Fall back to local artifacts when the blob store is a typed nil

Why: an unset S3 client passed through the Store interface is not a nil interface, so uploads panic instead of using the local artifact directory.
Evidence: TestIsNil and TestFinishOpenTypedNilS3UsesLocalArtifacts failed before this change and pass after it. The PostgreSQL case skips unless AGENT_PG_TEST_DSN is set.
Impact: only an unset blob store falls back; a constructed S3 or local store is unchanged.
Refs: internal/blobstore/blobstore.go internal/store/store.go
Co-authored-by: Cursor <cursoragent@cursor.com>

internal/blobstore/blobstore.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
+	"reflect"
 	"strings"
 	"sync"
 )
@@ -19,6 +20,21 @@ type Store interface {
 	Delete(ref string) error
 }
 
+// IsNil 判断对象存储是否未配置。nil 接口，以及放进接口后的带类型空指针
+// （例如未设置端点时的 (*S3)(nil)），都算未配置。已构造的实现返回 false。
+func IsNil(s Store) bool {
+	if s == nil {
+		return true
+	}
+	v := reflect.ValueOf(s)
+	switch v.Kind() {
+	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Pointer, reflect.Slice:
+		return v.IsNil()
+	default:
+		return false
+	}
+}
+
 // Local 是本地目录实现（data/artifacts；多实例时把目录指向共享卷即可）。
 type Local struct {
 	dir string

internal/blobstore/nil_test.go

@@ -0,0 +1,29 @@
+package blobstore
+
+import "testing"
+
+func TestIsNil(t *testing.T) {
+	var unset Store
+	if !IsNil(unset) {
+		t.Fatal("nil interface must count as unset")
+	}
+	var typed *S3
+	var asStore Store = typed
+	if !IsNil(asStore) {
+		t.Fatal("typed nil *S3 must count as unset")
+	}
+	local, err := NewLocal(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if IsNil(local) {
+		t.Fatal("local store must count as configured")
+	}
+	s3, err := NewS3("http://127.0.0.1:9/bucket", "us-east-1", "access", "secret", "art/")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if IsNil(s3) {
+		t.Fatal("configured S3 must count as configured")
+	}
+}

internal/store/store.go

@@ -212,6 +212,7 @@ func OpenPostgresWithBlobs(dsn, artifactsDir string, blobs blobstore.Store) (*St
 
 // OpenPostgresWithOptions 按 KTD12 连接预算打开 PG 档；QueryTimeoutSec>0 时
 // 以 statement_timeout 运行参数附着到 DSN（对 URL 与键值两种形式均生效）。
+// blobs 为 nil（含带类型的空指针，例如未配置端点时的 (*blobstore.S3)(nil)）时回落本地目录。
 func OpenPostgresWithOptions(dsn, artifactsDir string, pool PoolOptions, blobs blobstore.Store) (*Store, error) {
 	return openPostgresWithOptions(dsn, artifactsDir, pool, blobs, true)
 }
@@ -263,7 +264,7 @@ func AppendPGRuntimeParam(dsn, key, value string) string {
 }
 
 func finishOpen(db *sql.DB, d dialect, artifactsDir string, blobs blobstore.Store, pool PoolOptions, createArtifacts bool) (*Store, error) {
-	if blobs == nil {
+	if blobstore.IsNil(blobs) {
 		var err error
 		if createArtifacts {
 			blobs, err = blobstore.NewLocal(artifactsDir)

