Add the generative-ui plugin, capability gating, and surface projection

Why: Generative UI U3 - the agent needs a real submission path and the
next turn needs to see prior pages: a built-in in-process plugin
registers generative-ui.present (exposeAsTool) carrying the catalog
(prompt=validation single source) with a schema-repair strategy
measured against real MiniMax-M3 deviations; the command bus gains an
owner-scoped tool gate so a disabled plugin stops injecting its tool
(execution guard remains in surfacesvc); ctxasm projects saved surfaces
back into context so the model can revise existing structure; doc-refs
are authorized against the owner's real artifacts.

Evidence: unit suites green (genui guards/epoch/doc-ref, gate fail-closed,
projection content); full go test ./... green; cmdbus/ctxasm also green
under AGENT_PG_TEST_DSN; real-model closed loop (env-gated
TestRealModelSurfaceLoop) passes: task->spec->save->projection->revise
with revision 1->2 and structure change, CNY 0.08 total.

Impact: New internal/genui package; additive cmdbus/ctxasm/runmgr/
runtime hooks; no storage or contract changes (U2 layer untouched).

Refs: Documents proposal r2 U3; Core PR #25/#26; Backend #143; Dev task
feature/generative-ui-u3

internal/ctxasm/ctxasm.go

@@ -41,6 +41,9 @@ type AssembleOptions struct {
 	// ThinkReplay 为真时，历史 assistant 消息的思考部件以 <think> 块原样回传
 	//（交错思考模型如 MiniMax 的官方要求：丢弃思考内容会降低后续轮性能）。
 	ThinkReplay bool
+	// Surfaces 是当前会话最近保存的生成页面（U3/R6）：以语义投影并入上下文，
+	// 使下一轮模型能解释并修改已有结构（修改走 generative-ui.present 重提）。
+	Surfaces []core.SurfaceSnapshot
 }
 
 // AssembleInput 组装模型输入消息。sys 为提示词库组装出的 system 段（可为多段；
@@ -58,6 +61,17 @@ func AssembleInput(prof core.AgentProfile, eff core.EffectiveSettings, history [
 		msgs = append(msgs, agentllm.Message{Role: agentllm.RoleSystem, Content: prof.SystemPrompt})
 		rep.Items = append(rep.Items, "system(画像自定义段)")
 	}
+	if len(opts.Surfaces) > 0 {
+		var b strings.Builder
+		b.WriteString("[本会话已保存的生成页面（结构摘要；正文以预览区为准）]\n")
+		for _, snap := range opts.Surfaces {
+			b.WriteString(projectSurface(snap))
+			b.WriteString("\n")
+		}
+		b.WriteString("用户要求调整页面时，按结构摘要理解现状并用 generative-ui.present 提交修订（带 surfaceId 与 baseRevision）。")
+		msgs = append(msgs, agentllm.Message{Role: agentllm.RoleSystem, Content: b.String()})
+		rep.Items = append(rep.Items, fmt.Sprintf("surface(%d)", len(opts.Surfaces)))
+	}
 
 	maxHist := prof.Context.MaxHistoryMessages
 	if maxHist <= 0 {
@@ -499,3 +513,42 @@ func InjectMemory(sys []agentllm.Message, entries []core.MemoryEntry) []agentllm
 	out = append(out, agentllm.Message{Role: agentllm.RoleSystem, Content: b.String()})
 	return out
 }
+
+// projectSurface 是 ctxasm 侧的结构摘要投影（与 surfacesvc.ProjectSurface 同义；
+// 独立实现避免 ctxasm→surfacesvc 依赖边）。
+func projectSurface(snap core.SurfaceSnapshot) string {
+	var b strings.Builder
+	fmt.Fprintf(&b, "- 页面 %s（修订 %d）%q", string(snap.Identity.SurfaceID), snap.Revision, snap.Spec.Title)
+	if snap.SemanticText != "" {
+		fmt.Fprintf(&b, "：%s", snap.SemanticText)
+	}
+	b.WriteString("\n  结构：")
+	var walk func(n core.UINode)
+	first := true
+	walk = func(n core.UINode) {
+		label := string(n.Type)
+		if n.Title != "" {
+			label += "(\"" + n.Title + "\")"
+		}
+		if n.ID != "" {
+			label += "#" + n.ID
+		}
+		if len(n.Source) > 0 {
+			label += "[" + strings.Join(n.Source, ",") + "]"
+		}
+		if first {
+			b.WriteString(label)
+			first = false
+		} else {
+			b.WriteString(" > " + label)
+		}
+		for _, c := range n.Children {
+			walk(c)
+		}
+	}
+	for _, n := range snap.Spec.Nodes {
+		walk(n)
+	}
+	b.WriteString("\n  修订此页：present 带 surfaceId=" + string(snap.Identity.SurfaceID) + " 与 baseRevision=" + fmt.Sprint(snap.Revision) + "。")
+	return b.String()
+}

internal/ctxasm/surface_proj_test.go

@@ -0,0 +1,52 @@
+package ctxasm
+
+// U3/R6：已保存页面的语义投影并入上下文——下一轮模型能看到结构、来源与修订
+// 入口（present + baseRevision），可据此解释并修改已有 table/compare/tabs。
+
+import (
+	"strings"
+	"testing"
+
+	agentllm "agent-native/runtime/llm"
+	core "agent-system-core"
+)
+
+func surfaceSnap() core.SurfaceSnapshot {
+	return core.SurfaceSnapshot{
+		Identity: core.SurfaceIdentity{SurfaceID: "surf_x", Owner: "alice", PluginID: "generative-ui", ConversationID: "c1"},
+		Revision: 2,
+		Spec: core.SurfaceSpec{Title: "选型对比", Nodes: []core.UINode{
+			{Type: core.UISection, ID: "n1", Title: "概览", Children: []core.UINode{
+				{Type: core.UIMarkdown, ID: "n1a", Source: []string{"doc:a"}, Markdown: "结论"},
+			}},
+			{Type: core.UITable, ID: "n2", Source: []string{"doc:a", "doc:b"}},
+		}},
+		SemanticText: "三工具对比页",
+	}
+}
+
+func TestSurfaceProjectionInContext(t *testing.T) {
+	msgs, rep := AssembleInput(core.AgentProfile{}, nil, nil,
+		core.Message{Role: core.RoleUser, Parts: []core.Part{{Type: core.PartText, Text: "改一下"}}},
+		nil, nil, nil, nil, nil, nil, AssembleOptions{Surfaces: []core.SurfaceSnapshot{surfaceSnap()}})
+	joined := make([]string, len(msgs))
+	for i, m := range msgs {
+		joined[i] = m.Content
+	}
+	all := strings.Join(joined, "\n---\n")
+	for _, need := range []string{"surf_x", "修订 2", "选型对比", "section(\"概览\")#n1", "markdown#n1a[doc:a]", "table#n2", "baseRevision=2"} {
+		if !strings.Contains(all, need) {
+			t.Fatalf("projection missing %q in assembled context:\n%s", need, all)
+		}
+	}
+	found := false
+	for _, it := range rep.Items {
+		if strings.HasPrefix(it, "surface(") {
+			found = true
+		}
+	}
+	if !found {
+		t.Fatalf("report should count surface injection: %v", rep.Items)
+	}
+	_ = agentllm.RoleSystem
+}