diff --git a/DECISIONS.md b/DECISIONS.md
index da72b33c..ca3d87d4 100644
--- a/DECISIONS.md
+++ b/DECISIONS.md
@@ -896,3 +896,4 @@ One line per decision: `[YYYY-MM-DD] <decision>: <why>`. Appended by agents and
 [2026-08-13] ChannelQuestionAsked/Answered/Expired registered in processing_event_types rather than dropping the appends: appendQuestionHistory swallows the FK violation by design so the WhatsApp reply still goes out, which turned a missing catalog row into a per-question production error nobody saw, and the question exchange is part of how the underlag was obtained (BFNAR 2013:2 kap 8).
 [2026-08-13] Underlag failures resolve the response where it fails (getResponseErrorMessage + status) and an expired session announces itself on the existing session-timeout BroadcastChannel, instead of a global authenticated-fetch wrapper: `throw new Error(json.error)` printed "[object Object]" for the structured envelope, so the middleware 401 on a backgrounded mobile tab surfaced as the generic "Något gick fel" with no way back; a wrapper would have to be threaded through every call site to buy the same thing here. Upload failures also post metadata (status, size, mime, resolved reason) to /api/log, the one API path exempt from the timeout gate, because a request answered before the route runs leaves nothing in the function logs and the user-reported failures were invisible there.
 [2026-08-13] Oversized phone photos are re-encoded in the browser (2400px long edge, JPEG q0.85 stepping down) rather than raising a platform limit or streaming straight to storage: hosted rejects any request body over 4.5 MB itself (measured against prod: 4.4 MB reaches the route, 4.6 MB returns a plain-text FUNCTION_PAYLOAD_TOO_LARGE), before the route runs and therefore invisibly in the function logs, while the route advertises 10 MB it can never receive. A downscaled photo is still a faithful, durably readable reproduction (BFL 7 kap), which a refusal is not. What cannot be shrunk (PDF, or HEIC where the browser will not decode it) is refused client-side with its actual size named, and 413 was added to the HTTP status map so a rejection in transit still says what happened. Direct-to-storage upload, which would remove the ceiling for PDFs too, is the follow-up, not this fix: it moves sha256/WORM integrity off the server.
+[2026-08-13] The book-route underlag fix landed as a pinned-document leg inside propagateUnderlagForBookedTransaction rather than the planned "extract categorize-core's propagation block into a shared helper": PR #1547 had already done that extraction overnight and wired /book and bulk-book to the shared helper, but the helper only walked matched inbox items, so a document pinned via transactions.document_id with no unconsumed inbox item (direct upload, or item consumed elsewhere) still booked to "Underlag saknas". Anchoring the pin inside the helper fixes /book, categorize, bulk-book and attach-after-book in one place; the pin is read fresh (not from the caller's pre-booking snapshot) so a concurrent attach still anchors, and the bulk-book RPC's own atomic doc-linking makes the leg a no-op there.
diff --git a/app/api/transactions/[id]/book/__tests__/route.test.ts b/app/api/transactions/[id]/book/__tests__/route.test.ts
index d9852d93..8de3896a 100644
--- a/app/api/transactions/[id]/book/__tests__/route.test.ts
+++ b/app/api/transactions/[id]/book/__tests__/route.test.ts
@@ -10,7 +10,7 @@ import {
 } from '@/tests/helpers'
 import { eventBus } from '@/lib/events'
 
-const { supabase: mockSupabase, enqueue, reset } = createQueuedMockSupabase()
+const { supabase: mockSupabase, enqueue, reset, findCalls } = createQueuedMockSupabase()
 
 const requireAuthMock = vi.fn()
 vi.mock('@/lib/auth/require-auth', () => ({
@@ -251,6 +251,85 @@ describe('POST /api/transactions/[id]/book', () => {
     expect(body.error).toBe('Failed to update transaction')
   })
 
