feat(transactions): inline transfer icon + FK error message

Issue #142 / Bilan #4 — non-regressive transfer awareness in the
transactions table + clean error mapping on bulk delete.

- `TransactionTable.tsx`: optional new prop
  `linkedTransfersByTxId?: Map<txId, links[]>`. When supplied, a small
  `<Link2>` icon appears next to the description for every linked
  transaction; tooltip lists the account name(s) and direction(s).
  Without the prop, the table renders byte-for-byte identical to
  before — preserves the spec's non-regression invariant.
- `TransactionsPage.tsx`: loads the linked-transfers map once on mount
  via `listAllLinkedTransfersForTooltip()` (one batch SELECT) and
  threads it through to the table. Failure to load the map degrades
  gracefully to an empty map (icon simply doesn't appear).
- `transactionService.ts`: new `deleteTransaction(id)` helper +
  `TransactionLinkedToBalanceError` (typed FK guard). Pre-checks
  `balance_account_transfers` before attempting the DELETE so the
  error carries the offending account names; falls back to the FK
  pattern matcher if a race linked the transaction between the
  SELECT and the DELETE.
- `importedFileService.ts`: both bulk delete paths
  (`deleteImportWithTransactions`, `deleteAllImportsWithTransactions`)
  now pre-check for any linked transfer and surface the same typed
  error before they would explode on FK RESTRICT. The pre-check has
  a `LIMIT 50` safety cap on the global path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/transactions/TransactionTable.tsx

@@ -1,12 +1,13 @@
 import { Fragment, useState, useMemo } from "react";
 import { useTranslation } from "react-i18next";
-import { ChevronUp, ChevronDown, MessageSquare, Tag, Split } from "lucide-react";
+import { ChevronUp, ChevronDown, MessageSquare, Tag, Split, Link2 } from "lucide-react";
 import type {
   TransactionRow,
   TransactionSort,
   Category,
   SplitChild,
 } from "../../shared/types";
+import type { LinkedTransferTooltipRow } from "../../services/balance.service";
 import CategoryCombobox from "../shared/CategoryCombobox";
 import SplitAdjustmentModal from "./SplitAdjustmentModal";
 
@@ -22,6 +23,14 @@ interface TransactionTableProps {
   onSaveSplit: (parentId: number, entries: Array<{ category_id: number; amount: number; description: string }>) => Promise<void>;
   onDeleteSplit: (parentId: number) => Promise<void>;
   onRowContextMenu?: (event: React.MouseEvent, row: TransactionRow) => void;
+  /**
+   * Issue #142 — when supplied, a small Link2 icon appears next to the
+   * description for every transaction whose id is a key in the map. The
+   * icon's tooltip lists the linked accounts. The lookup is intentionally
+   * done by the parent (one batch SELECT, in-memory `.has()` thereafter)
+   * to avoid an N+1 hit on the table render.
+   */
+  linkedTransfersByTxId?: Map<number, LinkedTransferTooltipRow[]>;
 }
 
 function SortIcon({
@@ -52,6 +61,7 @@ export default function TransactionTable({
   onSaveSplit,
   onDeleteSplit,
   onRowContextMenu,
+  linkedTransfersByTxId,
 }: TransactionTableProps) {
   const { t } = useTranslation();
   const [expandedId, setExpandedId] = useState<number | null>(null);
@@ -141,8 +151,31 @@ export default function TransactionTable({
                 className="hover:bg-[var(--muted)] transition-colors"
               >
                 <td className="px-3 py-2 whitespace-nowrap">{row.date}</td>
-                <td className="px-3 py-2 max-w-xs truncate" title={row.description}>
-                  {row.description}
+                <td className="px-3 py-2 max-w-xs">
+                  <div className="flex items-center gap-1.5">
+                    <span className="truncate" title={row.description}>
+                      {row.description}
+                    </span>
+                    {linkedTransfersByTxId?.has(row.id) && (
+                      <span
+                        className="inline-flex items-center text-[var(--primary)] shrink-0"
+                        title={
+                          // Build a human-readable list: "TFSA (in), RRSP (out)".
+                          (() => {
+                            const links = linkedTransfersByTxId.get(row.id) ?? [];
+                            const parts = links.map(
+                              (l) =>
+                                `${l.account_name} (${t(`balance.transfers.direction.${l.direction}`)})`
+                            );
+                            return `${t("transactions.transferIcon.tooltip")}: ${parts.join(", ")}`;
+                          })()
+                        }
+                        aria-label={t("transactions.transferIcon.ariaLabel")}
+                      >
+                        <Link2 size={12} />
+                      </span>
+                    )}
+                  </div>
                 </td>
                 <td
                   className={`px-3 py-2 text-right font-mono whitespace-nowrap ${

