feat(import): score the detected format and run detection on its own

Detection handed back a configuration it had never tested, and only ever
ran behind the magic-wand button. A source opened for the first time
therefore started on `defaultConfig` — `;`, `DD/MM/YYYY`, columns 0/1/2 —
plausible enough to import a whole file wrong rather than fail visibly.

`detectImportFormat` now REPLAYS what it just decided over every data row
of the file and returns the rate as a `DetectionScore`. The replay runs
`mapRow`, the same pure function `parseFilesInternal` runs at import time,
under the same column-level decimal arbitration: two mappers would be the
exact divergence this chantier removes — a score reading 100 % while the
import wrote different amounts. A test asserts the two agree row for row
on every fixture of the corpus.

The threshold is 90 %, and it only colours the banner. Below it the panel
warns and prints the detailed count ("132 of 150 rows read"); at or above
it the banner is neutral. Nothing is blocked, because a perfect score says
nothing about the SIGN of what was read — `all-positive` scores 100 %
while every credit imports as an expense — and the preview step (#329) is
the real net, traversed at every import.

Detection now also fires on its own, guarded on `!existing`: a source that
has never been configured. A source that HAS one is never re-detected, the
stored format wins. The condition is deliberately not `!restored` — a
stored format that fails to decode already reports its own error, and
detecting over it would replace that message with a silent guess.

The button and the automatic run share one `detectFormatForFile`, so the
button replays detection instead of running a second, drifting variant of
it. The score is cleared when its source changes, when the format is
edited by hand (compared through the codec, so a rename keeps it) and when
a template overwrites the format — a banner vouching for a configuration
nobody measured is the misinformation it exists to remove.

Finally, the sign-convention selector is hidden in debit/credit mode.
`mapRow` computes `credit - debit` on magnitudes there and never reads
`signConvention`, so the control changed nothing. Hidden, not reset: the
stored value is left untouched.

Tests: 1054 vitest (+20), build and cargo check green. No DB migration.
CHANGELOG and docs are centralized in link 10 of the stack per the plan.

Resolves #328

src/components/import/SourceConfigPanel.tsx

@@ -1,6 +1,6 @@
 import { useState } from "react";
 import { useTranslation } from "react-i18next";
-import { Wand2, Check, Save, X } from "lucide-react";
+import { Wand2, Check, Save, X, AlertTriangle } from "lucide-react";
 import type {
   ScannedSource,
   ScannedFile,
@@ -9,6 +9,7 @@ import type {
   ColumnMapping,
   ImportConfigTemplate,
 } from "../../shared/types";
+import type { DetectionScore } from "../../utils/csvAutoDetect";
 import ColumnMappingEditor from "./ColumnMappingEditor";
 
 interface SourceConfigPanelProps {
@@ -27,6 +28,8 @@ interface SourceConfigPanelProps {
   onUpdateTemplate: () => void;
   onDeleteTemplate: (id: number) => void;
   selectedTemplateId: number | null;
+  /** Result of the last detection run, or null when none ran on this source. */
+  detectionScore?: DetectionScore | null;
   isLoading?: boolean;
 }
 
@@ -46,6 +49,7 @@ export default function SourceConfigPanel({
   onUpdateTemplate,
   onDeleteTemplate,
   selectedTemplateId,
+  detectionScore,
   isLoading,
 }: SourceConfigPanelProps) {
   const { t } = useTranslation();
@@ -76,6 +80,52 @@ export default function SourceConfigPanel({
         </button>
       </div>
 
+      {/*
+        Detection result. Present only when a detection actually ran on THIS
+        source — a source opened on its stored format shows nothing, because
+        that format was chosen once and is not being re-guessed.
+
+        The threshold colours the banner and nothing else: both arms leave every
+        control editable and every button enabled. A low score is a reason to
+        look at the preview, not a refusal to import.
+      */}
+      {detectionScore && (
+        <div
+          className={`p-3 rounded-xl bg-[var(--card)] border-2 flex items-start gap-2 ${
+            detectionScore.confident
+              ? "border-[var(--border)]"
+              : "border-[var(--accent)]"
+          }`}
+        >
+          {detectionScore.confident ? (
+            <Check size={16} className="text-[var(--positive)] shrink-0 mt-0.5" />
+          ) : (
+            <AlertTriangle
+              size={16}
+              className="text-[var(--accent)] shrink-0 mt-0.5"
+            />
+          )}
+          <div>
+            <p className="text-sm text-[var(--foreground)]">
+              {t(
+                detectionScore.confident
+                  ? "import.config.detectionRecognized"
+                  : "import.config.detectionUncertain",
+                {
+                  read: detectionScore.readRows,
+                  total: detectionScore.totalRows,
+                }
+              )}
+            </p>
+            {!detectionScore.confident && (
+              <p className="text-xs text-[var(--muted-foreground)] mt-0.5">
+                {t("import.config.detectionUncertainHint")}
+              </p>
+            )}
+          </div>
+        </div>
+      )}
+
       {/* Template row */}
       <div className="flex items-center gap-3 flex-wrap">
         <div className="flex items-center gap-2 flex-1 min-w-[200px]">
@@ -270,7 +320,16 @@ export default function SourceConfigPanel({
         </div>
       </div>
 