+  // ── Underlag propagation (pinned document + matched inbox items) ──────
+  // Attach-before-book: a document pinned to the transaction (or an inbox
+  // item hand-matched to it) must land on the new verifikat, or every
+  // underlag surface reads "Underlag saknas" for a booking that HAS its
+  // underlag (the 2026-08-13 user report).
+
+  it('anchors the pinned document to the new verifikat (attach-before-book)', async () => {
+    const tx = makeTransaction({ id: 'tx-1', amount: -500, journal_entry_id: null })
+    const je = makeJournalEntry({ id: 'je-new' })
+    enqueue({ data: tx, error: null }) // fetch transaction
+    mockCreateJournalEntry.mockResolvedValue(je)
+    enqueue({ data: null, error: null }) // update transaction
+    enqueue({ data: { document_id: 'doc-1' } }) // propagate: tx pin lookup
+    enqueue({ data: { journal_entry_id: null } }) // pinned doc unanchored
+    enqueue({ data: { id: 'je-new' } }) // linkToJournalEntry: entry ownership check
+    enqueue({ data: { id: 'doc-1', journal_entry_id: 'je-new' } }) // doc update
+    enqueue({ data: [] }) // no matched inbox items
+
+    const request = createMockRequest('/api/transactions/tx-1/book', {
+      method: 'POST',
+      body: validBody,
+    })
+    const response = await POST(request, createMockRouteParams({ id: 'tx-1' }))
+    const { status } = await parseJsonResponse(response)
+
+    expect(status).toBe(200)
+    expect(findCalls('document_attachments', 'update')).toContainEqual([
+      { journal_entry_id: 'je-new', journal_entry_line_id: null },
+    ])
+  })
+
+  it('stamps a matched inbox item consumed by the booking', async () => {
+    const tx = makeTransaction({ id: 'tx-1', amount: -500, journal_entry_id: null })
+    const je = makeJournalEntry({ id: 'je-new' })
+    enqueue({ data: tx, error: null }) // fetch transaction
+    mockCreateJournalEntry.mockResolvedValue(je)
+    enqueue({ data: null, error: null }) // update transaction
+    enqueue({ data: { document_id: null } }) // propagate: nothing pinned
+    enqueue({ data: [{ id: 'i1', document_id: null }] }) // matched inbox item
+    enqueue({ data: null }) // stamp update
+
+    const request = createMockRequest('/api/transactions/tx-1/book', {
+      method: 'POST',
+      body: validBody,
+    })
+    const response = await POST(request, createMockRouteParams({ id: 'tx-1' }))
+    const { status } = await parseJsonResponse(response)
+
+    expect(status).toBe(200)
+    expect(findCalls('invoice_inbox_items', 'update')).toContainEqual([
+      { created_journal_entry_id: 'je-new' },
+    ])
+  })
+
+  it('still returns success when underlag propagation fails (best-effort)', async () => {
+    const tx = makeTransaction({ id: 'tx-1', amount: -500, journal_entry_id: null })
+    const je = makeJournalEntry({ id: 'je-new' })
+    enqueue({ data: tx, error: null }) // fetch transaction
+    mockCreateJournalEntry.mockResolvedValue(je)
+    enqueue({ data: null, error: null }) // update transaction
+    enqueue({ data: { document_id: 'doc-1' } }) // propagate: tx pin lookup
+    enqueue({ data: { journal_entry_id: null } }) // pinned doc unanchored
+    enqueue({ data: null }) // linkToJournalEntry: entry lookup fails -> throws
+    enqueue({ data: [] }) // no matched inbox items
+
+    const request = createMockRequest('/api/transactions/tx-1/book', {
+      method: 'POST',
+      body: validBody,
+    })
+    const response = await POST(request, createMockRouteParams({ id: 'tx-1' }))
+    const { status, body } = await parseJsonResponse<{ success: boolean }>(response)
+
+    // The verifikat is already posted: a propagation failure is logged and
+    // repaired by re-running, never allowed to fail the booking.
+    expect(status).toBe(200)
+    expect(body.success).toBe(true)
+    expect(findCalls('document_attachments', 'update')).toEqual([])
+  })
+
   // ── Booking-time duplicate guard ──────────────────────────────────────
 
