diff --git a/scripts/ci/simple_pool_picker.py b/scripts/ci/simple_pool_picker.py
index dcd41ef9f71e..be818bd5523b 100644
--- a/scripts/ci/simple_pool_picker.py
+++ b/scripts/ci/simple_pool_picker.py
@@ -232,10 +232,20 @@ def write_outputs(choice: Choice, jobs: int, path: str | None = None,
             owned_jobs.append("lag")
         if env.get("RUN_CLI") == "true":
             owned_jobs.append("cli-product")
+        # swift-package-tests first builds the Release Ghostty CLI helper
+        # against an SDK 15 Xcode when this run is a full suite that also
+        # checks the Release build. Only the Blacksmith macOS 15 image carries
+        # that SDK; the minis have Xcode 26.6 alone, where ci-macos.yml's
+        # "Select helper Xcode" exits non-zero rather than falling back. So the
+        # lane takes an owned Mac only when it builds no helper
+        # (pr_runner_pool.package_lane_owned()).
+        helper_build = env.get("RUN_FULL_SUITE") == "true" and env.get("RUN_RELEASE_BUILD") == "true"
         for key, lane in (("RUN_CLAUDE_WRAPPER", "claude-wrapper"),
                           ("RUN_REMOTE_DAEMON", "remote-daemon"),
                           ("RUN_SWIFT_PACKAGES", "swift-package"),
                           ("RUN_RELEASE_BUILD", "release-build")):
+            if lane == "swift-package" and helper_build:
+                continue
             if env.get(key) == "true":
                 owned_jobs.append(lane)
     values.update(runner=choice.label, xcode_app=choice.xcode_app, retry_runner=choice.label,
diff --git a/tests/test_ci_simple_pool_picker.py b/tests/test_ci_simple_pool_picker.py
index 6b712a5060f1..fbea3238b80e 100644
--- a/tests/test_ci_simple_pool_picker.py
+++ b/tests/test_ci_simple_pool_picker.py
@@ -109,6 +109,19 @@ def test_outputs_keep_workflow_contract_for_owned_choice(self):
         self.assertEqual(values["root_runner"], "glaeda-root-std-xcode-26.6")
         self.assertEqual(values["admission_runner"], '["glaeda-root-std-xcode-26.6"]')
 
+    def test_full_suite_release_build_keeps_swift_package_off_the_minis(self):
+        """swift-package-tests builds the SDK 15 helper there, which the minis cannot."""
+        owned = picker.Choice("glaeda-std-xcode-26.6", "owned", owned=True)
+        helper = picker.write_outputs(owned, 3, env={
+            "RUN_MACOS": "true", "RUN_FULL_SUITE": "true",
+            "RUN_SWIFT_PACKAGES": "true", "RUN_RELEASE_BUILD": "true"})
+        self.assertNotIn(" swift-package ", helper["owned_jobs"])
+        self.assertIn(" release-build ", helper["owned_jobs"])
+
+        routed = picker.write_outputs(owned, 1, env={
+            "RUN_MACOS": "true", "RUN_SWIFT_PACKAGES": "true"})
+        self.assertIn(" swift-package ", routed["owned_jobs"])
+
     def test_only_explicitly_allowed_fork_can_use_owned_pool(self):
         base = {
             "GITHUB_REPOSITORY": "manaflow-ai/cmux",