feat: wrap skill content in <skill-name> XML tags

Skill content is now wrapped in XML tags matching the skill name
(e.g., <commit>...</commit>) so the agent can detect already-loaded
skills in the conversation turn.

👾 Generated with [Letta Code](https://letta.com)

Co-Authored-By: Letta <noreply@letta.com>

src/tools/impl/Skill.ts

@@ -155,8 +155,12 @@ export async function skill(args: SkillArgs): Promise<SkillResult> {
     const fullContent = `${dirHeader}${processedContent}`;
 
     // Queue the skill content for harness-level injection as a user message part
+    // Wrap in <skill-name> XML tags so the agent can detect already-loaded skills
     if (toolCallId) {
-      queueSkillContent(toolCallId, fullContent);
+      queueSkillContent(
+        toolCallId,
+        `<${skillName}>\n${fullContent}\n</${skillName}>`,
+      );
     }
 
     return { message: `Launching skill: ${skillName}` };