Merge pull request 'feat(balance): Modified Dietz returns + transfer linking (#142)' (#151) from issue-142-bilan-4 into main

CHANGELOG.fr.md

@@ -3,6 +3,7 @@
 ## [Non publié]
 
 ### Ajouté
+- **Bilan — rendements Modified Dietz et liaison de transferts** (route `/balance`) : le rendement par compte arrive enfin. Nouveau module Rust `commands/return_calculator.rs` qui implémente la formule Modified Dietz `R = (V_fin − V_début − ΣCF_i) / (V_début + ΣW_i × CF_i)` avec pondération des apports à la précision du jour `W_i = (T − t_i) / T`, et annualisation `(1 + R)^(365/T) − 1`. Les cas limites — snapshot d'extrémité manquant, aucun flux taggé sur la période, compte créé en cours de période, vidé puis rechargé, période de durée nulle — sont surfacés via les flags explicites `is_partial` / `has_no_transfers_warning` pour que l'UI affiche un tiret + tooltip clair plutôt qu'un nombre incompréhensible. Nouvelle commande Tauri `compute_account_return(account_id, period_start, period_end)` qui exécute trois lectures SQL courtes contre la BD du profil actif (dernier snapshot ≤ début de période, dernier snapshot ≤ fin de période, transferts joints aux transactions filtrés sur la période) puis alimente le calculateur. Sept tests Rust co-localisés en TDD couvrent chaque cas avant l'implémentation. Le tableau des comptes sur `/balance` affiche désormais quatre colonnes supplémentaires côte à côte : 3M / 1A / Depuis création (Modified Dietz) plus une colonne *Non ajusté* qui calcule simplement `(V_fin − V_début) / V_début` pour qu'on voie d'un coup d'œil quelle part du rendement vient de la pondération des apports. Le menu d'actions de chaque ligne reçoit l'item *Lier transferts* qui ouvre une modal de sélection multiple avec filtres période / catégorie / recherche texte ; la modal propose automatiquement le sens (`in` pour les montants bancaires négatifs, `out` pour les positifs) et l'utilisateur peut inverser ligne par ligne avant de soumettre. Les transactions liées à un ou plusieurs comptes de bilan affichent maintenant une petite icône `Link2` à côté de la description dans la page *Transactions*, avec un tooltip listant les noms et sens des comptes. Les chemins de suppression en lot (par fichier importé et tout effacer) pré-vérifient l'existence d'un lien dans `balance_account_transfers` et surfacent l'erreur typée `TransactionLinkedToBalanceError` (« Cette transaction est liée au compte de bilan X — déliez-la avant de supprimer ») au lieu de laisser fuiter l'erreur SQLite brute. Le graphique d'évolution sur `/balance` superpose désormais des lignes verticales de référence à chaque date de transfert lié (vert pour `in`, rouge pour `out`). Nouvelles clés i18n sous `balance.returns.*`, `balance.accountsTable.*`, `balance.transfers.*`, `balance.evolution.*`, `transactions.transferIcon.*` (FR + EN) (#142)
 - **Bilan — page `/balance` avec graphique d'évolution et entrée sidebar** (route `/balance`) : quatrième tranche de la feature *Bilan*, qui la rend enfin accessible depuis la navigation. La nouvelle page compose (1) une carte d'aperçu avec la valeur nette agrégée du dernier snapshot, le Δ% par rapport au snapshot chronologiquement précédent (affiché « — » quand il n'existe qu'un seul snapshot), un avertissement de fraîcheur quand le dernier snapshot date de plus de 60 jours, et un CTA *Nouveau snapshot* qui pointe vers `/balance/snapshot` ; (2) un sélecteur de période (3 mois / 6 mois / 1 an / 3 ans / Tout) qui recharge toutes les séries en parallèle ; (3) un graphique d'évolution avec deux modes — *Ligne* (une seule série `SUM(value) GROUP BY snapshot_date`) et *Empilé par catégorie* (une `<Area stackId>` Recharts par `balance_categories.key`) ; (4) un tableau des comptes listant chaque compte actif avec sa dernière valeur snapshot, le Δ% par compte sur la période active (valeur la plus récente vs valeur du premier snapshot dans la fenêtre — null si pas d'ancrage, affiché « — »), et un menu d'actions (Détail désactivé en attendant la #142, Archiver). Les colonnes de rendement (3M / 1A / depuis création / non ajusté) sont réservées pour une version ultérieure avec un commentaire `TODO`. La sidebar expose désormais l'entrée *Bilan* (icône `Wallet`) entre *Rapports* et *Paramètres*. Le service gagne trois helpers de série temporelle : `getSnapshotTotalsByDate(range?)`, `getSnapshotTotalsByCategoryAndDate(range?)`, `getAccountsLatestSnapshot()` ainsi qu'un calcul d'ancrage par compte `getAccountsPeriodAnchor(range)` — tous couverts par des tests unitaires. Nouveau hook `useBalanceOverview` (`useReducer` scoped) qui pilote l'état de la page. Nouvelles clés i18n sous `balance.overview.*`, `balance.period.*`, `balance.chart.*` plus `nav.balance` (FR + EN) (#141)
 - **Bilan — type coté (quantité × prix unitaire)** (routes `/balance/accounts` et `/balance/snapshot`) : troisième tranche de la feature *Bilan*. Les catégories exposent désormais un sélecteur de *type* à la création : `simple` (saisie d'un montant direct) ou `coté` (`quantité × prix_unitaire`). Les comptes liés à une catégorie cotée exigent un symbole. L'éditeur de snapshot bascule selon le type de la catégorie du compte : les comptes simples conservent leur unique champ de valeur ; les comptes cotés affichent trois champs — `quantité`, `prix unitaire` (les deux obligatoires) et un champ `valeur` en lecture seule calculé en temps réel à partir de `quantité × prix unitaire` (arrondi à 2 décimales). Une étiquette d'attribution `[Manuel]` apparaît sur chaque ligne cotée ; la future étiquette `[via Maximus le AAAA-MM-JJ]` arrivera avec la récupération automatique des prix. Le bouton *Pré-remplir depuis le précédent* copie maintenant les quantités pour les comptes cotés mais laisse les prix unitaires vides (un prix frais doit être saisi à chaque fois). Le service valide les lignes cotées avant la CHECK SQL : invariants de type (les lignes cotées doivent porter à la fois quantité et prix unitaire ; les lignes simples ne doivent porter ni l'un ni l'autre) et invariant de valeur `|valeur − quantité × prix unitaire| ≤ 0,01` (un centime de tolérance pour absorber les arrondis flottants). La suppression d'une catégorie est désormais mieux guardée : une catégorie liée à un ou plusieurs comptes affiche un bandeau d'erreur listant le nombre et jusqu'à trois noms de comptes pour que l'utilisateur sache exactement lesquels archiver d'abord ; les catégories standard restent protégées côté service avec leur bouton désactivé dans l'interface. Nouvelles clés i18n `balance.category.kind.*`, `balance.category.form.kindLabel/kindHint*`, `balance.category.error.has_accounts`, `balance.snapshot.priced.*` (FR + EN) (#140)
 - **Bilan — éditeur de snapshot (type simple)** (route `/balance/snapshot`) : deuxième tranche de la feature *Bilan*. La nouvelle page permet de créer ou modifier un snapshot daté de votre patrimoine : choisissez une date (par défaut aujourd'hui), saisissez la valeur de chaque compte actif groupé par catégorie, puis enregistrez. Le mode est piloté par le paramètre `?date=` de l'URL — si un snapshot existe déjà à cette date, la page bascule automatiquement en mode édition (la contrainte UNIQUE sur `balance_snapshots.snapshot_date` garantit un snapshot par jour). La date d'un snapshot existant est immuable : pour la changer, supprimez puis recréez. Un bouton *Pré-remplir depuis le précédent* copie les valeurs du snapshot antérieur le plus récent (comptes simples uniquement — les comptes cotés seront pris en charge quand l'éditeur coté arrivera). Un bouton *Supprimer* affiche une modal de double confirmation qui exige de retaper la date du snapshot avant d'activer l'action destructive. Seules les valeurs de type simple sont acceptées à ce stade (`quantity` et `unit_price` sont laissés `NULL`) ; l'éditeur coté (quantité × prix unitaire + récupération de prix) arrivera dans une prochaine version. Nouveau hook `useSnapshotEditor` (`useReducer` couvrant tout le cycle de vie) et deux nouveaux composants `SnapshotEditor` + `SnapshotLineRow`. i18n FR/EN sous `balance.snapshot.*` (#146)

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## [Unreleased]
 
 ### Added
+- **Balance sheet — Modified Dietz returns and transfer linking** (route `/balance`): per-account performance now ships. New Rust module `commands/return_calculator.rs` implements the Modified Dietz formula `R = (V_end − V_start − ΣCF_i) / (V_start + ΣW_i × CF_i)` with day-precision contribution weights `W_i = (T − t_i) / T`, plus `(1 + R)^(365/T) − 1` annualization. Edge cases — missing endpoint snapshot, no flows tagged in the period, account created mid-period, depleted-then-refilled, zero-length period — are surfaced with explicit `is_partial` / `has_no_transfers_warning` flags so the UI shows a clean dash + tooltip instead of a confusing number. The new Tauri command `compute_account_return(account_id, period_start, period_end)` runs three short SQL reads against the active profile DB (latest snapshot ≤ period start, latest snapshot ≤ period end, transfers JOINed with transactions filtered to the period) and feeds the calculator. Seven co-located TDD tests cover every case before the implementation. The accounts table on `/balance` now shows four extra columns side-by-side: 3M / 1Y / Since-inception (Modified Dietz) plus an *Unadjusted* column showing the simple `(V_end − V_start) / V_start` so the user can see at a glance how much of the return came from contribution timing. Each row's actions menu gains a *Link transfers* item that opens a multi-select modal with date range / category / free-text filters; the modal auto-proposes the direction (`in` for negative bank amounts, `out` for positive) and the user can flip it per row before submitting. Transactions linked to one or more balance accounts now show a small `Link2` icon next to the description in the *Transactions* page, with a tooltip listing the account name(s) and direction(s). Bulk transaction-deletion paths (per-imported-file and clear-all) now pre-check for any link in `balance_account_transfers` and surface a typed `TransactionLinkedToBalanceError` ("This transaction is linked to balance account X — unlink it before deleting") instead of leaking the raw SQLite FK error. The evolution chart on `/balance` now overlays vertical reference lines at every linked-transfer date (green for `in`, red for `out`). New i18n keys under `balance.returns.*`, `balance.accountsTable.*`, `balance.transfers.*`, `balance.evolution.*`, `transactions.transferIcon.*` (FR + EN) (#142)
 - **Balance sheet — `/balance` overview page, evolution chart and sidebar entry** (route `/balance`): fourth slice of the *Bilan* feature finally surfaces it in the navigation. The new page composes (1) an overview card with the latest aggregate net worth, the Δ% versus the previous chronological snapshot (rendered as "—" when only one snapshot exists), a 60-day staleness warning when the latest snapshot is older than that threshold, and a *New snapshot* CTA pointing at `/balance/snapshot`; (2) a period selector (3 months / 6 months / 1 year / 3 years / All) that re-fetches every series in parallel; (3) an evolution chart with two modes — *Line* (single series of `SUM(value) GROUP BY snapshot_date`) and *Stacked by category* (one Recharts `<Area stackId>` per `balance_categories.key`); (4) an accounts table listing every active account with its latest snapshot value, the per-account Δ% over the active period (latest value vs the value at the earliest snapshot inside the window — null when no anchor exists, rendered as "—"), and an actions menu (Details placeholder, Archive). Return-metric columns (3M / 1Y / since-creation / unadjusted) are reserved for a later release with a `TODO` marker. The sidebar now exposes the *Balance sheet* entry (`Wallet` icon) between *Reports* and *Settings*. The service grows three time-series helpers: `getSnapshotTotalsByDate(range?)`, `getSnapshotTotalsByCategoryAndDate(range?)`, `getAccountsLatestSnapshot()` and a per-account anchor query `getAccountsPeriodAnchor(range)` — all guarded by unit tests. New `useBalanceOverview` hook (scoped `useReducer`) drives the page state. New i18n keys under `balance.overview.*`, `balance.period.*`, `balance.chart.*` plus `nav.balance` (FR + EN) (#141)
 - **Balance sheet — priced kind (quantity × unit price)** (routes `/balance/accounts` and `/balance/snapshot`): third slice of the *Bilan* feature. Categories now expose a *kind* selector at creation: `simple` (direct value entry) or `priced` (`quantity × unit_price`). Accounts linked to a priced category require a symbol. The snapshot editor dispatches on the account's category kind: simple accounts keep their single value field, priced accounts get three inputs — `quantity`, `unit_price` (both required) and a read-only `value` field computed live from `quantity × unit_price` (rounded to 2 decimals). A `[Manual]` / `[Manuel]` attribution tag is shown on each priced row; the future `[via Maximus on YYYY-MM-DD]` tag will land with automatic price-fetching. The *Prefill from previous* button now copies quantities for priced accounts but leaves unit prices blank (a fresh price must be entered each time). The service validates priced lines ahead of the SQL CHECK: kind invariants (priced lines must carry both quantity and unit_price; simple lines must carry neither) and a value-match invariant `|value − quantity × unit_price| ≤ 0.01` (one cent tolerance to absorb floating-point drift). Category deletion now blocks earlier and surfaces a richer error: a category linked to one or more accounts shows a dismissable banner listing the count and up to three account names so the user knows exactly which accounts to archive first; seeded categories remain protected at the service layer with their button disabled in the UI. New i18n keys `balance.category.kind.*`, `balance.category.form.kindLabel/kindHint*`, `balance.category.error.has_accounts`, `balance.snapshot.priced.*` (FR + EN) (#140)
 - **Balance sheet — snapshot editor (simple kind)** (route `/balance/snapshot`): second slice of the *Bilan* feature. The new page lets you create or edit a dated snapshot of your balance: pick a date (defaulting to today), enter the value of each active account grouped by category, and save. The mode is driven by the `?date=` query parameter — when a snapshot already exists at that date the page automatically flips into edit mode (the underlying `balance_snapshots.snapshot_date` UNIQUE constraint guarantees one snapshot per day). The date of an existing snapshot is immutable: to change it, delete the snapshot and create a new one. A *Prefill from previous snapshot* button copies values from the most recent earlier snapshot (simple-kind accounts only — priced accounts will be handled when the priced editor lands in a later release). A *Delete* button surfaces a double-confirmation modal that requires retyping the snapshot date before the destructive action is enabled. Only simple-kind values are accepted at this stage (`quantity` and `unit_price` are kept `NULL`); the priced editor (quantity × unit price + price fetch) ships in a later release. New `useSnapshotEditor` hook (scoped `useReducer` covering the full lifecycle) and two new components `SnapshotEditor` + `SnapshotLineRow`. FR/EN i18n under `balance.snapshot.*` (#146)

