Coalesce concurrent requests for the same schema

src/lib/EnvelopeEditor.svelte

@@ -4,7 +4,7 @@
   import { envelopeDocumentJSON } from '$lib/helpers/envelope'
   import EditorCode from './editor/code/EditorCode.svelte'
   import EditorForm from './editor/form/EditorForm.svelte'
-  import { isEnvelope, setApiBaseUrl, DEFAULT_API_BASE_URL } from '$lib/gobl/client'
+  import { isEnvelope, setApiBaseUrl } from '$lib/gobl/client'
   import { problemSeverityMap } from './editor/EditorProblem.js'
   import * as actions from './editor/actions'
   import type { BuildOptions, DocumentHeader, State } from './types/editor'
@@ -19,7 +19,7 @@
 
   let {
     jsonSchemaURL = '',
-    apiBaseUrl = DEFAULT_API_BASE_URL,
+    apiBaseUrl = '',
     data = $bindable(''),
     state: initialState = $bindable('init'),
     problems = $bindable([]),
@@ -41,7 +41,9 @@
   }: EnvelopeEditorProps = $props()
 
   // Configure the GOBL API endpoint before any operation runs. The initial
-  // value is applied eagerly during init; the effect keeps it in sync.
+  // value is applied eagerly during init; the effect keeps it in sync. An
+  // empty prop is a no-op so an editor without an explicit endpoint inherits
+  // the currently-configured one instead of resetting it to the default.
   // svelte-ignore state_referenced_locally
   setApiBaseUrl(apiBaseUrl)
   $effect(() => {

src/lib/ObjectEditor.svelte

@@ -2,21 +2,23 @@
   import DynamicForm from '$lib/editor/form/DynamicForm.svelte'
   import { getUIModel } from '$lib/editor/form/utils/model'
   import type { SchemaValue } from '$lib/editor/form/utils/schema'
-  import { setApiBaseUrl, DEFAULT_API_BASE_URL } from '$lib/gobl/client'
+  import { setApiBaseUrl } from '$lib/gobl/client'
   import { createBuilderContext } from './store/builder'
   import type { ObjectEditorProps } from './types/editor'
 
   let {
     jsonSchemaURL = '',
-    apiBaseUrl = DEFAULT_API_BASE_URL,
+    apiBaseUrl = '',
     data = undefined,
     id = `editor-${Math.random().toString(36).slice(2, 7)}`,
     readOnly = false,
     model = $bindable(undefined)
   }: ObjectEditorProps = $props()
 
   // Configure the GOBL API endpoint before any schema is fetched. The initial
-  // value is applied eagerly during init; the effect keeps it in sync.
+  // value is applied eagerly during init; the effect keeps it in sync. An
+  // empty prop is a no-op so nested editors (e.g. the correct/headers modals)
+  // inherit the embedder's endpoint instead of resetting it to the default.
   // svelte-ignore state_referenced_locally
   setApiBaseUrl(apiBaseUrl)
   $effect(() => {

src/lib/editor/form/utils/schema.ts

@@ -35,16 +35,34 @@ function getRelativeSchema(parentSchema: Schema, id: string, del = '/'): Schema
   return path(parentSchema, id, del)
 }
 
-async function fetchExternalSchema(id: string): Promise<Schema> {
-  let schema = SchemaRegistry[id]
-  if (schema) return schema
+// In-flight schema requests, keyed by URL, so that concurrent consumers
+// (the form parser branches and the Monaco preload) share a single fetch
+// instead of each missing the registry cache and requesting the same
+// schema again.
+const pendingSchemas: Record<string, Promise<Schema>> = {}
+
+function fetchExternalSchemaStrict(id: string): Promise<Schema> {
+  const schema = SchemaRegistry[id]
+  if (schema) return Promise.resolve(schema)
+
+  let req = pendingSchemas[id]
+  if (!req) {
+    req = fetchJsonSchema(id)
+      .then((fetched) => {
+        SchemaRegistry[id] = fetched
+        return fetched
+      })
+      .finally(() => {
+        delete pendingSchemas[id]
+      })
+    pendingSchemas[id] = req
+  }
+  return req
+}
 
+async function fetchExternalSchema(id: string): Promise<Schema> {
   try {
-    schema = await fetchJsonSchema(id)
-
-    SchemaRegistry[id] = schema
-
-    return schema
+    return await fetchExternalSchemaStrict(id)
   } catch (error) {
     return EMPTY_SCHEMA
   }
@@ -72,9 +90,7 @@ async function fetchSchema(id: string): Promise<Schema> {
 // degrade to an empty placeholder instead.
 export async function loadSchemaSet(url: string): Promise<Array<{ uri: string; schema: Schema }>> {
   const rootId = url.split('#')[0]
-  if (!SchemaRegistry[rootId]) {
-    SchemaRegistry[rootId] = await fetchJsonSchema(rootId)
-  }
+  await fetchExternalSchemaStrict(rootId)
 
   const found = new Map<string, Schema>()
   const queue = [rootId]

src/lib/types/editor.ts

@@ -205,9 +205,11 @@ export interface EnvelopeEditorProps {
   // Used for JSON Schema validation within Monaco Editor. When set, this should  be the JSON Schema URL of a GOBL document, e.g. an invoice. Not an envelope.
   jsonSchemaURL?: string
   // Base URL of the GOBL API used for build, sign, validate, correct,
-  // replicate, keygen and schema operations. Defaults to the public service at
-  // `https://gobl.dev/v0`. Embedders may point this at a same-origin path
-  // (e.g. `/api/gobl`) that proxies the GOBL API and adds authentication.
+  // replicate, keygen and schema operations. Embedders may point this at a
+  // same-origin path (e.g. `/api/gobl`) that proxies the GOBL API and adds
+  // authentication. When left unset the editor keeps whatever endpoint is
+  // already configured (the public `https://gobl.dev/v0` service initially),
+  // so nested editors never reset an embedder's choice.
   apiBaseUrl?: string
   // Data is used for setting editor contents. Note: there is "one way" binding;
   // e.g. you can set data but changes are not bound to the parent. Use the