fix: exclude unset grace_period_seconds from deployment concurrency_options (#19784)

Co-authored-by: Claude <[email protected]>

Author: zzstoatzz

src/prefect/client/orchestration/_deployments/client.py

@@ -157,6 +157,12 @@ def create_deployment(
             payload["version_info"] = deployment_create.version_info.model_dump(
                 mode="json"
             )
+        if deployment_create.concurrency_options:
+            payload["concurrency_options"] = (
+                deployment_create.concurrency_options.model_dump(
+                    mode="json", exclude_unset=True
+                )
+            )
 
         try:
             response = self.request("POST", "/deployments/", json=payload)
@@ -823,6 +829,12 @@ async def create_deployment(
             payload["version_info"] = deployment_create.version_info.model_dump(
                 mode="json"
             )
+        if deployment_create.concurrency_options:
+            payload["concurrency_options"] = (
+                deployment_create.concurrency_options.model_dump(
+                    mode="json", exclude_unset=True
+                )
+            )
 
         try:
             response = await self.request("POST", "/deployments/", json=payload)

tests/client/schemas/test_concurrency.py

@@ -92,3 +92,31 @@ def test_collision_strategy_cancel_new(self):
         """Test that collision_strategy can be set to CANCEL_NEW."""
         config = ConcurrencyLimitConfig(limit=1, collision_strategy="CANCEL_NEW")
         assert config.collision_strategy == "CANCEL_NEW"
+
+
+class TestConcurrencyOptionsSerialization:
+    """Tests for ConcurrencyOptions serialization behavior.
+
+    Regression tests for https://github.com/PrefectHQ/prefect/issues/19778
+    """
+
+    def test_grace_period_seconds_excluded_when_unset(self):
+        """Test that grace_period_seconds is excluded when not explicitly set.
+
+        When grace_period_seconds is not provided, model_dump(exclude_unset=True)
+        should not include it in the output. This prevents API 422 errors.
+        """
+        options = ConcurrencyOptions(collision_strategy="ENQUEUE")
+        payload = options.model_dump(mode="json", exclude_unset=True)
+
+        assert "grace_period_seconds" not in payload
+
+    def test_grace_period_seconds_included_when_set(self):
+        """Test that grace_period_seconds IS included when explicitly set."""
+        options = ConcurrencyOptions(
+            collision_strategy="ENQUEUE", grace_period_seconds=120
+        )
+        payload = options.model_dump(mode="json", exclude_unset=True)
+
+        assert "grace_period_seconds" in payload
+        assert payload["grace_period_seconds"] == 120