diff --git a/vscode/src/codeReader/rules/fastapi.test.ts b/vscode/src/codeReader/rules/fastapi.test.ts
index f6be1b8..93bdb82 100644
--- a/vscode/src/codeReader/rules/fastapi.test.ts
+++ b/vscode/src/codeReader/rules/fastapi.test.ts
@@ -1,9 +1,10 @@
 import type { BlockView } from '../blockView'
-import type { Inline, PropertyRow, RuleContext, Segment } from '../contract'
+import type { CodeBlock, Inline, PropertyRow, RuleContext, Segment } from '../contract'
 import type { DefinitionStart } from '../nameResolution'
 import { describe, expect, it, vi } from 'vitest'
 import { toBlockViews } from '../blockView'
 import { createPythonAdapter } from '../languages/python'
+import { importsIn } from '../libraryRules'
 import { DocumentLookups } from '../ruleLookups'
 import { flatSegments, inlineOf, MemoryIndexHost, propertyLines, readFixture, WASM_DIR, withBlocks } from '../testSupport'
 import { pythonZhTranslator } from '../translators/pythonZh'
@@ -526,3 +527,25 @@ def dynamic_route():
     expect((await route(source, 'dynamic_route')).callTree).toBeUndefined()
   })
 })
+
+describe('整份文件的扫描', () => {
+  it('同一份文档的各块共用一遍扫描（宿主给的 context 是同一个），认出的卡片和每块各扫一遍一样', async () => {
+    const cards = (context: () => RuleContext, blocks: readonly CodeBlock[]): unknown[] => {
+      const all = (list: readonly CodeBlock[]): CodeBlock[] => list.flatMap(block => [block, ...all(block.children)])
+      return all(blocks).map(block => fastapiRule.claim(block, context()))
+    }
+    await withBlocks(py, 'python', ROUTES, (blocks) => {
+      const imports = importsIn(blocks)
+      let reads = 0
+      const base = { document: { source: ROUTES, language: py, markers: [] }, translate: () => [], doc: () => undefined, lookup: () => undefined }
+      const shared: RuleContext = { ...base, get imports() {
+        reads++
+        return imports
+      } }
+      const once = cards(() => shared, blocks)
+      expect(reads).toBe(1)
+      expect(once.filter(Boolean).length).toBeGreaterThan(2)
+      expect(once).toEqual(cards(() => ({ ...base, imports }), blocks))
+    })
+  })
+})
diff --git a/vscode/src/codeReader/rules/fastapi.ts b/vscode/src/codeReader/rules/fastapi.ts
index 4c9545c..7c9045a 100644
--- a/vscode/src/codeReader/rules/fastapi.ts
+++ b/vscode/src/codeReader/rules/fastapi.ts
@@ -241,8 +241,8 @@ function namesOf(imports: readonly ImportFacts[]): LibraryNames {
 }
 
 /** 调用的是 fastapi / starlette 里的哪个名字（`Query(...)`、`fastapi.APIRouter(...)`）。 */
-function calledName(node: Node | null | undefined, env: Env): string | undefined {
-  return node?.type === 'call' ? libraryName(node.childForFieldName('function'), env.names) : undefined
+function calledName(node: Node | null | undefined, names: LibraryNames): string | undefined {
+  return node?.type === 'call' ? libraryName(node.childForFieldName('function'), names) : undefined
 }
 
 /** 列表、元组的各项；别的写法当一项。 */
@@ -262,13 +262,13 @@ interface Router {
   responses?: Node
 }
 
-function routersOf(root: Node, env: Env): Map<string, Router> {
+function routersOf(root: Node, names: LibraryNames): Map<string, Router> {
   const routers = new Map<string, Router>()
   for (const statement of syntaxChildren(root)) {
     const [assignment] = statement.type === 'expression_statement' ? syntaxChildren(statement) : []
     const target = assignment?.type === 'assignment' ? assignment.childForFieldName('left') : null
     const value = assignment?.childForFieldName('right')
-    const kind = calledName(value, env)
+    const kind = calledName(value, names)
     const call = callOf(value, new Map())
     if (target?.type !== 'identifier' || !call || (kind !== 'APIRouter' && kind !== 'FastAPI'))
       continue
@@ -311,16 +311,40 @@ interface RouteOn {
   name: Node
 }
 