   it('returns 409 duplicate warning when a booked sibling shares date+amount', async () => {
diff --git a/lib/pending-operations/__tests__/executors.test.ts b/lib/pending-operations/__tests__/executors.test.ts
index 8538a4a3..23ac896e 100644
--- a/lib/pending-operations/__tests__/executors.test.ts
+++ b/lib/pending-operations/__tests__/executors.test.ts
@@ -1024,6 +1024,7 @@ describe('commitPendingOperation: attach_document_to_transaction', () => {
     enqueue({ data: { journal_entry_id: 'je-7' }, error: null }) // UPDATE returning post-state
     enqueue({ data: null, error: null }) // invoice_inbox_items best-effort link
     enqueue({ data: null, error: null }) // doc propagation update
+    enqueue({ data: { document_id: null }, error: null }) // completion: tx pin lookup
     enqueue({ data: [], error: null }) // completion: matched inbox items (none)
     enqueue({ data: null, error: null }) // dispatcher commit update
 
@@ -1048,6 +1049,7 @@ describe('commitPendingOperation: attach_document_to_transaction', () => {
     enqueue({ data: { journal_entry_id: null }, error: null }) // UPDATE returning (still null)
     enqueue({ data: null, error: null }) // invoice_inbox_items best-effort link
     enqueue({ data: [{ transaction_id: 'tx-1', journal_entry_id: 'je-9' }], error: null }) // voucher links
+    enqueue({ data: { document_id: null }, error: null }) // propagation: tx pin lookup
     enqueue({ data: [{ id: 'inbox-9', document_id: null }], error: null }) // matched inbox items
     enqueue({ data: null, error: null }) // created_journal_entry_id stamp
     enqueue({ data: null, error: null }) // dispatcher commit update
diff --git a/lib/transactions/__tests__/categorize-core.bulk.test.ts b/lib/transactions/__tests__/categorize-core.bulk.test.ts
index fdb88a50..04c839ca 100644
--- a/lib/transactions/__tests__/categorize-core.bulk.test.ts
+++ b/lib/transactions/__tests__/categorize-core.bulk.test.ts
@@ -519,14 +519,15 @@ describe('bulkBookMatchedInboxItems: WhatsApp channel-context notes threading',
 })
 
 describe('bulkBookMatchedInboxItems: intra-batch duplicate handling', () => {
-  /** Six queued from() results for one successfully-booked item. */
+  /** Seven queued from() results for one successfully-booked item. */
   const bookableItem = (itemId: string, txId: string, amount: number) => [
     { data: { id: itemId, matched_transaction_id: txId, created_journal_entry_id: null, created_supplier_invoice_id: null } },
     { data: { id: txId, date: '2026-06-01', amount, currency: 'SEK', cash_account_id: null, journal_entry_id: null } },
     { data: { entity_type: 'aktiebolag', fiscal_year_start_month: 1 } },
     { data: [{ id: 'fp-1' }] },
     { error: null },
-    { data: [] },
+    { data: { document_id: null } }, // propagation: tx pin lookup
+    { data: [] }, // propagation: matched inbox items
   ]
 
   it('books BOTH distinct transactions that share (date, amount) in one bulk run', async () => {
diff --git a/lib/transactions/__tests__/inbox-underlag.test.ts b/lib/transactions/__tests__/inbox-underlag.test.ts
index ec178650..16bcac2f 100644
--- a/lib/transactions/__tests__/inbox-underlag.test.ts
+++ b/lib/transactions/__tests__/inbox-underlag.test.ts
@@ -65,6 +65,7 @@ describe('propagateUnderlagForBookedTransaction', () => {
 
   it('links the document and stamps the matched item', async () => {
     const { supabase, enqueue, findCalls } = createQueuedMockSupabase()
+    enqueue({ data: { document_id: null } }) // tx pin lookup: nothing pinned
     enqueue({ data: [{ id: 'i1', document_id: 'doc-1' }] }) // matched items
     enqueue({ data: { journal_entry_id: null } }) // doc not yet anchored
     enqueue({ data: null }) // stamp update
@@ -83,6 +84,7 @@ describe('propagateUnderlagForBookedTransaction', () => {
 