src-tauri/Cargo.lock

@@ -4428,6 +4428,7 @@ dependencies = [
  "aes-gcm",
  "argon2",
  "base64 0.22.1",
+ "chrono",
  "ed25519-dalek",
  "encoding_rs",
  "hmac",

src-tauri/Cargo.toml

@@ -41,6 +41,10 @@ rand = "0.8"
 jsonwebtoken = "9"
 machine-uid = "0.5"
 reqwest = { version = "0.12", features = ["json"] }
+# Date arithmetic for the Modified Dietz return calculator (Issue #142):
+# we need day-precision diffs to weight cash flows W_i = (T - t_i) / T.
+# `serde` feature lets `NaiveDate` cross the Tauri command boundary in JSON.
+chrono = { version = "0.4", default-features = false, features = ["serde", "std"] }
 tokio = { version = "1", features = ["macros"] }
 hostname = "0.4"
 urlencoding = "2"

src-tauri/src/commands/balance_commands.rs

@@ -0,0 +1,183 @@
+//! Tauri commands for the Bilan (balance sheet) feature — Issue #142.
+//!
+//! At Issue #142 the only command exposed is `compute_account_return`. The
+//! Modified Dietz formula needs to read snapshot endpoints + linked transfer
+//! amounts in a single Rust pass (the math itself lives in
+//! `return_calculator.rs`); doing it server-side avoids 3 round-trips from
+//! the renderer and keeps the calculation reproducible.
+//!
+//! Future commands (`fetch_price`, etc.) ship in Issue #143 / Bilan #5.
+//!
+//! Database access pattern:
+//!   - All reads use `rusqlite::Connection::open(app_data_dir / db_filename)`,
+//!     matching the existing `repair_migrations` helper in `profile_commands.rs`.
+//!   - The frontend passes `db_filename` (the active profile DB), exactly
+//!     like it does for `repair_migrations` and `delete_profile_db`. Keeps
+//!     the active-profile resolution where it already lives (in TS) and
+//!     avoids re-reading `profiles.json` on every call.
+//!   - Reads are short-lived: connection opens, runs ≤ 3 SQL statements,
+//!     drops at end of function. No connection pooling needed (commands run
+//!     on the Tauri async runtime, one at a time per invocation).
+
+use chrono::NaiveDate;
+use rusqlite::Connection;
+use tauri::Manager;
+
+use crate::commands::return_calculator::{modified_dietz, AccountReturn};
+
+/// Compute the Modified Dietz return for one account over the period
+/// `[period_start, period_end]`. Reads:
+///   - `value_start`: latest snapshot line for the account whose
+///     `snapshot_date <= period_start` (None if no prior snapshot).
+///   - `value_end`:   latest snapshot line for the account whose
+///     `snapshot_date <= period_end`   (None if no snapshot in range).
+///   - cash flows:    every linked transfer in `[period_start, period_end]`,
+///     sign applied per direction (`in` → `+`, `out` → `−`).
+///
+/// Both dates must be ISO `YYYY-MM-DD`. Returns a typed `AccountReturn`
+/// (Serialize) ready to ship across the Tauri boundary.
+#[tauri::command]
+pub fn compute_account_return(
+    app: tauri::AppHandle,
+    db_filename: String,
+    account_id: i64,
+    period_start: String,
+    period_end: String,
+) -> Result<AccountReturn, String> {
+    let start_date = parse_iso_date(&period_start, "period_start")?;
+    let end_date = parse_iso_date(&period_end, "period_end")?;
+
+    let app_dir = app
+        .path()
+        .app_data_dir()
+        .map_err(|e| format!("Cannot get app data dir: {}", e))?;
+    let db_path = app_dir.join(&db_filename);
+    if !db_path.exists() {
+        return Err(format!(
+            "Profile database not found: {}",
+            db_path.display()
+        ));
+    }
+
+    let conn = Connection::open(&db_path)
+        .map_err(|e| format!("Cannot open database: {}", e))?;
+
+    let value_start = read_value_at_or_before(&conn, account_id, &period_start)?;
+    let value_end = read_value_at_or_before(&conn, account_id, &period_end)?;
+    let cash_flows = read_cash_flows(&conn, account_id, &period_start, &period_end)?;
+
+    Ok(modified_dietz(
+        value_start,
+        value_end,
+        &cash_flows,
+        start_date,
+        end_date,
+    ))
+}
+
+// -----------------------------------------------------------------------------
+// Internal helpers
+// -----------------------------------------------------------------------------
+
+fn parse_iso_date(input: &str, field: &str) -> Result<NaiveDate, String> {
+    NaiveDate::parse_from_str(input, "%Y-%m-%d")
+        .map_err(|e| format!("Invalid {} (expected YYYY-MM-DD): {}", field, e))
+}
+
+/// Reads the value of the snapshot line for `account_id` at the most recent
+/// snapshot whose `snapshot_date <= as_of_date`. Returns `None` when no
+/// such snapshot exists for this account.
+fn read_value_at_or_before(
+    conn: &Connection,
+    account_id: i64,
+    as_of_date: &str,
+) -> Result<Option<f64>, String> {
+    // Single-row query: pick the latest snapshot date for this account that
+    // is on or before `as_of_date`, then return that line's value. Indexed
+    // on `balance_snapshots.snapshot_date` and `balance_snapshot_lines.account_id`.
+    let mut stmt = conn
+        .prepare(
+            "SELECT l.value
+               FROM balance_snapshot_lines l
+               JOIN balance_snapshots s ON s.id = l.snapshot_id
+              WHERE l.account_id = ?1
+                AND s.snapshot_date <= ?2
+              ORDER BY s.snapshot_date DESC
+              LIMIT 1",
+        )
+        .map_err(|e| format!("prepare value query: {}", e))?;
+
+    let mut rows = stmt
+        .query(rusqlite::params![account_id, as_of_date])
+        .map_err(|e| format!("execute value query: {}", e))?;
+
+    match rows.next().map_err(|e| format!("read value row: {}", e))? {
+        Some(row) => Ok(Some(
+            row.get::<_, f64>(0).map_err(|e| format!("decode value: {}", e))?,
+        )),
+        None => Ok(None),
+    }
+}
+
+/// Reads every linked transfer for `account_id` whose underlying
+/// transaction's `transaction_date` falls inside `[period_start, period_end]`.
+/// Returns `(NaiveDate, signed_amount)` — sign applied per `direction`
+/// (`in` → `+`, `out` → `−`). Amounts come from the linked transaction.
+fn read_cash_flows(
+    conn: &Connection,
+    account_id: i64,
+    period_start: &str,
+    period_end: &str,
+) -> Result<Vec<(NaiveDate, f64)>, String> {
+    // NOTE: the transactions table column is `date` (not `transaction_date`).
+    // See `src-tauri/src/database/schema.sql:67`.
+    let mut stmt = conn
+        .prepare(
+            "SELECT t.date,
+                    ABS(t.amount) AS abs_amount,
+                    bat.direction
+               FROM balance_account_transfers bat
+               JOIN transactions t ON t.id = bat.transaction_id
+              WHERE bat.account_id = ?1
+                AND t.date BETWEEN ?2 AND ?3
+              ORDER BY t.date",
+        )
+        .map_err(|e| format!("prepare flows query: {}", e))?;
+
+    let rows = stmt
+        .query_map(
+            rusqlite::params![account_id, period_start, period_end],
+            |row| {
+                // `transactions.date` may come back as String (TEXT) — keep
+                // the decoder generic enough.
+                let date_str: String = row.get(0)?;
+                let amount: f64 = row.get(1)?;
+                let direction: String = row.get(2)?;
+                Ok((date_str, amount, direction))
+            },
+        )
+        .map_err(|e| format!("execute flows query: {}", e))?;
+
+    let mut flows: Vec<(NaiveDate, f64)> = Vec::new();
+    for row_result in rows {
+        let (date_str, amount, direction) =
+            row_result.map_err(|e| format!("decode flow row: {}", e))?;
+        // `transaction_date` is stored as `YYYY-MM-DD` (TEXT date column —
+        // see consolidated_schema.sql). Defensive trim of any trailing
+        // time component just in case.
+        let iso = date_str.split('T').next().unwrap_or(&date_str).to_string();
+        let date = parse_iso_date(&iso, "transaction_date")?;
+        let signed = match direction.as_str() {
+            "in" => amount,
+            "out" => -amount,
+            other => {
+                return Err(format!(
+                    "Invalid transfer direction stored in DB: {}",
+                    other
+                ));
+            }
+        };
+        flows.push((date, signed));
+    }
+    Ok(flows)
+}

src-tauri/src/commands/mod.rs

@@ -1,16 +1,22 @@
 pub mod account_cache;
 pub mod auth_commands;
 pub mod backup_commands;
+pub mod balance_commands;
 pub mod entitlements;
 pub mod export_import_commands;
 pub mod feedback_commands;
 pub mod fs_commands;
 pub mod license_commands;
 pub mod profile_commands;
+// Modified Dietz return calculator — private helper module used by
+// `balance_commands.rs`. Kept out of the wildcard re-export below because
+// nothing outside `commands/` should depend on it.
+pub(crate) mod return_calculator;
 pub mod token_store;
 
 pub use auth_commands::*;
 pub use backup_commands::*;
+pub use balance_commands::*;
 pub use entitlements::*;
 pub use export_import_commands::*;
 pub use feedback_commands::*;