-      {/* Sign convention */}
+      {/*
+        Sign convention — single-amount mode ONLY.
+
+        `mapRow` computes `credit - debit` on magnitudes in debit/credit mode and
+        never reads `signConvention` there; the direction is carried by which
+        column holds the value. Showing the selector anyway offered a control
+        that changed nothing, which reads as "the app ignored my setting".
+        The stored value is left untouched: hidden, not reset.
+      */}
+      {config.amountMode === "single" && (
         <div>
           <label className="block text-sm text-[var(--muted-foreground)] mb-1">
             {t("import.config.signConvention")}
@@ -304,6 +363,7 @@ export default function SourceConfigPanel({
             </label>
           </div>
         </div>
+      )}
 
       {/* Column mapping */}
       {headers.length > 0 && (

src/hooks/useImportWizard.ts

@@ -42,6 +42,7 @@ import {
 import {
   preprocessQuotedCSV,
   detectImportFormat as runAutoDetect,
+  type DetectionScore,
 } from "../utils/csvAutoDetect";
 import {
   detectAmountSeparators,
@@ -78,6 +79,11 @@ interface WizardState {
   importedFilesBySource: Map<string, Set<string>>;
   configTemplates: ImportConfigTemplate[];
   selectedTemplateId: number | null;
+  /**
+   * Result of the LAST detection run on the selected source, or null when none
+   * ran — a source opened on its stored format, which is never re-detected.
+   */
+  detectionScore: DetectionScore | null;
 }
 
 type WizardAction =
@@ -99,6 +105,7 @@ type WizardAction =
   | { type: "SET_CONFIGURED_SOURCES"; payload: { names: Set<string>; files: Map<string, Set<string>> } }
   | { type: "SET_CONFIG_TEMPLATES"; payload: ImportConfigTemplate[] }
   | { type: "SET_SELECTED_TEMPLATE_ID"; payload: number | null }
+  | { type: "SET_DETECTION_SCORE"; payload: DetectionScore | null }
   | { type: "RESET" };
 
 const defaultConfig: SourceConfig = {
@@ -133,6 +140,7 @@ const initialState: WizardState = {
   importedFilesBySource: new Map(),
   configTemplates: [],
   selectedTemplateId: null,
+  detectionScore: null,
 };
 
 function reducer(state: WizardState, action: WizardAction): WizardState {
@@ -148,7 +156,10 @@ function reducer(state: WizardState, action: WizardAction): WizardState {
     case "SET_SCANNED_SOURCES":
       return { ...state, scannedSources: action.payload, isLoading: false };
     case "SET_SELECTED_SOURCE":
-      return { ...state, selectedSource: action.payload };
+      // The score belongs to the source it was measured on. Carrying it over
+      // would let a source opened on its stored format inherit the confidence
+      // of the previous one, which is worse than showing nothing.
+      return { ...state, selectedSource: action.payload, detectionScore: null };
     case "SET_SELECTED_FILES":
       return { ...state, selectedFiles: action.payload };
     case "SET_SOURCE_CONFIG":
@@ -199,6 +210,8 @@ function reducer(state: WizardState, action: WizardAction): WizardState {
       return { ...state, configTemplates: action.payload };
     case "SET_SELECTED_TEMPLATE_ID":
       return { ...state, selectedTemplateId: action.payload };
+    case "SET_DETECTION_SCORE":
+      return { ...state, detectionScore: action.payload };
     case "RESET":
       return {
         ...initialState,
@@ -291,8 +304,59 @@ export function useImportWizard() {
     }
   }, [state.importFolder, scanFolderInternal]);
 
