diff --git a/src/hooks/useImportWizard.ts b/src/hooks/useImportWizard.ts
index 79a207f..9029bab 100644
--- a/src/hooks/useImportWizard.ts
+++ b/src/hooks/useImportWizard.ts
@@ -41,7 +41,7 @@ import {
 } from "../services/importConfigTemplateService";
 import {
   preprocessQuotedCSV,
-  autoDetectConfig as runAutoDetect,
+  detectImportFormat as runAutoDetect,
 } from "../utils/csvAutoDetect";
 import {
   detectAmountSeparators,
@@ -868,9 +868,10 @@ export function useImportWizard() {
         encoding: state.sourceConfig.encoding,
       });
 
-      const result = runAutoDetect(content);
+      const outcome = runAutoDetect(content);
 
-      if (result) {
+      if (outcome.status === "ok") {
+        const result = outcome.config;
         const newConfig = {
           ...state.sourceConfig,
           delimiter: result.delimiter,
@@ -893,9 +894,16 @@ export function useImportWizard() {
           newConfig.hasHeader
         );
       } else {
+        // A refused format states WHY (#327): "I cannot read this file" and
+        // "this file is a shape this version would import backwards" are not
+        // the same news, and only the second one is the app's own limitation.
+        // `SET_ERROR` clears the loading flag on its own.
         dispatch({
           type: "SET_ERROR",
-          payload: "Auto-detection failed. Please configure manually.",
+          payload:
+            outcome.status === "rejected"
+              ? outcome.reason
+              : "import.errors.autoDetectFailed",
         });
       }
     } catch (e) {
diff --git a/src/i18n/locales/en.json b/src/i18n/locales/en.json
index cc74728..3a55f8f 100644
--- a/src/i18n/locales/en.json
+++ b/src/i18n/locales/en.json
@@ -189,7 +189,9 @@
     "errors": {
       "unsupportedAmountMode": "The amount mode saved for this source is not recognized. Reconfigure the source before importing.",
       "unsupportedSignConvention": "The sign convention saved for this source is not recognized. Reconfigure the source before importing.",
-      "invalidColumnMapping": "The column mapping saved for this source cannot be read. Reconfigure the source before importing."
+      "invalidColumnMapping": "The column mapping saved for this source cannot be read. Reconfigure the source before importing.",
+      "absoluteIndicatorFormat": "This file uses positive amounts with a separate column giving the direction (D for debit, C for credit). That format is not supported yet: importing it now would record every deposit as an expense. Export the statement with signed amounts, or with separate debit and credit columns.",
+      "autoDetectFailed": "Auto-detection could not read this file. Configure the format manually."
     },
     "rowErrors": {
       "invalidDate": "Unreadable date",
diff --git a/src/i18n/locales/fr.json b/src/i18n/locales/fr.json
index 4aa1c97..370a021 100644
--- a/src/i18n/locales/fr.json
+++ b/src/i18n/locales/fr.json
@@ -189,7 +189,9 @@
     "errors": {
       "unsupportedAmountMode": "Le mode de montant enregistré pour cette source n'est pas reconnu. Reconfigurez la source avant d'importer.",
       "unsupportedSignConvention": "La convention de signe enregistrée pour cette source n'est pas reconnue. Reconfigurez la source avant d'importer.",
-      "invalidColumnMapping": "Le mapping de colonnes enregistré pour cette source est illisible. Reconfigurez la source avant d'importer."
+      "invalidColumnMapping": "Le mapping de colonnes enregistré pour cette source est illisible. Reconfigurez la source avant d'importer.",
+      "absoluteIndicatorFormat": "Ce fichier utilise des montants positifs accompagnés d'une colonne indiquant le sens (D pour débit, C pour crédit). Ce format n'est pas encore pris en charge : l'importer maintenant enregistrerait chaque dépôt comme une dépense. Exportez le relevé avec des montants signés ou avec deux colonnes débit et crédit.",
+      "autoDetectFailed": "La détection automatique n'a pas pu lire ce fichier. Configurez le format manuellement."
     },
     "rowErrors": {
       "invalidDate": "Date illisible",
diff --git a/src/utils/csvAutoDetect.test.ts b/src/utils/csvAutoDetect.test.ts
index 328ef90..821ef40 100644
--- a/src/utils/csvAutoDetect.test.ts
+++ b/src/utils/csvAutoDetect.test.ts
@@ -18,6 +18,7 @@ import {
   autoDetectHoldingColumns,
   analyzeHoldingsCsv,
   autoDetectConfig,
+  detectImportFormat,
   preprocessQuotedCSV,
 } from "./csvAutoDetect";
 import type { DecimalSeparator } from "./amountParser";
@@ -27,6 +28,8 @@ import {
   readCsvFixture,
   type CsvFixtureName,
 } from "../__fixtures__/csv";
+import fr from "../i18n/locales/fr.json";
+import en from "../i18n/locales/en.json";
 
 describe("autoDetectHoldingColumns (#245)", () => {
   it("detects symbol/quantity/price/book_cost from EN headers", () => {
@@ -220,12 +223,23 @@ describe("corpus integrity (#326)", () => {
     }
   });
 
-  it("detects a configuration for every fixture (none returns null)", () => {
+  it("detects a configuration for every fixture but the refused one", () => {
+    // `absolute-indicator` left this list in #327: it is the one shape
+    // detection now REFUSES instead of configuring, and it says so — the case
+    // below asserts the reason rather than a bare null.
     for (const name of CSV_FIXTURE_NAMES) {
+      if (name === "absolute-indicator") continue;
       expect(autoDetectConfig(readCsvFixture(name)), name).not.toBeNull();
     }
   });
 
+  it("never fails silently: every fixture is a config or a stated reason", () => {
+    for (const name of CSV_FIXTURE_NAMES) {
+      const outcome = detectImportFormat(readCsvFixture(name));
+      expect(outcome.status, name).not.toBe("failed");
+    }
+  });
+
   it("runs the production rule, with no mirror left to drift (#325)", () => {
     // The guard that used to live here pinned five expressions of
     // `parseFilesInternal` so the hand-written mirror could not drift. Both are
@@ -301,36 +315,42 @@ describe("autoDetectConfig — debit/credit pair (#326)", () => {
   });
 });
 
-describe("autoDetectConfig — KNOWN DEFECT: debit/credit order guessed by position (#326, fixed by #328)", () => {
-  // `detectAmountMode` assigns the LEFTMOST column of a complementary pair to
-  // `debitAmount` and the rightmost to `creditAmount` (csvAutoDetect.ts:461-470).
-  // It never looks at the header labels. A file laid out `Credit;Debit` is
-  // therefore mapped backwards, and every sign in the import is inverted.
+describe("autoDetectConfig — debit/credit order read from the labels (#326, fixed by #327)", () => {
+  // FIXED. `detectAmountMode` used to assign the LEFTMOST column of a
+  // complementary pair to `debitAmount` and the rightmost to `creditAmount`
+  // (the loop enumerates `a < b`), without ever looking at the header labels.
+  // A file laid out `Credit;Debit` was mapped backwards and every sign of the
+  // import came out inverted.
   //
-  // #328 resolves the order from the header dictionary instead of the position.
+  // The pair is still found by shape — sparse and complementary — but which
+  // half is the debit now comes from the dictionary (`orderDebitCredit`).
 