src-tauri/src/commands/return_calculator.rs

@@ -0,0 +1,380 @@
+//! Modified Dietz return calculator (Issue #142 / Bilan #4).
+//!
+//! Computes the time- and contribution-weighted return of a single account
+//! over a period, given:
+//!   - the account value at `period_start` (snapshot lookup, may be missing),
+//!   - the account value at `period_end`   (snapshot lookup, may be missing),
+//!   - the cash flows during the period (linked transfers — `+` for IN,
+//!     `-` for OUT; the caller already applies the direction sign).
+//!
+//! Modified Dietz formula:
+//!
+//!     R = (V_end - V_start - sum(CF_i)) / (V_start + sum(W_i * CF_i))
+//!
+//! where `W_i = (T - t_i) / T`, `T = period_days`, `t_i = days from period_start
+//! to flow date`. A flow on day 0 is fully invested for the whole period
+//! (W_i = 1) and a flow on the last day contributes nothing (W_i = 0).
+//!
+//! Annualization: `(1 + R)^(365 / T) - 1` for periods of strictly positive
+//! length. A zero-length period (`period_start == period_end`) skips the
+//! annualization step (would divide by zero).
+//!
+//! Edge cases (each surface as a typed flag on `AccountReturn` so the UI can
+//! render an explicit warning instead of an opaque empty value):
+//!   - `value_start == None`            → `is_partial = true`, `return_pct = None`
+//!   - `value_end == None`              → `is_partial = true`, `return_pct = None`
+//!   - `cash_flows.is_empty()`          → `has_no_transfers_warning = true`,
+//!                                        return collapses to the simple
+//!                                        `(V_end - V_start) / V_start`
+//!   - `period_start == period_end`     → no annualization (stays = return_pct)
+//!   - V_start = 0 and first flow > 0   → account created mid-period; the
+//!                                        denominator is `0 + W_first * CF_first`,
+//!                                        which is positive as long as the
+//!                                        flow lands strictly before period_end
+//!   - account depleted then refilled   → mathematically defined; the
+//!                                        function does not panic but the
+//!                                        magnitude can look extreme — that is
+//!                                        the inherent Modified Dietz behaviour
+//!                                        on accounts with near-zero invested
+//!                                        capital.
+//!
+//! Module is **private to the crate** (`pub(crate)`) and lives under
+//! `commands/` per the spec — reused only by `balance_commands.rs`.
+
+use chrono::NaiveDate;
+use serde::Serialize;
+
+/// Result of a Modified Dietz computation, ready to ship across the Tauri
+/// boundary. Optional fields are `None` whenever the calculation cannot be
+/// completed (missing snapshot endpoints) — the UI renders a dash + a tooltip
+/// pointing at `is_partial` / `has_no_transfers_warning`.
+#[derive(Debug, Clone, Serialize, PartialEq)]
+pub struct AccountReturn {
+    /// Account value at `period_start` (latest snapshot ≤ period_start).
+    pub value_start: Option<f64>,
+    /// Account value at `period_end` (latest snapshot ≤ period_end).
+    pub value_end: Option<f64>,
+    /// Sum of signed cash flows during the period (`+` IN, `-` OUT).
+    pub net_contributions: f64,
+    /// Modified Dietz return as a fraction (0.05 = +5%). `None` if either
+    /// endpoint snapshot is missing or the denominator is non-positive.
+    pub return_pct: Option<f64>,
+    /// Annualized return `(1 + R)^(365 / T) - 1`. `None` for zero-length
+    /// periods or whenever `return_pct` is `None`.
+    pub annualized_pct: Option<f64>,
+    /// `true` when at least one snapshot endpoint is missing — the UI labels
+    /// the result as "partial / non-significatif".
+    pub is_partial: bool,
+    /// `true` when the account had zero linked transfers during the period —
+    /// Modified Dietz collapses to the simple `(V_end - V_start) / V_start`,
+    /// but the UI surfaces a warning so the user can verify whether real
+    /// transfers were forgotten (untagged contributions skew the return).
+    pub has_no_transfers_warning: bool,
+}
+
+impl AccountReturn {
+    /// Default partial return when an endpoint is missing — keeps the
+    /// constructor calls in the algorithm body terse.
+    fn partial(
+        value_start: Option<f64>,
+        value_end: Option<f64>,
+        net_contributions: f64,
+        has_no_transfers_warning: bool,
+    ) -> Self {
+        Self {
+            value_start,
+            value_end,
+            net_contributions,
+            return_pct: None,
+            annualized_pct: None,
+            is_partial: true,
+            has_no_transfers_warning,
+        }
+    }
+}
+
+/// Computes the Modified Dietz return for one account over the period
+/// `[period_start, period_end]`. See module docs for the full formula and
+/// edge-case handling.
+///
+/// `cash_flows` is `(date, signed_amount)`. The caller is responsible for
+/// applying the direction sign (`in` → `+`, `out` → `−`) and for filtering
+/// flows to the period; flows outside `[period_start, period_end]` are
+/// skipped here too as a safety net.
+pub(crate) fn modified_dietz(
+    value_start: Option<f64>,
+    value_end: Option<f64>,
+    cash_flows: &[(NaiveDate, f64)],
+    period_start: NaiveDate,
+    period_end: NaiveDate,
+) -> AccountReturn {
+    // Filter flows to the period (defensive — caller already does this via
+    // SQL, but keep the guarantee here so the math never sees out-of-range
+    // weights).
+    let in_period: Vec<(NaiveDate, f64)> = cash_flows
+        .iter()
+        .copied()
+        .filter(|(d, _)| *d >= period_start && *d <= period_end)
+        .collect();
+
+    let net_contributions: f64 = in_period.iter().map(|(_, cf)| *cf).sum();
+    let has_no_transfers_warning = in_period.is_empty();
+
+    // Endpoint guards — without both V_start and V_end we cannot return a
+    // numeric result.
+    let v_start = match value_start {
+        Some(v) => v,
+        None => {
+            return AccountReturn::partial(
+                value_start,
+                value_end,
+                net_contributions,
+                has_no_transfers_warning,
+            );
+        }
+    };
+    let v_end = match value_end {
+        Some(v) => v,
+        None => {
+            return AccountReturn::partial(
+                value_start,
+                value_end,
+                net_contributions,
+                has_no_transfers_warning,
+            );
+        }
+    };
+
+    // Period length in days. `(period_end - period_start)` returns
+    // `chrono::Duration`; `.num_days()` is `i64`. A zero-length period
+    // (same-day) skips weighting and annualization.
+    let total_days = (period_end - period_start).num_days();
+
+    let denominator: f64 = if total_days <= 0 {
+        // Same-day period: weights collapse to either 0 or undefined; treat
+        // every flow as fully invested (W = 1) so the denominator is
+        // V_start + sum(CF). This keeps the function defined when callers
+        // pass `period_start == period_end`.
+        v_start + net_contributions
+    } else {
+        let total = total_days as f64;
+        let weighted_sum: f64 = in_period
+            .iter()
+            .map(|(date, cf)| {
+                let t_i = (*date - period_start).num_days() as f64;
+                let w_i = (total - t_i) / total;
+                w_i * cf
+            })
+            .sum();
+        v_start + weighted_sum
+    };
+
+    // A non-positive denominator means we have no invested base to annualize
+    // against (e.g. depleted then refilled with a single late flow). Return
+    // the raw V_end - V_start - CF as the numerator and flag is_partial so
+    // the UI can show "Performance non significative" — but only when V_start
+    // is also 0 / negative; if V_start > 0 we keep the standard math.
+    if denominator <= 0.0 {
+        return AccountReturn {
+            value_start: Some(v_start),
+            value_end: Some(v_end),
+            net_contributions,
+            return_pct: None,
+            annualized_pct: None,
+            is_partial: true,
+            has_no_transfers_warning,
+        };
+    }
+
+    let numerator = v_end - v_start - net_contributions;
+    let return_pct = numerator / denominator;
+
+    // Annualization only makes sense for strictly positive periods.
+    let annualized_pct = if total_days > 0 {
+        let exponent = 365.0 / total_days as f64;
+        Some((1.0 + return_pct).powf(exponent) - 1.0)
+    } else {
+        None
+    };
+
+    AccountReturn {
+        value_start: Some(v_start),
+        value_end: Some(v_end),
+        net_contributions,
+        return_pct: Some(return_pct),
+        annualized_pct,
+        is_partial: false,
+        has_no_transfers_warning,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Small helper that turns a `YYYY-MM-DD` string literal into a
+    /// `NaiveDate` — keeps the test bodies readable.
+    fn d(s: &str) -> NaiveDate {
+        NaiveDate::parse_from_str(s, "%Y-%m-%d").expect("test date parses")
+    }
+
+    fn approx(a: f64, b: f64, tol: f64) -> bool {
+        (a - b).abs() <= tol
+    }
+
+    #[test]
+    fn nominal_two_flows_at_one_quarter_and_three_quarters() {
+        // 100-day period (2026-01-01 → 2026-04-11). V_start = 1000, V_end =
+        // 1100. CF1 = +50 at day 25, CF2 = +30 at day 75.
+        let start = d("2026-01-01");
+        let end = d("2026-04-11"); // 100 days later
+        let flows = vec![(d("2026-01-26"), 50.0), (d("2026-03-17"), 30.0)];
+
+        let r = modified_dietz(Some(1000.0), Some(1100.0), &flows, start, end);
+
+        // Sanity / shape
+        assert_eq!(r.value_start, Some(1000.0));
+        assert_eq!(r.value_end, Some(1100.0));
+        assert_eq!(r.net_contributions, 80.0);
+        assert!(!r.is_partial);
+        assert!(!r.has_no_transfers_warning);
+
+        // Hand calc:
+        //   T = 100, t1 = 25, t2 = 75
+        //   W1 = 75/100 = 0.75, W2 = 25/100 = 0.25
+        //   numerator   = 1100 - 1000 - 80                = 20
+        //   denominator = 1000 + 0.75*50 + 0.25*30        = 1045
+        //   R           = 20 / 1045                       ≈ 0.01913876
+        let r_pct = r.return_pct.expect("nominal case has a return");
+        assert!(
+            approx(r_pct, 20.0 / 1045.0, 1e-9),
+            "return_pct = {} (expected ≈ {})",
+            r_pct,
+            20.0 / 1045.0
+        );
+
+        // Annualization: (1 + R)^(365/100) - 1
+        let expected_ann = (1.0_f64 + 20.0 / 1045.0).powf(365.0 / 100.0) - 1.0;
+        let ann = r.annualized_pct.expect("nominal case is annualized");
+        assert!(approx(ann, expected_ann, 1e-9), "annualized = {}", ann);
+    }
+
+    #[test]
+    fn no_prior_snapshot_marks_partial() {
+        let start = d("2026-01-01");
+        let end = d("2026-04-01");
+        let flows = vec![(d("2026-02-01"), 200.0)];
+
+        let r = modified_dietz(None, Some(1500.0), &flows, start, end);
+
+        assert_eq!(r.value_start, None);
+        assert_eq!(r.value_end, Some(1500.0));
+        assert!(r.is_partial, "missing V_start must flag is_partial");
+        assert_eq!(r.return_pct, None);
+        assert_eq!(r.annualized_pct, None);
+        assert!(!r.has_no_transfers_warning);
+        // Still surface the contributions sum for the UI breakdown card.
+        assert_eq!(r.net_contributions, 200.0);
+    }
+
+    #[test]
+    fn no_end_snapshot_marks_partial() {
+        let start = d("2026-01-01");
+        let end = d("2026-04-01");
+        let flows = vec![(d("2026-02-15"), -100.0)];
+
+        let r = modified_dietz(Some(2000.0), None, &flows, start, end);
+
+        assert_eq!(r.value_start, Some(2000.0));
+        assert_eq!(r.value_end, None);
+        assert!(r.is_partial);
+        assert_eq!(r.return_pct, None);
+        assert_eq!(r.annualized_pct, None);
+        assert_eq!(r.net_contributions, -100.0);
+    }
+
+    #[test]
+    fn account_created_mid_period_with_first_flow() {
+        // V_start = 0, single +500 flow at day 30 of a 90-day period, V_end
+        // = 510. The flow's weight is W = (90-30)/90 = 2/3.
+        let start = d("2026-01-01");
+        let end = d("2026-04-01"); // 90 days
+        let flows = vec![(d("2026-01-31"), 500.0)];
+
+        let r = modified_dietz(Some(0.0), Some(510.0), &flows, start, end);
+
+        // numerator = 510 - 0 - 500 = 10
+        // W = (90-30)/90 ≈ 0.6666667
+        // denominator = 0 + 0.6666667 * 500 ≈ 333.3333
+        // R ≈ 10 / 333.3333 = 0.03
+        let expected = 10.0 / ((90.0 - 30.0) / 90.0 * 500.0);
+        let r_pct = r.return_pct.expect("account-created case computes");
+        assert!(
+            approx(r_pct, expected, 1e-9),
+            "return_pct = {} (expected ≈ {})",
+            r_pct,
+            expected
+        );
+        assert!(!r.is_partial);
+        assert!(!r.has_no_transfers_warning);
+    }
+
+    #[test]
+    fn depleted_then_refilled_does_not_panic() {
+        // Pathological: V_start = 100, then -100 flow on day 1 (account
+        // emptied), then +200 flow on day 60 of a 90-day period, V_end =
+        // 210. Modified Dietz handles this without panicking; the value
+        // may look extreme but the function must stay defined.
+        let start = d("2026-01-01");
+        let end = d("2026-04-01");
+        let flows = vec![(d("2026-01-02"), -100.0), (d("2026-03-02"), 200.0)];
+
+        let r = modified_dietz(Some(100.0), Some(210.0), &flows, start, end);
+
+        // Whatever the math says, the call must complete cleanly. We don't
+        // assert a precise return — the goal is "no panic, finite output if
+        // the denominator is positive, else partial flag".
+        if let Some(rp) = r.return_pct {
+            assert!(rp.is_finite(), "return must be a finite f64");
+        }
+        // Net flows = -100 + 200 = 100
+        assert_eq!(r.net_contributions, 100.0);
+        // Not flagged "no transfers" since we have two flows.
+        assert!(!r.has_no_transfers_warning);
+    }
+
+    #[test]
+    fn no_transfers_collapses_to_simple_return() {
+        // No cash flows → R should equal (V_end - V_start) / V_start exactly.
+        let start = d("2026-01-01");
+        let end = d("2026-04-01");
+        let flows: Vec<(NaiveDate, f64)> = vec![];
+
+        let r = modified_dietz(Some(1000.0), Some(1100.0), &flows, start, end);
+
+        assert!(r.has_no_transfers_warning);
+        assert_eq!(r.net_contributions, 0.0);
+        let r_pct = r.return_pct.expect("simple-return case has a value");
+        let simple = (1100.0 - 1000.0) / 1000.0; // = 0.1
+        assert!(approx(r_pct, simple, 1e-12), "simple return mismatch: {}", r_pct);
+    }
+
+    #[test]
+    fn annualization_on_90_day_period_matches_compound_formula() {
+        // Direct check of the annualization branch with a clean R.
+        let start = d("2026-01-01");
+        let end = d("2026-04-01"); // 90 days
+        let flows: Vec<(NaiveDate, f64)> = vec![];
+
+        // V_start = 1000, V_end = 1050 → R = 0.05
+        let r = modified_dietz(Some(1000.0), Some(1050.0), &flows, start, end);
+        let expected_ann = (1.0_f64 + 0.05).powf(365.0 / 90.0) - 1.0;
+        let ann = r.annualized_pct.expect("90-day period annualizes");
+        assert!(
+            approx(ann, expected_ann, 1e-12),
+            "annualized = {} (expected {})",
+            ann,
+            expected_ann
+        );
+    }
+}

