diff --git a/.env.example b/.env.example
index 1a7607f6..39392f30 100644
--- a/.env.example
+++ b/.env.example
@@ -99,7 +99,6 @@ MULTI_INTENT_U9_SEGMENT=false
 MULTI_INTENT_U10_MUTATE=false
 MULTI_INTENT_U11_DOCGOV=false
 MULTI_INTENT_U12_RUN_CONTROL=false
-SEMANTIC_FALLBACK_ENABLED=false
 # W2: shadow only. Do not set SEMANTIC_SUMMARY_REPLACE=true; REPLACE is unwired.
 SEMANTIC_SUMMARY_SHADOW=false
 SEMANTIC_SUMMARY_REPLACE=false
diff --git a/docker-compose.dev.yml b/docker-compose.dev.yml
index 5e140f44..1d753d58 100644
--- a/docker-compose.dev.yml
+++ b/docker-compose.dev.yml
@@ -114,7 +114,6 @@ services:
       MULTI_INTENT_U10_MUTATE: ${MULTI_INTENT_U10_MUTATE:-false}
       MULTI_INTENT_U11_DOCGOV: ${MULTI_INTENT_U11_DOCGOV:-false}
       MULTI_INTENT_U12_RUN_CONTROL: ${MULTI_INTENT_U12_RUN_CONTROL:-false}
-      SEMANTIC_FALLBACK_ENABLED: ${SEMANTIC_FALLBACK_ENABLED:-false}
       # W2 PU6: shadow semantic summary; REPLACE stays unwired even if env is true
       SEMANTIC_SUMMARY_SHADOW: ${SEMANTIC_SUMMARY_SHADOW:-false}
       SEMANTIC_SUMMARY_REPLACE: ${SEMANTIC_SUMMARY_REPLACE:-false}
diff --git a/docker-compose.main.yml b/docker-compose.main.yml
index 2a5bdbb2..d1ebb18a 100644
--- a/docker-compose.main.yml
+++ b/docker-compose.main.yml
@@ -116,7 +116,6 @@ services:
       MULTI_INTENT_U10_MUTATE: ${MULTI_INTENT_U10_MUTATE:-false}
       MULTI_INTENT_U11_DOCGOV: ${MULTI_INTENT_U11_DOCGOV:-false}
       MULTI_INTENT_U12_RUN_CONTROL: ${MULTI_INTENT_U12_RUN_CONTROL:-false}
-      SEMANTIC_FALLBACK_ENABLED: ${SEMANTIC_FALLBACK_ENABLED:-false}
       SEMANTIC_SUMMARY_SHADOW: ${SEMANTIC_SUMMARY_SHADOW:-false}
       PI_CHANGE_REPORT_NARRATIVE: ${PI_CHANGE_REPORT_NARRATIVE:-false}
       FAV_DEGRADED_READ: "false"
diff --git a/docker-compose.test.yml b/docker-compose.test.yml
index 4a4aa978..af9112c7 100644
--- a/docker-compose.test.yml
+++ b/docker-compose.test.yml
@@ -113,7 +113,6 @@ services:
       MULTI_INTENT_U10_MUTATE: ${MULTI_INTENT_U10_MUTATE:-false}
       MULTI_INTENT_U11_DOCGOV: ${MULTI_INTENT_U11_DOCGOV:-false}
       MULTI_INTENT_U12_RUN_CONTROL: ${MULTI_INTENT_U12_RUN_CONTROL:-false}
-      SEMANTIC_FALLBACK_ENABLED: ${SEMANTIC_FALLBACK_ENABLED:-false}
       SEMANTIC_SUMMARY_SHADOW: ${SEMANTIC_SUMMARY_SHADOW:-false}
       PI_CHANGE_REPORT_NARRATIVE: ${PI_CHANGE_REPORT_NARRATIVE:-false}
       FAV_DEGRADED_READ: ${FAV_DEGRADED_READ:-false}
diff --git a/internal/app/app.go b/internal/app/app.go
index e4ad17fa..22d6ee19 100644
--- a/internal/app/app.go
+++ b/internal/app/app.go
@@ -286,7 +286,6 @@ func sysadminFeatureValues(cfg *config.Config) func() map[string]string {
 			"INTENT_V2_DECISION_TIER":      string(iflags.V2DecisionTier),
 			"WORKFLOW_INTENTS_ENABLED":     strconv.FormatBool(iflags.WorkflowIntentsEnabled),
 			"MULTI_INTENT_ENABLED":         strconv.FormatBool(iflags.MultiIntentEnabled),
-			"SEMANTIC_FALLBACK_ENABLED":    strconv.FormatBool(iflags.SemanticFallbackEnabled),
 			"MULTI_INTENT_PLAN_TIER":       string(pflags.PlanTier),
 			"MULTI_INTENT_U9_SEGMENT":      strconv.FormatBool(pflags.U9Segment),
 			"MULTI_INTENT_U10_MUTATE":      strconv.FormatBool(pflags.U10Mutate),
diff --git a/internal/config/compose_flag_declaration_test.go b/internal/config/compose_flag_declaration_test.go
index 818ea3ef..038a237d 100644
--- a/internal/config/compose_flag_declaration_test.go
+++ b/internal/config/compose_flag_declaration_test.go
@@ -99,3 +99,13 @@ func TestComposeNoDeadCursorRunnerConfig(t *testing.T) {
 		}
 	}
 }
+
+// X-1: SEMANTIC_FALLBACK_ENABLED has zero Go readers repo-wide and no design
+// doc describing intended semantics; Wave 5 decision = delete, not re-declare.
+func TestComposeNoDeadSemanticFallbackConfig(t *testing.T) {
+	for _, name := range composeFilesForFlagCheck {
+		if strings.Contains(readComposeFile(t, name), "SEMANTIC_FALLBACK_ENABLED") {
+			t.Errorf("%s: dead SEMANTIC_FALLBACK_ENABLED must stay removed (Wave5 X-1)", name)
+		}
+	}
+}
diff --git a/internal/intent/flags.go b/internal/intent/flags.go
index ed5a3854..2286f4db 100644
--- a/internal/intent/flags.go
+++ b/internal/intent/flags.go
@@ -20,12 +20,11 @@ const (
 