+  /**
+   * Run detection on one file and report the outcome. Returns the detected
+   * format merged onto `base`, or null when detection produced no usable
+   * configuration (the reason is dispatched as the page error).
+   *
+   * THE single detection path, shared by the two things that start one: the
+   * magic-wand button and the automatic run on a source that has never been
+   * configured. Everything it needs is a parameter, so it never reads a piece of
+   * `state` its caller has just dispatched but not yet re-rendered — which is
+   * exactly why the automatic run could not simply call the button's callback.
+   *
+   * `base` keeps the fields detection does not decide (the source name, the
+   * encoding), and the spread of `outcome.config` writes every field it does —
+   * naming them one by one is how a field gets silently dropped (#324).
+   */
+  const detectFormatForFile = useCallback(
+    async (filePath: string, base: SourceConfig): Promise<SourceConfig | null> => {
+      const content = await invoke<string>("read_file_content", {
+        filePath,
+        encoding: base.encoding,
+      });
+
+      const outcome = runAutoDetect(content);
+
+      if (outcome.status !== "ok") {
+        // 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_DETECTION_SCORE", payload: null });
+        dispatch({
+          type: "SET_ERROR",
+          payload:
+            outcome.status === "rejected"
+              ? outcome.reason
+              : "import.errors.autoDetectFailed",
+        });
+        return null;
+      }
+
+      dispatch({ type: "SET_DETECTION_SCORE", payload: outcome.score });
+      return { ...base, ...outcome.config };
+    },
+    []
+  );
+
   const selectSource = useCallback(
     async (source: ScannedSource) => {
+      // The banner is page-wide: an error left by the previous source must not
+      // survive into this one. Cleared here, before anything that may set a new
+      // one — a stored format that will not decode, a detection that refuses.
+      dispatch({ type: "SET_ERROR", payload: null });
+
       // Sort files: new files first, then already-imported
       const importedNames = state.importedFilesBySource.get(source.folder_name);
       const sorted = [...source.files].sort((a, b) => {
@@ -362,14 +426,35 @@ export function useImportWizard() {
             }
           }
 
-          dispatch({
+          const fresh: SourceConfig = {
-            type: "SET_SOURCE_CONFIG",
-            payload: {
             ...defaultConfig,
             name: source.folder_name,
             encoding: activeEncoding,
-            },
+          };
-          });
+
+          // Detection fires on its own HERE and nowhere else: the arm reached
+          // when the source has no stored format at all. `defaultConfig` is
+          // `;` + `DD/MM/YYYY` + columns 0/1/2 — plausible enough to import a
+          // whole file wrong rather than fail, so leaving a never-configured
+          // source sitting on it is the defect (#328).
+          //
+          // The condition is `!existing`, not `!restored`: a source whose stored
+          // format will not decode already carries an explicit error, and
+          // re-detecting over it would replace that message with a silent guess.
+          // Its wand button is still there.
+          let active = fresh;
+          if (!existing && source.files.length > 0) {
+            const detected = await detectFormatForFile(
+              source.files[0].file_path,
+              fresh
+            );
+            if (detected) active = detected;
+          }
+
+          dispatch({ type: "SET_SOURCE_CONFIG", payload: active });
+          activeDelimiter = active.delimiter;
+          activeSkipLines = active.skipLines;
+          activeHasHeader = active.hasHeader;
         }
 
         // Load preview headers from first file
@@ -433,6 +518,19 @@ export function useImportWizard() {
     (config: SourceConfig) => {
       dispatch({ type: "SET_SOURCE_CONFIG", payload: config });
 
+      // The score measures the format DETECTION produced. The moment any of
+      // those eight fields is edited by hand, the number stops describing what
+      // the wizard would read — a banner still claiming "147 of 150 rows" over
+      // a mapping nobody measured is the same misinformation this chantier is
+      // removing. Comparing through the codec keeps a rename (the ninth field,
+      // which changes nothing about reading) from clearing it.
+      if (
+        JSON.stringify(formatToRow(config)) !==
+        JSON.stringify(formatToRow(state.sourceConfig))
+      ) {
+        dispatch({ type: "SET_DETECTION_SCORE", payload: null });
+      }
+
       // Reload headers when delimiter, encoding, skipLines, or hasHeader changes
       if (state.selectedFiles.length > 0) {
         loadHeadersWithConfig(
@@ -444,7 +542,7 @@ export function useImportWizard() {
         );
       }
     },
-    [state.selectedFiles, loadHeadersWithConfig]
+    [state.selectedFiles, state.sourceConfig, loadHeadersWithConfig]
   );
 
