fix(graph_sqlite): add busy_timeout + stale WAL/SHM cleanup on startup

Root cause: No busy_timeout set → immediate 'database is locked' on restart
when stale WAL/SHM/journal files remain from crashed previous instance.

Fix:
- On open(): clean stale -wal/-shm/-journal files (only if main db exists)
- After sqlite3_open(): set busy_timeout=10000ms (10s wait for locks)
- This eliminates the InMemoryGraph fallback on restart

go/internal/governance/graph_sqlite.go

@@ -7,12 +7,16 @@ package governance
 #cgo LDFLAGS: -lsqlite3
 #include <sqlite3.h>
 #include <stdlib.h>
+
+// busy_timeout 是 Go/C 混合文件中直接使用 C 函数
+// sqlite3_busy_timeout 在 sqlite3.h 中声明
 */
 import "C"
 
 import (
 	"encoding/json"
 	"fmt"
+	"os"
 	"strings"
 	"sync"
 	"unicode"
@@ -32,6 +36,18 @@ func NewSQLiteGraphStore(dbPath string) (*SQLiteGraphStore, error) {
 	if dbPath == "" {
 		dbPath = "/var/lib/memoryweave/graph.db"
 	}
+
+	// 清理 stale WAL/SHM 文件（防止旧进程崩溃后留下这些文件导致锁失败）
+	// 只有当主 db 文件存在时才清理（避免误删新建库的场景）
+	if _, err := os.Stat(dbPath); err == nil {
+		for _, suffix := range []string{"-wal", "-shm", "-journal"} {
+			f := dbPath + suffix
+			if _, err := os.Stat(f); err == nil {
+				os.Remove(f)
+			}
+		}
+	}
+
 	cPath := C.CString(dbPath)
 	defer C.free(unsafe.Pointer(cPath))
 
@@ -43,6 +59,9 @@ func NewSQLiteGraphStore(dbPath string) (*SQLiteGraphStore, error) {
 		return nil, fmt.Errorf("sqlite open graph: %s", msg)
 	}
 
+	// 设 10s busy_timeout——等待旧进程/跨进程锁释放，不立即报 "database is locked"
+	C.sqlite3_busy_timeout(db, 10000)
+
 	gs := &SQLiteGraphStore{db: db, path: dbPath}
 	if err := gs.migrate(); err != nil {
 		C.sqlite3_close(db)