diff --git a/internal/projectinstance/document_access.go b/internal/projectinstance/document_access.go
index f92480ab..8d1a6639 100644
--- a/internal/projectinstance/document_access.go
+++ b/internal/projectinstance/document_access.go
@@ -2,6 +2,8 @@ package projectinstance
 
 import (
 	"context"
+
+	"chat-agent-system/internal/workflowdef"
 )
 
 const (
@@ -67,7 +69,7 @@ func (s *Service) CheckDocTaskAccess(
 	var stageKey string
 	for _, st := range detail.Stages {
 		for i := range st.DocTasks {
-			if st.DocTasks[i].TaskKey == taskKey {
+			if workflowdef.SameTaskKey(st.DocTasks[i].TaskKey, taskKey) {
 				copyDoc := st.DocTasks[i]
 				docInst = &copyDoc
 				stageKey = st.StageKey
@@ -119,7 +121,7 @@ func (s *Service) CheckDocTaskAccess(
 func findDocTaskPlan(plan WorkflowPlan, taskKey string) *DocTaskPlan {
 	for _, st := range plan.Stages {
 		for i := range st.DocTasks {
-			if st.DocTasks[i].TaskKey == taskKey {
+			if workflowdef.SameTaskKey(st.DocTasks[i].TaskKey, taskKey) {
 				return &st.DocTasks[i]
 			}
 		}
diff --git a/internal/projectinstance/message_scope.go b/internal/projectinstance/message_scope.go
index cca29b54..17557b3a 100644
--- a/internal/projectinstance/message_scope.go
+++ b/internal/projectinstance/message_scope.go
@@ -4,6 +4,8 @@ import (
 	"context"
 	"errors"
 	"fmt"
+
+	"chat-agent-system/internal/workflowdef"
 )
 
 const (
@@ -144,7 +146,7 @@ func (s *Service) ResolveMessageScopeForTask(ctx context.Context, projectID int6
 	var matches []MessageScope
 	for _, st := range detail.Stages {
 		for _, dt := range st.DocTasks {
-			if dt.TaskKey == taskKey {
+			if workflowdef.SameTaskKey(dt.TaskKey, taskKey) {
 				matches = append(matches, MessageScope{
 					ScopeKind:          ScopeWorkflowStage,
 					WorkflowInstanceID: gov.ID,
diff --git a/internal/projectinstance/message_scope_test.go b/internal/projectinstance/message_scope_test.go
index dedfca98..b5e9731e 100644
--- a/internal/projectinstance/message_scope_test.go
+++ b/internal/projectinstance/message_scope_test.go
@@ -122,6 +122,70 @@ func TestMessageVisible_LegacyUnscopedOwnerWhenRestricted(t *testing.T) {
 	}
 }
 
+func TestResolveMessageScopeForTask_LegacyKeyMatchesCanonicalSnapshot(t *testing.T) {
+	ctx := context.Background()
+	store := newMemStore()
+	_ = SeedProjectMeta(store, 42, LifecyclePlanning, "", 1, 0)
+	svc := NewService(store, testResolver(), nil, nil)
+	mustActivateTestPlan(t, svc, 42, 1)
+
+	store.mu.Lock()
+	live := store.live[42]
+	live.ConfigSnapshot.Stages[0].DocTasks[0].TaskKey = "bd_intake"
+	for i := range store.stages[live.ID] {
+		for j := range store.stages[live.ID][i].tasks {
+			if store.stages[live.ID][i].tasks[j].taskKey == "intake" {
+				store.stages[live.ID][i].tasks[j].taskKey = "bd_intake"
+			}
+		}
+	}
+	store.mu.Unlock()
+
+	scope, err := svc.ResolveMessageScopeForTask(ctx, 42, "intake")
+	if err != nil {
+		t.Fatalf("legacy intake must resolve against bd_intake snapshot: %v", err)
+	}
+	if scope.ScopeKind != ScopeWorkflowStage || scope.StageKey != "V0.1_triage" {
+		t.Fatalf("want V0.1_triage workflow_stage, got %+v", scope)
+	}
+}
+
+func TestResolveMessageScopeForTask_CanonicalAliasAmbiguousAcrossStages(t *testing.T) {
+	ctx := context.Background()
+	store := newMemStore()
+	_ = SeedProjectMeta(store, 43, LifecyclePlanning, "", 1, 0)
+	svc := NewService(store, testResolver(), nil, nil)
+	mustActivateTestPlan(t, svc, 43, 1)
+
+	store.mu.Lock()
+	live := store.live[43]
+	live.ConfigSnapshot.Stages = append(live.ConfigSnapshot.Stages, StagePlan{
+		StageKey: "V0.5_feasibility", Enabled: true,
+		DocTasks: []DocTaskPlan{{TaskKey: "bd_intake", Enabled: true}},
+	})
+	store.stages[live.ID] = append(store.stages[live.ID], memStageRecord{
+		id: live.ID + 100, stageKey: "V0.5_feasibility", position: 1, enabled: true, status: StagePending,
+		tasks: []memDocTaskRecord{{id: 900, taskKey: "bd_intake", enabled: true, status: "pending"}},
+	})
+	store.mu.Unlock()
+
+	_, err := svc.ResolveMessageScopeForTask(ctx, 43, "intake")
+	if err == nil || !errors.Is(err, ErrTaskScopeNotResolved) {
+		t.Fatalf("same task in two stages must stay unresolved, got %v", err)
+	}
+}
+
+func TestTaskKeyToStage_LegacyAlias(t *testing.T) {
+	plan := validPlan()
+	plan.Stages[0].DocTasks[0].TaskKey = "bd_user_requirements"
+	if got := TaskKeyToStage(plan, "user_requirements"); got != "V0.1_triage" {
+		t.Fatalf("TaskKeyToStage=%q", got)
+	}
+	if got := TaskKeyToStage(plan, "intake"); got != "" {
+		t.Fatalf("unrelated legacy key must miss, got %q", got)
+	}
+}
+
 func TestScopeFromMetadata_RoundTrip(t *testing.T) {
 	meta := map[string]any{
 		"scope_kind":           ScopeWorkflowStage,
diff --git a/internal/projectinstance/stage_access.go b/internal/projectinstance/stage_access.go
index 253322d7..497b0699 100644
--- a/internal/projectinstance/stage_access.go
+++ b/internal/projectinstance/stage_access.go
@@ -152,7 +152,7 @@ func MessageStageKey(metadata map[string]any) string {
 func TaskKeyToStage(plan WorkflowPlan, taskKey string) string {
 	for _, st := range plan.Stages {
 		for _, dt := range st.DocTasks {
-			if dt.TaskKey == taskKey {
+			if workflowdef.SameTaskKey(dt.TaskKey, taskKey) {
 				return st.StageKey
 			}
 		}