   const toggleFile = useCallback(
@@ -863,56 +961,35 @@ export function useImportWizard() {
     dispatch({ type: "SET_ERROR", payload: null });
 
     try {
-      const content = await invoke<string>("read_file_content", {
+      const filePath = state.selectedFiles[0].file_path;
-        filePath: state.selectedFiles[0].file_path,
+      // Same path the automatic run takes, so the button REPLAYS detection
-        encoding: state.sourceConfig.encoding,
+      // rather than running a second, drifting variant of it.
-      });
+      const newConfig = await detectFormatForFile(filePath, state.sourceConfig);
+      if (!newConfig) return; // reason already dispatched, loading already off
 
-      const outcome = runAutoDetect(content);
-
-      if (outcome.status === "ok") {
-        const result = outcome.config;
-        const newConfig = {
-          ...state.sourceConfig,
-          delimiter: result.delimiter,
-          hasHeader: result.hasHeader,
-          skipLines: result.skipLines,
-          dateFormat: result.dateFormat,
-          columnMapping: result.columnMapping,
-          amountMode: result.amountMode,
-          signConvention: result.signConvention,
-        };
       dispatch({ type: "SET_SOURCE_CONFIG", payload: newConfig });
       dispatch({ type: "SET_LOADING", payload: false });
 
       // Refresh column headers with new config
       await loadHeadersWithConfig(
-          state.selectedFiles[0].file_path,
+        filePath,
         newConfig.delimiter,
         newConfig.encoding,
         newConfig.skipLines,
         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:
-            outcome.status === "rejected"
-              ? outcome.reason
-              : "import.errors.autoDetectFailed",
-        });
-      }
     } catch (e) {
       dispatch({
         type: "SET_ERROR",
         payload: e instanceof Error ? e.message : String(e),
       });
     }
-  }, [state.selectedFiles, state.sourceConfig, loadHeadersWithConfig]);
+  }, [
+    state.selectedFiles,
+    state.sourceConfig,
+    detectFormatForFile,
+    loadHeadersWithConfig,
+  ]);
 
   const saveConfigAsTemplate = useCallback(async (name: string) => {
     await createTemplate({ name, ...formatToRow(state.sourceConfig) });
@@ -939,6 +1016,9 @@ export function useImportWizard() {
     // Applying a template COPIES its format onto the source. The id recorded
     // here is provenance only — the copy is what the next import reads.
     dispatch({ type: "SET_SELECTED_TEMPLATE_ID", payload: templateId });
+    // The format is the template's now, so a score measured on the detected
+    // one would be vouching for a configuration it never saw.
+    dispatch({ type: "SET_DETECTION_SCORE", payload: null });
 
     // Reload headers with new config
     if (state.selectedFiles.length > 0) {

src/i18n/locales/en.json

@@ -113,7 +113,10 @@
       "templateSaved": "Template saved",
       "deleteTemplate": "Delete template",
       "noTemplates": "No templates saved",
-      "updateTemplate": "Update template"
+      "updateTemplate": "Update template",
+      "detectionRecognized": "Format recognized — {{read}} of {{total}} rows read",
+      "detectionUncertain": "Uncertain format — only {{read}} of {{total}} rows read",
+      "detectionUncertainHint": "Check the column mapping and the date format, then look at the preview before importing."
     },
     "preview": {
       "title": "Data Preview",

src/i18n/locales/fr.json

@@ -113,7 +113,10 @@
       "templateSaved": "Modèle sauvegardé",
       "deleteTemplate": "Supprimer le modèle",
       "noTemplates": "Aucun modèle sauvegardé",
-      "updateTemplate": "Mettre à jour le modèle"
+      "updateTemplate": "Mettre à jour le modèle",
+      "detectionRecognized": "Format reconnu — {{read}} des {{total}} lignes lues",
+      "detectionUncertain": "Format incertain — {{read}} des {{total}} lignes lues seulement",
+      "detectionUncertainHint": "Vérifiez le mapping des colonnes et le format de date, puis regardez l'aperçu avant d'importer."
     },
     "preview": {
       "title": "Aperçu des données",

