fix(tip): raise a DM fee floor to the regional minimum

FlipcashCore/Sources/FlipcashCore/Models/TipFloor.swift

@@ -53,7 +53,7 @@ extension TipFloor {
 
     /// The floor for the tip that *opens* a DM with a recipient: the fee they
     /// charge, restated in `currency`, falling back to the regional preset when
-    /// they charge nothing. Nil when neither is known.
+    /// they charge nothing or their fee is below it. Nil when neither is known.
     ///
     /// The fallback also covers a fee that can't be converted — stating a floor
     /// in a currency the entry isn't using would be worse than stating the
@@ -67,11 +67,24 @@ extension TipFloor {
         // Rounded up: a half-up floor can land under the fee, pass `isMet`,
         // and be denied by the server.
         if let fee = recipientFee?.converted(to: currency, rates: rates, roundingUp: true), fee.isPositive {
+            // Every tip carries the regional minimum, so a fee under it would
+            // pass the fee check and be denied for the minimum.
+            if let presets, !clears(fee, presets, rates: rates) {
+                return .preset(presets)
+            }
             return .recipientFee(fee)
         }
         return systemMinimum(presets: presets)
     }
 
+    /// Whether `fee` meets the preset row's minimum, compared the way
+    /// `TipPresets.meetsMinimum` compares an entry. A fee that can't be
+    /// restated in the row's currency keeps its own floor.
+    private static func clears(_ fee: FiatAmount, _ presets: UserFlags.TipPresets, rates: [CurrencyCode: Rate]) -> Bool {
+        guard let restated = fee.converted(to: presets.currency, rates: rates) else { return true }
+        return restated.value >= presets.minimum
+    }
+
     /// The regional minimum every tip carries, regardless of recipient.
     public static func systemMinimum(presets: UserFlags.TipPresets?) -> TipFloor? {
         presets.map { .preset($0) }

FlipcashCore/Tests/FlipcashCoreTests/TipFloorTests.swift

@@ -71,6 +71,43 @@ struct TipFloorTests {
         #expect(floor == .preset(presets))
     }
 
+    @Test("A fee below the regional minimum is raised to the minimum")
+    func feeBelowPresetUsesPreset() {
+        let floor = TipFloor.toOpenDM(
+            recipientFee: FiatAmount(value: Decimal(string: "0.50")!, currency: .usd),
+            presets: presets,
+            in: .usd,
+            rates: rates
+        )
+
+        #expect(floor == .preset(presets))
+    }
+
+    @Test("A fee below the USD fallback minimum is raised to it")
+    func feeBelowFallbackPresetUsesPreset() {
+        // CAD 1 is USD 0.50, under the USD row's minimum of 1.
+        let floor = TipFloor.toOpenDM(
+            recipientFee: FiatAmount(value: 1, currency: .cad),
+            presets: presets,
+            in: .cad,
+            rates: rates
+        )
+
+        #expect(floor == .preset(presets))
+    }
+
+    @Test("A fee at the regional minimum stays the fee")
+    func feeAtPresetStaysFee() {
+        let floor = TipFloor.toOpenDM(
+            recipientFee: FiatAmount(value: 2, currency: .cad),
+            presets: presets,
+            in: .cad,
+            rates: rates
+        )
+
+        #expect(floor == .recipientFee(FiatAmount(value: 2, currency: .cad)))
+    }
+
     @Test("No fee and no presets leaves no floor")
     func nilWithoutEither() {
         #expect(TipFloor.toOpenDM(recipientFee: nil, presets: nil, in: .usd, rates: rates) == nil)