fix(skill): resolve namespaced skills by short name

When a skill has a namespaced name like 'superpowers/systematic-debugging',
users see the short name 'systematic-debugging' in the listing but can't
invoke it — the resolver only accepts exact full names.

Add short-name fallback: if exact match fails, try matching the basename
of namespaced skills. Only resolves when unambiguous (single match).

- Exact match still takes priority
- Ambiguous short names (multiple namespaces) fall through to error
- 4 new tests covering all cases

Fixes #2971

src/tools/skill/tools.test.ts

@@ -670,3 +670,58 @@ describe("skill tool - nativeSkills integration", () => {
     expect(result).toContain("External plugin skill body")
   })
 })
+
+describe("skill tool - short name resolution", () => {
+  it("resolves namespaced skill by short name when unambiguous", async () => {
+    // given
+    const loadedSkills = [createMockSkill("superpowers/systematic-debugging")]
+    const tool = createSkillTool({ skills: loadedSkills })
+
+    // when
+    const result = await tool.execute({ name: "systematic-debugging" }, mockContext)
+
+    // then
+    expect(result).toContain("superpowers/systematic-debugging")
+  })
+
+  it("still resolves by exact full name", async () => {
+    // given
+    const loadedSkills = [createMockSkill("superpowers/systematic-debugging")]
+    const tool = createSkillTool({ skills: loadedSkills })
+
+    // when
+    const result = await tool.execute({ name: "superpowers/systematic-debugging" }, mockContext)
+
+    // then
+    expect(result).toContain("superpowers/systematic-debugging")
+  })
+
+  it("does not resolve short name when ambiguous (multiple matches)", async () => {
+    // given
+    const loadedSkills = [
+      createMockSkill("superpowers/debugging"),
+      createMockSkill("utils/debugging"),
+    ]
+    const tool = createSkillTool({ skills: loadedSkills })
+
+    // when / then — should not resolve (ambiguous), should suggest both
+    await expect(tool.execute({ name: "debugging" }, mockContext)).rejects.toThrow(
+      "not found"
+    )
+  })
+
+  it("prefers exact match over short name match", async () => {
+    // given — "debugging" exists as both exact and as part of a namespace
+    const loadedSkills = [
+      createMockSkill("debugging"),
+      createMockSkill("superpowers/debugging"),
+    ]
+    const tool = createSkillTool({ skills: loadedSkills })
+
+    // when
+    const result = await tool.execute({ name: "debugging" }, mockContext)
+
+    // then — should match "debugging" exactly, not "superpowers/debugging"
+    expect(result).toContain("## Skill: debugging")
+  })
+})