fix(ai): support config read/write when semantic index vector service is unavailable

When sqlite-vec fails to load, use SemanticIndexConfigStore directly to
back the GET/PUT /_web/ai/semantic-index/config routes so users can still
configure the vector model from settings. Session management routes (enable,
build, search, etc.) remain unavailable since they require the vector store.

Export SemanticIndexConfigStore, SEMANTIC_INDEX_CONFIG_FILE, and
isSemanticIndexConfigured from node-runtime and semantic-index packages.

packages/http-routes/src/routes/web/ai-semantic-index.ts

@@ -5,22 +5,34 @@
  * AI pipeline 直接调用 SemanticIndexService，不经过这些 HTTP 路由。
  */
 
+import path from 'node:path'
 import type { FastifyInstance } from 'fastify'
 import type { HttpRouteContext } from '../../context'
 import type { SemanticIndexConfig } from '@openchatlab/node-runtime'
-import { defaultSemanticIndexConfig } from '@openchatlab/node-runtime'
+import {
+  SemanticIndexConfigStore,
+  SEMANTIC_INDEX_CONFIG_FILE,
+  isSemanticIndexConfigured,
+} from '@openchatlab/node-runtime'
 
 export function registerSemanticIndexRoutes(server: FastifyInstance, ctx: HttpRouteContext): void {
   const service = ctx.semanticIndexService
 
-  // When the service is unavailable (e.g. sqlite-vec failed to load), register read-only stubs
-  // so the settings UI can still open without 404 errors.
+  // When the vector service is unavailable (e.g. sqlite-vec failed to load), register config
+  // routes backed by the config-only store so the settings UI can still read/write configuration.
   if (!service) {
-    server.get('/_web/ai/semantic-index/config', async () => ({
-      config: defaultSemanticIndexConfig(),
-      apiKeySet: false,
-      configured: false,
-    }))
+    if (ctx.aiDataDir) {
+      const configStore = new SemanticIndexConfigStore(path.join(ctx.aiDataDir, SEMANTIC_INDEX_CONFIG_FILE))
+      server.get('/_web/ai/semantic-index/config', async () => ({
+        config: configStore.get(),
+        apiKeySet: false,
+        configured: isSemanticIndexConfigured(configStore.get()),
+      }))
+      server.put<{ Body: { config: SemanticIndexConfig } }>('/_web/ai/semantic-index/config', async (request) => {
+        const config = configStore.set(request.body.config)
+        return { config, apiKeySet: false, configured: isSemanticIndexConfigured(config) }
+      })
+    }
     server.get('/_web/ai/semantic-index/enabled', async () => ({ sessions: [] }))
     return
   }

packages/node-runtime/src/index.ts

@@ -348,7 +348,14 @@ export * as exportService from './services/export-service'
 export * as ownerProfileService from './services/owner-profile-service'
 // Semantic index (Phase 1 vector search) — independent of legacy ai/rag
 export * as semanticIndex from './semantic-index'
-export { SemanticIndexService, createSemanticIndexService, defaultSemanticIndexConfig } from './semantic-index'
+export {
+  SemanticIndexService,
+  createSemanticIndexService,
+  defaultSemanticIndexConfig,
+  SemanticIndexConfigStore,
+  SEMANTIC_INDEX_CONFIG_FILE,
+  isSemanticIndexConfigured,
+} from './semantic-index'
 export type {
   SemanticIndexServiceOptions,
   SemanticIndexSessionStatus,

packages/node-runtime/src/semantic-index/index.ts

@@ -46,6 +46,7 @@ export { estimateTokens } from './tokens'
 export {
   SemanticIndexConfigStore,
   defaultSemanticIndexConfig,
+  isSemanticIndexConfigured,
   resolveModelId,
   clampSearchMaxResults,
   SEMANTIC_INDEX_CONFIG_VERSION,