-  it("maps Credit to debitAmount and Debit to creditAmount", () => {
+  it("maps Debit to debitAmount and Credit to creditAmount", () => {
     const cfg = autoDetectConfig(readCsvFixture("debit-credit-reversed"))!;
     // Column 2 is labelled "Credit" and column 3 "Debit" in the fixture.
-    expect(cfg.columnMapping.debitAmount).toBe(2); // DEFECT — should be 3
-    expect(cfg.columnMapping.creditAmount).toBe(3); // DEFECT — should be 2
+    expect(cfg.columnMapping.debitAmount).toBe(3);
+    expect(cfg.columnMapping.creditAmount).toBe(2);
     expect(cfg.amountMode).toBe("debit_credit");
   });
 
-  it("inverts every sign end to end — groceries become income", () => {
-    expect(amountsOf("debit-credit-reversed")).toEqual(
-      // DEFECT — should be REFERENCE_AMOUNTS
-      [84.32, -1250, 142.18, 56.75, -300, 6.95]
-    );
+  it("parses end to end to the reference amounts", () => {
+    expect(amountsOf("debit-credit-reversed")).toEqual(REFERENCE_AMOUNTS);
   });
 
-  it("still nets to the same total, which is why the bug hides", () => {
-    // The signs are wrong one by one, but the sum is merely negated — no
-    // aggregate check catches it. Only a per-row review does.
+  it("reads the reversed file identically to its Debit-first twin", () => {
+    // The same six transactions, columns swapped. Nothing but the labels tells
+    // them apart, which is the whole point of the lexical layer.
+    expect(amountsOf("debit-credit-reversed")).toEqual(amountsOf("debit-credit"));
+  });
+
+  it("nets to the reference total, no longer to its negation", () => {
+    // While the bug was live the signs were wrong one by one but the sum was
+    // merely negated, so no aggregate check could catch it. That is why the
+    // per-row equality above is the assertion that matters.
     const sum = (xs: (number | string)[]) =>
       xs.reduce<number>((a, b) => a + (typeof b === "number" ? b : 0), 0);
     expect(sum(amountsOf("debit-credit-reversed"))).toBeCloseTo(
-      -sum(REFERENCE_AMOUNTS),
+      sum(REFERENCE_AMOUNTS),
       6
     );
   });
@@ -419,11 +439,12 @@ describe("autoDetectConfig — header cell starting with digits (#326, fixed by
   // normalizes to "2025Montant"; `parseFloat` returned the 2025 prefix,
   // `hasNumber` flipped true, and the header row was taken for data.
   //
-  // Link 1's note: "#328 adds a lexical signal to `detectHeader`, and #325
+  // Link 1's note: "#327 adds a lexical signal to `detectHeader`, and #325
   // anchors the parser so a numeric prefix no longer reads as a number. Either
   // fix closes this." #325 landed first — the anchored parser returns NaN for
   // that cell, so `detectHeader` sees a row with no number and no date.
-  // #328 keeps its lexical signal for header cells that carry a BARE number.
+  // #327 keeps its lexical signal for header cells that carry a BARE number,
+  // which the anchored parser reads as a number by design (see below).
 
   it("recognises the header row", () => {
     const cfg = autoDetectConfig(readCsvFixture("header-numeric-label"))!;
@@ -530,41 +551,265 @@ describe("preprocessQuotedCSV + autoDetectConfig — whole-line-quoted file (#32
   });
 });
 
-describe("autoDetectConfig — KNOWN DEFECT: absolute amount + D/C indicator (#326, fixed by #328)", () => {
-  // The third amount mode: one column of unsigned magnitudes plus a
-  // single-letter D/C column carrying the direction. Nothing reads that
-  // column. Detection sees only positive numbers, picks `positive_expense`,
-  // and every credit is imported as an expense.
+describe("autoDetectConfig — absolute amount + D/C indicator, refused (#326, fixed by #327)", () => {
+  // FIXED, by refusing rather than by reading. The third amount mode is one
+  // column of unsigned magnitudes plus a single-letter D/C column carrying the
+  // direction. Nothing reads that column: detection saw only positive numbers,
+  // picked `positive_expense`, and every credit was imported as an expense —
+  // the file was indistinguishable from `all-positive`, byte for byte of
+  // config.
   //
-  // #328 must DETECT this shape and REFUSE the file with a dedicated message,
-  // rather than import it backwards. The spec decision is explicit: refused,
-  // not silently mis-imported.
+  // The spec decision is explicit — such a file is refused, not silently
+  // mis-imported — and `amount_mode` carries no CHECK constraint, so reading
+  // this shape properly can ship later without a migration.
 
