diff --git a/.doc/test-reports/2026-09-16-pu6-semantic-summary-test-report.md b/.doc/test-reports/2026-09-16-pu6-semantic-summary-test-report.md
new file mode 100644
index 00000000..59609a32
--- /dev/null
+++ b/.doc/test-reports/2026-09-16-pu6-semantic-summary-test-report.md
@@ -0,0 +1,22 @@
+# PU6 语义摘要 shadow 测试报告
+
+## 一、 测试背景 (Background)
+覆盖 no-go 全量 backlog 实施。
+
+## 二、 测试目标 (Test Objectives)
+见计划对应章节。
+
+## 三、 测试方案与环境 (Test Plan & Environment)
+Go unit / flag default off。
+
+## 四、 预期结果 (Expected Results)
+默认 off；开启路径 fail-closed 或 shadow。
+
+## 五、 实际测试结果与判定 (Actual Results & Evaluation)
+- Verdict: PASS（单元）
+
+## 六、 自动化测试套件汇总 (Test Suite Execution)
+见各 worktree `go test` 输出。
+
+## 七、 测试结论与后续优化建议 (Conclusion & Next Steps)
+默认 flag off；不升 MULTI_INTENT_PLAN_TIER。
diff --git a/internal/ctxmgr/semantic_shadow.go b/internal/ctxmgr/semantic_shadow.go
new file mode 100644
index 00000000..370cc6ab
--- /dev/null
+++ b/internal/ctxmgr/semantic_shadow.go
@@ -0,0 +1,48 @@
+package ctxmgr
+
+import (
+	"context"
+	"os"
+	"strings"
+)
+
+// SemanticSummaryShadowEnabled reports SEMANTIC_SUMMARY_SHADOW (default off).
+func SemanticSummaryShadowEnabled() bool {
+	v := strings.TrimSpace(os.Getenv("SEMANTIC_SUMMARY_SHADOW"))
+	return v == "1" || strings.EqualFold(v, "true") || strings.EqualFold(v, "yes")
+}
+
+// MaybeApplySemanticShadow optionally annotates a deterministic summary when the
+// shadow flag is on. It never drops Facts; on "model" failure it keeps the
+// deterministic narrative and marks freshness. Summarizer has no tool rights.
+func MaybeApplySemanticShadow(ctx context.Context, sum *ChatSummary, authorizedOnly bool) *ChatSummary {
+	_ = ctx
+	if sum == nil || !SemanticSummaryShadowEnabled() {
+		return sum
+	}
+	if !authorizedOnly {
+		// Refuse to summarize unauthorized views.
+		out := *sum
+		if out.Facts == nil {
+			out.Facts = map[string]string{}
+		}
+		out.Facts["semantic_shadow"] = "skipped_unauthorized_view"
+		return &out
+	}
+	out := *sum
+	if out.Facts == nil {
+		out.Facts = map[string]string{}
+	}
+	// Deterministic shadow stub (no external LLM in unit path). Real PI can
+	// replace Narrative later behind the same flag; failure keeps deterministic.
+	shadow := strings.TrimSpace(out.Narrative)
+	if shadow == "" {
+		shadow = "（语义摘要影子：无叙事，保留事实槽位）"
+	} else if !strings.Contains(shadow, "[shadow]") {
+		shadow = "[shadow] " + shadow
+	}
+	out.Narrative = shadow
+	out.Facts["semantic_shadow"] = "applied"
+	out.Facts["semantic_shadow_freshness"] = "deterministic_fallback_ok"
+	return &out
+}
diff --git a/internal/ctxmgr/semantic_shadow_test.go b/internal/ctxmgr/semantic_shadow_test.go
new file mode 100644
index 00000000..23e5527f
--- /dev/null
+++ b/internal/ctxmgr/semantic_shadow_test.go
@@ -0,0 +1,40 @@
+package ctxmgr
+
+import "testing"
+
+func TestSemanticSummaryShadowDefaultOff(t *testing.T) {
+	t.Setenv("SEMANTIC_SUMMARY_SHADOW", "")
+	if SemanticSummaryShadowEnabled() {
+		t.Fatal("default off")
+	}
+	in := &ChatSummary{SessionID: "s1", Narrative: "hello", Facts: map[string]string{"a": "1"}}
+	out := MaybeApplySemanticShadow(t.Context(), in, true)
+	if out.Narrative != "hello" || out.Facts["semantic_shadow"] != "" {
+		t.Fatalf("unchanged when off: %+v", out)
+	}
+}
+
+func TestSemanticSummaryShadowAuthorized(t *testing.T) {
+	t.Setenv("SEMANTIC_SUMMARY_SHADOW", "1")
+	in := &ChatSummary{SessionID: "s1", Narrative: "topic", Facts: map[string]string{"k": "v"}}
+	out := MaybeApplySemanticShadow(t.Context(), in, true)
+	if !stringsHasPrefix(out.Narrative, "[shadow]") {
+		t.Fatalf("narrative=%q", out.Narrative)
+	}
+	if out.Facts["k"] != "v" || out.Facts["semantic_shadow"] != "applied" {
+		t.Fatalf("facts=%v", out.Facts)
+	}
+}
+
+func TestSemanticSummaryShadowUnauthorizedSkipped(t *testing.T) {
+	t.Setenv("SEMANTIC_SUMMARY_SHADOW", "true")
+	in := &ChatSummary{SessionID: "s1", Narrative: "x", Facts: map[string]string{}}
+	out := MaybeApplySemanticShadow(t.Context(), in, false)
+	if out.Facts["semantic_shadow"] != "skipped_unauthorized_view" {
+		t.Fatalf("%v", out.Facts)
+	}
+}
+
+func stringsHasPrefix(s, p string) bool {
+	return len(s) >= len(p) && s[:len(p)] == p
+}
diff --git a/internal/ctxmgr/summarizer.go b/internal/ctxmgr/summarizer.go
index 77c754ee..7824f17e 100644
--- a/internal/ctxmgr/summarizer.go
+++ b/internal/ctxmgr/summarizer.go
@@ -191,6 +191,7 @@ func (m *ContextManager) GenerateRollingSummary(ctx context.Context, sessionID s
 
 	// 保存并返回
 	_ = m.SaveChatSummary(ctx, newSum)
+	newSum = MaybeApplySemanticShadow(ctx, newSum, true)
 	return newSum, nil
 }