   it('skips the document write when it already points at the verifikat', async () => {
     const { supabase, enqueue, findCalls } = createQueuedMockSupabase()
+    enqueue({ data: { document_id: null } }) // tx pin lookup: nothing pinned
     enqueue({ data: [{ id: 'i1', document_id: 'doc-1' }] })
     enqueue({ data: { journal_entry_id: JE1 } }) // already anchored to JE1
     enqueue({ data: null }) // stamp update
@@ -106,6 +108,7 @@ describe('propagateUnderlagForBookedTransaction', () => {
     // mismatch from every future run and from manual reconciliation
     // (BFL 5 kap 6-7 §).
     const { supabase, enqueue, findCalls } = createQueuedMockSupabase()
+    enqueue({ data: { document_id: null } }) // tx pin lookup: nothing pinned
     enqueue({ data: [{ id: 'i1', document_id: 'doc-1' }] })
     enqueue({ data: { journal_entry_id: 'je-other' } })
 
@@ -122,6 +125,7 @@ describe('propagateUnderlagForBookedTransaction', () => {
 
   it('stamps an item without a document (no document read)', async () => {
     const { supabase, enqueue, findCalls } = createQueuedMockSupabase()
+    enqueue({ data: { document_id: null } }) // tx pin lookup: nothing pinned
     enqueue({ data: [{ id: 'i1', document_id: null }] })
     enqueue({ data: null }) // stamp update
 
@@ -144,6 +148,7 @@ describe('propagateUnderlagForBookedTransaction', () => {
     // items only the first stamp lands. The rest must resolve quietly: the
     // inbox list derives "booked" from the transaction's state for them.
     const { supabase, enqueue } = createQueuedMockSupabase()
+    enqueue({ data: { document_id: null } }) // tx pin lookup: nothing pinned
     enqueue({ data: [{ id: 'i1', document_id: null }] })
     enqueue({ data: null, error: { code: '23505', message: 'duplicate key value' } })
 
@@ -164,6 +169,7 @@ describe('propagateUnderlagForBookedTransaction', () => {
     // and nothing left to surface or repair it.
     vi.mocked(linkToJournalEntry).mockRejectedValueOnce(new Error('period locked'))
     const { supabase, enqueue, findCalls } = createQueuedMockSupabase()
+    enqueue({ data: { document_id: null } }) // tx pin lookup: nothing pinned
     enqueue({ data: [{ id: 'i1', document_id: 'doc-1' }] })
     enqueue({ data: { journal_entry_id: null } })
 