-  it("ignores the indicator column entirely", () => {
-    const cfg = autoDetectConfig(readCsvFixture("absolute-indicator"))!;
+  it("refuses the file with a dedicated reason", () => {
+    const outcome = detectImportFormat(readCsvFixture("absolute-indicator"));
+    expect(outcome.status).toBe("rejected");
+    expect(outcome).toEqual({
+      status: "rejected",
+      reason: "import.errors.absoluteIndicatorFormat",
+    });
+  });
+
+  it("produces no configuration, so no row can be imported backwards", () => {
+    expect(autoDetectConfig(readCsvFixture("absolute-indicator"))).toBeNull();
+    // Rows 2 and 5 are flagged "C" in the fixture; they used to import as
+    // -1250 and -300.
+    expect(() => amountsOf("absolute-indicator")).toThrow();
+  });
+
+  it("is no longer indistinguishable from the all-positive fixture", () => {
+    // Same amount column, same absence of negatives — the indicator column is
+    // the only discriminator, and it is now read.
+    const without = autoDetectConfig(readCsvFixture("all-positive"))!;
+    expect(without.signConvention).toBe("positive_expense");
+    expect(autoDetectConfig(readCsvFixture("absolute-indicator"))).toBeNull();
+  });
+
+  it("refuses on the values alone, with no header row to help", () => {
+    const headerless = readCsvFixture("absolute-indicator")
+      .split("\n")
+      .slice(1)
+      .join("\n");
+    expect(detectImportFormat(headerless).status).toBe("rejected");
+  });
+
+  it("carries a translated message in both languages", () => {
+    // The reason is an i18n key, resolved by the error banner
+    // (`ImportPage.tsx`) like every other key the wizard reports.
+    expect(fr.import.errors.absoluteIndicatorFormat.length).toBeGreaterThan(0);
+    expect(en.import.errors.absoluteIndicatorFormat.length).toBeGreaterThan(0);
+  });
+
+  it("is the reason the wizard reports, in place of an English literal", () => {
+    // The hook lives in a `useCallback` and the repository has no jsdom, so
+    // the wiring is asserted on the source — same technique as the guard above.
+    const SRC = readFileSync(
+      resolve(import.meta.dirname, "..", "hooks", "useImportWizard.ts"),
+      "utf-8"
+    );
+    expect(SRC).toContain("detectImportFormat as runAutoDetect");
+    expect(SRC).toContain("outcome.reason");
+    // The banner used to render this literal, in English, whatever the
+    // interface language.
+    expect(SRC).not.toContain("Auto-detection failed. Please configure");
+  });
+});
+
+// =============================================================================
+// Issue #327 — the lexical layer, beyond what the corpus covers
+// =============================================================================
+//
+// The corpus fixtures are frozen files with FR labels. These cases exercise the
+// clauses they cannot: EN labels, a header row the shape test alone cannot
+// classify, and the fall-back to shape when the labels say nothing.
+
+/** Build a semicolon CSV from a header line and the standard six rows. */
+function withHeader(header: string, rows: string[]): string {
+  return [header, ...rows].join("\n") + "\n";
+}
+
+const SIGNED_ROWS = [
+  "05/01/2025;EPICERIE METRO SAINTE-FOY;-84,32",
+  "15/01/2025;DEPOT PAIE EMPLOYEUR;1250,00",
+  "18/01/2025;HYDRO QUEBEC PREAUTORISE;-142,18",
+  "22/01/2025;RESTAURANT LE BISTRO;-56,75",
+  "27/01/2025;VIREMENT RECU;300,00",
+  "31/01/2025;FRAIS MENSUELS;-6,95",
+];
+
+const PAIR_ROWS = [
+  "05/01/2025;EPICERIE METRO SAINTE-FOY;;84,32",
+  "15/01/2025;DEPOT PAIE EMPLOYEUR;1250,00;",
+  "18/01/2025;HYDRO QUEBEC PREAUTORISE;;142,18",
+  "22/01/2025;RESTAURANT LE BISTRO;;56,75",
+  "27/01/2025;VIREMENT RECU;300,00;",
+  "31/01/2025;FRAIS MENSUELS;;6,95",
+];
+
+describe("detectHeader — lexical signal on a bare-number header cell (#327)", () => {
+  // The residual case link 1 named. `2025 Montant` is closed by #325's anchored
+  // parser, but a column titled `2025` outright IS a number by every rule the
+  // parser has, and the shape test reads `hasNumber` as "this row is data".
+  const csv = withHeader("Date;Description;2025", SIGNED_ROWS);
+
+  it("recognises the header row from its labels", () => {
+    const cfg = autoDetectConfig(csv)!;
+    expect(cfg.hasHeader).toBe(true);
+    expect(cfg.columnMapping).toEqual({ date: 0, description: 1, amount: 2 });
+  });
+
+  it("keeps the label row out of the data", () => {
+    const cfg = autoDetectConfig(csv)!;
+    const rows = Papa.parse(csv, {
+      delimiter: cfg.delimiter,
+      skipEmptyLines: true,
+    }).data as string[][];
+    const parsed = rows
+      .slice(cfg.hasHeader ? 1 : 0)
+      .map((raw) => mapCorpusRow(raw, cfg));
+    expect(parsed).toHaveLength(6);
+    expect(parsed.every((r) => !("error" in r))).toBe(true);
+  });
+
+  it("needs two named roles, not one", () => {
+    // A single keyword hit proves nothing: a description cell like `DEPOT PAIE
+    // EMPLOYEUR` contains `depot`. One label plus one number is left to shape.
+    const oneRole = withHeader("Compte;Description;2025", SIGNED_ROWS);
+    expect(autoDetectConfig(oneRole)!.hasHeader).toBe(false);
+  });
+
+  it("leaves a row carrying a real date to the shape test", () => {
+    // The date test stays absolute — a data row is data however its other
+    // cells read, which is what stops a transaction from being eaten as a
+    // header.
+    expect(autoDetectConfig(readCsvFixture("no-header"))!.hasHeader).toBe(false);
+  });
+});
+
+describe("autoDetectConfig — English labels (#327)", () => {
+  it("orders a Withdrawal/Deposit pair from the labels", () => {
+    const cfg = autoDetectConfig(
+      withHeader("Date;Description;Deposit;Withdrawal", PAIR_ROWS)
+    )!;
+    expect(cfg.amountMode).toBe("debit_credit");
+    expect(cfg.columnMapping.debitAmount).toBe(3);
+    expect(cfg.columnMapping.creditAmount).toBe(2);
+  });
+
+  it("reads an Amount/Balance file without mapping the balance", () => {
+    const cfg = autoDetectConfig(
+      withHeader("Date;Description;Amount;Balance", [
+        "05/01/2025;EPICERIE METRO SAINTE-FOY;-84,32;1415,68",
+        "15/01/2025;DEPOT PAIE EMPLOYEUR;1250,00;2665,68",
+        "18/01/2025;HYDRO QUEBEC PREAUTORISE;-142,18;2523,50",
+      ])
+    )!;
     expect(cfg.amountMode).toBe("single");
     expect(cfg.columnMapping.amount).toBe(2);
-    // Column 3 ("Sens", values D/C) appears nowhere in the mapping.
-    expect(Object.values(cfg.columnMapping)).not.toContain(3);
-    expect(cfg.signConvention).toBe("positive_expense");
   });
 
-  it("imports both credit rows as expenses", () => {
-    const amounts = amountsOf("absolute-indicator");
-    // Rows 2 and 5 are flagged "C" in the fixture.
-    expect(amounts[1]).toBe(-1250); // DEFECT — should be +1250
-    expect(amounts[4]).toBe(-300); // DEFECT — should be +300
-    expect(amounts.every((a) => typeof a === "number" && a < 0)).toBe(true);
+  it("excludes a balance column the arithmetic cannot recognise", () => {
+    // The running-balance test needs the column to reconcile row to row. These
+    // rows do not — a mid-period export whose opening balance is missing — and
+    // the balance is the only column carrying cents, which is what
+    // `pickBestAmountColumn` goes by.
+    const rows = [
+      "05/01/2025;EPICERIE METRO SAINTE-FOY;-84,00;1415,68",
+      "15/01/2025;DEPOT PAIE EMPLOYEUR;1250,00;9002,11",
+      "18/01/2025;HYDRO QUEBEC PREAUTORISE;-142,00;4477,03",
+    ];
+
+    // Labelled with a word the dictionary does not know, shape wins and maps
+    // the balance as the amount.
+    expect(
+      autoDetectConfig(withHeader("Date;Description;Sortie;Cumul", rows))!
+        .columnMapping.amount
+    ).toBe(3);
+
+    // Labelled `Solde`, it is excluded and the real amount column is mapped.
+    expect(
+      autoDetectConfig(withHeader("Date;Description;Sortie;Solde", rows))!
+        .columnMapping.amount
+    ).toBe(2);
+  });
+});
+
+describe("autoDetectConfig — one labelled half is enough (#327)", () => {
+  it("infers the credit column from the labelled debit", () => {
+    // `Sorties` is not in the dictionary; `Débit` is. Knowing one half names
+    // the other, because the pair has exactly two members.
+    const cfg = autoDetectConfig(
+      withHeader("Date;Description;Sorties;Debit", PAIR_ROWS)
+    )!;
+    expect(cfg.columnMapping.debitAmount).toBe(3);
+    expect(cfg.columnMapping.creditAmount).toBe(2);
+  });
+});
+
+describe("autoDetectConfig — falling back to shape when labels are mute (#327)", () => {
+  it("keeps the positional order when neither half is labelled", () => {
+    const cfg = autoDetectConfig(
+      withHeader("Date;Description;Sorties;Entrees", PAIR_ROWS)
+    )!;
+    // Unknown labels: the leftmost column of the pair stays the debit, exactly
+    // as before #327. The file reads backwards — and that is the honest
+    // outcome, since nothing in it says otherwise.
+    expect(cfg.columnMapping.debitAmount).toBe(2);
+    expect(cfg.columnMapping.creditAmount).toBe(3);
   });
 
