Gate Antigravity nudges on the invocation counter

src/Capacitor.Cli/Commands/Harness/AntigravityHookCommand.cs

@@ -206,9 +206,14 @@ HookBudget  budget
         // subtracts HookBudget.Safety — do NOT subtract it again. Written even when the watcher-spawn
         // gate below returns early — a withheld watcher must not suppress injection.
         var fragment = await SessionStartMemoryHookSupport.AwaitBounded(memoryTask, budget);
-        var workItemsNudge = HarnessNudgeEmitter.Combine(
-            WorkItemsNudgeEmitter.Resolve(SessionStartHarness.Antigravity, sessionId, activeProfile?.DisableWorkItemsNudge is true),
-            HarnessNudgeEmitter.ResolveFragmentForHook(activeProfile?.DisableHarnessNudge is true, config));
+        // Nudges are unleased pure functions of the session id, so on this repeating callback they
+        // must be gated by the vendor's own per-conversation counter: without the gate every turn
+        // re-injects them as another persistent userMessage step.
+        var workItemsNudge = IsFirstInvocation(payload)
+            ? HarnessNudgeEmitter.Combine(
+                WorkItemsNudgeEmitter.Resolve(SessionStartHarness.Antigravity, sessionId, activeProfile?.DisableWorkItemsNudge is true),
+                HarnessNudgeEmitter.ResolveFragmentForHook(activeProfile?.DisableHarnessNudge is true, config))
+            : null;
         WritePreInvocationOutput(stdout, fragment, workItemsNudge);
         await stdout.FlushAsync();
 
@@ -309,6 +314,17 @@ internal static SessionMemoryLifecycle LifecycleFor(string sessionId) =>
         }
     }
 
+    /// <summary>
+    /// Whether this PreInvocation is the conversation's first, read from the vendor's own
+    /// <c>invocationNum</c> counter — the one payload field that varies between callbacks. An absent
+    /// or non-numeric value reads as first: a payload without the counter cannot distinguish
+    /// callbacks, and emitting once too often beats never emitting.
+    /// </summary>
+    internal static bool IsFirstInvocation(JsonObject payload) =>
+        payload["invocationNum"] is not JsonValue value
+     || !value.TryGetValue<long>(out var invocation)
+     || invocation <= 1;
+
     /// <summary>The event name — the first positional token after <c>--antigravity</c>.</summary>
     internal static string? EventArg(string[] args) {
         var idx = Array.IndexOf(args, "--antigravity");

test/Capacitor.Cli.Tests.Unit/Harness/Antigravity/AntigravitySessionStartMemoryTests.cs

@@ -242,4 +242,26 @@ public async Task HandleCore_consults_the_fallback_for_an_empty_workspacePaths_p
         await Assert.That(sw.ToString()).IsEqualTo("");
         await Assert.That(consulted).IsTrue();
     }
+
+    // The nudges carry no lease, so on this repeating callback only the invocation counter keeps
+    // them from re-injecting a persistent userMessage step every turn.
+
+    [Test]
+    public async Task The_first_invocation_emits_nudges() {
+        await Assert.That(AntigravityHookCommand.IsFirstInvocation(Payload("""{"invocationNum":1}"""))).IsTrue();
+    }
+
+    [Test]
+    public async Task A_later_invocation_suppresses_nudges() {
+        await Assert.That(AntigravityHookCommand.IsFirstInvocation(Payload("""{"invocationNum":2}"""))).IsFalse();
+        await Assert.That(AntigravityHookCommand.IsFirstInvocation(Payload("""{"invocationNum":97}"""))).IsFalse();
+    }
+
+    // Fail-open: a payload that cannot distinguish callbacks must still emit.
+    [Test]
+    public async Task A_missing_or_non_numeric_counter_reads_as_the_first_invocation() {
+        await Assert.That(AntigravityHookCommand.IsFirstInvocation(Payload("{}"))).IsTrue();
+        await Assert.That(AntigravityHookCommand.IsFirstInvocation(Payload("""{"invocationNum":"2"}"""))).IsTrue();
+        await Assert.That(AntigravityHookCommand.IsFirstInvocation(Payload("""{"invocationNum":0}"""))).IsTrue();
+    }
 }