diff --git a/internal/docgov/engine.go b/internal/docgov/engine.go
index cc8c55cc..9e650e44 100644
--- a/internal/docgov/engine.go
+++ b/internal/docgov/engine.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"log"
 	"strings"
 	"sync"
 	"time"
@@ -13,6 +14,15 @@ import (
 	"github.com/jackc/pgx/v5/pgxpool"
 )
 
+// nullIfZero maps unset duty holders (0) to SQL NULL so nullable FK columns
+// (author_id/reviewer_id/approver_id → users.id) accept optional duties.
+func nullIfZero(id int64) any {
+	if id <= 0 {
+		return nil
+	}
+	return id
+}
+
 // ModificationCheckResult 智能体或人员发起修改前的认领与授权判定结果
 type ModificationCheckResult struct {
 	AllowedDirectEdit bool            `json:"allowed_direct_edit"` // 是否允许直接执行修改
@@ -153,12 +163,15 @@ func (e *GovernanceEngine) CreateOrGetDocument(
 		}
 
 		ensureUser := func(uid int64, uname, urole string) {
-			if uid > 0 {
-				_, _ = e.pool.Exec(ctx, `
-					INSERT INTO users (id, account_id, name, role)
-					VALUES ($1, $2, $3, $4)
-					ON CONFLICT (id) DO NOTHING
-				`, uid, fmt.Sprintf("acc_%d", uid), uname, urole)
+			if uid <= 0 {
+				return
+			}
+			if _, err := e.pool.Exec(ctx, `
+				INSERT INTO users (id, account_id, name, role)
+				VALUES ($1, $2, $3, $4)
+				ON CONFLICT (id) DO NOTHING
+			`, uid, fmt.Sprintf("acc_%d", uid), uname, urole); err != nil {
+				log.Printf("[docgov] ensureUser id=%d role=%s failed: %v", uid, urole, err)
 			}
 		}
 		ensureUser(doc.AuthorID, doc.AuthorName, "engineer")
@@ -185,7 +198,8 @@ func (e *GovernanceEngine) CreateOrGetDocument(
 		err := e.pool.QueryRow(ctx, query,
 			doc.DocID, doc.ProjectID, doc.TaskKey, doc.Title, doc.Stage, doc.Version,
 			string(doc.CurrentState), doc.IsLocked, doc.IsTemplateOnly, doc.WorkDir,
-			doc.AuthorID, doc.AuthorName, doc.ReviewerID, doc.ReviewerName, doc.ApproverID, doc.ApproverName,
+			nullIfZero(doc.AuthorID), doc.AuthorName, nullIfZero(doc.ReviewerID), doc.ReviewerName,
+			nullIfZero(doc.ApproverID), doc.ApproverName,
 			cfgJSON, doc.CreatedAt, doc.UpdatedAt,
 		).Scan(&id, &currState, &isLocked, &isTmpl, &authClaim, &revClaim, &appClaim)
 		if err != nil {
diff --git a/internal/docgov/engine_db_test.go b/internal/docgov/engine_db_test.go
index 2bed3a44..1fbf869f 100644
--- a/internal/docgov/engine_db_test.go
+++ b/internal/docgov/engine_db_test.go
@@ -97,3 +97,64 @@ func TestDocGov_DatabaseIntegration(t *testing.T) {
 		t.Fatalf("expected doc locked in reviewing")
 	}
 }
+
+// TestDocGov_CreateOrGetDocument_OptionalDutiesNullFK ensures reviewer/approver=0
+// persist as SQL NULL (optional DutyMode) instead of FK-violating 0.
+func TestDocGov_CreateOrGetDocument_OptionalDutiesNullFK(t *testing.T) {
+	cfg, err := config.Load(".env")
+	if err != nil || cfg == nil || cfg.ContextDbHost == "" {
+		t.Skip("Skipping DB integration test: context DB not configured")
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	pool, err := pgxpool.New(ctx, cfg.ContextDSN())
+	if err != nil || pool.Ping(ctx) != nil {
+		t.Skipf("Skipping DB integration test: cannot connect to %s: %v", cfg.ContextDSN(), err)
+	}
+	defer pool.Close()
+
+	engine := docgov.NewGovernanceEngine(pool)
+	testDocID := fmt.Sprintf("doc_opt_duty_%d", time.Now().UnixNano())
+	projectID := time.Now().UnixNano()%900000 + 100000
+
+	doc, err := engine.CreateOrGetDocument(
+		ctx,
+		testDocID,
+		projectID,
+		"intake",
+		"可选职责空审核人",
+		"V0.5_feasibility",
+		"",
+		9, "系统管理员",
+		0, "",
+		0, "",
+	)
+	if err != nil {
+		t.Fatalf("CreateOrGetDocument with reviewer/approver=0 failed: %v", err)
+	}
+	if doc.DocID != testDocID {
+		t.Fatalf("unexpected docID: %s", doc.DocID)
+	}
+
+	var reviewerNull, approverNull bool
+	var authorID int64
+	err = pool.QueryRow(ctx, `
+		SELECT author_id,
+		       reviewer_id IS NULL,
+		       approver_id IS NULL
+		FROM document_records WHERE doc_id = $1
+	`, testDocID).Scan(&authorID, &reviewerNull, &approverNull)
+	if err != nil {
+		t.Fatalf("query document_records: %v", err)
+	}
+	if authorID != 9 {
+		t.Fatalf("author_id=%d want 9", authorID)
+	}
+	if !reviewerNull || !approverNull {
+		t.Fatalf("expected NULL reviewer/approver, got reviewerNull=%v approverNull=%v", reviewerNull, approverNull)
+	}
+
+	_, _ = pool.Exec(ctx, `DELETE FROM document_records WHERE doc_id = $1`, testDocID)
+}
diff --git a/internal/docgov/null_if_zero_test.go b/internal/docgov/null_if_zero_test.go
new file mode 100644
index 00000000..a769ec0e
--- /dev/null
+++ b/internal/docgov/null_if_zero_test.go
@@ -0,0 +1,16 @@
+package docgov
+
+import "testing"
+
+func TestNullIfZero(t *testing.T) {
+	t.Parallel()
+	if got := nullIfZero(0); got != nil {
+		t.Fatalf("nullIfZero(0)=%v want nil", got)
+	}
+	if got := nullIfZero(-1); got != nil {
+		t.Fatalf("nullIfZero(-1)=%v want nil", got)
+	}
+	if got := nullIfZero(9); got != int64(9) {
+		t.Fatalf("nullIfZero(9)=%v want 9", got)
+	}
+}