-  it("is currently indistinguishable from the all-positive fixture", () => {
-    // Same detected config, same wrong outcome — which is exactly why #328
-    // needs the indicator column as its discriminator.
-    const withIndicator = autoDetectConfig(readCsvFixture("absolute-indicator"))!;
-    const without = autoDetectConfig(readCsvFixture("all-positive"))!;
-    expect(withIndicator.amountMode).toBe(without.amountMode);
-    expect(withIndicator.signConvention).toBe(without.signConvention);
-    expect(withIndicator.columnMapping).toEqual(without.columnMapping);
+  it("keeps mapping a headerless file positionally", () => {
+    expect(autoDetectConfig(readCsvFixture("no-header"))!.hasHeader).toBe(false);
+    expect(amountsOf("no-header")).toEqual(REFERENCE_AMOUNTS);
+  });
+
+  it("ignores a label the data contradicts", () => {
+    // The column labelled `Date` holds no date; the one that does is mapped.
+    const cfg = autoDetectConfig(
+      withHeader("Date de production;Description;Date;Montant", [
+        "N/A;EPICERIE METRO SAINTE-FOY;05/01/2025;-84,32",
+        "N/A;DEPOT PAIE EMPLOYEUR;15/01/2025;1250,00",
+        "N/A;HYDRO QUEBEC PREAUTORISE;18/01/2025;-142,18",
+      ])
+    )!;
+    expect(cfg.columnMapping.date).toBe(2);
+    expect(cfg.columnMapping.amount).toBe(3);
+  });
+
+  it("maps a Solde column rather than nothing when it is all there is", () => {
+    // The lexical exclusion of a balance column must never empty the candidate
+    // list: a mapping the user can fix beats a file that cannot be configured.
+    const cfg = autoDetectConfig(
+      withHeader("Date;Description;Solde", SIGNED_ROWS)
+    )!;
+    expect(cfg.amountMode).toBe("single");
+    expect(cfg.columnMapping.amount).toBe(2);
+  });
+});
+
+describe("autoDetectConfig — description column read from the labels (#327)", () => {
+  it("prefers the labelled column over the longest one", () => {
+    const cfg = autoDetectConfig(
+      withHeader("Date;Libelle;Note;Montant", [
+        "05/01/2025;EPICERIE METRO;une note nettement plus longue que le libelle;-84,32",
+        "15/01/2025;DEPOT PAIE;une autre note nettement plus longue encore ici;1250,00",
+        "18/01/2025;HYDRO QUEBEC;troisieme note nettement plus longue que tout;-142,18",
+      ])
+    )!;
+    expect(cfg.columnMapping.description).toBe(1);
+  });
+
+  it("falls back to the longest column when no label names one", () => {
+    const cfg = autoDetectConfig(
+      withHeader("Date;Ref;Note;Montant", [
+        "05/01/2025;A1;une note nettement plus longue que la reference;-84,32",
+        "15/01/2025;B2;une autre note nettement plus longue encore ici;1250,00",
+        "18/01/2025;C3;troisieme note nettement plus longue que tout;-142,18",
+      ])
+    )!;
+    expect(cfg.columnMapping.description).toBe(2);
   });
 });
 
diff --git a/src/utils/csvAutoDetect.ts b/src/utils/csvAutoDetect.ts
index e6bd16a..79a5c5f 100644
--- a/src/utils/csvAutoDetect.ts
+++ b/src/utils/csvAutoDetect.ts
@@ -1,6 +1,15 @@
 import Papa from "papaparse";
 import { parseDate } from "./dateParser";
 import { parseFrenchAmount } from "./amountParser";
+import {
+  CREDIT_INDICATOR_TOKENS,
+  DEBIT_INDICATOR_TOKENS,
+  matchHeaderColumn,
+  matchTransactionHeaders,
+  MIN_HEADER_ROLE_MATCHES,
+  normalizeHeaderCell,
+  type LexicalHeaderMap,
+} from "./headerDictionary";
 import type { ColumnMapping, AmountMode, SignConvention } from "../shared/types";
 
 export interface AutoDetectResult {
@@ -13,6 +22,26 @@ export interface AutoDetectResult {
   signConvention: SignConvention;
 }
 
+/**
+ * i18n key of a file detection recognised but REFUSES to configure. Refusing is
+ * a feature: the alternative for this shape is a config that imports every
+ * debit as income (see `findDirectionIndicatorColumn`).
+ */
+export type AutoDetectRejectionKey = "import.errors.absoluteIndicatorFormat";
+
+/**
+ * The full-fidelity outcome of detection.
+ *
+ * `autoDetectConfig` keeps its `AutoDetectResult | null` shape for the callers
+ * that only need the configuration, but null cannot say WHY: "I could not read
+ * this file" and "I read this file and it is a format this version imports
+ * backwards" call for different messages. `detectImportFormat` separates them.
+ */
+export type AutoDetectOutcome =
+  | { status: "ok"; config: AutoDetectResult }
+  | { status: "rejected"; reason: AutoDetectRejectionKey }
+  | { status: "failed" };
+
 const DATE_FORMATS = [
   "DD/MM/YYYY",
   "MM/DD/YYYY",
@@ -25,6 +54,12 @@ const DATE_FORMATS = [
 
 const DELIMITERS = [",", ";", "\t"];
 
+/** Every token a direction-indicator column may hold, both directions. */
+const DIRECTION_INDICATOR_TOKENS = new Set([
+  ...DEBIT_INDICATOR_TOKENS,
+  ...CREDIT_INDICATOR_TOKENS,
+]);
+
 /**
  * Detect and unwrap Desjardins-style CSVs where each entire line is
  * wrapped in quotes with "" escaping inside.
@@ -52,20 +87,41 @@ export function preprocessQuotedCSV(content: string): string {
 
 /**
  * Analyze raw CSV content and return a suggested configuration,
- * or null if detection fails.
+ * or null if detection fails OR the file is a refused format.
+ *
+ * Callers that must tell those two apart — the wizard, which owes the user a
+ * message — use `detectImportFormat` instead.
  */
 export function autoDetectConfig(rawContent: string): AutoDetectResult | null {
+  const outcome = detectImportFormat(rawContent);
+  return outcome.status === "ok" ? outcome.config : null;
+}
+
+/**
+ * Analyze raw CSV content and return a suggested configuration, the reason the
+ * file is refused, or a plain failure.
+ *
+ * The pipeline is unchanged in its bones — delimiter, preamble, header, date,
+ * numeric columns, amount mode — with a LEXICAL layer in front of it: when the
+ * file has a header row, `matchTransactionHeaders` reads its labels and the
+ * labels win. Every lexical hint is a preference, never a constraint: a label
+ * naming a column the data contradicts (a "Date" column nothing parses as a
+ * date, a "Solde" column that is the only amount candidate left) is dropped and
+ * the shape heuristic decides, exactly as it did before #327.
+ */
+export function detectImportFormat(rawContent: string): AutoDetectOutcome {
+  const failed: AutoDetectOutcome = { status: "failed" };
   const content = preprocessQuotedCSV(rawContent);
   const lines = content.split(/\r?\n/).filter((l) => l.trim());
-  if (lines.length < 2) return null;
+  if (lines.length < 2) return failed;
 
   // Step 1: Detect delimiter
   const delimiter = detectDelimiter(lines.slice(0, 10));
-  if (!delimiter) return null;
+  if (!delimiter) return failed;
 
   const parsed = Papa.parse(content, { delimiter, skipEmptyLines: true });
   const data = parsed.data as string[][];
-  if (data.length < 2) return null;
+  if (data.length < 2) return failed;
 
