feat(skills): 技能加载/校验/真执行第一片（design/09 §6 定稿落地）

- 加载器/校验：目录式 configs/skills/<id>/skill.yaml（兼容旧单文件 <id>.yaml，先目录后文件）；
  新字段 version/when-to-use/invocation(三态)/triggers/paths/allowed-tools/disallowed-tools/
  context(ine|fork)/agent/model/effort/metadata；**依赖环 ⇒ 加载期拒**（运行期绝不挂死）；
  depends 指向不存在步骤 ⇒ 拒；同一工具同时在 allowed 与 disallowed ⇒ 拒；错误可分类（哨兵 + %w）
- Runner.Run 真执行（替换 ErrRunPending）：步骤拓扑（无依赖可并行、上限 2）+ guardrail 强制点
  （enforced 违反 ⇒ 中止并如实报「哪条、哪一步」；否则 WARN 继续）+ 失败不静默跳过 + ctx 取消传播
- 🔴 能力收缩只收不放：该轮可用工具 = allowed-tools ∩ 安全闸 ∩ 注册表，再减 disallowed-tools
- 另有渐进披露相关的 listing/surface/activation（清单投影与激活判定）

⚠️ 未接线：本片是库与执行器，尚未把技能清单接进模型面（见 report 的分阶段）。

internal/capability/skills/listing_test.go

@@ -0,0 +1,98 @@
+package skills
+
+import (
+	"strings"
+	"testing"
+
+	"git.yeij.top/AskaEth/Cyrene_v2/pkg/plugins/sdk"
+)
+
+// 本文件专测 design/09 §6.3 的清单投影：只有 name + description(+when-to-use)、
+// 三态过滤、单条预算、条数上限**如实标 truncated**。
+
+func TestBuildListing_三态(t *testing.T) {
+	t.Parallel()
+	both := mustSpecSkill(t, "both", "做 A", "在做 A 时", sdk.InvocationBoth)
+	modelOnly := mustSpecSkill(t, "model-only", "做 B", "", sdk.InvocationModelOnly)
+	userOnly := mustSpecSkill(t, "user-only", "做 C", "", sdk.InvocationUserOnly)
+
+	listing := BuildListing([]sdk.Skill{both, modelOnly, userOnly})
+	if len(listing.Entries) != 3 {
+		t.Fatalf("条目数 = %d, want 3（user-only 也要在清单里可见）", len(listing.Entries))
+	}
+	if got := listing.Entries[0].Description; got != "做 A Use when: 在做 A 时" {
+		t.Fatalf("both 描述 = %q, want 拼接 description + when-to-use", got)
+	}
+	if !listing.Entries[0].ModelInvocable || !listing.Entries[0].UserInvocable {
+		t.Fatalf("both 应当人与模型都可调：%+v", listing.Entries[0])
+	}
+	if listing.Entries[1].Description != "" || !listing.Entries[1].ModelInvocable || listing.Entries[1].UserInvocable {
+		t.Fatalf("model-only 应当「清单不带描述、只有模型可调」：%+v", listing.Entries[1])
+	}
+	if listing.Entries[2].Description == "" || listing.Entries[2].ModelInvocable || !listing.Entries[2].UserInvocable {
+		t.Fatalf("user-only 应当「清单带描述、模型不可调」：%+v", listing.Entries[2])
+	}
+}
+
+// TestBuildListing_正文不进清单 断言渐进披露的硬规格：清单里没有正文（prompt /
+// 步骤文本）—— 上面那些字段是唯一进清单的东西。
+func TestBuildListing_正文不进清单(t *testing.T) {
+	t.Parallel()
+	skill := mustSpecSkill(t, "s", "描述", "", sdk.InvocationBoth)
+	listing := BuildListing([]sdk.Skill{skill})
+	if len(listing.Entries) != 1 {
+		t.Fatalf("条目数 = %d, want 1", len(listing.Entries))
+	}
+	if strings.Contains(listing.Entries[0].Description, "base prompt") {
+		t.Fatalf("正文泄漏进清单：%q", listing.Entries[0].Description)
+	}
+}
+
+func TestBuildListing_单条预算截断(t *testing.T) {
+	t.Parallel()
+	skill := mustSpecSkill(t, "long", strings.Repeat("描", SkillListingDescriptionBudget+500), "", sdk.InvocationBoth)
+	entry := BuildListing([]sdk.Skill{skill}).Entries[0]
+	if !entry.Truncated {
+		t.Fatal("超预算的描述必须被标 Truncated")
+	}
+	if got := len([]rune(entry.Description)); got != SkillListingDescriptionBudget {
+		t.Fatalf("截断后长度 = %d, want %d", got, SkillListingDescriptionBudget)
+	}
+	if !strings.HasSuffix(entry.Description, SkillListingTruncatedMarker) {
+		t.Fatalf("截断没有显式标记：%q", entry.Description[len(entry.Description)-20:])
+	}
+}
+
+func TestBuildListing_条数上限如实标(t *testing.T) {
+	t.Parallel()
+	list := make([]sdk.Skill, 0, SkillListingMaxEntries+3)
+	for i := 0; i < SkillListingMaxEntries+3; i++ {
+		list = append(list, mustSpecSkill(t, "s"+string(rune('a'+i%26))+string(rune('0'+i/26)), "d", "", sdk.InvocationBoth))
+	}
+	listing := BuildListing(list)
+	if len(listing.Entries) != SkillListingMaxEntries {
+		t.Fatalf("条目数 = %d, want %d", len(listing.Entries), SkillListingMaxEntries)
+	}
+	if !listing.Truncated || listing.Note == "" {
+		t.Fatalf("超上限必须如实标 Truncated 且给出说明：%+v", listing)
+	}
+}
+
+func TestBuildListing_跳过nil(t *testing.T) {
+	t.Parallel()
+	listing := BuildListing([]sdk.Skill{nil, mustSpecSkill(t, "s", "d", "", sdk.InvocationBoth), nil})
+	if len(listing.Entries) != 1 || listing.Truncated {
+		t.Fatalf("Listing = %+v, want 1 条且未截断", listing)
+	}
+}
+
+// mustSpecSkill 构造一个带 description/when-to-use/invocation 的技能。
+func mustSpecSkill(t *testing.T, name, description, whenToUse string, invocation sdk.Invocation) *Skill {
+	t.Helper()
+	skill, err := New(name, description, "base prompt", nil, nil, nil,
+		WithSpec(Spec{WhenToUse: whenToUse, Invocation: invocation}))
+	if err != nil {
+		t.Fatalf("New(%s): %v", name, err)
+	}
+	return skill
+}