fix: generate skill/slashcommand descriptions synchronously when pre-provided (#1087)

* fix: generate skill/slashcommand tool descriptions synchronously when pre-provided

When skills are passed via options (pre-resolved), build the tool description
synchronously instead of fire-and-forget async. This eliminates the race
condition where the description getter returns the bare prefix before the
async cache-warming microtask completes.

Fixes #1039

* chore: changes by sisyphus-dev-ai

---------

Co-authored-by: sisyphus-dev-ai <sisyphus-dev-ai@users.noreply.github.com>

src/tools/skill/tools.test.ts

@@ -57,6 +57,45 @@ const mockContext = {
   abort: new AbortController().signal,
 }
 
+describe("skill tool - synchronous description", () => {
+  it("includes available_skills immediately when skills are pre-provided", () => {
+    // #given
+    const loadedSkills = [createMockSkill("test-skill")]
+
+    // #when
+    const tool = createSkillTool({ skills: loadedSkills })
+
+    // #then
+    expect(tool.description).toContain("<available_skills>")
+    expect(tool.description).toContain("test-skill")
+  })
+
+  it("includes all pre-provided skills in available_skills immediately", () => {
+    // #given
+    const loadedSkills = [
+      createMockSkill("playwright"),
+      createMockSkill("frontend-ui-ux"),
+      createMockSkill("git-master"),
+    ]
+
+    // #when
+    const tool = createSkillTool({ skills: loadedSkills })
+
+    // #then
+    expect(tool.description).toContain("playwright")
+    expect(tool.description).toContain("frontend-ui-ux")
+    expect(tool.description).toContain("git-master")
+  })
+
+  it("shows no-skills message immediately when empty skills are pre-provided", () => {
+    // #given / #when
+    const tool = createSkillTool({ skills: [] })
+
+    // #then
+    expect(tool.description).toContain("No skills are currently available")
+  })
+})
+
 describe("skill tool - agent restriction", () => {
   it("allows skill without agent restriction to any agent", async () => {
     // #given

src/tools/skill/tools.ts

@@ -147,7 +147,14 @@ export function createSkillTool(options: SkillLoadOptions = {}): ToolDefinition
     return cachedDescription
   }
 
-  getDescription()
+  if (options.skills) {
+    const skillInfos = options.skills.map(loadedSkillToInfo)
+    cachedDescription = skillInfos.length === 0
+      ? TOOL_DESCRIPTION_NO_SKILLS
+      : TOOL_DESCRIPTION_PREFIX + formatSkillsXml(skillInfos)
+  } else {
+    getDescription()
+  }
 
   return tool({
     get description() {