src/pages/ImportPage.tsx

@@ -108,6 +108,7 @@ export default function ImportPage() {
             onUpdateTemplate={updateConfigTemplate}
             onDeleteTemplate={deleteConfigTemplate}
             selectedTemplateId={state.selectedTemplateId}
+            detectionScore={state.detectionScore}
             isLoading={state.isLoading}
           />
           <div className="flex items-center justify-between pt-6 border-t border-[var(--border)]">

src/utils/csvAutoDetect.test.ts

@@ -18,6 +18,7 @@ import {
   autoDetectHoldingColumns,
   analyzeHoldingsCsv,
   autoDetectConfig,
+  CONFIDENCE_THRESHOLD,
   detectImportFormat,
   preprocessQuotedCSV,
 } from "./csvAutoDetect";
@@ -826,3 +827,260 @@ describe("autoDetectConfig — degenerate input (#326)", () => {
     ).toBeNull();
   });
 });
+
+// =============================================================================
+// Issue #328 — the confidence score, and detection running on its own
+// =============================================================================
+//
+// Detection used to hand back a configuration it had never tested. These cases
+// pin the replay: a measured rate, computed by the production row rule, over the
+// rows of the real file.
+
+/** The score of a fixture, or a failure the test can name. */
+function scoreOf(name: CsvFixtureName) {
+  const outcome = detectImportFormat(readCsvFixture(name));
+  if (outcome.status !== "ok") {
+    throw new Error(`${name}: detection returned ${outcome.status}`);
+  }
+  return outcome.score;
+}
+
+describe("detectImportFormat — confidence score (#328)", () => {
+  it("scores every fixture the corpus expects a configuration for", () => {
+    for (const name of CSV_FIXTURE_NAMES) {
+      // `absolute-indicator` is REFUSED (#327), so it carries no score at all.
+      if (name === "absolute-indicator") continue;
+      const score = scoreOf(name);
+      expect(score.totalRows, name).toBeGreaterThan(0);
+      expect(score.readRows, name).toBe(score.totalRows);
+      expect(score.ratio, name).toBe(1);
+      expect(score.confident, name).toBe(true);
+    }
+  });
+
+  it("counts data rows only — header and preamble excluded", () => {
+    // Both files carry the same six transactions; `preamble` puts three lines
+    // of statement banner in front of the header. A score that counted them
+    // would report 6/10 on a file it reads perfectly.
+    expect(scoreOf("signed-amount").totalRows).toBe(6);
+    expect(scoreOf("preamble").totalRows).toBe(6);
+    expect(scoreOf("no-header").totalRows).toBe(6);
+  });
+
+  it("says nothing about the SIGN of what it read (#329)", () => {
+    // `all-positive` is the corpus' known defect: unsigned magnitudes, detected
+    // as `negative_expense`, so every credit imports as an expense. Every row
+    // still PARSES, so the score is a perfect 100 % — which is precisely why the
+    // threshold blocks nothing and the preview step stays mandatory.
+    const score = scoreOf("all-positive");
+    expect(score.ratio).toBe(1);
+    expect(score.confident).toBe(true);
+  });
+
+  it("carries no score on a refused format", () => {
+    const outcome = detectImportFormat(readCsvFixture("absolute-indicator"));
+    expect(outcome.status).toBe("rejected");
+    expect(outcome).not.toHaveProperty("score");
+  });
+});
+
+/**
+ * Ten rows, `unreadable` of which carry an empty date cell.
+ *
+ * An empty cell is skipped by the date-column scan (it divides on non-empty
+ * cells), so the column is still detected at a perfect rate while `mapRow`
+ * rejects those rows — which is what lets these cases move the score without
+ * moving the configuration.
+ */
+function withUnreadableRows(unreadable: number): string {
+  const rows: string[] = [];
+  for (let i = 0; i < 10; i++) {
+    const day = String(i + 1).padStart(2, "0");
+    rows.push(
+      i < unreadable
