feat: P0 recall fallback + P2 trust scoring for graph edges

P0: When bge-embed/IPC recall fails, fall back to graph.db keyword search (FallbackTextSearch) instead of 500 error. Response includes X-Fallback: graph header.

P2: Add trust_score, retrieval_count, helpful_count columns to graph_edges table. New POST /api/v1/graph/edge/feedback endpoint. UpdateEdgeTrustScores batch calculation.

go/internal/api/routes/core.go

@@ -23,9 +23,10 @@ type API struct {
 	Reranker        *storage.Reranker
 	Pipeline        *storage.RecallPipeline
 	ConflictDetector *governance.ConflictDetector
+	GraphStore      governance.GraphStore
 }
 
-func NewAPI(ldb storage.LanceDB, emb *storage.Embedder, rerank *storage.Reranker, cd *governance.ConflictDetector) *API {
+func NewAPI(ldb storage.LanceDB, emb *storage.Embedder, rerank *storage.Reranker, cd *governance.ConflictDetector, gs governance.GraphStore) *API {
 	pipeline := storage.NewRecallPipeline(emb, ldb, rerank)
 	pipeline.SetPrefetchPusher(&WSPrefetchAdapter{})
 	return &API{
@@ -34,6 +35,7 @@ func NewAPI(ldb storage.LanceDB, emb *storage.Embedder, rerank *storage.Reranker
 		Reranker:        rerank,
 		Pipeline:        pipeline,
 		ConflictDetector: cd,
+		GraphStore:      gs,
 	}
 }
 
@@ -238,8 +240,15 @@ func (a *API) Recall(w http.ResponseWriter, r *http.Request) {
 	results, err := a.Pipeline.Recall(
 		req.Query, req.Namespace, req.Limit, req.Diversity)
 	if err != nil {
-		respondError(w, 500, "recall failed: "+err.Error())
-		return
+		// P0: 降级到 graph.db 关键词搜索
+		fallbackResults := a.GraphStore.FallbackTextSearch(req.Query, req.Namespace, req.Limit)
+		if len(fallbackResults) > 0 {
+			results = convertFallbackResults(fallbackResults)
+			w.Header().Set("X-Fallback", "graph")
+		} else {
+			respondError(w, 500, "recall failed: "+err.Error())
+			return
+		}
 	}
 
 	// E4.2: 跨 agent 知识共享 — recall 结果 < 3 时，补充搜索 "shared" namespace
@@ -652,3 +661,70 @@ func minInt3(a, b int) int {
 	}
 	return b
 }
+
+// convertFallbackResults 将 FallbackTextSearch 结果（map）转换为 RecallResult 格式
+func convertFallbackResults(rows []map[string]interface{}) []models.RecallResult {
+	results := make([]models.RecallResult, 0, len(rows))
+	for _, r := range rows {
+		score := 0.5
+		if pr, ok := r["pagerank"].(float64); ok {
+			score = pr
+		}
+		id := ""
+		if v, ok := r["id"]; ok {
+			id = fmt.Sprintf("%v", v)
+		}
+		name := ""
+		if v, ok := r["name"]; ok {
+			name = fmt.Sprintf("%v", v)
+		}
+		relation := ""
+		if v, ok := r["relation"]; ok {
+			relation = fmt.Sprintf("%v", v)
+		}
+		source := ""
+		if v, ok := r["source"]; ok {
+			source = fmt.Sprintf("%v", v)
+		}
+		target := ""
+		if v, ok := r["target"]; ok {
+			target = fmt.Sprintf("%v", v)
+		}
+		// Build readable content from graph edge info
+		content := fmt.Sprintf("[graph] %s --[%s]--> %s", source, relation, target)
+		if name != "" {
+			content = fmt.Sprintf("[graph] %s: %s --[%s]--> %s", name, source, relation, target)
+		}
+		results = append(results, models.RecallResult{
+			ID:       id,
+			Content:  content,
+			Category: "graph_fallback",
+			Score:    score,
+		})
+	}
+	return results
+}
+
+// POST /api/v1/graph/edge/feedback — P2: 边反馈
+func (a *API) EdgeFeedback(w http.ResponseWriter, r *http.Request) {
+	var req struct {
+		EdgeID  string `json:"edge_id"`
+		Helpful bool   `json:"helpful"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		respondError(w, 400, "invalid body")
+		return
+	}
+	if req.EdgeID == "" {
+		respondError(w, 400, "edge_id required")
+		return
+	}
+	err := a.GraphStore.AddEdgeFeedback(req.EdgeID, req.Helpful)
+	if err != nil {
+		respondError(w, 500, "feedback update failed: "+err.Error())
+		return
+	}
+	// 触发信任评分更新
+	_ = a.GraphStore.UpdateEdgeTrustScores()
+	respond(w, 200, map[string]string{"status": "ok"})
+}

