diff --git a/src/resources/extensions/gsd/auto-prompts.ts b/src/resources/extensions/gsd/auto-prompts.ts
index d683102dc..102aebb63 100644
--- a/src/resources/extensions/gsd/auto-prompts.ts
+++ b/src/resources/extensions/gsd/auto-prompts.ts
@@ -421,7 +421,9 @@ function resolvePreferredSkillNames(
 
 function formatSkillActivationBlock(skillNames: string[]): string {
   if (skillNames.length === 0) return "";
-  const calls = skillNames.map(name => `Call Skill('${name}')`).join('. ');
+  // Use explicit parameter syntax so LLMs pass { skill: "..." } instead of { name: "..." }.
+  // Positional-looking `Skill('name')` caused validation failures — see #2224.
+  const calls = skillNames.map(name => `Call Skill({ skill: '${name}' })`).join('. ');
   return `<skill_activation>${calls}.</skill_activation>`;
 }
 
diff --git a/src/resources/extensions/gsd/tests/skill-activation.test.ts b/src/resources/extensions/gsd/tests/skill-activation.test.ts
index 673e8911c..312c078bf 100644
--- a/src/resources/extensions/gsd/tests/skill-activation.test.ts
+++ b/src/resources/extensions/gsd/tests/skill-activation.test.ts
@@ -75,7 +75,7 @@ test("buildSkillActivationBlock activates skills via prefer_skills when context
       prefer_skills: ["react"],
     });
 
-    assert.match(result, /Call Skill\('react'\)/);
+    assert.match(result, /Call Skill\(\{ skill: 'react' \}\)/);
     assert.doesNotMatch(result, /swiftui/);
   } finally {
     cleanup(base);
@@ -92,7 +92,7 @@ test("buildSkillActivationBlock includes always_use_skills from preferences usin
       always_use_skills: ["swift-testing"],
     });
 
-    assert.equal(result, "<skill_activation>Call Skill('swift-testing').</skill_activation>");
+    assert.equal(result, "<skill_activation>Call Skill({ skill: 'swift-testing' }).</skill_activation>");
   } finally {
     cleanup(base);
   }
@@ -120,8 +120,8 @@ test("buildSkillActivationBlock includes skill_rules matches and task-plan skill
       skill_rules: [{ when: "prisma database schema", use: ["prisma"] }],
     });
 
-    assert.match(result, /Call Skill\('accessibility'\)/);
-    assert.match(result, /Call Skill\('prisma'\)/);
+    assert.match(result, /Call Skill\(\{ skill: 'accessibility' \}\)/);
+    assert.match(result, /Call Skill\(\{ skill: 'prisma' \}\)/);
   } finally {
     cleanup(base);
   }