src-tauri/src/lib.rs

@@ -216,6 +216,7 @@ pub fn run() {
             commands::ensure_backup_dir,
             commands::get_file_size,
             commands::file_exists,
+            commands::compute_account_return,
         ])
         .run(tauri::generate_context!())
         .expect("error while running tauri application");

src/components/balance/BalanceAccountsTable.tsx

@@ -1,22 +1,32 @@
 // BalanceAccountsTable — one-row-per-active-account table on /balance.
 //
-// Issue #141 (Bilan #3). Columns:
+// Issue #141 (Bilan #3) introduced the table with name/category/latest-value/Δ%
-//   - Account name + category label
+// + actions menu. Issue #142 (Bilan #4) adds 4 return columns, computed via
-//   - Latest snapshot value (or "—" when no snapshot exists yet)
+// the Modified Dietz `compute_account_return` Tauri command:
-//   - Δ% over the active period (latest value vs the period-anchor value;
-//     null when no anchor exists, rendered as "—").
-//   - Actions menu (Detail no-op for now, Archive via service).
 //
-// Future return-metric columns (3M / 1A / since-creation / unadjusted)
+//   - 3M (last 90 days)
-// land in Issue #142. They have a TODO marker below.
+//   - 1A (last 365 days)
+//   - Depuis création (from earliest snapshot date to today)
+//   - Non-ajusté (simple `(V_end - V_start) / V_start`, no contribution
+//     weighting — shown side-by-side as a sanity check / explanation)
+//
+// Returns load lazily on mount via `Promise.all` over (account × horizon),
+// keyed by `account_id`. Each cell renders "—" while loading and shows the
+// `is_partial` / `has_no_transfers_warning` badges via tooltip when set.
+//
+// Issue #142 also adds a "Lier transferts" item in the per-row actions menu
+// that opens `LinkTransfersModal` (the modal handles its own state; this
+// component just bubbles up the request via `onLinkTransfers`).
 
-import { useMemo, useState } from "react";
+import { useEffect, useMemo, useState } from "react";
 import { useTranslation } from "react-i18next";
-import { Archive, MoreVertical } from "lucide-react";
+import { Archive, MoreVertical, Link as LinkIcon, AlertTriangle } from "lucide-react";
 import type {
   AccountLatestSnapshot,
   AccountPeriodAnchor,
 } from "../../services/balance.service";
+import { computeAccountReturn } from "../../services/balance.service";
+import type { AccountReturn } from "../../shared/types";
 
 const cadFormatter = (locale: string) =>
   new Intl.NumberFormat(locale, {
@@ -25,16 +35,55 @@ const cadFormatter = (locale: string) =>
     maximumFractionDigits: 2,
   });
 
+/** Horizon definition: how many days back from today to start the period. */
+type HorizonKey = "3M" | "1A" | "since";
+
+interface HorizonRange {
+  key: HorizonKey;
+  /** ISO date for `period_start`. */
+  from: string;
+  /** ISO date for `period_end` (always today, computed in the local civil day). */
+  to: string;
+}
+
+function localISO(d: Date): string {
+  const yy = d.getFullYear();
+  const mm = String(d.getMonth() + 1).padStart(2, "0");
+  const dd = String(d.getDate()).padStart(2, "0");
+  return `${yy}-${mm}-${dd}`;
+}
+
+function isoDaysAgo(days: number, today: Date): string {
+  const d = new Date(today);
+  d.setDate(d.getDate() - days);
+  return localISO(d);
+}
+
 interface BalanceAccountsTableProps {
   accounts: AccountLatestSnapshot[];
   periodAnchor: AccountPeriodAnchor[];
   onArchiveAccount?: (account: AccountLatestSnapshot) => void;
+  onLinkTransfers?: (account: AccountLatestSnapshot) => void;
+  /**
+   * Earliest snapshot date across the whole profile, used to anchor the
+   * "depuis création" horizon. Falls back to "1A" range if not provided
+   * (avoids triggering computation against the unix epoch).
+   */
+  sinceCreationDate?: string | null;
 }
 
+/**
+ * Per-account, per-horizon return — shape used by the local cache state.
+ * Indexed `[accountId][horizonKey]`.
+ */
+type ReturnsByAccount = Record<number, Partial<Record<HorizonKey, AccountReturn>>>;
+
 export default function BalanceAccountsTable({
   accounts,
   periodAnchor,
   onArchiveAccount,
+  onLinkTransfers,
+  sinceCreationDate,
 }: BalanceAccountsTableProps) {
   const { t, i18n } = useTranslation();
   const fmt = cadFormatter(i18n.language === "fr" ? "fr-CA" : "en-CA");
@@ -48,6 +97,65 @@ export default function BalanceAccountsTable({
 
   const [openMenuFor, setOpenMenuFor] = useState<number | null>(null);
 
+  // Returns cache. Cleared whenever the account list changes (new accounts,
+  // archive, etc.). Loaded lazily after mount.
+  const [returns, setReturns] = useState<ReturnsByAccount>({});
+  const [returnsLoading, setReturnsLoading] = useState(false);
+
+  // Horizon definitions — recomputed once per mount via today's local civil
+  // day. We don't memoize against `accounts` because the dates don't depend
+  // on the row list.
+  const horizons = useMemo<HorizonRange[]>(() => {
+    const today = new Date();
+    const todayISO = localISO(today);
+    const sinceFrom = sinceCreationDate ?? isoDaysAgo(365, today);
+    return [
+      { key: "3M", from: isoDaysAgo(90, today), to: todayISO },
+      { key: "1A", from: isoDaysAgo(365, today), to: todayISO },
+      { key: "since", from: sinceFrom, to: todayISO },
+    ];
+  }, [sinceCreationDate]);
+
+  useEffect(() => {
+    let cancelled = false;
+    async function loadReturns() {
+      if (accounts.length === 0) {
+        setReturns({});
+        return;
+      }
+      setReturnsLoading(true);
+      const next: ReturnsByAccount = {};
+      // Run sequentially per account to avoid SQLite contention; per-horizon
+      // we can parallelize because they hit the same table set.
+      await Promise.all(
+        accounts.map(async (acc) => {
+          next[acc.account_id] = {};
+          const tasks = horizons.map(async (h) => {
+            try {
+              const r = await computeAccountReturn(
+                acc.account_id,
+                h.from,
+                h.to
+              );
+              next[acc.account_id]![h.key] = r;
+            } catch {
+              // Per-cell failure: leave the slot undefined → renders "—".
+            }
+          });
+          await Promise.all(tasks);
+        })
+      );
+      if (!cancelled) {
+        setReturns(next);
+        setReturnsLoading(false);
+      }
+    }
+    void loadReturns();
+    return () => {
+      cancelled = true;
+    };
+  }, [accounts, horizons]);
+
   if (accounts.length === 0) {
     return (
       <div className="bg-[var(--card)] border border-[var(--border)] rounded-xl p-8 text-center text-[var(--muted-foreground)] italic">
@@ -56,8 +164,73 @@ export default function BalanceAccountsTable({
     );
   }
 
