fix(arsredovisning): unblock the signing flow, accept foreign parent org nr, explain Fortnox underlag failures (#1738)

Batch from a real migration walkthrough (Fortnox -> Accounted, 2026-08-20):

- Årsredovisning: the "Låst version" select was empty with no explanation
  because the only version was a draft and "Lås version för underskrift"
  is disabled while the four Lagstadgade upplysningar checkboxes and the
  content confirmation count as blockers. The select is now disabled with a
  hint that names the blocker count and links to Fullständighetskontroll,
  the four AR-NOTE-*-UNCONFIRMED issues carry remediation text, the lock
  button explains why it is grey, and "Markera som signerad" says what it
  still needs (locked version, bevisreferens, date).
- Moderföretagets org.nr accepts a foreign registration identifier
  (CHE-123.456.789, HRB 12345, 923 609 016); personnummer shapes stay out.
- Fortnox underlag discovery: log status, body and Fortnox's message on
  failure, show the message in the UI, treat a 400 with behörighet/scope
  text as scopes-required, and fall back to an unfiltered
  voucherfileconnections list when the financialyear filter answers 400.
- Kontomapping: the Momskod column had min-w only; table-fixed collapsed it
  and its selects overflowed into Konfidens. Real w-72 now.
- SIE import warnings pluralise correctly for one skipped voucher; the
  Verifikationsserie option says the source series is preserved.

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

extensions/general/arcim-migration/index.ts

@@ -36,6 +36,7 @@ import { BAS_REFERENCE } from '@/lib/bookkeeping/bas-reference'
 import type { ProviderName } from '@/lib/providers/types'
 import { errorResponseFromCode } from '@/lib/errors/get-structured-error'
 import { classifyProviderError } from '@/lib/providers/with-provider-call'
+import { FortnoxApiError, fortnoxErrorMessage } from '@/lib/providers/fortnox/client'
 import { createLogger } from '@/lib/logger'
 
 const moduleLog = createLogger('extensions/arcim-migration')
@@ -1371,7 +1372,18 @@ export const arcimMigrationExtension: Extension = {
           })
           return NextResponse.json({ success: true, dryRun, result })
         } catch (error) {
-          log.error('arcim import-documents failed', error as Error)
+          // "400 Bad Request" alone told us nothing when a live Fortnox
+          // discovery failed (2026-08-20): keep status, Fortnox's own
+          // message and a body excerpt in the log, and hand the message
+          // to the UI so the user sees what the source system said.
+          const providerStatus = error instanceof FortnoxApiError ? error.statusCode : undefined
+          const providerMessage = fortnoxErrorMessage(error)
+          log.error('arcim import-documents failed', error as Error, {
+            providerStatus,
+            providerMessage,
+            providerBody:
+              error instanceof FortnoxApiError ? error.body?.slice(0, 500) : undefined,
+          })
           if (error instanceof FortnoxDocumentScopesRequiredError) {
             return errorResponseFromCode(
               'PROVIDER_DOCUMENT_SCOPES_REQUIRED',
@@ -1380,7 +1392,11 @@ export const arcimMigrationExtension: Extension = {
             )
           }
           return errorResponseFromCode('PROVIDER_IMPORT_DOCUMENTS_FAILED', moduleLog, {
-            details: { reason: error instanceof Error ? error.message : 'unknown' },
+            details: {
+              reason: error instanceof Error ? error.message : 'unknown',
+              ...(providerStatus ? { providerStatus } : {}),
+              ...(providerMessage ? { providerMessage } : {}),
+            },
           })
         }
       },

extensions/general/arcim-migration/lib/import-documents.ts

@@ -35,7 +35,11 @@ import {
   downloadBokioUpload,
   type BokioUpload,
 } from '@/lib/providers/bokio/attachments'
-import { FortnoxApiError, FortnoxClient } from '@/lib/providers/fortnox/client'
+import {
+  FortnoxApiError,
+  FortnoxClient,
+  isFortnoxPermissionError,
+} from '@/lib/providers/fortnox/client'
 import {
   downloadFortnoxArchiveFile,
   fetchFortnoxFileConnections,
@@ -213,7 +217,7 @@ function fortnoxSource(
           }
         })
       } catch (error) {
-        if (error instanceof FortnoxApiError && error.statusCode === 403) {
+        if (isFortnoxPermissionError(error)) {
           throw new FortnoxDocumentScopesRequiredError()
         }
         throw error
@@ -386,11 +390,7 @@ export async function importProviderDocuments(
         }
       }
 
-      if (
-        provider === 'fortnox' &&
-        finalError instanceof FortnoxApiError &&
-        finalError.statusCode === 403
-      ) {
+      if (provider === 'fortnox' && isFortnoxPermissionError(finalError)) {
         throw new FortnoxDocumentScopesRequiredError()
       }