   // Step 1b: Detect preamble lines to skip
   // Find the expected column count (most frequent count > 1)
@@ -92,20 +148,24 @@ export function autoDetectConfig(rawContent: string): AutoDetectResult | null {
   }
 
   const effectiveData = data.slice(skipLines);
-  if (effectiveData.length < 2) return null;
+  if (effectiveData.length < 2) return failed;
 
   // Step 2: Detect header
   const hasHeader = detectHeader(effectiveData[0]);
 
+  // Step 2b: Read the header labels. A headerless file yields no map at all,
+  // which is the explicit fall-back: every step below then runs on shape only.
+  const lexical = hasHeader ? matchTransactionHeaders(effectiveData[0]) : null;
+
   const dataStartIdx = hasHeader ? 1 : 0;
   const sampleRows = effectiveData.slice(dataStartIdx, dataStartIdx + 20);
-  if (sampleRows.length === 0) return null;
+  if (sampleRows.length === 0) return failed;
 
   const colCount = Math.max(...effectiveData.slice(0, 10).map((r) => r.length));
 
   // Step 3: Detect date column + format
-  const dateResult = detectDateColumn(sampleRows, colCount);
-  if (!dateResult) return null;
+  const dateResult = detectDateColumn(sampleRows, colCount, lexical?.date);
+  if (!dateResult) return failed;
 
   // Step 3b: Find ALL date-like columns (to exclude from amount candidates)
   const dateLikeCols = new Set<number>();
@@ -129,23 +189,51 @@ export function autoDetectConfig(rawContent: string): AutoDetectResult | null {
   // Step 4: Detect numeric columns
   const numericCols = detectNumericColumns(sampleRows, colCount);
 
-  // Step 5: Detect balance columns and exclude them + date-like columns
+  // Step 5: Detect balance columns and exclude them + date-like columns.
+  // A column LABELLED "Solde"/"Balance" is excluded too — the arithmetic test
+  // needs three consecutive rows and a matching amount column to fire, so a
+  // short file or a statement whose balance does not reconcile keeps its
+  // running balance in the running for the amount column. The exclusion is
+  // dropped if it would leave nothing to map (see `narrowCandidates`).
   const balanceCols = detectBalanceColumns(sampleRows, numericCols);
-  const amountCandidates = numericCols.filter(
+  const shapeCandidates = numericCols.filter(
     (c) => !balanceCols.has(c) && !dateLikeCols.has(c)
   );
+  const amountCandidates = narrowCandidates(
+    shapeCandidates,
+    (c) => c !== lexical?.balance
+  );
 
   // Step 6: Detect description column
   const descriptionCol = detectDescriptionColumn(
     sampleRows,
     colCount,
     dateResult.column,
-    new Set([...numericCols, ...dateLikeCols])
+    new Set([...numericCols, ...dateLikeCols]),
+    lexical?.description
   );
 
   // Step 7: Determine amount mode
-  const amountResult = detectAmountMode(sampleRows, amountCandidates);
-  if (!amountResult) return null;
+  const amountResult = detectAmountMode(sampleRows, amountCandidates, lexical);
+  if (!amountResult) return failed;
+
+  // Step 7b: Refuse the third amount format — unsigned magnitudes plus a
+  // neighbouring D/C column. Nothing here reads that column, so the file would
+  // be configured as `positive_expense` and every credit imported as an
+  // expense. Detected, refused, and left to a future `absolute_indicator` mode.
+  if (amountResult.mode === "single") {
+    const indicatorCol = findDirectionIndicatorColumn(
+      sampleRows,
+      amountResult.amountCol,
+      colCount
+    );
+    if (indicatorCol !== null) {
+      return {
+        status: "rejected",
+        reason: "import.errors.absoluteIndicatorFormat",
+      };
+    }
+  }
 
   const mapping: ColumnMapping = {
     date: dateResult.column,
@@ -163,16 +251,35 @@ export function autoDetectConfig(rawContent: string): AutoDetectResult | null {
   }
 
   return {
-    delimiter,
-    hasHeader,
-    skipLines,
-    dateFormat: dateResult.format,
-    columnMapping: mapping,
-    amountMode: amountResult.mode,
-    signConvention,
+    status: "ok",
+    config: {
+      delimiter,
+      hasHeader,
+      skipLines,
+      dateFormat: dateResult.format,
+      columnMapping: mapping,
+      amountMode: amountResult.mode,
+      signConvention,
+    },
   };
 }
 
+/**
+ * Apply a lexical restriction to a candidate list, unless it would empty it.
+ *
+ * The lexical layer must never be able to turn "detected, possibly wrong" into
+ * "detected nothing": a file whose only amount column happens to be labelled
+ * `Solde` is still importable, and a user can fix a mapping far more easily
+ * than a refusal to configure.
+ */
+function narrowCandidates(
+  candidates: number[],
+  keep: (col: number) => boolean
+): number[] {
+  const narrowed = candidates.filter(keep);
+  return narrowed.length > 0 ? narrowed : candidates;
+}
+
 function detectDelimiter(lines: string[]): string | null {
   let bestDelimiter: string | null = null;
   let bestScore = 0;
@@ -211,6 +318,24 @@ function detectDelimiter(lines: string[]): string | null {
   return bestDelimiter;
 }
 
+/**
+ * Decide whether the first row is a header.
+ *
+ * The shape test — no parseable date, no parseable number — is kept and comes
+ * first. It cannot classify a header whose cells carry bare numbers (a column
+ * literally titled `2025`), and treating that row as data costs one lost
+ * transaction plus a mapping computed from a sample that starts with a label
+ * row. So a row the shape test rejects ONLY because of a number is put to the
+ * lexical layer: two named roles in one row is a header.
+ *
+ * The date test stays absolute. A row carrying a parseable date is data, no
+ * matter what its other cells spell — that is the guard that keeps a
+ * transaction like `DEPOT PAIE EMPLOYEUR` (which contains the credit keyword
+ * `depot`) from being swallowed as a header.
+ *
+ * The holdings flow calls this too. Its headers name no transaction role, so
+ * the lexical clause never fires there.
+ */
 function detectHeader(firstRow: string[]): boolean {
   // A header row typically has no parseable dates and no parseable numbers
   let hasDate = false;
@@ -234,33 +359,59 @@ function detectHeader(firstRow: string[]): boolean {
     }
   }
 
-  return !hasDate && !hasNumber;
+  if (hasDate) return false;
+  if (!hasNumber) return true;
+
+  return matchTransactionHeaders(firstRow).roleCount >= MIN_HEADER_ROLE_MATCHES;
 }
 