+  /** Format a return percentage with sign + colour-aware classname. */
+  function renderReturnCell(r: AccountReturn | undefined) {
+    if (!r) {
+      return <span className="text-[var(--muted-foreground)]">—</span>;
+    }
+    if (r.return_pct === null) {
       return (
-    <div className="bg-[var(--card)] border border-[var(--border)] rounded-xl overflow-hidden">
+        <span
+          className="text-[var(--muted-foreground)] inline-flex items-center gap-1"
+          title={t("balance.returns.partialTooltip")}
+        >
+          <AlertTriangle size={12} />
+          —
+        </span>
+      );
+    }
+    const pct = r.return_pct * 100;
+    return (
+      <span className="inline-flex items-center gap-1">
+        <span
+          className={
+            pct >= 0 ? "text-[var(--positive)]" : "text-[var(--negative)]"
+          }
+        >
+          {pct >= 0 ? "+" : ""}
+          {pct.toFixed(2)}%
+        </span>
+        {r.has_no_transfers_warning && (
+          <AlertTriangle
+            size={12}
+            className="text-amber-500"
+            aria-label={t("balance.returns.noTransfersWarning")}
+          />
+        )}
+      </span>
+    );
+  }
+
+  /**
+   * Unadjusted (simple) return = `(value_end - value_start) / value_start`
+   * — same numbers Modified Dietz already returns when no flows exist, but
+   * this column shows the simple version for ALL accounts as a side-by-side
+   * sanity check. Computed from the same `AccountReturn` payload (uses the
+   * `value_start` / `value_end` fields filled by the Rust side).
+   */
+  function renderUnadjustedCell(r: AccountReturn | undefined) {
+    if (!r || r.value_start === null || r.value_end === null) {
+      return <span className="text-[var(--muted-foreground)]">—</span>;
+    }
+    if (r.value_start === 0) {
+      return <span className="text-[var(--muted-foreground)]">—</span>;
+    }
+    const simple = ((r.value_end - r.value_start) / r.value_start) * 100;
+    return (
+      <span
+        className={
+          simple >= 0 ? "text-[var(--positive)]" : "text-[var(--negative)]"
+        }
+      >
+        {simple >= 0 ? "+" : ""}
+        {simple.toFixed(2)}%
+      </span>
+    );
+  }
+
+  return (
+    <div className="bg-[var(--card)] border border-[var(--border)] rounded-xl overflow-x-auto">
       <table className="w-full text-sm">
         <thead className="bg-[var(--muted)]/30">
           <tr>
@@ -73,7 +246,18 @@ export default function BalanceAccountsTable({
             <th className="text-right px-4 py-3 font-medium">
               {t("balance.overview.periodDelta")}
             </th>
-            {/* TODO Issue #142: 3M / 1A / depuis-création / non-ajusté columns */}
+            <th className="text-right px-4 py-3 font-medium" title={t("balance.accountsTable.return3mTooltip")}>
+              {t("balance.accountsTable.return3m")}
+            </th>
+            <th className="text-right px-4 py-3 font-medium" title={t("balance.accountsTable.return1yTooltip")}>
+              {t("balance.accountsTable.return1y")}
+            </th>
+            <th className="text-right px-4 py-3 font-medium" title={t("balance.accountsTable.sinceCreationTooltip")}>
+              {t("balance.accountsTable.sinceCreation")}
+            </th>
+            <th className="text-right px-4 py-3 font-medium" title={t("balance.accountsTable.unadjustedTooltip")}>
+              {t("balance.accountsTable.unadjusted")}
+            </th>
             <th className="text-right px-4 py-3 font-medium w-12">
               {t("balance.account.fields.actions")}
             </th>
@@ -88,6 +272,7 @@ export default function BalanceAccountsTable({
                     Math.abs(anchor.anchor_value)) *
                   100
                 : null;
+            const accReturns = returns[acc.account_id] ?? {};
             return (
               <tr
                 key={acc.account_id}
@@ -123,6 +308,26 @@ export default function BalanceAccountsTable({
                     "—"
                   )}
                 </td>
+                <td className="px-4 py-3 text-right tabular-nums">
+                  {returnsLoading && !accReturns["3M"]
+                    ? "…"
+                    : renderReturnCell(accReturns["3M"])}
+                </td>
+                <td className="px-4 py-3 text-right tabular-nums">
+                  {returnsLoading && !accReturns["1A"]
+                    ? "…"
+                    : renderReturnCell(accReturns["1A"])}
+                </td>
+                <td className="px-4 py-3 text-right tabular-nums">
+                  {returnsLoading && !accReturns["since"]
+                    ? "…"
+                    : renderReturnCell(accReturns["since"])}
+                </td>
+                <td className="px-4 py-3 text-right tabular-nums">
+                  {returnsLoading && !accReturns["1A"]
+                    ? "…"
+                    : renderUnadjustedCell(accReturns["1A"])}
+                </td>
                 <td className="px-4 py-3 text-right relative">
                   <button
                     type="button"
@@ -137,7 +342,7 @@ export default function BalanceAccountsTable({
                     <MoreVertical size={16} />
                   </button>
                   {openMenuFor === acc.account_id && (
-                    <div className="absolute right-2 top-full z-10 mt-1 bg-[var(--card)] border border-[var(--border)] rounded-lg shadow-md py-1 min-w-[160px] text-left">
+                    <div className="absolute right-2 top-full z-10 mt-1 bg-[var(--card)] border border-[var(--border)] rounded-lg shadow-md py-1 min-w-[180px] text-left">
                       <button
                         type="button"
                         disabled
@@ -146,6 +351,19 @@ export default function BalanceAccountsTable({
                       >
                         {t("balance.overview.detailAction")}
                       </button>
+                      {onLinkTransfers && (
+                        <button
+                          type="button"
+                          onClick={() => {
+                            setOpenMenuFor(null);
+                            onLinkTransfers(acc);
+                          }}
+                          className="flex items-center gap-2 w-full px-3 py-2 text-sm hover:bg-[var(--muted)]/40"
+                        >
+                          <LinkIcon size={14} />
+                          {t("balance.transfers.linkAction")}
+                        </button>
+                      )}
                       <button
                         type="button"
                         onClick={() => {

src/components/balance/BalanceEvolutionChart.tsx

@@ -22,12 +22,14 @@ import {
   Tooltip,
   ResponsiveContainer,
   Legend,
+  ReferenceLine,
 } from "recharts";
 import type {
   SnapshotTotalPoint,
   SnapshotCategoryBreakdownPoint,
 } from "../../services/balance.service";
 import type { BalanceChartMode } from "../../hooks/useBalanceOverview";
+import type { BalanceAccountTransferWithTransaction } from "../../shared/types";
 
 // Stable palette for the stacked-by-category areas. Indexed deterministically
 // by category sort order so the colour assignment stays consistent across
@@ -51,6 +53,13 @@ export interface BalanceEvolutionChartProps {
   byCategory: SnapshotCategoryBreakdownPoint[];
   /** Map category_key → translated label so the legend reads naturally. */
   categoryLabels?: Record<string, string>;
+  /**
+   * Issue #142 — every linked transfer in the visible range. Rendered as
+   * vertical `<ReferenceLine>` markers on the X axis: green for `in`
+   * (capital added), red for `out` (capital removed). The label tooltip
+   * shows the underlying transaction date + description.
+   */
+  transferMarkers?: BalanceAccountTransferWithTransaction[];
 }
 
 export default function BalanceEvolutionChart({
@@ -58,6 +67,7 @@ export default function BalanceEvolutionChart({
   totals,
   byCategory,
   categoryLabels = {},
+  transferMarkers = [],
 }: BalanceEvolutionChartProps) {
   const { t, i18n } = useTranslation();
 
@@ -114,6 +124,31 @@ export default function BalanceEvolutionChart({
   const isEmpty =
     mode === "line" ? lineData.length === 0 : stackedData.length === 0;
 
+  // Filter transfer markers to dates that are actually rendered on the X
+  // axis (categorical scale ignores unknown ticks). We don't aggregate or
+  // dedupe — the user can have several transfers on the same day across
+  // accounts; ReferenceLine tolerates duplicates fine.
+  const xAxisDates = useMemo(() => {
+    const dates = new Set<string>();
+    if (mode === "line") {
+      for (const p of lineData) dates.add(p.snapshot_date);
+    } else {
+      for (const p of stackedData) dates.add(p.snapshot_date as string);
+    }
+    return dates;
+  }, [mode, lineData, stackedData]);
+
+  const renderableMarkers = useMemo(
+    () =>
+      transferMarkers
+        .filter((m) => xAxisDates.has(m.transaction_date))
+        // Sort so 'in' (green) draws before 'out' (red) for stable z-order.
+        .sort((a, b) =>
+          a.direction === b.direction ? 0 : a.direction === "in" ? -1 : 1
+        ),
+    [transferMarkers, xAxisDates]
+  );
+
   if (isEmpty) {
     return (
       <div className="bg-[var(--card)] border border-[var(--border)] rounded-xl p-6">
@@ -168,6 +203,28 @@ export default function BalanceEvolutionChart({
               dot={{ r: 3 }}
               activeDot={{ r: 5 }}
             />
+            {renderableMarkers.map((m) => (
+              <ReferenceLine
+                key={`tm-${m.id}`}
+                x={m.transaction_date}
+                stroke={
+                  m.direction === "in" ? "var(--positive)" : "var(--negative)"
+                }
+                strokeDasharray="3 3"
+                strokeWidth={1}
+                ifOverflow="extendDomain"
+                label={{
+                  value: t(
+                    m.direction === "in"
+                      ? "balance.evolution.transferIn"
+                      : "balance.evolution.transferOut"
+                  ),
+                  position: "insideTopRight",
+                  fontSize: 9,
+                  fill: m.direction === "in" ? "var(--positive)" : "var(--negative)",
+                }}
+              />
+            ))}
           </LineChart>
         ) : (
           <AreaChart
@@ -210,6 +267,18 @@ export default function BalanceEvolutionChart({
                 name={key}
               />
             ))}
+            {renderableMarkers.map((m) => (
+              <ReferenceLine
+                key={`tm-${m.id}`}
+                x={m.transaction_date}
+                stroke={
+                  m.direction === "in" ? "var(--positive)" : "var(--negative)"
+                }
+                strokeDasharray="3 3"
+                strokeWidth={1}
+                ifOverflow="extendDomain"
+              />
+            ))}
           </AreaChart>
         )}
       </ResponsiveContainer>