src/pages/TransactionsPage.tsx

@@ -1,4 +1,4 @@
-import { useState } from "react";
+import { useEffect, useState } from "react";
 import { useTranslation } from "react-i18next";
 import { Wand2, Tag } from "lucide-react";
 import { PageHelp } from "../components/shared/PageHelp";
@@ -9,6 +9,10 @@ import TransactionTable from "../components/transactions/TransactionTable";
 import TransactionPagination from "../components/transactions/TransactionPagination";
 import ContextMenu from "../components/shared/ContextMenu";
 import AddKeywordDialog from "../components/categories/AddKeywordDialog";
+import {
+  listAllLinkedTransfersForTooltip,
+  type LinkedTransferTooltipRow,
+} from "../services/balance.service";
 import type { TransactionRow } from "../shared/types";
 
 export default function TransactionsPage() {
@@ -18,6 +22,18 @@ export default function TransactionsPage() {
   const [resultMessage, setResultMessage] = useState<string | null>(null);
   const [menu, setMenu] = useState<{ x: number; y: number; row: TransactionRow } | null>(null);
   const [pending, setPending] = useState<TransactionRow | null>(null);
+  // Issue #142 — single batch lookup for the inlined transfer icon. One
+  // SELECT on mount gives us a Map<txId, links[]> the table consults via
+  // `.has()` per row. Avoids an N+1 hit on the rendered page.
+  const [linkedTransfersByTxId, setLinkedTransfersByTxId] = useState<
+    Map<number, LinkedTransferTooltipRow[]>
+  >(new Map());
+
+  useEffect(() => {
+    listAllLinkedTransfersForTooltip()
+      .then(setLinkedTransfersByTxId)
+      .catch(() => setLinkedTransfersByTxId(new Map()));
+  }, []);
 
   const handleRowContextMenu = (e: React.MouseEvent, row: TransactionRow) => {
     e.preventDefault();
@@ -95,6 +111,7 @@ export default function TransactionsPage() {
             onSaveSplit={saveSplit}
             onDeleteSplit={deleteSplit}
             onRowContextMenu={handleRowContextMenu}
+            linkedTransfersByTxId={linkedTransfersByTxId}
           />
 
           <TransactionPagination

src/services/importedFileService.ts

@@ -1,4 +1,6 @@
 import { getDb } from "./db";
+import { isLinkedTransactionFkError } from "./balance.service";
+import { TransactionLinkedToBalanceError } from "./transactionService";
 import type { ImportedFile, ImportedFileWithSource } from "../shared/types";
 
 export async function getFilesBySourceId(
@@ -94,10 +96,39 @@ export async function deleteImportWithTransactions(
   );
   const sourceId = files.length > 0 ? files[0].source_id : null;
 
-  const result = await db.execute(
-    "DELETE FROM transactions WHERE file_id = $1",
+  // Pre-flight: if any transaction in this file is linked to a balance
+  // account via `balance_account_transfers`, the FK RESTRICT will fire on
+  // the bulk DELETE. Surface a typed error BEFORE touching the row so the
+  // UI can prompt the user to unlink first (Issue #142).
+  const linked = await db.select<
+    Array<{ transaction_id: number; account_id: number; account_name: string; direction: "in" | "out" }>
+  >(
+    `SELECT bat.transaction_id AS transaction_id,
+            bat.account_id AS account_id,
+            a.name AS account_name,
+            bat.direction AS direction
+       FROM balance_account_transfers bat
+       JOIN transactions t ON t.id = bat.transaction_id
+       JOIN balance_accounts a ON a.id = bat.account_id
+      WHERE t.file_id = $1`,
     [fileId]
   );
+  if (linked.length > 0) {
+    throw new TransactionLinkedToBalanceError(null, linked);
+  }
+
+  let result;
+  try {
+    result = await db.execute(
+      "DELETE FROM transactions WHERE file_id = $1",
+      [fileId]
+    );
+  } catch (err) {
+    if (isLinkedTransactionFkError(err)) {
+      throw new TransactionLinkedToBalanceError(null, []);
+    }
+    throw err;
+  }
   await db.execute("DELETE FROM imported_files WHERE id = $1", [fileId]);
 
