fix(skill): recognize empty catalog tombstones

packages/skill/tool-skill/src/index.ts

@@ -18,7 +18,7 @@ export const inject = ['agents', 'tools', 'skills']
 
 const DEFAULT_CATALOG_DESCRIPTION_MAX_LENGTH = 500
 const CATALOG_ENTRIES_START = '<available_skills>\n'
-const CATALOG_ENTRIES_END = '\n</available_skills>'
+const CATALOG_ENTRIES_END = '</available_skills>'
 const PLUGIN_SOURCE = { kind: 'plugin', plugin: 'dsh-tool-skill' } as const
 
 /** Model-facing skill catalog configuration. */
@@ -275,7 +275,9 @@ function catalogContentDigest(content: UserMessage['content']): string | undefin
   const entriesStart = start + CATALOG_ENTRIES_START.length
   const end = text.indexOf(CATALOG_ENTRIES_END, entriesStart)
   if (end === -1) return undefined
-  return digestCatalogEntries(text.slice(entriesStart, end))
+  const renderedEntries = text.slice(entriesStart, end)
+  const entries = renderedEntries.endsWith('\n') ? renderedEntries.slice(0, -1) : renderedEntries
+  return digestCatalogEntries(entries)
 }
 
 function catalogDescription(value: string, maxLength: number): string {

packages/skill/tool-skill/tests/tool-skill.spec.ts

@@ -320,6 +320,9 @@ describe('dsh-tool-skill', () => {
     expect(JSON.stringify(removal.data.content)).toContain('No skills are currently available')
     expect(JSON.stringify(removal.data.content)).not.toContain('first-skill')
     expect(JSON.stringify(removal.data.content)).not.toContain('second-skill')
+
+    await fireStep(ctx, agent, 1, 4)
+    expect(catalogMessages(session)).toHaveLength(3)
   })
 
   it('resumes from the latest valid visible catalog content', async () => {