@@ -177,6 +183,102 @@ describe('propagateUnderlagForBookedTransaction', () => {
     ).resolves.toBeUndefined()
     expect(findCalls('invoice_inbox_items', 'update')).toEqual([])
   })
+
+  // ── The transaction's own pinned document (transactions.document_id) ──
+  // A doc attached directly to the transaction has no inbox item to carry
+  // it, so the propagation must anchor it itself: this was the 2026-08-13
+  // "Underlag saknas" gap (attach-before-book via the manual booking dialog).
+
+  it('anchors the pinned document even when no inbox item exists', async () => {
+    const { supabase, enqueue, findCalls } = createQueuedMockSupabase()
+    enqueue({ data: { document_id: 'doc-pin' } }) // tx pin lookup
+    enqueue({ data: { journal_entry_id: null } }) // pinned doc not yet anchored
+    enqueue({ data: [] }) // no matched inbox items
+
+    await propagateUnderlagForBookedTransaction(
+      supabase as unknown as SupabaseClient,
+      COMPANY,
+      TX1,
+      JE1,
+    )
+
+    expect(linkToJournalEntry).toHaveBeenCalledWith(expect.anything(), COMPANY, 'doc-pin', JE1)
+    expect(findCalls('invoice_inbox_items', 'update')).toEqual([])
+  })
+
+  it('leaves a pinned document that already points at this verifikat alone', async () => {
+    const { supabase, enqueue } = createQueuedMockSupabase()
+    enqueue({ data: { document_id: 'doc-pin' } })
+    enqueue({ data: { journal_entry_id: JE1 } }) // already anchored here
+    enqueue({ data: [] })
+
+    await propagateUnderlagForBookedTransaction(
+      supabase as unknown as SupabaseClient,
+      COMPANY,
+      TX1,
+      JE1,
+    )
+
+    expect(linkToJournalEntry).not.toHaveBeenCalled()
+  })
+
+  it('never steals a pinned document anchored to another verifikat', async () => {
+    const { supabase, enqueue } = createQueuedMockSupabase()
+    enqueue({ data: { document_id: 'doc-pin' } })
+    enqueue({ data: { journal_entry_id: 'je-other' } })
+    enqueue({ data: [] })
+
+    await propagateUnderlagForBookedTransaction(
+      supabase as unknown as SupabaseClient,
+      COMPANY,
+      TX1,
+      JE1,
+    )
+
+    expect(linkToJournalEntry).not.toHaveBeenCalled()
+  })
+
+  it('still processes inbox items when the pinned-document link fails', async () => {
+    vi.mocked(linkToJournalEntry).mockRejectedValueOnce(new Error('period locked'))
+    const { supabase, enqueue, findCalls } = createQueuedMockSupabase()
+    enqueue({ data: { document_id: 'doc-pin' } })
+    enqueue({ data: { journal_entry_id: null } }) // pinned doc; link will throw
+    enqueue({ data: [{ id: 'i1', document_id: null }] }) // docless matched item
+    enqueue({ data: null }) // stamp update
+
+    await expect(
+      propagateUnderlagForBookedTransaction(
+        supabase as unknown as SupabaseClient,
+        COMPANY,
+        TX1,
+        JE1,
+      ),
+    ).resolves.toBeUndefined()
+    expect(findCalls('invoice_inbox_items', 'update')).toContainEqual([
+      { created_journal_entry_id: JE1 },
+    ])
+  })
+
+  it('links a document shared by the pin and a matched item only once', async () => {
+    const { supabase, enqueue, findCalls } = createQueuedMockSupabase()
+    enqueue({ data: { document_id: 'doc-1' } }) // pin points at the same doc
+    enqueue({ data: { journal_entry_id: null } }) // pin leg links it
+    enqueue({ data: [{ id: 'i1', document_id: 'doc-1' }] }) // matched item, same doc
+    enqueue({ data: { journal_entry_id: JE1 } }) // item leg finds it anchored
+    enqueue({ data: null }) // stamp update
+
+    await propagateUnderlagForBookedTransaction(
+      supabase as unknown as SupabaseClient,
+      COMPANY,
+      TX1,
+      JE1,
+    )
+
+    expect(linkToJournalEntry).toHaveBeenCalledTimes(1)
+    expect(findCalls('invoice_inbox_items', 'update')).toContainEqual([
+      { created_journal_entry_id: JE1 },
+    ])
+  })
 })
 
 describe('completeInboxItemsForBookedTransaction', () => {
@@ -196,8 +298,9 @@ describe('completeInboxItemsForBookedTransaction', () => {
     expect(findCalls('invoice_inbox_items', 'select').length).toBe(0)
   })
 
-  it('skips the transaction fetch when the caller passes the direct id', async () => {
+  it('skips the resolution fetch when the caller passes the direct id', async () => {
     const { supabase, enqueue, findCalls } = createQueuedMockSupabase()
+    enqueue({ data: { document_id: null } }) // tx pin lookup inside propagate
     enqueue({ data: [] }) // matched items (none)
 
     const result = await completeInboxItemsForBookedTransaction(
@@ -207,12 +310,15 @@ describe('completeInboxItemsForBookedTransaction', () => {
       { directJournalEntryId: JE1 },
     )
     expect(result).toBe(JE1)
-    expect(findCalls('transactions', 'select').length).toBe(0)
+    // The only transactions read is the pin lookup inside the propagation:
+    // the id/journal_entry_id resolution query never runs.
+    expect(findCalls('transactions', 'select')).toEqual([['document_id']])
   })
 
   it('resolves the samlingsverifikat through voucher links when the direct id is null', async () => {
     const { supabase, enqueue, findCalls } = createQueuedMockSupabase()
     enqueue({ data: [{ transaction_id: TX1, journal_entry_id: JE2 }] }) // voucher links
+    enqueue({ data: { document_id: null } }) // tx pin lookup inside propagate
     enqueue({ data: [{ id: 'i1', document_id: null }] }) // matched items
     enqueue({ data: null }) // stamp update
 