go/internal/api/server.go

@@ -59,7 +59,14 @@ func NewServer() http.Handler {
 
 	// 冲突检测器（E4.1: Commit 时矛盾检测依赖此实例）
 	conflictDetector := governance.NewConflictDetector()
-	api := routes.NewAPI(ldb, emb, rerank, conflictDetector)
+
+	// 图谱（带 Navigate 结果缓存：TTL 5min，容量 500，热点实体缓存命中加速）
+	graphStore, cachedGraphStoreRef := storage.NewCachedGraphStore(initGraphStore())
+
+	api := routes.NewAPI(ldb, emb, rerank, conflictDetector, graphStore)
+
+	// G1: Recall 管线挂图谱扩展
+	api.Pipeline.SetGraphExpander(graphStore)
 
 	// 启动时初始化 Prometheus 指标
 	go func() {
@@ -76,13 +83,10 @@ func NewServer() http.Handler {
 	}()
 
 	// 图谱（带 Navigate 结果缓存：TTL 5min，容量 500，热点实体缓存命中加速）
-	graphStore, cachedGraphStoreRef := storage.NewCachedGraphStore(initGraphStore())
+	// 已在上面初始化
 	graphUpdater := governance.NewAutoGraphUpdater(graphStore)
 	graphAPI := routes.NewGraphAPI(graphStore)
 
-	// G1: Recall 管线挂图谱扩展
-	api.Pipeline.SetGraphExpander(graphStore)
-
 	// G4: 自动蒸馏 → 注入图谱更新器
 	routes.SetGraphUpdater(graphUpdater)
 
@@ -315,6 +319,8 @@ func NewServer() http.Handler {
 	mux.HandleFunc("/api/v1/graph/stats", graphAPI.Stats)
 	mux.HandleFunc("/api/v1/graph/query", graphAPI.Query)
 	mux.HandleFunc("/api/v1/graph/navigate", graphAPI.Navigate)
+	// P2: 边反馈
+	mux.HandleFunc("/api/v1/graph/edge/feedback", api.EdgeFeedback)
 	// 新增：添加关系边（POST JSON body: {"from":"实体A","to":"实体B","relation":"关系类型","namespace":""}）
 	mux.HandleFunc("/api/v1/graph/edge", func(w http.ResponseWriter, r *http.Request) {
 		if r.Method != "POST" {

go/internal/governance/graph_file.go

@@ -442,6 +442,16 @@ func (fg *FileGraph) CleanupNoiseNodes(dryRun bool) (int, []string, error) {
 	return 0, nil, nil
 }
 