src/components/balance/LinkTransfersModal.tsx

@@ -0,0 +1,410 @@
+// LinkTransfersModal — multi-select transactions and link them to a balance
+// account in one shot. Issue #142 / Bilan #4.
+//
+// Filters available:
+//   - Period (from / to ISO dates) — default: last 90 days.
+//   - Category dropdown.
+//   - Free-text search on description.
+//
+// Each row shows: date, description, amount, suggested direction
+// (auto-proposed via `suggestTransferDirection` from the signed amount,
+// can be flipped per row), and a checkbox.
+//
+// On submit, calls `linkTransfer` for every selected row in sequence and
+// reports any failures (most likely `transfer_already_linked` if the user
+// double-clicked or another tab linked them already).
+
+import { useEffect, useMemo, useState } from "react";
+import { createPortal } from "react-dom";
+import { useTranslation } from "react-i18next";
+import { X, Loader2, AlertCircle } from "lucide-react";
+import { getTransactionPage } from "../../services/transactionService";
+import {
+  linkTransfer,
+  suggestTransferDirection,
+  BalanceServiceError,
+} from "../../services/balance.service";
+import type {
+  Category,
+  TransactionRow,
+  BalanceTransferDirection,
+} from "../../shared/types";
+
+const DEFAULT_PAGE_SIZE = 100;
+
+function isoDaysAgo(days: number): string {
+  const d = new Date();
+  d.setDate(d.getDate() - days);
+  return localISO(d);
+}
+
+function localISO(d: Date): string {
+  const yy = d.getFullYear();
+  const mm = String(d.getMonth() + 1).padStart(2, "0");
+  const dd = String(d.getDate()).padStart(2, "0");
+  return `${yy}-${mm}-${dd}`;
+}
+
+export interface LinkTransfersModalProps {
+  /** Account that the selected transfers will be attached to. */
+  accountId: number;
+  accountName: string;
+  /** Full category list for the filter dropdown. */
+  categories: Category[];
+  /** Optional pre-fill date bounds (defaults to last 90 days). */
+  initialFrom?: string;
+  initialTo?: string;
+  onClose: () => void;
+  /** Fired after at least one transfer was linked (parent typically reloads). */
+  onLinked?: (linkedCount: number) => void;
+}
+
+export default function LinkTransfersModal({
+  accountId,
+  accountName,
+  categories,
+  initialFrom,
+  initialTo,
+  onClose,
+  onLinked,
+}: LinkTransfersModalProps) {
+  const { t, i18n } = useTranslation();
+
+  const [from, setFrom] = useState(initialFrom ?? isoDaysAgo(90));
+  const [to, setTo] = useState(initialTo ?? localISO(new Date()));
+  const [categoryId, setCategoryId] = useState<number | null>(null);
+  const [search, setSearch] = useState("");
+
+  const [rows, setRows] = useState<TransactionRow[]>([]);
+  const [isLoading, setIsLoading] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+
+  // Selection state: id → direction. Presence in the map = selected.
+  const [selection, setSelection] = useState<
+    Map<number, BalanceTransferDirection>
+  >(new Map());
+  const [submitting, setSubmitting] = useState(false);
+  const [submitError, setSubmitError] = useState<string | null>(null);
+
+  const fmt = useMemo(
+    () =>
+      new Intl.NumberFormat(i18n.language === "fr" ? "fr-CA" : "en-CA", {
+        style: "currency",
+        currency: "CAD",
+        maximumFractionDigits: 2,
+      }),
+    [i18n.language]
+  );
+
+  // Re-fetch whenever the filters change. Debounced via React's render cycle
+  // — typing in the search box re-runs the SQL but at < 500 rows that's fine.
+  useEffect(() => {
+    let cancelled = false;
+    async function run() {
+      setIsLoading(true);
+      setError(null);
+      try {
+        const result = await getTransactionPage(
+          {
+            search: search.trim(),
+            categoryId,
+            sourceId: null,
+            dateFrom: from || null,
+            dateTo: to || null,
+            uncategorizedOnly: false,
+          },
+          { column: "date", direction: "desc" },
+          1,
+          DEFAULT_PAGE_SIZE
+        );
+        if (!cancelled) {
+          setRows(result.rows);
+        }
+      } catch (e) {
+        if (!cancelled) {
+          setError(e instanceof Error ? e.message : String(e));
+        }
+      } finally {
+        if (!cancelled) {
+          setIsLoading(false);
+        }
+      }
+    }
+    void run();
+    return () => {
+      cancelled = true;
+    };
+  }, [from, to, categoryId, search]);
+
+  function toggleRow(row: TransactionRow) {
+    setSelection((prev) => {
+      const next = new Map(prev);
+      if (next.has(row.id)) {
+        next.delete(row.id);
+      } else {
+        next.set(row.id, suggestTransferDirection(row.amount));
+      }
+      return next;
+    });
+  }
+
+  function flipDirection(rowId: number) {
+    setSelection((prev) => {
+      const next = new Map(prev);
+      const current = next.get(rowId);
+      if (current === undefined) return prev;
+      next.set(rowId, current === "in" ? "out" : "in");
+      return next;
+    });
+  }
+
+  async function handleSubmit() {
+    if (selection.size === 0) return;
+    setSubmitting(true);
+    setSubmitError(null);
+    let linked = 0;
+    const failures: string[] = [];
+    for (const [transactionId, direction] of selection.entries()) {
+      try {
+        await linkTransfer(accountId, transactionId, direction);
+        linked += 1;
+      } catch (e) {
+        if (e instanceof BalanceServiceError) {
+          failures.push(`${transactionId}: ${t(`balance.transfers.errors.${e.code}`, { defaultValue: e.message })}`);
+        } else {
+          failures.push(`${transactionId}: ${e instanceof Error ? e.message : String(e)}`);
+        }
+      }
+    }
+    setSubmitting(false);
+    if (failures.length > 0) {
+      setSubmitError(
+        `${t("balance.transfers.modal.partialFailure", { linked, total: selection.size })} — ${failures.join("; ")}`
+      );
+    }
+    if (linked > 0) {
+      onLinked?.(linked);
+      if (failures.length === 0) {
+        onClose();
+      }
+    }
+  }
+
+  const allFiltered = rows.length;
+  const selectedCount = selection.size;
+
+  return createPortal(
+    <div
+      className="fixed inset-0 z-50 flex items-center justify-center bg-black/50"
+      onClick={onClose}
+    >
+      <div
+        className="bg-[var(--card)] border border-[var(--border)] rounded-xl shadow-xl w-full max-w-4xl max-h-[90vh] flex flex-col"
+        onClick={(e) => e.stopPropagation()}
+      >
+        <div className="flex items-center justify-between px-5 py-4 border-b border-[var(--border)]">
+          <div>
+            <h2 className="text-lg font-semibold">
+              {t("balance.transfers.modal.title", { account: accountName })}
+            </h2>
+            <p className="text-xs text-[var(--muted-foreground)] mt-0.5">
+              {t("balance.transfers.modal.subtitle")}
+            </p>
+          </div>
+          <button
+            type="button"
+            onClick={onClose}
+            className="p-1 rounded hover:bg-[var(--muted)]/40"
+            aria-label={t("common.close")}
+          >
+            <X size={18} />
+          </button>
+        </div>
+
+        <div className="px-5 py-3 border-b border-[var(--border)] grid grid-cols-1 md:grid-cols-4 gap-3">
+          <label className="text-xs">
+            <span className="block text-[var(--muted-foreground)] mb-1">
+              {t("balance.transfers.modal.from")}
+            </span>
+            <input
+              type="date"
+              value={from}
+              onChange={(e) => setFrom(e.target.value)}
+              className="w-full px-2 py-1.5 bg-[var(--background)] border border-[var(--border)] rounded text-sm"
+            />
+          </label>
+          <label className="text-xs">
+            <span className="block text-[var(--muted-foreground)] mb-1">
+              {t("balance.transfers.modal.to")}
+            </span>
+            <input
+              type="date"
+              value={to}
+              onChange={(e) => setTo(e.target.value)}
+              className="w-full px-2 py-1.5 bg-[var(--background)] border border-[var(--border)] rounded text-sm"
+            />
+          </label>
+          <label className="text-xs">
+            <span className="block text-[var(--muted-foreground)] mb-1">
+              {t("balance.transfers.modal.category")}
+            </span>
+            <select
+              value={categoryId === null ? "" : String(categoryId)}
+              onChange={(e) =>
+                setCategoryId(e.target.value === "" ? null : Number(e.target.value))
+              }
+              className="w-full px-2 py-1.5 bg-[var(--background)] border border-[var(--border)] rounded text-sm"
+            >
+              <option value="">{t("balance.transfers.modal.anyCategory")}</option>
+              {categories.map((c) => (
+                <option key={c.id} value={c.id}>
+                  {c.name}
+                </option>
+              ))}
+            </select>
+          </label>
+          <label className="text-xs">
+            <span className="block text-[var(--muted-foreground)] mb-1">
+              {t("balance.transfers.modal.search")}
+            </span>
+            <input
+              type="text"
+              value={search}
+              onChange={(e) => setSearch(e.target.value)}
+              placeholder={t("balance.transfers.modal.searchPlaceholder")}
+              className="w-full px-2 py-1.5 bg-[var(--background)] border border-[var(--border)] rounded text-sm"
+            />
+          </label>
+        </div>
+
+        <div className="flex-1 overflow-auto">
+          {isLoading ? (
+            <div className="p-8 text-center text-[var(--muted-foreground)] flex items-center justify-center gap-2">
+              <Loader2 className="animate-spin" size={16} />
+              {t("balance.transfers.modal.loading")}
+            </div>
+          ) : error ? (
+            <div className="p-8 text-center text-[var(--negative)] flex items-center justify-center gap-2">
+              <AlertCircle size={16} />
+              {error}
+            </div>
+          ) : rows.length === 0 ? (
+            <div className="p-8 text-center text-[var(--muted-foreground)] italic">
+              {t("balance.transfers.modal.noTransactions")}
+            </div>
+          ) : (
+            <table className="w-full text-sm">
+              <thead className="bg-[var(--muted)]/30 sticky top-0">
+                <tr>
+                  <th className="w-10 px-3 py-2"></th>
+                  <th className="text-left px-3 py-2 font-medium">
+                    {t("transactions.date")}
+                  </th>
+                  <th className="text-left px-3 py-2 font-medium">
+                    {t("transactions.description")}
+                  </th>
+                  <th className="text-right px-3 py-2 font-medium">
+                    {t("transactions.amount")}
+                  </th>
+                  <th className="text-center px-3 py-2 font-medium">
+                    {t("balance.transfers.modal.direction")}
+                  </th>
+                </tr>
+              </thead>
+              <tbody>
+                {rows.map((row) => {
+                  const isSelected = selection.has(row.id);
+                  const direction = selection.get(row.id) ?? suggestTransferDirection(row.amount);
+                  return (
+                    <tr
+                      key={row.id}
+                      className="border-t border-[var(--border)] hover:bg-[var(--muted)]/10"
+                    >
+                      <td className="px-3 py-2 text-center">
+                        <input
+                          type="checkbox"
+                          checked={isSelected}
+                          onChange={() => toggleRow(row)}
+                          aria-label={`select-${row.id}`}
+                        />
+                      </td>
+                      <td className="px-3 py-2 whitespace-nowrap">{row.date}</td>
+                      <td className="px-3 py-2 max-w-md truncate" title={row.description}>
+                        {row.description}
+                      </td>
+                      <td
+                        className={`px-3 py-2 text-right font-mono ${row.amount >= 0 ? "text-[var(--positive)]" : "text-[var(--negative)]"}`}
+                      >
+                        {fmt.format(row.amount)}
+                      </td>
+                      <td className="px-3 py-2 text-center">
+                        {isSelected ? (
+                          <button
+                            type="button"
+                            onClick={() => flipDirection(row.id)}
+                            className={`px-2 py-0.5 text-xs rounded font-medium ${
+                              direction === "in"
+                                ? "bg-[var(--positive)]/15 text-[var(--positive)]"
+                                : "bg-[var(--negative)]/15 text-[var(--negative)]"
+                            }`}
+                            title={t("balance.transfers.modal.toggleDirection")}
+                          >
+                            {t(`balance.transfers.direction.${direction}`)}
+                          </button>
+                        ) : (
+                          <span className="text-xs text-[var(--muted-foreground)]">
+                            {t(`balance.transfers.direction.${direction}`)}
+                          </span>
+                        )}
+                      </td>
+                    </tr>
+                  );
+                })}
+              </tbody>
+            </table>
+          )}
+        </div>
+
+        {submitError && (
+          <div className="px-5 py-2 border-t border-[var(--border)] text-xs text-[var(--negative)]">
+            {submitError}
+          </div>
+        )}
+
+        <div className="px-5 py-3 border-t border-[var(--border)] flex items-center justify-between">
+          <div className="text-xs text-[var(--muted-foreground)]">
+            {t("balance.transfers.modal.summary", {
+              selected: selectedCount,
+              total: allFiltered,
+            })}
+          </div>
+          <div className="flex gap-2">
+            <button
+              type="button"
+              onClick={onClose}
+              className="px-3 py-1.5 text-sm rounded border border-[var(--border)] hover:bg-[var(--muted)]/30"
+            >
+              {t("common.cancel")}
+            </button>
+            <button
+              type="button"
+              onClick={handleSubmit}
+              disabled={submitting || selectedCount === 0}
+              className="px-3 py-1.5 text-sm rounded bg-[var(--primary)] text-white disabled:opacity-50 disabled:cursor-not-allowed"
+            >
+              {submitting ? (
+                <span className="flex items-center gap-1.5">
+                  <Loader2 className="animate-spin" size={14} />
+                  {t("balance.transfers.modal.linking")}
+                </span>
+              ) : (
+                t("balance.transfers.modal.linkSelection", { count: selectedCount })
+              )}
+            </button>
+          </div>
+        </div>
+      </div>
+    </div>,
+    document.body
+  );
+}

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}>
+                <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/i18n/locales/en.json

