fix(mission): receive prints a completion once

Sources/Nirux/Model/MissionEventCLI.swift

@@ -274,13 +274,16 @@ enum MissionEventCLI {
 
     /// Wait for the next unconsumed child question/completion belonging to
     /// this parent column. Questions stay pending until a response is sent;
-    /// completion is acknowledged immediately after it is printed.
+    /// completion is acknowledged after it is printed, and `receive` returns
+    /// only once Nirux recorded that (or after `confirmationTimeout`), so
+    /// running it again right away does not print the same completion again.
     static func receive(
         arguments: [String],
         environment: [String: String] = ProcessInfo.processInfo.environment,
         now: @escaping () -> TimeInterval = { Date().timeIntervalSince1970 },
         eventsURL: URL = MissionEventCenter.defaultEventsURL,
         missionsURL: URL = MissionStore.defaultFileURL,
+        confirmationTimeout: TimeInterval = 5,
         pollInterval: TimeInterval = 0.2
     ) -> Int32 {
         guard let context = parentContext(environment) else { return notAMissionTerminal(child: false) }
@@ -340,6 +343,13 @@ enum MissionEventCLI {
                 timestamp: now()
             )
             guard append(acknowledgement, to: eventsURL) else { return 1 }
+            _ = waitForLedger(
+                &ledger, timeout: confirmationTimeout, pollInterval: pollInterval
+            ) { missions in
+                missions.lazy.flatMap(\.events).contains(where: {
+                    $0.id == event.id && $0.parentConsumedAt != nil
+                }) ? true : nil
+            }
         }
         return 0
     }

Tests/NiruxTests/MissionAskTests.swift

@@ -271,6 +271,7 @@ final class MissionAskTests: XCTestCase {
                 environment: parentEnvironment,
                 eventsURL: fixture.eventsURL,
                 missionsURL: fixture.missionsURL,
+                confirmationTimeout: 0,
                 pollInterval: 0.01
             )
         }
@@ -301,6 +302,35 @@ final class MissionAskTests: XCTestCase {
         ), 1)
     }
 
+    func testReceiveDeliversACompletionOnceWhenRunAgainRightAway() async throws {
+        let fixture = try makeFixture()
+        complete(fixture)
+        let environment = parentEnvironment
+        let eventsURL = fixture.eventsURL
+        let missionsURL = fixture.missionsURL
+        let receive: @Sendable () -> Int32 = {
+            MissionEventCLI.receive(
+                arguments: ["--timeout", "0"],
+                environment: environment,
+                eventsURL: eventsURL,
+                missionsURL: missionsURL,
+                pollInterval: 0.01
+            )
+        }
+        // The parent runs `receive` again as soon as the first one returns.
+        let twice = Task.detached { (receive(), receive()) }
+        // Nirux drains the queue a moment after the acknowledgement lands.
+        try await Task.sleep(nanoseconds: 200_000_000)
+        let deadline = Date().addingTimeInterval(5)
+        while fixture.store.missions[0].events[0].parentConsumedAt == nil, Date() < deadline {
+            fixture.center.drain()
+            try await Task.sleep(nanoseconds: 10_000_000)
+        }
+        let (first, second) = await twice.value
+        XCTAssertEqual(first, 0, "prints the completion")
+        XCTAssertEqual(second, 4, "the completion is not printed again")
+    }
+
     func testReplyStopsWhenTheQuestionWasAlreadyAnswered() throws {
         let fixture = try makeFixture()
         XCTAssertEqual(ask("Which API?", in: fixture), 3)

Tests/NiruxTests/MissionTellTests.swift

@@ -234,6 +234,7 @@ final class MissionTellTests: XCTestCase {
                 environment: parentEnvironment(),
                 eventsURL: fixture.eventsURL,
                 missionsURL: fixture.missionsURL,
+                confirmationTimeout: 0,
                 pollInterval: 0.01
             )
         }

Tests/NiruxTests/MissionTests.swift

@@ -208,6 +208,7 @@ final class MissionTests: XCTestCase {
             now: { 40 },
             eventsURL: eventsURL,
             missionsURL: missionsURL,
+            confirmationTimeout: 0,
             pollInterval: 0.01
         ), 0)
         let acknowledgement = try decodeSingleEvent(from: eventsURL)
@@ -387,6 +388,7 @@ extension MissionTests {
             now: { 40 },
             eventsURL: eventsURL,
             missionsURL: missionsURL,
+            confirmationTimeout: 0,
             pollInterval: 0.01
         ), 0)
         let center = MissionEventCenter(store: store, eventsURL: eventsURL, isEnabled: { true })