+/**
+ * Pick the date column and its format.
+ *
+ * `preferred` is the column the header labels name. It wins only if the data
+ * agrees — same 0.8 parse rate the shape scan demands — so a file whose "Date
+ * de production" column holds no date falls back to the best-parsing column
+ * rather than mapping a label nothing supports. Its real job is arbitrating
+ * between several equally parseable date columns (`Date de transaction` vs
+ * `Date comptable`), which the rate alone cannot do.
+ */
 function detectDateColumn(
   rows: string[][],
-  colCount: number
+  colCount: number,
+  preferred?: number | null
 ): { column: number; format: string } | null {
+  const rateOf = (col: number, fmt: string): number => {
+    let success = 0;
+    let total = 0;
+    for (const row of rows) {
+      const cell = row[col]?.trim();
+      if (!cell) continue;
+      total++;
+      if (parseDate(cell, fmt)) success++;
+    }
+    return total === 0 ? 0 : success / total;
+  };
+
+  if (preferred !== undefined && preferred !== null && preferred < colCount) {
+    let bestFormat = "";
+    let bestRate = 0;
+    for (const fmt of DATE_FORMATS) {
+      const rate = rateOf(preferred, fmt);
+      if (rate > bestRate) {
+        bestRate = rate;
+        bestFormat = fmt;
+      }
+    }
+    if (bestRate >= 0.8) return { column: preferred, format: bestFormat };
+  }
+
   let bestCol = -1;
   let bestFormat = "";
   let bestRate = 0;
 
   for (let col = 0; col < colCount; col++) {
     for (const fmt of DATE_FORMATS) {
-      let success = 0;
-      let total = 0;
-
-      for (const row of rows) {
-        const cell = row[col]?.trim();
-        if (!cell) continue;
-        total++;
-        if (parseDate(cell, fmt)) {
-          success++;
-        }
-      }
-
-      if (total === 0) continue;
-      const rate = success / total;
+      const rate = rateOf(col, fmt);
       if (rate > bestRate) {
         bestRate = rate;
         bestCol = col;
@@ -401,12 +552,32 @@ function detectBalanceColumns(
   return balanceCols;
 }
 
+/**
+ * Pick the description column: the one the header labels name, else the
+ * longest-on-average text column.
+ *
+ * The label is only honoured for a column the shape test would have been
+ * allowed to pick at all — not the date column, not a numeric one. A file
+ * labelling its amount column `Détail du montant` therefore cannot end up with
+ * its amounts in the description.
+ */
 function detectDescriptionColumn(
   rows: string[][],
   colCount: number,
   dateCol: number,
-  numericCols: Set<number>
+  numericCols: Set<number>,
+  preferred?: number | null
 ): number {
+  if (
+    preferred !== undefined &&
+    preferred !== null &&
+    preferred < colCount &&
+    preferred !== dateCol &&
+    !numericCols.has(preferred)
+  ) {
+    return preferred;
+  }
+
   let bestCol = 0;
   let bestAvgLen = 0;
 
@@ -449,7 +620,8 @@ type AmountModeResult = SingleAmountResult | DebitCreditResult;
 
 function detectAmountMode(
   rows: string[][],
-  amountCandidates: number[]
+  amountCandidates: number[],
+  lexical: LexicalHeaderMap | null
 ): AmountModeResult | null {
   if (amountCandidates.length === 0) return null;
 
@@ -464,16 +636,113 @@ function detectAmountMode(
       const colB = amountCandidates[b];
 
       if (isSparseComplementary(rows, colA, colB)) {
-        return { mode: "debit_credit", debitCol: colA, creditCol: colB };
+        return orderDebitCredit(colA, colB, lexical);
       }
     }
   }
 
-  // No complementary pair found — pick best single amount column
-  const bestCol = pickBestAmountColumn(rows, amountCandidates);
+  // No complementary pair found — the labelled amount column if there is one,
+  // else the best single amount column by shape.
+  const preferred = lexical?.amount;
+  const bestCol =
+    preferred !== undefined &&
+    preferred !== null &&
+    amountCandidates.includes(preferred)
+      ? preferred
+      : pickBestAmountColumn(rows, amountCandidates);
   return detectSingleAmount(rows, bestCol);
 }
 
+/**
+ * Assign the two halves of a complementary pair to debit and credit.
+ *
+ * The loop above enumerates `a < b`, so before #327 the LEFTMOST column was the
+ * debit, always: a file laid out `Date;Description;Crédit;Débit` was mapped
+ * backwards and every sign of the import came out inverted — silently, since
+ * the total is merely negated and no aggregate check notices.
+ *
+ * The labels decide when they name either half; position remains the fall-back
+ * for a headerless file or labels the dictionary does not know. Knowing ONE of
+ * the two is enough: the other column is the other role.
+ */
+function orderDebitCredit(
+  colA: number,
+  colB: number,
+  lexical: LexicalHeaderMap | null
+): DebitCreditResult {
+  const debitFirst = {
+    mode: "debit_credit",
+    debitCol: colA,
+    creditCol: colB,
+  } as const;
+  const creditFirst = {
+    mode: "debit_credit",
+    debitCol: colB,
+    creditCol: colA,
+  } as const;
+
+  if (lexical?.debit === colA || lexical?.credit === colB) return debitFirst;
+  if (lexical?.debit === colB || lexical?.credit === colA) return creditFirst;
+  return debitFirst;
+}
+
+/**
+ * Find a direction-indicator column next to an all-positive amount column —
+ * the third amount format, refused rather than imported.
+ *
+ * Three conditions, each one narrowing a way to raise a false alarm:
+ *  - the amount column carries no negative value, since a file that signs its
+ *    amounts needs no indicator and reads correctly today;
+ *  - the candidate is IMMEDIATELY next to it, as every export of this shape
+ *    writes the flag beside the magnitude. A file-wide scan would refuse
+ *    perfectly importable files over an unrelated one-letter flag column, and
+ *    a refusal the user cannot work around is worse than a mapping they can;
+ *  - it holds at least two DISTINCT tokens of the D/C alphabet. A column stuck
+ *    on a single value carries no direction, and a statement of pure expenses
+ *    imports correctly as `positive_expense`.
+ */
+function findDirectionIndicatorColumn(
+  rows: string[][],
+  amountCol: number,
+  colCount: number
+): number | null {
+  let seen = 0;
+  for (const row of rows) {
+    const cell = row[amountCol]?.trim();
+    if (!cell) continue;
+    const val = parseFrenchAmount(cell);
+    if (isNaN(val)) continue;
+    seen++;
+    if (val < 0) return null;
+  }
+  if (seen === 0) return null;
+
+  for (const col of [amountCol - 1, amountCol + 1]) {
+    if (col < 0 || col >= colCount) continue;
+
+    const distinct = new Set<string>();
+    let nonEmpty = 0;
+    let inAlphabet = 0;
+
+    for (const row of rows) {
+      const cell = row[col]?.trim();
+      if (!cell) continue;
+      nonEmpty++;
+      const token = cell.toLowerCase();
+      if (DIRECTION_INDICATOR_TOKENS.has(token)) {
+        inAlphabet++;
+        distinct.add(token);
+      }
+    }
+
+    if (nonEmpty > 0 && inAlphabet === nonEmpty && distinct.size >= 2) {
+      return col;
+    }
+  }
+
+  return null;
+}
+
 /** Pick the best amount column: prefer columns with decimal values (cents). */
 function pickBestAmountColumn(rows: string[][], candidates: number[]): number {
   let bestCol = candidates[0];
@@ -627,40 +896,12 @@ const BOOKCOST_HEADER_KEYWORDS = [
   "cout",
 ];
 // Value/market-value columns must never be auto-picked as price or book_cost.
+// NOTE `montant` is an EXCLUSION token here and the PRIMARY amount keyword of
+// the transaction dictionary (`headerDictionary.ts`) \u2014 which is why the two
+// tables are separate modules. `normalizeHeaderCell` and `matchHeaderColumn`
+// are the generic part, shared from there and unchanged.
 const VALUE_HEADER_KEYWORDS = ["value", "valeur", "montant", "marchande"];
 