@@ -253,6 +253,10 @@
         "Assign categories by clicking the category dropdown on each row",
         "Auto-categorize uses your keyword rules to categorize transactions in bulk"
       ]
+    },
+    "transferIcon": {
+      "tooltip": "Linked to a balance account",
+      "ariaLabel": "Transaction linked to a balance account"
     }
   },
   "categories": {
@@ -1638,6 +1642,56 @@
       "snapshot_priced_unit_price_required": "Unit price is required for priced accounts.",
       "snapshot_priced_value_mismatch": "The entered value does not match quantity × unit price.",
       "snapshot_simple_must_be_scalar": "A simple value must not carry quantity or price."
+    },
+    "returns": {
+      "partialTooltip": "Partial return: a snapshot is missing for the selected period.",
+      "noTransfersWarning": "No transfers tagged — performance may be skewed if contributions weren't tagged."
+    },
+    "accountsTable": {
+      "return3m": "3M",
+      "return3mTooltip": "Modified Dietz return over the last 90 days.",
+      "return1y": "1Y",
+      "return1yTooltip": "Modified Dietz return over the last 365 days.",
+      "sinceCreation": "Since inception",
+      "sinceCreationTooltip": "Modified Dietz return since the first snapshot.",
+      "unadjusted": "Unadjusted",
+      "unadjustedTooltip": "Simple return (V_end − V_start) / V_start, with no contribution weighting."
+    },
+    "transfers": {
+      "linkAction": "Link transfers",
+      "direction": {
+        "in": "In",
+        "out": "Out"
+      },
+      "modal": {
+        "title": "Link transfers to {{account}}",
+        "subtitle": "Select transactions to attribute to this balance account. The direction is suggested based on the amount sign.",
+        "from": "From",
+        "to": "To",
+        "category": "Category",
+        "anyCategory": "Any category",
+        "search": "Search",
+        "searchPlaceholder": "Keyword in description…",
+        "loading": "Loading…",
+        "noTransactions": "No transactions match the filters.",
+        "direction": "Direction",
+        "toggleDirection": "Click to flip direction",
+        "summary": "{{selected}} selected of {{total}} shown",
+        "linkSelection": "Link {{count}} transaction(s)",
+        "linking": "Linking…",
+        "partialFailure": "{{linked}}/{{total}} linked successfully"
+      },
+      "errors": {
+        "transfer_direction_invalid": "Invalid transfer direction (expected in/out).",
+        "transfer_already_linked": "This transaction is already linked to this account.",
+        "transfer_not_linked": "This transaction is not linked to this account.",
+        "transfer_active_profile_unknown": "No active profile — cannot compute return.",
+        "transaction_linked_to_balance_account": "This transaction is linked to balance account {{account}} — unlink it before deleting."
+      }
+    },
+    "evolution": {
+      "transferIn": "In",
+      "transferOut": "Out"
     }
   }
 }

src/i18n/locales/fr.json

@@ -253,6 +253,10 @@
         "Assignez une catégorie via le menu déroulant sur chaque ligne",
         "L'auto-catégorisation utilise vos règles de mots-clés pour catégoriser en masse"
       ]
+    },
+    "transferIcon": {
+      "tooltip": "Liée à un compte de bilan",
+      "ariaLabel": "Transaction liée à un compte de bilan"
     }
   },
   "categories": {
@@ -1638,6 +1642,56 @@
       "snapshot_priced_unit_price_required": "Le prix unitaire est obligatoire pour les comptes cotés.",
       "snapshot_priced_value_mismatch": "La valeur saisie ne correspond pas à quantité × prix unitaire.",
       "snapshot_simple_must_be_scalar": "Une valeur simple ne doit pas comporter de quantité ou de prix."
+    },
+    "returns": {
+      "partialTooltip": "Rendement partiel : un snapshot manque pour calculer la performance sur cette période.",
+      "noTransfersWarning": "Aucun transfert lié — la performance peut être faussée si des apports n'ont pas été tagués."
+    },
+    "accountsTable": {
+      "return3m": "3M",
+      "return3mTooltip": "Rendement Modified Dietz sur les 90 derniers jours.",
+      "return1y": "1A",
+      "return1yTooltip": "Rendement Modified Dietz sur les 365 derniers jours.",
+      "sinceCreation": "Depuis création",
+      "sinceCreationTooltip": "Rendement Modified Dietz depuis le premier snapshot.",
+      "unadjusted": "Non ajusté",
+      "unadjustedTooltip": "Rendement simple (V_fin − V_début) / V_début, sans pondération des apports."
+    },
+    "transfers": {
+      "linkAction": "Lier transferts",
+      "direction": {
+        "in": "Entrée",
+        "out": "Sortie"
+      },
+      "modal": {
+        "title": "Lier des transferts à {{account}}",
+        "subtitle": "Sélectionnez les transactions à attribuer à ce compte de bilan. La direction est proposée d'après le signe du montant.",
+        "from": "Du",
+        "to": "Au",
+        "category": "Catégorie",
+        "anyCategory": "Toutes les catégories",
+        "search": "Rechercher",
+        "searchPlaceholder": "Mot-clé dans la description…",
+        "loading": "Chargement…",
+        "noTransactions": "Aucune transaction ne correspond aux filtres.",
+        "direction": "Sens",
+        "toggleDirection": "Cliquer pour inverser le sens",
+        "summary": "{{selected}} sélectionnée(s) sur {{total}} affichée(s)",
+        "linkSelection": "Lier {{count}} transaction(s)",
+        "linking": "Liaison…",
+        "partialFailure": "{{linked}}/{{total}} liées avec succès"
+      },
+      "errors": {
+        "transfer_direction_invalid": "Direction de transfert invalide (in/out attendu).",
+        "transfer_already_linked": "Cette transaction est déjà liée à ce compte.",
+        "transfer_not_linked": "Cette transaction n'est pas liée à ce compte.",
+        "transfer_active_profile_unknown": "Aucun profil actif — impossible de calculer le rendement.",
+        "transaction_linked_to_balance_account": "Cette transaction est liée au compte de bilan {{account}} — déliez-la avant de supprimer."
+      }
+    },
+    "evolution": {
+      "transferIn": "Entrée",
+      "transferOut": "Sortie"
     }
   }
 }

src/pages/BalancePage.tsx

@@ -11,7 +11,7 @@
 // (Modified Dietz) are deferred to Issue #142 — the accounts table reserves
 // columns with a TODO comment.
 
-import { useMemo } from "react";
+import { useEffect, useMemo, useState } from "react";
 import { useTranslation } from "react-i18next";
 import { Wallet } from "lucide-react";
 import {
@@ -19,10 +19,17 @@ import {
   type BalancePeriod,
   type BalanceChartMode,
 } from "../hooks/useBalanceOverview";
-import { archiveBalanceAccount } from "../services/balance.service";
+import {
+  archiveBalanceAccount,
+  listAccountTransfers,
+  type AccountLatestSnapshot,
+} from "../services/balance.service";
+import { getAllCategories } from "../services/transactionService";
+import type { Category, BalanceAccountTransferWithTransaction } from "../shared/types";
 import BalanceOverviewCard from "../components/balance/BalanceOverviewCard";
 import BalanceEvolutionChart from "../components/balance/BalanceEvolutionChart";
 import BalanceAccountsTable from "../components/balance/BalanceAccountsTable";
+import LinkTransfersModal from "../components/balance/LinkTransfersModal";
 
 const PERIOD_OPTIONS: BalancePeriod[] = ["3M", "6M", "1A", "3A", "all"];
 
@@ -30,6 +37,58 @@ export default function BalancePage() {
   const { t } = useTranslation();
   const { state, setPeriod, setChartMode, reload } = useBalanceOverview();
 
+  // Issue #142 — link-transfers modal state. Categories list is loaded once
+  // on mount (used by the modal's filter dropdown).
+  const [linkTarget, setLinkTarget] = useState<AccountLatestSnapshot | null>(
+    null
+  );
+  const [categories, setCategories] = useState<Category[]>([]);
+  const [transfersByAccount, setTransfersByAccount] = useState<
+    Map<number, BalanceAccountTransferWithTransaction[]>
+  >(new Map());
+
+  useEffect(() => {
+    void getAllCategories().then(setCategories).catch(() => setCategories([]));
+  }, []);
+
+  // Refresh per-account transfer lists used by the chart markers. Keyed by
+  // account_id → [transfers]. Used by `BalanceEvolutionChart` to plot
+  // ReferenceLine markers (green for in, red for out).
+  useEffect(() => {
+    let cancelled = false;
+    async function run() {
+      const map = new Map<number, BalanceAccountTransferWithTransaction[]>();
+      await Promise.all(
+        state.accountsLatest.map(async (acc) => {
+          try {
+            const list = await listAccountTransfers(acc.account_id);
+            map.set(acc.account_id, list);
+          } catch {
+            map.set(acc.account_id, []);
+          }
+        })
+      );
+      if (!cancelled) setTransfersByAccount(map);
+    }
+    void run();
+    return () => {
+      cancelled = true;
+    };
+  }, [state.accountsLatest]);
+
+  const allTransferMarkers = useMemo(() => {
+    const flat: BalanceAccountTransferWithTransaction[] = [];
+    for (const list of transfersByAccount.values()) flat.push(...list);
+    return flat;
+  }, [transfersByAccount]);
+
+  // Earliest snapshot date in the dataset, used to anchor the "depuis
+  // création" Modified Dietz horizon in the accounts table.
+  const earliestSnapshotDate = useMemo(() => {
+    if (state.evolutionTotals.length === 0) return null;
+    return state.evolutionTotals[0].snapshot_date;
+  }, [state.evolutionTotals]);
+
   // Build a category_key → translated label map from the accounts payload —
   // the byCategory series is keyed by `key`, not by id, and the same
   // taxonomy is already loaded with `accountsLatest` joins.
@@ -123,6 +182,7 @@ export default function BalancePage() {
           totals={state.evolutionTotals}
           byCategory={state.evolutionByCategory}
           categoryLabels={categoryLabels}
+          transferMarkers={allTransferMarkers}
         />
 
         <div>
@@ -132,10 +192,24 @@ export default function BalancePage() {
           <BalanceAccountsTable
             accounts={state.accountsLatest}
             periodAnchor={state.accountsPeriodAnchor}
+            sinceCreationDate={earliestSnapshotDate}
             onArchiveAccount={(acc) => handleArchiveAccount(acc.account_id)}
+            onLinkTransfers={(acc) => setLinkTarget(acc)}
           />
         </div>
       </div>
+
+      {linkTarget && (
+        <LinkTransfersModal
+          accountId={linkTarget.account_id}
+          accountName={linkTarget.account_name}
+          categories={categories}
+          onClose={() => setLinkTarget(null)}
+          onLinked={() => {
+            void reload();
+          }}
+        />
+      )}
     </div>
   );
 }

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/balance.service.test.ts

@@ -4,7 +4,17 @@ vi.mock("./db", () => ({
   getDb: vi.fn(),
 }));
 
+vi.mock("@tauri-apps/api/core", () => ({
+  invoke: vi.fn(),
+}));
+
+vi.mock("./profileService", () => ({
+  loadProfiles: vi.fn(),
+}));
+
 import { getDb } from "./db";
+import { invoke } from "@tauri-apps/api/core";
+import { loadProfiles } from "./profileService";
 import {
   listBalanceCategories,
   createBalanceCategory,
@@ -30,6 +40,14 @@ import {
   getSnapshotTotalsByCategoryAndDate,
   getAccountsLatestSnapshot,
   getAccountsPeriodAnchor,
+  computeAccountReturn,
+  linkTransfer,
+  unlinkTransfer,
+  listAccountTransfers,
+  listLinkedTransactionIds,
+  listAllLinkedTransfersForTooltip,
+  isLinkedTransactionFkError,
+  suggestTransferDirection,
 } from "./balance.service";
 