+// P0: FallbackTextSearch FileGraph stub（已迁移到 SQLite）
+func (fg *FileGraph) FallbackTextSearch(query, namespace string, limit int) []map[string]interface{} {
+	return nil
+}
+
+// P2: 信任评分 stub（FileGraph 不持久化信任数据）
+func (fg *FileGraph) AddEdgeFeedback(edgeID string, helpful bool) error { return nil }
+func (fg *FileGraph) IncrementEdgeRetrieval(edgeID string) error { return nil }
+func (fg *FileGraph) UpdateEdgeTrustScores() error { return nil }
+
 // ─── 图谱扩展 ────────────────────────────────────────────
 
 func (fg *FileGraph) ExpandFromResults(results []models.RecallResult, namespace string, maxHops int) []models.RecallResult {

go/internal/governance/graph_file_windows.go

@@ -76,4 +76,13 @@ func (fg *FileGraph) lockFile(fd *os.File, exclusive bool) error {
 
 // unlockFile 暂不实现（no-op）
 func (fg *FileGraph) unlockFile(fd *os.File) {
-}
+}
+
+// ─── P0/P2 Stubs（Windows FileGraph）────────────────────
+
+func (fg *FileGraph) FallbackTextSearch(query, namespace string, limit int) []map[string]interface{} {
+	return nil
+}
+func (fg *FileGraph) AddEdgeFeedback(edgeID string, helpful bool) error { return nil }
+func (fg *FileGraph) IncrementEdgeRetrieval(edgeID string) error { return nil }
+func (fg *FileGraph) UpdateEdgeTrustScores() error { return nil }

go/internal/governance/graph_mem.go

@@ -501,6 +501,17 @@ func (g *InMemoryGraph) ListNodes(namespace string) []map[string]interface{} {
 	return g.ListNodesByType("", namespace)
 }
 
+// P0: FallbackTextSearch 内存版 stub
+func (g *InMemoryGraph) FallbackTextSearch(query, namespace string, limit int) []map[string]interface{} {
+	// InMemoryGraph 不支持 SQL LIKE，降级到 SearchNodes
+	return g.SearchNodes(query, namespace)
+}
+
+// P2: 信任评分 stub（InMemoryGraph 不持久化）
+func (g *InMemoryGraph) AddEdgeFeedback(edgeID string, helpful bool) error { return nil }
+func (g *InMemoryGraph) IncrementEdgeRetrieval(edgeID string) error { return nil }
+func (g *InMemoryGraph) UpdateEdgeTrustScores() error { return nil }
+
 func searchSubstring(s, substr string) bool {
 	for i := 0; i <= len(s)-len(substr); i++ {
 		if s[i:i+len(substr)] == substr {

go/internal/governance/graph_sqlite.go

@@ -136,6 +136,11 @@ func (gs *SQLiteGraphStore) migrate() error {
 	// 修复孤儿边：自动补充缺失的节点
 	gs.repairOrphanEdges()
 
+	// P2: Trust scoring columns for graph_edges
+	gs.migrateAddColumn("graph_edges", "trust_score", "REAL DEFAULT 0.5")
+	gs.migrateAddColumn("graph_edges", "retrieval_count", "INTEGER DEFAULT 0")
+	gs.migrateAddColumn("graph_edges", "helpful_count", "INTEGER DEFAULT 0")
+
 	return nil
 }
 
@@ -981,6 +986,50 @@ func (gs *SQLiteGraphStore) GetEntityDegree(entity string) int {
 	return gs.EvidenceCount(entity)
 }
 