-/** Accent-strip + lowercase + keep alphanumerics only (for header matching). */
-function normalizeHeaderCell(s: string): string {
-  return (s ?? "")
-    .normalize("NFD")
-    .replace(/[\u0300-\u036f]/g, "")
-    .toLowerCase()
-    .replace(/[^a-z0-9]/g, "");
-}
-
-/**
- * Find the first unused column whose normalized header contains one of the
- * keywords (keywords tried in priority order). `exclude` skips columns whose
- * header contains any excluded token (e.g. a "value" column for price).
- */
-function matchHeaderColumn(
-  normalizedHeaders: string[],
-  keywords: string[],
-  used: Set<number>,
-  exclude: string[] = []
-): number | null {
-  for (const kw of keywords) {
-    for (let i = 0; i < normalizedHeaders.length; i++) {
-      if (used.has(i)) continue;
-      const h = normalizedHeaders[i];
-      if (!h) continue;
-      if (exclude.some((ex) => h.includes(ex))) continue;
-      if (h.includes(kw)) return i;
-    }
-  }
-  return null;
-}
-
 /** Pick the shortest-average-length non-numeric, unused text column (symbols
  *  are short tokens; a name/description column is longer). */
 function pickSymbolColumn(
diff --git a/src/utils/headerDictionary.test.ts b/src/utils/headerDictionary.test.ts
new file mode 100644
index 0000000..5de34b1
--- /dev/null
+++ b/src/utils/headerDictionary.test.ts
@@ -0,0 +1,160 @@
+// headerDictionary — the lexical layer of transaction-CSV detection (#327).
+//
+// `csvAutoDetect.test.ts` covers what the dictionary DOES to a detected
+// configuration; this file covers the dictionary itself: every keyword it
+// claims to know, the exclusions that keep a label from claiming the wrong
+// column, and the mute row that hands control back to the shape heuristics.
+
+import { describe, it, expect } from "vitest";
+import {
+  matchHeaderColumn,
+  matchTransactionHeaders,
+  normalizeHeaderCell,
+  MIN_HEADER_ROLE_MATCHES,
+} from "./headerDictionary";
+
+describe("normalizeHeaderCell (#245, shared by #327)", () => {
+  it("strips accents, case and punctuation", () => {
+    expect(normalizeHeaderCell("Débit")).toBe("debit");
+    expect(normalizeHeaderCell("Libellé")).toBe("libelle");
+    expect(normalizeHeaderCell("Date de l'opération")).toBe("datedeloperation");
+    expect(normalizeHeaderCell("Montant ($)")).toBe("montant");
+  });
+
+  it("keeps digits and tolerates an empty or missing cell", () => {
+    expect(normalizeHeaderCell("Solde 2024")).toBe("solde2024");
+    expect(normalizeHeaderCell("")).toBe("");
+    expect(normalizeHeaderCell(undefined as unknown as string)).toBe("");
+  });
+});
+
+describe("matchHeaderColumn (#245, shared by #327)", () => {
+  const headers = ["date", "libelle", "montant", "solde"];
+
+  it("returns the first unused column containing a keyword", () => {
+    expect(matchHeaderColumn(headers, ["montant"], new Set())).toBe(2);
+  });
+
+  it("honours keyword priority order over column order", () => {
+    expect(matchHeaderColumn(headers, ["solde", "date"], new Set())).toBe(3);
+  });
+
+  it("skips used and excluded columns, and returns null on no match", () => {
+    expect(matchHeaderColumn(headers, ["date"], new Set([0]))).toBeNull();
+    expect(matchHeaderColumn(headers, ["mont"], new Set(), ["solde"])).toBe(2);
+    expect(matchHeaderColumn(headers, ["quantite"], new Set())).toBeNull();
+  });
+});
+
+describe("matchTransactionHeaders — the FR/EN dictionary (#327)", () => {
+  it("reads a French signed-amount header", () => {
+    const m = matchTransactionHeaders(["Date", "Description", "Montant", "Solde"]);
+    expect(m).toEqual({
+      date: 0,
+      description: 1,
+      amount: 2,
+      debit: null,
+      credit: null,
+      balance: 3,
+      roleCount: 4,
+    });
+  });
+
+  it("reads an English signed-amount header", () => {
+    const m = matchTransactionHeaders(["Date", "Description", "Amount", "Balance"]);
+    expect(m.amount).toBe(2);
+    expect(m.balance).toBe(3);
+  });
+
+  it.each([
+    ["Débit", "debit"],
+    ["Retrait", "debit"],
+    ["Déboursé", "debit"],
+    ["Withdrawal", "debit"],
+    ["Crédit", "credit"],
+    ["Dépôt", "credit"],
+    ["Encaissement", "credit"],
+    ["Deposit", "credit"],
+  ] as const)("knows %s as the %s column", (label, role) => {
+    const m = matchTransactionHeaders(["Date", "Description", label]);
+    expect(m[role]).toBe(2);
+  });
+
+  it.each([
+    ["Libellé", 1],
+    ["Détail", 1],
+    ["Transaction", 1],
+    ["Description", 1],
+  ] as const)("knows %s as the description column", (label, col) => {
+    expect(matchTransactionHeaders(["Date", label, "Montant"]).description).toBe(
+      col
+    );
+  });
+
+  it("resolves a reversed pair by label, not by position", () => {
+    const m = matchTransactionHeaders(["Date", "Description", "Credit", "Debit"]);
+    expect(m.debit).toBe(3);
+    expect(m.credit).toBe(2);
+  });
+
+  it("claims a column once, so debit/credit beat the amount keyword", () => {
+    // Both columns contain `montant`. Resolving debit and credit first is what
+    // stops `Montant débit` from being read as THE amount column.
+    const m = matchTransactionHeaders([
+      "Date",
+      "Libelle",
+      "Montant debit",
+      "Montant credit",
+    ]);
+    expect(m.debit).toBe(2);
+    expect(m.credit).toBe(3);
+    expect(m.amount).toBeNull();
+  });
+
+  it("never reads a Solde column as the amount", () => {
+    const m = matchTransactionHeaders(["Date", "Libelle", "Solde du compte"]);
+    expect(m.balance).toBe(2);
+    expect(m.amount).toBeNull();
+  });
+
+  it("never reads a date column as the description", () => {
+    // `Date de transaction` contains the description keyword `transaction`.
+    const m = matchTransactionHeaders([
+      "Date de transaction",
+      "Date comptable",
+      "Montant",
+    ]);
+    expect(m.date).toBe(0);
+    expect(m.description).toBeNull();
+  });
+
+  it("returns a map of nulls for labels it does not know", () => {
+    const m = matchTransactionHeaders(["Col A", "Col B", "Col C"]);
+    expect(m).toEqual({
+      date: null,
+      description: null,
+      amount: null,
+      debit: null,
+      credit: null,
+      balance: null,
+      roleCount: 0,
+    });
+  });
+
+  it("scores a data row below the header threshold", () => {
+    // `DEPOT PAIE EMPLOYEUR` contains the credit keyword `depot` — one role,
+    // which is exactly why one is not enough to call a row a header.
+    const m = matchTransactionHeaders([
+      "05/01/2025",
+      "DEPOT PAIE EMPLOYEUR",
+      "-84,32",
+    ]);
+    expect(m.credit).toBe(1);
+    expect(m.roleCount).toBeLessThan(MIN_HEADER_ROLE_MATCHES);
+  });
+
+  it("tolerates empty cells and a ragged row", () => {
+    expect(matchTransactionHeaders([]).roleCount).toBe(0);
+    expect(matchTransactionHeaders(["", "Date", ""]).date).toBe(1);