   // Clean up orphaned source if no files remain
@@ -116,7 +147,32 @@ export async function deleteImportWithTransactions(
 
 export async function deleteAllImportsWithTransactions(): Promise<number> {
   const db = await getDb();
-  const result = await db.execute("DELETE FROM transactions");
+  // Same pre-flight as the per-file path: if ANY transaction is linked to
+  // a balance account, the bulk wipe would explode on FK RESTRICT — surface
+  // a typed error so the UI can prompt the user to unlink first.
+  const linked = await db.select<
+    Array<{ transaction_id: number; account_id: number; account_name: string; direction: "in" | "out" }>
+  >(
+    `SELECT bat.transaction_id AS transaction_id,
+            bat.account_id AS account_id,
+            a.name AS account_name,
+            bat.direction AS direction
+       FROM balance_account_transfers bat
+       JOIN balance_accounts a ON a.id = bat.account_id
+      LIMIT 50`
+  );
+  if (linked.length > 0) {
+    throw new TransactionLinkedToBalanceError(null, linked);
+  }
+  let result;
+  try {
+    result = await db.execute("DELETE FROM transactions");
+  } catch (err) {
+    if (isLinkedTransactionFkError(err)) {
+      throw new TransactionLinkedToBalanceError(null, []);
+    }
+    throw err;
+  }
   await db.execute("DELETE FROM imported_files");
   await db.execute("DELETE FROM import_sources");
   return result.rowsAffected;

src/services/transactionService.ts

@@ -1,5 +1,9 @@
 import { getDb } from "./db";
 import { categorizeBatch } from "./categorizationService";
+import {
+  isLinkedTransactionFkError,
+  type LinkedTransferTooltipRow,
+} from "./balance.service";
 import type {
   Transaction,
   TransactionRow,
@@ -11,6 +15,85 @@ import type {
   SplitChild,
 } from "../shared/types";
 
+/**
+ * Thrown when a deletion path is blocked by `balance_account_transfers.transaction_id`
+ * FK RESTRICT. Carries the offending `transaction_id`(s) so the UI can format a
+ * precise message ("Cette transaction est liée au compte de bilan X — déliez-la
+ * avant de supprimer") and can offer a deep link to the linked account.
+ *
+ * `linkedAccounts` is best-effort: when known (single-row delete) the array
+ * lists every account currently linking the transaction. For bulk deletes
+ * the array may be empty — the UI just shows the generic message in that
+ * case.
+ */
+export class TransactionLinkedToBalanceError extends Error {
+  readonly code = "transaction_linked_to_balance_account" as const;
+  readonly transactionId: number | null;
+  readonly linkedAccounts: LinkedTransferTooltipRow[];
+  constructor(
+    transactionId: number | null,
+    linkedAccounts: LinkedTransferTooltipRow[],
+    message?: string
+  ) {
+    super(
+      message ??
+        "Transaction is linked to one or more balance accounts; unlink before deleting"
+    );
+    this.name = "TransactionLinkedToBalanceError";
+    this.transactionId = transactionId;
+    this.linkedAccounts = linkedAccounts;
+  }
+}
+
+/**
+ * Delete one transaction by id. Throws `TransactionLinkedToBalanceError` if
+ * the transaction has any row in `balance_account_transfers` (FK RESTRICT)
+ * — UI surfaces "Cette transaction est liée au compte de bilan X — déliez-la
+ * avant de supprimer" with a link to the offending account.
+ *
+ * Pre-checks the link table so the error carries account names; falls back
+ * to the FK-error pattern matcher if the constraint fires for any other
+ * reason.
+ */
+export async function deleteTransaction(transactionId: number): Promise<void> {
+  const db = await getDb();
+  // Pre-check: if any transfer references this transaction, surface a clean
+  // typed error WITHOUT touching the row. Cheaper than catching the FK
+  // exception and provides the account names for the UI message.
+  const linked = await db.select<
+    Array<{ account_id: number; account_name: string; direction: "in" | "out" }>
+  >(
+    `SELECT bat.account_id AS account_id,
+            a.name AS account_name,
+            bat.direction AS direction
+       FROM balance_account_transfers bat
+       JOIN balance_accounts a ON a.id = bat.account_id
+      WHERE bat.transaction_id = $1`,
+    [transactionId]
+  );
+  if (linked.length > 0) {
+    throw new TransactionLinkedToBalanceError(
+      transactionId,
+      linked.map((l) => ({
+        transaction_id: transactionId,
+        account_id: l.account_id,
+        account_name: l.account_name,
+        direction: l.direction,
+      }))
+    );
+  }
+  try {
+    await db.execute("DELETE FROM transactions WHERE id = $1", [transactionId]);
+  } catch (err) {
+    // Defensive: a race could have linked the transaction between the
+    // SELECT and the DELETE. Surface the typed error in that case too.
+    if (isLinkedTransactionFkError(err)) {
+      throw new TransactionLinkedToBalanceError(transactionId, []);
+    }
+    throw err;
+  }
+}
+
 export async function insertBatch(
   transactions: Array<{
     date: string;