+        ? `;ACHAT DIVERS ${i};-1${i},00`
+        : `${day}/03/2025;ACHAT DIVERS ${i};-1${i},00`
+    );
+  }
+  return withHeader("Date;Description;Montant", rows);
+}
+
+describe("detectImportFormat — the 90 % threshold (#328)", () => {
+  it("reports the real count of rows it could not read", () => {
+    const outcome = detectImportFormat(withUnreadableRows(3));
+    if (outcome.status !== "ok") throw new Error(outcome.status);
+    expect(outcome.score.totalRows).toBe(10);
+    expect(outcome.score.readRows).toBe(7);
+    expect(outcome.score.ratio).toBeCloseTo(0.7);
+    expect(outcome.score.confident).toBe(false);
+  });
+
+  it("is confident AT the threshold, not merely above it", () => {
+    const outcome = detectImportFormat(withUnreadableRows(1));
+    if (outcome.status !== "ok") throw new Error(outcome.status);
+    expect(outcome.score.ratio).toBeCloseTo(CONFIDENCE_THRESHOLD);
+    expect(outcome.score.confident).toBe(true);
+  });
+
+  it("drops below the threshold one row further down", () => {
+    const outcome = detectImportFormat(withUnreadableRows(2));
+    if (outcome.status !== "ok") throw new Error(outcome.status);
+    expect(outcome.score.confident).toBe(false);
+  });
+
+  it("ignores a trailing blank line rather than counting it unread", () => {
+    const source = withHeader("Date;Description;Montant", SIGNED_ROWS);
+    const clean = detectImportFormat(source);
+    const trailing = detectImportFormat(source + "\n\n");
+    if (clean.status !== "ok" || trailing.status !== "ok") {
+      throw new Error("detection failed on a well-formed file");
+    }
+    expect(trailing.score).toEqual(clean.score);
+  });
+});
+
+describe("the score runs the production row rule, not a copy (#328)", () => {
+  it("delegates to `mapRow` and its column-level separator arbitration", () => {
+    // The revision of #328 is explicit: the score must consume `mapRow`. Two
+    // mappers is the divergence class this chantier removes — the score would
+    // read 100 % while the import wrote different amounts.
+    const SRC = readFileSync(
+      resolve(import.meta.dirname, "csvAutoDetect.ts"),
+      "utf-8"
+    );
+    expect(SRC).toContain(
+      'import { detectAmountSeparators, mapRow } from "./importFormat"'
+    );
+    expect(SRC).toContain("mapRow(raw, format, { decimalSeparators })");
+  });
+
+  it("agrees row for row with an end-to-end parse of the same file", () => {
+    // Two paths over the same file: the score's internal replay, and the corpus
+    // helper that reproduces `parseFilesInternal`. They must not disagree.
+    for (const name of CSV_FIXTURE_NAMES) {
+      if (name === "absolute-indicator") continue;
+      const endToEnd = parseFixtureEndToEnd(name);
+      const read = endToEnd.rows.filter((r) => !("error" in r)).length;
+      const score = scoreOf(name);
+      expect(score.readRows, name).toBe(read);
+      expect(score.totalRows, name).toBe(endToEnd.rows.length);
+    }
+  });
+});
+
+// -----------------------------------------------------------------------------
+// Static guards: detection runs on its own, and ONLY on an unconfigured source.
+//
+// Both live inside `useCallback`s of a React hook and the repository has no
+// jsdom, so the wiring is asserted on the source — same technique as the guards
+// above and in importFormat.test.ts.
+// -----------------------------------------------------------------------------
+
+const WIZARD = readFileSync(
+  resolve(import.meta.dirname, "..", "hooks", "useImportWizard.ts"),
+  "utf-8"
+);
+
+/** The body of `selectSource`, up to the next `useCallback` declaration. */
+function selectSourceBody(): string {
+  const start = WIZARD.indexOf("const selectSource =");
+  const end = WIZARD.indexOf("const loadHeadersWithConfig =", start);
+  expect(start).toBeGreaterThan(-1);
+  expect(end).toBeGreaterThan(start);