+  });
+});
diff --git a/src/utils/headerDictionary.ts b/src/utils/headerDictionary.ts
new file mode 100644
index 0000000..c66a5c4
--- /dev/null
+++ b/src/utils/headerDictionary.ts
@@ -0,0 +1,176 @@
+/**
+ * Header dictionary for the TRANSACTION import flow (#327).
+ *
+ * Detection used to reason on the SHAPE of the data alone — which column parses
+ * as a date, which one carries the most characters, which pair is sparse and
+ * complementary. Shape cannot tell a debit column from a credit column, so a
+ * file laid out `Date;Description;Crédit;Débit` was mapped backwards and every
+ * sign of the import was inverted. This module is the lexical layer that reads
+ * the header labels; `csvAutoDetect.ts` puts it in FRONT of the shape
+ * heuristics and falls back to them whenever the labels are mute (no header
+ * row, unknown labels).
+ *
+ * WHY ITS OWN MODULE. The holdings flow (#245) already matches header labels,
+ * with its own keyword tables living in `csvAutoDetect.ts`. Merging the two
+ * tables is not possible: `montant` is an EXCLUSION token there
+ * (`VALUE_HEADER_KEYWORDS` — a market-value column must never be read as a unit
+ * price) and it is the PRIMARY amount keyword here. Two flows, two tables. Only
+ * the two matching helpers are generic, so they live here and the holdings flow
+ * imports them, unchanged — one direction of dependency, no cycle.
+ */
+
+// Keyword tables, matched as SUBSTRINGS against accent-stripped,
+// alphanumeric-only header cells, so `Date de l'opération` matches `date` and
+// `Débit ($)` matches `debit`. Bilingual FR + EN, order inside each list is
+// priority order. Kept deliberately tight: a keyword that fires on the wrong
+// column is worse than a keyword that never fires, because the shape heuristic
+// behind it is the behaviour the corpus already froze.
+export const DATE_HEADER_KEYWORDS = ["date"];
+export const DESCRIPTION_HEADER_KEYWORDS = [
+  "description",
+  "libelle",
+  "detail",
+  "transaction",
+];
+export const AMOUNT_HEADER_KEYWORDS = ["montant", "amount"];
+export const DEBIT_HEADER_KEYWORDS = [
+  "debit",
+  "retrait",
+  "debourse",
+  "withdrawal",
+];
+export const CREDIT_HEADER_KEYWORDS = [
+  "credit",
+  "depot",
+  "encaissement",
+  "deposit",
+];
+export const BALANCE_HEADER_KEYWORDS = ["solde", "balance"];
+
+/**
+ * A running-balance column is never an amount column, and `Date de
+ * transaction` is never the description column. Both are exclusion lists rather
+ * than ordering tricks, because substring matching has no notion of "the best
+ * match" — the first column containing the keyword wins.
+ */
+const AMOUNT_EXCLUDE = BALANCE_HEADER_KEYWORDS;
+const DESCRIPTION_EXCLUDE = DATE_HEADER_KEYWORDS;
+
+/** Accent-strip + lowercase + keep alphanumerics only (for header matching). */
+export function normalizeHeaderCell(s: string): string {
+  return (s ?? "")
+    .normalize("NFD")
+    .replace(/[\u0300-\u036f]/g, "")
+    .toLowerCase()
+    .replace(/[^a-z0-9]/g, "");
+}
+
+/**
+ * Find the first unused column whose normalized header contains one of the
+ * keywords (keywords tried in priority order). `exclude` skips columns whose
+ * header contains any excluded token (e.g. a "value" column for price).
+ */
+export function matchHeaderColumn(
+  normalizedHeaders: string[],
+  keywords: string[],
+  used: Set<number>,
+  exclude: string[] = []
+): number | null {
+  for (const kw of keywords) {
+    for (let i = 0; i < normalizedHeaders.length; i++) {
+      if (used.has(i)) continue;
+      const h = normalizedHeaders[i];
+      if (!h) continue;
+      if (exclude.some((ex) => h.includes(ex))) continue;
+      if (h.includes(kw)) return i;
+    }
+  }
+  return null;
+}
+
+/** What the labels of one header row say, role by role. */
+export interface LexicalHeaderMap {
+  date: number | null;
+  description: number | null;
+  amount: number | null;
+  debit: number | null;
+  credit: number | null;
+  balance: number | null;
+  /** Number of roles the row actually named — 0 when the labels are mute. */
+  roleCount: number;
+}
+
+/**
+ * Read one header row through the dictionary.
+ *
+ * Roles are resolved in the order balance -> date -> debit -> credit -> amount
+ * -> description, each claiming its column so a later role cannot steal it.
+ * That order is what makes `Montant débit` / `Montant crédit` resolve as a
+ * debit/credit pair instead of the first one being read as THE amount column.
+ *
+ * Every field is `null` when no column names that role: a mute row yields a map
+ * of nulls and `roleCount: 0`, which is the caller's signal to fall back to the
+ * shape heuristics.
+ */
+export function matchTransactionHeaders(
+  headerRow: readonly string[]
+): LexicalHeaderMap {
+  const normalized = headerRow.map(normalizeHeaderCell);
+  const used = new Set<number>();
+
+  const claim = (col: number | null): number | null => {
+    if (col !== null) used.add(col);
+    return col;
+  };
+
+  const balance = claim(
+    matchHeaderColumn(normalized, BALANCE_HEADER_KEYWORDS, used)
+  );
+  const date = claim(matchHeaderColumn(normalized, DATE_HEADER_KEYWORDS, used));
+  const debit = claim(
+    matchHeaderColumn(normalized, DEBIT_HEADER_KEYWORDS, used, AMOUNT_EXCLUDE)
+  );
+  const credit = claim(
+    matchHeaderColumn(normalized, CREDIT_HEADER_KEYWORDS, used, AMOUNT_EXCLUDE)
+  );
+  const amount = claim(
+    matchHeaderColumn(normalized, AMOUNT_HEADER_KEYWORDS, used, AMOUNT_EXCLUDE)
+  );
+  const description = claim(
+    matchHeaderColumn(
+      normalized,
+      DESCRIPTION_HEADER_KEYWORDS,
+      used,
+      DESCRIPTION_EXCLUDE
+    )
+  );
+
+  const roleCount = [date, description, amount, debit, credit, balance].filter(
+    (c) => c !== null
+  ).length;
+
+  return { date, description, amount, debit, credit, balance, roleCount };
+}
+
+/**
+ * How many named roles a row must carry before the lexical layer is allowed to
+ * call it a header row on its own.
+ *
+ * Two, not one: a description cell like `DEPOT PAIE EMPLOYEUR` contains
+ * `depot`, so a single match proves nothing. Two distinct roles in one row is a
+ * shape a data row does not produce, and the caller keeps the date test in
+ * front of this check anyway.
+ */
+export const MIN_HEADER_ROLE_MATCHES = 2;
+
+/**
+ * Tokens of a direction-indicator column: the third amount format, where the
+ * amount column holds unsigned magnitudes and a neighbouring column says which
+ * way each row goes. `D`/`C` in French exports, `DB`/`CR` in some English ones.
+ *
+ * The format is refused rather than imported (spec decision) — see
+ * `csvAutoDetect.ts`. Reading it correctly is a separate feature; reading it
+ * wrong imports every debit as income.
+ */
+export const DEBIT_INDICATOR_TOKENS = ["d", "db"];
+export const CREDIT_INDICATOR_TOKENS = ["c", "cr"];