-/** 这份文件模块顶层挂在 router 上的接口，照源码顺序；一个函数几个路由装饰器时同接口卡片，取第一个。 */
-function routesOn(root: Node, routers: ReadonlyMap<string, Router>, router: Router): RouteOn[] {
-  return syntaxChildren(root).flatMap((statement) => {
+/** 这份文件模块顶层挂在各路由对象上的接口，照源码顺序；一个函数几个路由装饰器时同接口卡片，取第一个。 */
+function routesOn(root: Node, routers: ReadonlyMap<string, Router>): Map<Router, RouteOn[]> {
+  const routes = new Map<Router, RouteOn[]>()
+  for (const statement of syntaxChildren(root)) {
     const definition = statement.type === 'decorated_definition' ? statement.childForFieldName('definition') : null
     const name = definition?.type === 'function_definition' ? definition.childForFieldName('name') : null
     if (!definition || !name)
-      return []
+      continue
     const route = syntaxChildren(statement).filter(child => child.type === 'decorator').map(decorator => routeOf(decorator, routers)).find(found => found !== undefined)
-    return route?.router === router ? [{ route, definition, name }] : []
-  })
+    if (route)
+      routes.set(route.router, [...routes.get(route.router) ?? [], { route, definition, name }])
+  }
+  return routes
+}
+
+/** 认接口要整份扫一遍才知道的：fastapi / starlette 的名字、模块顶层的路由对象、各路由对象上挂的接口。 */
+interface FileScan {
+  names: LibraryNames
+  routers: Map<string, Router>
+  routes: Map<Router, RouteOn[]>
+}
+
+/** 宿主每读一份文档给各块同一个 context：整份文件按它扫一遍，这份文档的各块共用。 */
+const scans = new WeakMap<RuleContext, FileScan>()
+
+function scanOf(root: Node, context: RuleContext): FileScan {
+  let scan = scans.get(context)
+  if (!scan) {
+    const names = namesOf(context.imports)
+    const routers = routersOf(root, names)
+    scan = { names, routers, routes: routesOn(root, routers) }
+    scans.set(context, scan)
+  }
+  return scan
 }
 
 /** 函数的参数名 → 定义处那个名字（`*args` 这种不算），路径里 `{参数}` 讲的是它。 */
@@ -428,10 +452,10 @@ function placeOf(parameter: ParameterFacts, inPath: ReadonlySet<string>, env: En
   const param = parameter.name
   if (param.type !== 'identifier')
     return undefined
-  const annotated = annotatedMarker(parameter.type, call => calledName(call, env))
+  const annotated = annotatedMarker(parameter.type, call => calledName(call, env.names))
   const type = annotated?.type ?? (parameter.type && unwrapType(parameter.type))
-  const markerCall = MARKER_PLACES[calledName(parameter.default, env) ?? ''] ? parameter.default : annotated?.marker
-  const marker = markerCall && calledName(markerCall, env)
+  const markerCall = MARKER_PLACES[calledName(parameter.default, env.names) ?? ''] ? parameter.default : annotated?.marker
+  const marker = markerCall && calledName(markerCall, env.names)
   if (markerCall && marker && MARKER_PLACES[marker] === 'dependency') {
     const call = callOf(markerCall, new Map())
     return { place: 'dependency', param, dependency: call?.positional[0] ?? call?.keywords.get('dependency') ?? type }
@@ -481,7 +505,7 @@ function dependencyText(node: Node, env: Env): Inline[] {
 /** `dependencies=[Depends(x), ...]` 里的各个 x。 */
 function listedDependencies(items: readonly Node[], env: Env): Inline[][] {
   return items.flatMap((item) => {
-    const call = MARKER_PLACES[calledName(item, env) ?? ''] === 'dependency' ? callOf(item, new Map()) : undefined
+    const call = MARKER_PLACES[calledName(item, env.names) ?? ''] === 'dependency' ? callOf(item, new Map()) : undefined
     const dependency = call?.positional[0] ?? call?.keywords.get('dependency')
     return dependency ? [dependencyText(dependency, env)] : []
   })
@@ -812,23 +836,21 @@ export const fastapiRule: LibraryRule = {
   languageIds: ['python'],
   libraries: ['fastapi'],
   claim: (block, context) => {
-    const env: Env = { context, words: WORDS[context.displayLanguage ?? ''] ?? ZH, names: namesOf(context.imports) }
-    const root = block.node.tree.rootNode
+    const { names, routers, routes } = scanOf(block.node.tree.rootNode, context)
+    const env: Env = { context, words: WORDS[context.displayLanguage ?? ''] ?? ZH, names }
     if (block.kind === 'function' && block.facts.decorators.length > 0) {
-      const routers = routersOf(root, env)
       for (const decorator of block.facts.decorators) {
         const route = routeOf(decorator, routers)
         if (route)
-          return routeCard(block, route, env, routesOn(root, routers, route.router))
+          return routeCard(block, route, env, routes.get(route.router) ?? [])
       }
     }
     // 路由对象只认模块顶层的赋值（routersOf），按赋值目标的位置认出是不是这一块
     if ((block.kind === 'const' || block.kind === 'variable') && block.facts.declarators.length === 1) {
-      const routers = routersOf(root, env)
       const target = block.facts.declarators[0].name
       const router = routers.get(target.text)
       if (router?.target.startIndex === target.startIndex)
-        return routerCard(block, router, routesOn(root, routers, router), env)
+        return routerCard(block, router, routes.get(router) ?? [], env)
     }
     return undefined
   },