+  return WIZARD.slice(start, end);
+}
+
+describe("useImportWizard — detection fires on its own (#328)", () => {
+  it("runs detection while opening a source, not only on the button", () => {
+    expect(selectSourceBody()).toContain("detectFormatForFile(");
+  });
+
+  it("guards that run on the ABSENCE of a stored source", () => {
+    // `!existing`, never `!restored`: a stored format that will not decode
+    // already reports its own error, and re-detecting over it would replace
+    // that message with a silent guess.
+    expect(selectSourceBody()).toContain(
+      "if (!existing && source.files.length > 0)"
+    );
+  });
+
+  it("never detects on the arm that restored a stored format", () => {
+    const body = selectSourceBody();
+    const armStart = body.indexOf("if (restored) {");
+    const restoreArm = body.slice(armStart, body.indexOf("} else {", armStart));
+    expect(restoreArm.length).toBeGreaterThan(0);
+    expect(restoreArm).not.toContain("detectFormatForFile");
+    expect(restoreArm).not.toContain("runAutoDetect");
+  });
+
+  it("keeps a single detection path for the button and the automatic run", () => {
+    // One detector, two callers: the wand button and `selectSource`.
+    expect(WIZARD.match(/runAutoDetect\(/g)).toHaveLength(1);
+    expect(WIZARD.match(/await detectFormatForFile\(/g)).toHaveLength(2);
+  });
+
+  it("drops the score as soon as the format is edited by hand", () => {
+    // A banner still claiming "147 of 150 rows" over a mapping nobody measured
+    // is the same misinformation the score exists to remove. Compared through
+    // the codec, so renaming the source — which changes nothing about reading —
+    // keeps it.
+    const body = WIZARD.slice(
+      WIZARD.indexOf("const updateConfig ="),
+      WIZARD.indexOf("const toggleFile =")
+    );
+    expect(body).toContain("JSON.stringify(formatToRow(config))");
+    expect(body).toContain('dispatch({ type: "SET_DETECTION_SCORE", payload: null })');
+  });
+
+  it("drops the score when a template overwrites the format", () => {
+    const body = WIZARD.slice(
+      WIZARD.indexOf("const applyConfigTemplate ="),
+      WIZARD.indexOf("const updateConfigTemplate =")
+    );
+    expect(body).toContain('dispatch({ type: "SET_DETECTION_SCORE", payload: null })');
+  });
+});
+
+describe("SourceConfigPanel — banner and sign convention (#328)", () => {
+  const PANEL = readFileSync(
+    resolve(
+      import.meta.dirname,
+      "..",
+      "components",
+      "import",
+      "SourceConfigPanel.tsx"
+    ),
+    "utf-8"
+  );
+
+  it("hides the sign convention in debit/credit mode", () => {
+    // `mapRow` computes `credit - debit` on magnitudes there and never reads
+    // `signConvention` — the selector changed nothing.
+    expect(PANEL).toContain('config.amountMode === "single" && (');
+  });
+
+  it("renders both arms of the score through i18n", () => {
+    expect(PANEL).toContain("import.config.detectionRecognized");
+    expect(PANEL).toContain("import.config.detectionUncertain");
+  });
+
+  it("carries every new string in both languages", () => {
+    for (const key of [
+      "detectionRecognized",
+      "detectionUncertain",
+      "detectionUncertainHint",
+    ] as const) {
+      expect(fr.import.config[key].length, `fr.${key}`).toBeGreaterThan(0);
+      expect(en.import.config[key].length, `en.${key}`).toBeGreaterThan(0);
+    }
+  });
+
+  it("interpolates the detailed count in both languages", () => {
+    for (const key of ["detectionRecognized", "detectionUncertain"] as const) {
+      expect(fr.import.config[key], `fr.${key}`).toContain("{{read}}");
+      expect(fr.import.config[key], `fr.${key}`).toContain("{{total}}");
+      expect(en.import.config[key], `en.${key}`).toContain("{{read}}");
+      expect(en.import.config[key], `en.${key}`).toContain("{{total}}");
+    }
+  });
+});