 // FeatureFlags Phase 5 意图识别灰度开关（环境变量覆盖，默认保守）
 type FeatureFlags struct {
-	IntentV2Shadow          bool
-	IntentV2Decision        bool
-	V2DecisionTier          V2DecisionTier
-	WorkflowIntentsEnabled  bool
-	MultiIntentEnabled      bool
-	SemanticFallbackEnabled bool
+	IntentV2Shadow         bool
+	IntentV2Decision       bool
+	V2DecisionTier         V2DecisionTier
+	WorkflowIntentsEnabled bool
+	MultiIntentEnabled     bool
 }
 
 var (
@@ -40,7 +39,6 @@ func defaultFeatureFlags() FeatureFlags {
 		V2DecisionTier:         parseV2DecisionTier(os.Getenv("INTENT_V2_DECISION_TIER")),
 		WorkflowIntentsEnabled: envBool("WORKFLOW_INTENTS_ENABLED", true),
 		MultiIntentEnabled:     envBool("MULTI_INTENT_ENABLED", true),
-		SemanticFallbackEnabled: envBool("SEMANTIC_FALLBACK_ENABLED", false),
 	}
 }
 
diff --git a/internal/sysadmin/features.go b/internal/sysadmin/features.go
index cd541ddd..aea369ae 100644
--- a/internal/sysadmin/features.go
+++ b/internal/sysadmin/features.go
@@ -37,7 +37,6 @@ var featureCatalog = []featureSpec{
 	{key: "INTENT_V2_DECISION_TIER", label: "意图 V2 决策档位", group: "intent", fallback: "none", description: "V2 灰度风险档位：none/query/generate/write_low/write_high/all"},
 	{key: "WORKFLOW_INTENTS_ENABLED", label: "工作流意图", group: "intent", fallback: "true", description: "识别工作流类意图"},
 	{key: "MULTI_INTENT_ENABLED", label: "多意图识别", group: "intent", fallback: "true", description: "单条消息多意图拆解"},
-	{key: "SEMANTIC_FALLBACK_ENABLED", label: "语义兜底", group: "intent", fallback: "false", description: "规则意图未命中时的语义兜底"},
 	{key: "MULTI_INTENT_PLAN_TIER", label: "多意图计划档位", group: "intentflow", fallback: "legacy", description: "意图计划灰度：legacy/shadow/auto_read/confirm/full"},
 	{key: "MULTI_INTENT_U9_SEGMENT", label: "U9 LLM 分段", group: "intentflow", fallback: "false", description: "LLM 意图分段提议"},
 	{key: "MULTI_INTENT_U10_MUTATE", label: "U10 变更适配器", group: "intentflow", fallback: "false", description: "低/中风险 mutate 动作适配器"},