internal/store/typed_nil_blob_test.go

@@ -0,0 +1,121 @@
+package store
+
+import (
+	"bytes"
+	"database/sql"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"testing"
+
+	"agent-system-backend/internal/blobstore"
+	core "agent-system-core"
+)
+
+func TestFinishOpenTypedNilS3UsesLocalArtifacts(t *testing.T) {
+	dir := t.TempDir()
+	st := openSQLiteWithBlobs(t, dir, (*blobstore.S3)(nil))
+	assertLocalArtifactRoundTrip(t, st, filepath.Join(dir, "artifacts"))
+}
+
+func TestFinishOpenKeepsConfiguredBlobStore(t *testing.T) {
+	dir := t.TempDir()
+	s3, err := blobstore.NewS3("http://127.0.0.1:9/bucket", "us-east-1", "access", "secret", "art/")
+	if err != nil {
+		t.Fatal(err)
+	}
+	st := openSQLiteWithBlobs(t, dir, s3)
+	if st.BlobStore() != s3 {
+		t.Fatalf("configured blob store was replaced: %T", st.BlobStore())
+	}
+}
+
+func TestOpenPostgresTypedNilS3UsesLocalArtifacts(t *testing.T) {
+	dsn := os.Getenv("AGENT_PG_TEST_DSN")
+	if dsn == "" {
+		t.Skip("AGENT_PG_TEST_DSN 未设置：真实 PG 门禁由 CI 的必跑 job 覆盖")
+	}
+	schema := "t_" + strings.ToLower(newID("s")) + "_" + strconv.Itoa(os.Getpid())
+	admin, err := sql.Open("pgx", dsn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ensurePGTrgm(t, admin)
+	if _, err := admin.Exec("CREATE SCHEMA " + schema); err != nil {
+		admin.Close()
+		t.Fatalf("create schema: %v", err)
+	}
+	t.Cleanup(func() {
+		_, _ = admin.Exec("DROP SCHEMA IF EXISTS " + schema + " CASCADE")
+		admin.Close()
+	})
+	arts := filepath.Join(t.TempDir(), "artifacts")
+	st, err := OpenPostgresWithOptions(withTestSearchPath(dsn, schema), arts, PoolOptions{}, (*blobstore.S3)(nil))
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { st.Close() })
+	assertLocalArtifactRoundTrip(t, st, arts)
+}
+
+func openSQLiteWithBlobs(t *testing.T, dir string, blobs blobstore.Store) *Store {
+	t.Helper()
+	dbPath := filepath.Join(dir, "test.db")
+	dsn := "file:" + dbPath + "?_pragma=busy_timeout(30000)&_pragma=journal_mode(WAL)&_pragma=foreign_keys(1)&_txlock=immediate"
+	db, err := sql.Open("sqlite", dsn)
+	if err != nil {
+		t.Fatal(err)
+	}
+	db.SetMaxOpenConns(1)
+	st, err := finishOpen(db, sqliteDialect{}, filepath.Join(dir, "artifacts"), blobs, PoolOptions{}, true)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { st.Close() })
+	return st
+}
+
+func assertLocalArtifactRoundTrip(t *testing.T, st *Store, arts string) {
+	t.Helper()
+	if _, ok := st.BlobStore().(*blobstore.Local); !ok {
+		t.Fatalf("unset blob store must fall back to local, got %T", st.BlobStore())
+	}
+	proj, err := st.CreateProject("k4", "k4")
+	if err != nil {
+		t.Fatal(err)
+	}
+	art := core.Artifact{Owner: "k4", ProjectID: proj.ID, Name: "a.txt", Kind: "data"}
+	if err := st.CreateArtifact(&art, []byte("hello")); err != nil {
+		t.Fatal(err)
+	}
+	got, err := st.ArtifactContentByID(art.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(got, []byte("hello")) {
+		t.Fatalf("read back %q", got)
+	}
+	if _, err := os.Stat(filepath.Join(arts, art.ID)); err != nil {
+		t.Fatalf("artifact file missing under local dir: %v", err)
+	}
+	if err := st.UpdateArtifactContent("k4", art.ID, []byte("next")); err != nil {
+		t.Fatal(err)
+	}
+	got, err = st.ArtifactContent("k4", art.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(got, []byte("next")) {
+		t.Fatalf("overwrite read back %q", got)
+	}
+	if err := st.DeleteArtifact("k4", art.ID); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := st.ArtifactContentByID(art.ID); err != ErrNotFound {
+		t.Fatalf("deleted artifact content: %v", err)
+	}
+	if _, err := os.Stat(filepath.Join(arts, art.ID)); !os.IsNotExist(err) {
+		t.Fatalf("deleted artifact file still present: %v", err)
+	}
+}