fix: prevent reading SKILL.md files when listing available skills

When users ask to list/show/display available skills, the model should
use the information already provided in <available_skills> instead of
reading each SKILL.md file unnecessarily.

Adds <if_user_asks_to_list_skills> section to the skills system prompt
to explicitly instruct the model to use the existing name, description,
and location fields for informational queries.

Closes #10393

src/core/prompts/sections/__tests__/skills.spec.ts

@@ -29,4 +29,25 @@ describe("getSkillsSection", () => {
 		await expect(getSkillsSection(undefined, "code")).resolves.toBe("")
 		await expect(getSkillsSection({ getSkillsForMode: vi.fn() }, undefined)).resolves.toBe("")
 	})
+
+	it("should include instructions to not read SKILL.md files when listing skills", async () => {
+		const mockSkillsManager = {
+			getSkillsForMode: vi.fn().mockReturnValue([
+				{
+					name: "test-skill",
+					description: "Test skill description",
+					path: "/path/to/test-skill/SKILL.md",
+					source: "global" as const,
+				},
+			]),
+		}
+
+		const result = await getSkillsSection(mockSkillsManager, "code")
+
+		// Verify the new section for listing skills is present
+		expect(result).toContain("<if_user_asks_to_list_skills>")
+		expect(result).toContain("</if_user_asks_to_list_skills>")
+		expect(result).toContain("use ONLY the information already provided in <available_skills>")
+		expect(result).toContain("Do NOT read any SKILL.md files for informational queries")
+	})
 })

src/core/prompts/sections/skills.ts

@@ -68,6 +68,13 @@ Step 2: Branching Decision
 - Do NOT respond outside the skill-defined flow.
 </if_skill_applies>
 
+<if_user_asks_to_list_skills>
+- When the user asks to list, show, display, or enumerate available skills, use ONLY the information already provided in <available_skills> above.
+- The <name>, <description>, and <location> fields provide all necessary information to describe available skills.
+- Do NOT read any SKILL.md files for informational queries about what skills exist.
+- This applies to requests like "list all skills", "what skills are available", "show me the skills", etc.
+</if_user_asks_to_list_skills>
+
 <if_no_skill_applies>
 - Proceed with a normal response.
 - Do NOT load any SKILL.md files.