src/utils/csvAutoDetect.ts

@@ -10,7 +10,13 @@ import {
   normalizeHeaderCell,
   type LexicalHeaderMap,
 } from "./headerDictionary";
-import type { ColumnMapping, AmountMode, SignConvention } from "../shared/types";
+import { detectAmountSeparators, mapRow } from "./importFormat";
+import type {
+  ColumnMapping,
+  AmountMode,
+  ImportFormat,
+  SignConvention,
+} from "../shared/types";
 
 export interface AutoDetectResult {
   delimiter: string;
@@ -29,6 +35,40 @@ export interface AutoDetectResult {
  */
 export type AutoDetectRejectionKey = "import.errors.absoluteIndicatorFormat";
 
+/**
+ * How well the detected configuration reads the file it was detected from.
+ *
+ * Detection used to return a configuration without ever testing it: a plausible
+ * delimiter, a plausible date column and a plausible amount column produced a
+ * result whether or not a single row survived them. The score closes that hole
+ * by REPLAYING the configuration — the confidence reported is measured, not
+ * asserted.
+ *
+ * What it does NOT measure is whether the amounts carry the right SIGN. A file
+ * of unsigned magnitudes (`all-positive` in the corpus) scores 100 % while every
+ * expense imports as income, because every row parses. That is why the threshold
+ * only colours the banner and blocks nothing: the preview step (#329) is the
+ * real net, and it is traversed at every import whatever the score says.
+ */
+export interface DetectionScore {
+  /** Rows whose date AND amount the configuration reads. */
+  readRows: number;
+  /** Data rows the replay ran on — header and skipped preamble excluded. */
+  totalRows: number;
+  /** `readRows / totalRows`, or 0 when the file carries no data row. */
+  ratio: number;
+  /** `ratio >= CONFIDENCE_THRESHOLD`. */
+  confident: boolean;
+}
+
+/**
+ * Share of rows that must be read for the result to be announced as recognised
+ * rather than doubtful (decided in planning). A statement mixing a few unusable
+ * lines into an otherwise clean file is common enough that a stricter bar would
+ * cry wolf; anything below this is a mapping worth a second look.
+ */
+export const CONFIDENCE_THRESHOLD = 0.9;
+
 /**
  * The full-fidelity outcome of detection.
  *
@@ -38,7 +78,7 @@ export type AutoDetectRejectionKey = "import.errors.absoluteIndicatorFormat";
  * backwards" call for different messages. `detectImportFormat` separates them.
  */
 export type AutoDetectOutcome =
-  | { status: "ok"; config: AutoDetectResult }
+  | { status: "ok"; config: AutoDetectResult; score: DetectionScore }
   | { status: "rejected"; reason: AutoDetectRejectionKey }
   | { status: "failed" };
 
@@ -250,9 +290,7 @@ export function detectImportFormat(rawContent: string): AutoDetectOutcome {
     signConvention = amountResult.signConvention;
   }
 
-  return {
+  const config: AutoDetectResult = {
-    status: "ok",
-    config: {
     delimiter,
     hasHeader,
     skipLines,
@@ -260,7 +298,62 @@ export function detectImportFormat(rawContent: string): AutoDetectOutcome {
     columnMapping: mapping,
     amountMode: amountResult.mode,
     signConvention,
-    },
+  };
+
+  // Step 8: Replay what we just decided, over the WHOLE file. The sample above
+  // is 20 rows because that is enough to decide a shape; the score is what the
+  // user is told, so it has to describe the actual file.
+  return { status: "ok", config, score: scoreConfig(config, data) };
+}
+
+/**
+ * Replay a detected configuration over the file's data rows and count how many
+ * of them it reads.
+ *
+ * Deliberately NOT a rule of its own: the row is mapped by `mapRow`, the same
+ * pure function `parseFilesInternal` runs at import time, under the same
+ * column-level decimal arbitration. Two mappers would be the exact class of
+ * divergence this chantier exists to remove — a score could then read 100 %
+ * while the import wrote different amounts.
+ *
+ * The row selection mirrors `parseFilesInternal` line for line, including the
+ * lone-empty-cell skip: a trailing blank line must not count as an unread row.
+ */
+function scoreConfig(
+  config: AutoDetectResult,
+  data: string[][]
+): DetectionScore {
+  // `mapRow` reads no byte and therefore never looks at `encoding` — the
+  // content reached us already decoded. Naming it here only satisfies the type.
+  const format: ImportFormat = { ...config, encoding: "utf-8" };
+
+  const dataRows: string[][] = [];
+  const startIdx = config.skipLines + (config.hasHeader ? 1 : 0);
+  for (let i = startIdx; i < data.length; i++) {
+    const raw = data[i];
+    if (raw.length <= 1 && raw[0]?.trim() === "") continue;
+    dataRows.push(raw);
+  }
+
+  const decimalSeparators = detectAmountSeparators(dataRows, format);
+
+  let readRows = 0;
+  for (const raw of dataRows) {
+    try {
+      if (mapRow(raw, format, { decimalSeparators }).parsed) readRows++;
+    } catch {
+      // `mapRow` is documented not to throw; if it ever did, that is one
+      // unreadable row, not a detection that collapses on the whole file.
+    }
+  }
+
+  const totalRows = dataRows.length;
+  const ratio = totalRows === 0 ? 0 : readRows / totalRows;
+  return {
+    readRows,
+    totalRows,
+    ratio,
+    confident: totalRows > 0 && ratio >= CONFIDENCE_THRESHOLD,
   };
 }