diff --git a/lib/transactions/inbox-underlag.ts b/lib/transactions/inbox-underlag.ts
index ddfcf4be..33e8f536 100644
--- a/lib/transactions/inbox-underlag.ts
+++ b/lib/transactions/inbox-underlag.ts
@@ -16,9 +16,14 @@
  *    covering both direct journal_entry_id and the bulk-book
  *    transaction_voucher_links shape (see lib/transactions/is-booked.ts for
  *    why the column alone is not "booked").
- *  - propagateUnderlagForBookedTransaction: link matched items' documents to
+ *  - propagateUnderlagForBookedTransaction: anchor the transaction's pinned
+ *    document (transactions.document_id) and link matched items' documents to
  *    the verifikat (BFL 5 kap 6 §: the verifikation must reference its
- *    underlag) and stamp created_journal_entry_id.
+ *    underlag), stamping created_journal_entry_id on the items. The pinned-doc
+ *    leg matters because a document attached directly to a transaction has no
+ *    inbox item to carry it: without it, booking through the manual dialog
+ *    left document_attachments.journal_entry_id null and every underlag
+ *    surface read "Underlag saknas" (the 2026-08-13 user report).
  *  - completeInboxItemsForBookedTransaction: the attach-time entry point that
  *    resolves first and propagates only when the transaction is booked.
  *
@@ -116,18 +121,69 @@ export async function resolveVoucherLinkedEntryIds(
 }
 