+// P0: FallbackTextSearch — 关键词降级搜索（向量搜索不可用时使用）
+func (gs *SQLiteGraphStore) FallbackTextSearch(query, namespace string, limit int) []map[string]interface{} {
+	gs.mu.RLock()
+	defer gs.mu.RUnlock()
+	nsClause := "1=1"
+	if namespace != "" {
+		nsClause = fmt.Sprintf("e.namespace = '%s'", escape(namespace))
+	}
+	// 模糊匹配 node name + edge relation，按 pagerank 排序
+	sql := fmt.Sprintf(
+		`SELECT DISTINCT e.id, e.source, e.target, e.relation, e.weight, n.name, n.pagerank
+		 FROM graph_edges e
+		 JOIN graph_nodes n ON e.source = n.id
+		 WHERE (n.name LIKE '%%%s%%' OR e.relation LIKE '%%%s%%') AND %s
+		 ORDER BY n.pagerank DESC
+		 LIMIT %d`,
+		escape(query), escape(query), nsClause, limit)
+	return queryRows(gs.db, sql)
+}
+
+// P2: AddEdgeFeedback 记录边反馈（helpful=true 增加 helpful_count，否则增加 retrieval_count）
+func (gs *SQLiteGraphStore) AddEdgeFeedback(edgeID string, helpful bool) error {
+	gs.mu.Lock()
+	defer gs.mu.Unlock()
+	if helpful {
+		return execSQL(gs.db, fmt.Sprintf("UPDATE graph_edges SET helpful_count = helpful_count + 1 WHERE id = '%s'", escape(edgeID)))
+	}
+	return execSQL(gs.db, fmt.Sprintf("UPDATE graph_edges SET retrieval_count = retrieval_count + 1 WHERE id = '%s'", escape(edgeID)))
+}
+
+// IncrementEdgeRetrieval 递增边的检索计数
+func (gs *SQLiteGraphStore) IncrementEdgeRetrieval(edgeID string) error {
+	gs.mu.Lock()
+	defer gs.mu.Unlock()
+	return execSQL(gs.db, fmt.Sprintf("UPDATE graph_edges SET retrieval_count = retrieval_count + 1 WHERE id = '%s'", escape(edgeID)))
+}
+
+// UpdateEdgeTrustScores 批量更新边的信任评分（trust_score = helpful_count / retrieval_count）
+func (gs *SQLiteGraphStore) UpdateEdgeTrustScores() error {
+	gs.mu.Lock()
+	defer gs.mu.Unlock()
+	return execSQL(gs.db, `UPDATE graph_edges SET trust_score = CASE WHEN retrieval_count > 0 THEN CAST(helpful_count AS REAL) / retrieval_count ELSE 0.5 END`)
+}
+
 // ─── CGO 工具 ──────────────────────────────────────────
 
 // UpdatePageRanks 批量更新节点的 pagerank 值（§2.5.5）

go/internal/governance/graph_store.go

@@ -44,4 +44,12 @@ type GraphStore interface {
 	// 清理图谱脏数据：删除名称含编码噪音的节点（如 fts=、括号不匹配等）
 	// 返回被删除的节点数和节点 ID 列表
 	CleanupNoiseNodes(dryRun bool) (int, []string, error)
+
+	// P0: 关键词文本搜索降级（当向量搜索不可用时）
+	FallbackTextSearch(query, namespace string, limit int) []map[string]interface{}
+
+	// P2: 信任评分
+	AddEdgeFeedback(edgeID string, helpful bool) error
+	IncrementEdgeRetrieval(edgeID string) error
+	UpdateEdgeTrustScores() error
 }

go/internal/storage/graph_cache.go

@@ -161,6 +161,22 @@ func (c *cachedGraphStore) CleanupNoiseNodes(dryRun bool) (int, []string, error)
 	return c.inner.CleanupNoiseNodes(dryRun)
 }
 
+// P0: FallbackTextSearch 透传到内层
+func (c *cachedGraphStore) FallbackTextSearch(query, namespace string, limit int) []map[string]interface{} {
+	return c.inner.FallbackTextSearch(query, namespace, limit)
+}
+
+// P2: 信任评分透传
+func (c *cachedGraphStore) AddEdgeFeedback(edgeID string, helpful bool) error {
+	return c.inner.AddEdgeFeedback(edgeID, helpful)
+}
+func (c *cachedGraphStore) IncrementEdgeRetrieval(edgeID string) error {
+	return c.inner.IncrementEdgeRetrieval(edgeID)
+}
+func (c *cachedGraphStore) UpdateEdgeTrustScores() error {
+	return c.inner.UpdateEdgeTrustScores()
+}
+
 // ── 缓存内部方法 ──
 
 func (c *cachedGraphStore) navigateKey(entity string, maxHops int, relFilter []string) string {