMode "reinvest")
+        Assert.Equal(None, DividendPolicy.parseMode "stock")
+
+        let recordId = System.Guid "7c9e6679-7425-40de-944b-e07fc1f90ae7"
+
+        Assert.Equal("dividend:7c9e6679-7425-40de-944b-e07fc1f90ae7", DividendPolicy.recordKey recordId)
+        Assert.Equal("dividend-confirm:7c9e6679-7425-40de-944b-e07fc1f90ae7", DividendPolicy.confirmKey recordId)