 /**
- * Propagate the underlag from matched invoice-inbox items onto the verifikat
- * that booked their transaction. Without this, BFL 7 kap is violated: a
- * verifikation exists with no underlag attached even though the user
- * explicitly linked an inbox item (with a document) to this transaction. We:
- *   1. find the inbox item(s) where matched_transaction_id = txId that no
+ * Anchor one document to the verifikat, with the guard semantics every
+ * booking path shares: a document already pointing at THIS verifikat is a
+ * no-op (a same-value rewrite would trip the period-lock trigger), a document
+ * anchored to ANOTHER verifikat is never stolen, and a failed link is
+ * reported so the caller can withhold any consumed-stamp. Returns true when
+ * the document ends up referencing the verifikat.
+ */
+async function anchorDocumentToJournalEntry(
+  supabase: SupabaseClient,
+  companyId: string,
+  documentId: string,
+  journalEntryId: string,
+  logContext: Record<string, unknown>,
+): Promise<boolean> {
+  const { data: doc } = await supabase
+    .from('document_attachments')
+    .select('journal_entry_id')
+    .eq('id', documentId)
+    .eq('company_id', companyId)
+    .maybeSingle()
+  const currentDocEntryId = (doc?.journal_entry_id as string | null) ?? null
+  if (currentDocEntryId === journalEntryId) return true
+  if (currentDocEntryId !== null) {
+    // Anchored to another verifikat: preserved, never stolen (BFL 5 kap 6-7 §).
+    log.warn('Document already anchored to another verifikat; leaving it', {
+      ...logContext,
+      document_id: documentId,
+      document_journal_entry_id: currentDocEntryId,
+      journal_entry_id: journalEntryId,
+    })
+    return false
+  }
+  try {
+    await linkToJournalEntry(supabase, companyId, documentId, journalEntryId)
+    return true
+  } catch (err) {
+    log.error('Failed to link document to journal entry', {
+      ...logContext,
+      document_id: documentId,
+      journal_entry_id: journalEntryId,
+      error: err instanceof Error ? err.message : String(err),
+    })
+    return false
+  }
+}
+
+/**
+ * Propagate the underlag onto the verifikat that booked a transaction.
+ * Without this, BFL 7 kap is violated: a verifikation exists with no underlag
+ * attached even though the user explicitly linked a document (or an inbox
+ * item with a document) to this transaction. We:
+ *   1. anchor the transaction's own pinned document (transactions.document_id)
+ *      when it does not reference a verifikat yet: a document attached
+ *      directly to the transaction has no inbox item, so nothing else carries
+ *      it onto the verifikat
+ *   2. find the inbox item(s) where matched_transaction_id = txId that no
  *      journal entry or supplier invoice has consumed yet
- *   2. for each item with a document_id, set
+ *   3. for each item with a document_id, set
  *      document_attachments.journal_entry_id = journalEntryId, skipped when
  *      the document already points at a verifikat: a same-value rewrite would
  *      trip the period-lock trigger, and a different verifikat's underlag is
  *      never stolen
- *   3. stamp invoice_inbox_items.created_journal_entry_id so the inbox row
+ *   4. stamp invoice_inbox_items.created_journal_entry_id so the inbox row
  *      visibly moves to "Bokförda" and shows "Öppna verifikation"
  * Errors are logged but never fail the caller: the verifikation itself is
  * already posted, and the link can be repaired by re-running this step.
@@ -139,6 +195,24 @@ export async function propagateUnderlagForBookedTransaction(
   journalEntryId: string,
 ): Promise<void> {
   try {
+    // The pin is read fresh here (not passed in from the caller's pre-booking
+    // snapshot) so an attach that lands concurrently with the booking is
+    // still anchored. The bulk-book RPC already anchors pins atomically;
+    // there this read finds the doc pointing at the same verifikat and no-ops.
+    const { data: tx } = await supabase
+      .from('transactions')
+      .select('document_id')
+      .eq('id', txId)
+      .eq('company_id', companyId)
+      .maybeSingle()
+    const pinnedDocumentId = (tx?.document_id as string | null) ?? null
+    if (pinnedDocumentId) {
+      await anchorDocumentToJournalEntry(supabase, companyId, pinnedDocumentId, journalEntryId, {
+        transaction_id: txId,
+        source: 'transaction_pin',
+      })
+    }
+
     const { data: matchedInboxItems } = await supabase
       .from('invoice_inbox_items')
       .select('id, document_id')
@@ -156,42 +230,18 @@ export async function propagateUnderlagForBookedTransaction(
       // (.is('created_journal_entry_id', null)), making the promised
       // "repaired by re-running" impossible and leaving a posted
       // verifikation with no underlag reference (BFL 5 kap 6-7 §) that
-      // nothing surfaces anymore.
+      // nothing surfaces anymore. Similarly, an item whose document is
+      // anchored to a DIFFERENT verifikat is not stamped: that would hide
+      // the very signal that the mismatch needs a human.
       let underlagSettled = true
       if (inbox.document_id) {
-        const { data: doc } = await supabase
-          .from('document_attachments')
-          .select('journal_entry_id')
-          .eq('id', inbox.document_id)
-          .eq('company_id', companyId)
-          .maybeSingle()
-        const currentDocEntryId = (doc?.journal_entry_id as string | null) ?? null
-        if (currentDocEntryId === null) {
-          try {
-            await linkToJournalEntry(supabase, companyId, inbox.document_id, journalEntryId)
-          } catch (err) {
-            underlagSettled = false
-            log.error('Failed to link inbox document to journal entry', {
-              inbox_item_id: inbox.id,
-              document_id: inbox.document_id,
-              journal_entry_id: journalEntryId,
-              error: err instanceof Error ? err.message : String(err),
-            })
-          }
-        } else if (currentDocEntryId !== journalEntryId) {
-          // Anchored to another verifikat: preserved, never stolen. But the
-          // verifikat that booked THIS transaction then has no underlag
-          // reference from this item, so it must NOT be stamped consumed:
-          // stamping would hide the very signal that the mismatch needs a
-          // human (BFL 5 kap 6-7 §).
-          underlagSettled = false
-          log.warn('Inbox document already anchored to another verifikat; leaving it', {
-            inbox_item_id: inbox.id,
-            document_id: inbox.document_id,
-            document_journal_entry_id: currentDocEntryId,
-            journal_entry_id: journalEntryId,
-          })
-        }
+        underlagSettled = await anchorDocumentToJournalEntry(
+          supabase,
+          companyId,
+          inbox.document_id,
+          journalEntryId,
+          { inbox_item_id: inbox.id, source: 'inbox_match' },
+        )
       }
       if (!underlagSettled) continue
       // CAS on the null predicate so a concurrent stamp stays a no-op, and