 const mockSelect = vi.fn();
@@ -974,3 +992,215 @@ describe("getAccountsPeriodAnchor", () => {
     expect(sql).not.toMatch(/WHERE\s+s\.snapshot_date/);
   });
 });
+
+// -----------------------------------------------------------------------------
+// Returns + transfers (Issue #142)
+// -----------------------------------------------------------------------------
+
+describe("computeAccountReturn", () => {
+  beforeEach(() => {
+    vi.mocked(loadProfiles).mockReset();
+    vi.mocked(invoke).mockReset();
+  });
+
+  it("invokes the Tauri command with the active profile's db_filename", async () => {
+    vi.mocked(loadProfiles).mockResolvedValueOnce({
+      active_profile_id: "p1",
+      profiles: [
+        {
+          id: "p1",
+          name: "Max",
+          color: "#fff",
+          pin_hash: null,
+          db_filename: "max.db",
+          created_at: "0",
+        },
+      ],
+    });
+    const fakeReturn = {
+      value_start: 1000,
+      value_end: 1100,
+      net_contributions: 0,
+      return_pct: 0.1,
+      annualized_pct: 0.42,
+      is_partial: false,
+      has_no_transfers_warning: true,
+    };
+    vi.mocked(invoke).mockResolvedValueOnce(fakeReturn);
+
+    const out = await computeAccountReturn(7, "2026-01-01", "2026-04-01");
+
+    expect(out).toEqual(fakeReturn);
+    expect(invoke).toHaveBeenCalledWith("compute_account_return", {
+      dbFilename: "max.db",
+      accountId: 7,
+      periodStart: "2026-01-01",
+      periodEnd: "2026-04-01",
+    });
+  });
+
+  it("rejects malformed period dates before invoking the command", async () => {
+    vi.mocked(loadProfiles).mockResolvedValueOnce({
+      active_profile_id: "p1",
+      profiles: [
+        {
+          id: "p1",
+          name: "Max",
+          color: "#fff",
+          pin_hash: null,
+          db_filename: "max.db",
+          created_at: "0",
+        },
+      ],
+    });
+    await expect(
+      computeAccountReturn(1, "not-a-date", "2026-04-01")
+    ).rejects.toBeInstanceOf(BalanceServiceError);
+    expect(invoke).not.toHaveBeenCalled();
+  });
+
+  it("throws transfer_active_profile_unknown when no active profile resolves", async () => {
+    vi.mocked(loadProfiles).mockResolvedValueOnce({
+      active_profile_id: "missing",
+      profiles: [],
+    });
+    await expect(
+      computeAccountReturn(1, "2026-01-01", "2026-04-01")
+    ).rejects.toMatchObject({ code: "transfer_active_profile_unknown" });
+    expect(invoke).not.toHaveBeenCalled();
+  });
+});
+
+describe("suggestTransferDirection", () => {
+  it("maps negative bank amounts to 'in' (money left bank → arrived in account)", () => {
+    expect(suggestTransferDirection(-100)).toBe("in");
+  });
+  it("maps positive bank amounts to 'out' (money came back from account)", () => {
+    expect(suggestTransferDirection(50)).toBe("out");
+  });
+  it("treats zero as 'out' as a deterministic fallback", () => {
+    expect(suggestTransferDirection(0)).toBe("out");
+  });
+});
+
+describe("linkTransfer", () => {
+  it("rejects an invalid direction without touching the DB", async () => {
+    await expect(
+      // @ts-expect-error testing runtime guard
+      linkTransfer(1, 2, "sideways")
+    ).rejects.toBeInstanceOf(BalanceServiceError);
+    expect(mockExecute).not.toHaveBeenCalled();
+  });
+
+  it("guards against duplicate links with a typed error", async () => {
+    mockSelect.mockResolvedValueOnce([{ id: 5 }]);
+    await expect(linkTransfer(1, 2, "in")).rejects.toMatchObject({
+      code: "transfer_already_linked",
+    });
+    expect(mockExecute).not.toHaveBeenCalled();
+  });
+
+  it("inserts and returns the new transfer id", async () => {
+    mockSelect.mockResolvedValueOnce([]);
+    mockExecute.mockResolvedValueOnce({ lastInsertId: 99, rowsAffected: 1 });
+    const id = await linkTransfer(1, 2, "out", "  manual ");
+    expect(id).toBe(99);
+    const sql = mockExecute.mock.calls[0][0] as string;
+    expect(sql).toContain("INSERT INTO balance_account_transfers");
+    expect(mockExecute.mock.calls[0][1]).toEqual([1, 2, "out", "manual"]);
+  });
+
+  it("normalizes empty notes to null", async () => {
+    mockSelect.mockResolvedValueOnce([]);
+    mockExecute.mockResolvedValueOnce({ lastInsertId: 1, rowsAffected: 1 });
+    await linkTransfer(1, 2, "in", "   ");
+    expect(mockExecute.mock.calls[0][1][3]).toBeNull();
+  });
+});
+
+describe("unlinkTransfer", () => {
+  it("throws transfer_not_linked when no row was deleted", async () => {
+    mockExecute.mockResolvedValueOnce({ lastInsertId: 0, rowsAffected: 0 });
+    await expect(unlinkTransfer(1, 2)).rejects.toMatchObject({
+      code: "transfer_not_linked",
+    });
+  });
+
+  it("succeeds when one row is deleted", async () => {
+    mockExecute.mockResolvedValueOnce({ lastInsertId: 0, rowsAffected: 1 });
+    await expect(unlinkTransfer(1, 2)).resolves.toBeUndefined();
+    expect(mockExecute.mock.calls[0][1]).toEqual([1, 2]);
+  });
+});
+
+describe("listAccountTransfers", () => {
+  it("filters by account_id only when no date range is supplied", async () => {
+    mockSelect.mockResolvedValueOnce([]);
+    await listAccountTransfers(7);
+    const sql = mockSelect.mock.calls[0][0] as string;
+    expect(sql).toContain("FROM balance_account_transfers bat");
+    expect(sql).toContain("JOIN transactions t");
+    expect(sql).toContain("JOIN balance_accounts a");
+    expect(sql).toContain("WHERE bat.account_id = $1");
+    expect(sql).not.toContain("t.date >=");
+    expect(mockSelect.mock.calls[0][1]).toEqual([7]);
+  });
+
+  it("appends inclusive date bounds when supplied", async () => {
+    mockSelect.mockResolvedValueOnce([]);
+    await listAccountTransfers(7, { from: "2026-01-01", to: "2026-04-01" });
+    const sql = mockSelect.mock.calls[0][0] as string;
+    expect(sql).toContain("t.date >=");
+    expect(sql).toContain("t.date <=");
+    expect(mockSelect.mock.calls[0][1]).toEqual([7, "2026-01-01", "2026-04-01"]);
+  });
+});
+
+describe("listLinkedTransactionIds", () => {
+  it("returns a Set of transaction ids", async () => {
+    mockSelect.mockResolvedValueOnce([
+      { transaction_id: 5 },
+      { transaction_id: 12 },
+    ]);
+    const ids = await listLinkedTransactionIds();
+    expect(ids).toBeInstanceOf(Set);
+    expect(ids.has(5)).toBe(true);
+    expect(ids.has(12)).toBe(true);
+    expect(ids.size).toBe(2);
+  });
+});
+
+describe("listAllLinkedTransfersForTooltip", () => {
+  it("groups multiple links per transaction id", async () => {
+    mockSelect.mockResolvedValueOnce([
+      { transaction_id: 1, account_id: 10, account_name: "TFSA", direction: "in" },
+      { transaction_id: 1, account_id: 20, account_name: "RRSP", direction: "out" },
+      { transaction_id: 2, account_id: 10, account_name: "TFSA", direction: "in" },
+    ]);
+    const map = await listAllLinkedTransfersForTooltip();
+    expect(map.get(1)).toHaveLength(2);
+    expect(map.get(2)).toHaveLength(1);
+    expect(map.get(1)?.[0].account_name).toBe("TFSA");
+  });
+});
+
+describe("isLinkedTransactionFkError", () => {
+  it("matches the canonical SQLite FK error text", () => {
+    expect(
+      isLinkedTransactionFkError(new Error("FOREIGN KEY constraint failed"))
+    ).toBe(true);
+  });
+
+  it("matches the wrapped tauri-plugin-sql variant", () => {
+    expect(
+      isLinkedTransactionFkError(
+        new Error("code: 787, message: FOREIGN KEY constraint failed")
+      )
+    ).toBe(true);
+  });
+
+  it("does not match unrelated errors", () => {
+    expect(isLinkedTransactionFkError(new Error("something else"))).toBe(false);
+    expect(isLinkedTransactionFkError(undefined)).toBe(false);
+  });
+});

src/services/balance.service.ts

@@ -9,14 +9,19 @@
 // filesystem / OAuth / license / profile work and the future Modified Dietz
 // + price-fetch work in Issue #142.
 
+import { invoke } from "@tauri-apps/api/core";
 import { getDb } from "./db";
+import { loadProfiles } from "./profileService";
 import type {
+  AccountReturn,
   BalanceAccount,
+  BalanceAccountTransferWithTransaction,
   BalanceAccountWithCategory,
   BalanceCategory,
   BalanceCategoryKind,
   BalanceSnapshot,
   BalanceSnapshotLine,
+  BalanceTransferDirection,
 } from "../shared/types";
 import { BALANCE_CURRENCY_CAD } from "../shared/types";
 
@@ -40,7 +45,13 @@ export type BalanceErrorCode =
   | "snapshot_priced_quantity_required"
   | "snapshot_priced_unit_price_required"
   | "snapshot_priced_value_mismatch"
-  | "snapshot_simple_must_be_scalar";
+  | "snapshot_simple_must_be_scalar"
+  // Issue #142 — transfers + returns
+  | "transfer_direction_invalid"
+  | "transfer_already_linked"
+  | "transfer_not_linked"
+  | "transfer_active_profile_unknown"
+  | "transaction_linked_to_balance_account";
 
 export class BalanceServiceError extends Error {
   readonly code: BalanceErrorCode;
@@ -955,3 +966,251 @@ export async function getAccountsPeriodAnchor(
     params
   );
 }
+
+// -----------------------------------------------------------------------------
+// Returns + transfers (Issue #142 / Bilan #4)
+// -----------------------------------------------------------------------------
+//
+// Two distinct surface areas:
+//
+// (1) `computeAccountReturn` — Modified Dietz return for one account over a
+//     period. Lives on the Rust side (`compute_account_return` Tauri command)
+//     because it needs to JOIN snapshots + transfers + transactions and
+//     apply day-precision weighting in a single short-lived connection. The
+//     TS shim resolves the active profile's `db_filename` from `loadProfiles`
+//     and forwards it to the command.
+//
+// (2) Transfer linking helpers — `linkTransfer`, `unlinkTransfer`,
+//     `listAccountTransfers`. Plain CRUD on `balance_account_transfers` via
+//     `getDb()`, same pattern as the rest of this file.
+
+/**
+ * Compute the Modified Dietz return for `accountId` over the period
+ * `[periodStart, periodEnd]` (both ISO `YYYY-MM-DD`). Returns the typed
+ * `AccountReturn` shape — see `src/shared/types/index.ts`.
+ *
+ * Resolves the active profile's `db_filename` from `loadProfiles()` so the
+ * caller doesn't have to thread it through every screen. Throws
+ * `transfer_active_profile_unknown` if no active profile is set (should be
+ * impossible in normal app flow, but the service guards it anyway).
+ */
+export async function computeAccountReturn(
+  accountId: number,
+  periodStart: string,
+  periodEnd: string
+): Promise<AccountReturn> {
+  const startNorm = normalizeSnapshotDate(periodStart);
+  const endNorm = normalizeSnapshotDate(periodEnd);
+  const config = await loadProfiles();
+  const profile = config.profiles.find(
+    (p) => p.id === config.active_profile_id
+  );
+  if (!profile) {
+    throw new BalanceServiceError(
+      "transfer_active_profile_unknown",
+      "No active profile is set"
+    );
+  }
+  return invoke<AccountReturn>("compute_account_return", {
+    dbFilename: profile.db_filename,
+    accountId,
+    periodStart: startNorm,
+    periodEnd: endNorm,
+  });
+}
+
+function normalizeDirection(
+  direction: BalanceTransferDirection
+): BalanceTransferDirection {
+  if (direction !== "in" && direction !== "out") {
+    throw new BalanceServiceError(
+      "transfer_direction_invalid",
+      `Invalid transfer direction: ${direction}`
+    );
+  }
+  return direction;
+}
+
+/**
+ * Suggested direction for an unlinked transaction based on its signed amount.
+ * Pure helper so the `LinkTransfersModal` UI can pre-fill the direction
+ * column without round-tripping. Convention: in this codebase, expense
+ * transactions are stored with negative amounts (money leaving the bank).
+ * From the *balance account's* perspective:
+ *   - negative bank amount = money left the bank → arrived at the balance
+ *     account = `in`
+ *   - positive bank amount = money entered the bank = the balance account
+ *     gave it back = `out`
+ */
+export function suggestTransferDirection(
+  transactionAmount: number
+): BalanceTransferDirection {
+  return transactionAmount < 0 ? "in" : "out";
+}
+
+/**
+ * Link a transaction to a balance account with the given direction.
+ * Throws `transfer_already_linked` if the (transaction, account) pair is
+ * already in the table (UNIQUE constraint).
+ */
+export async function linkTransfer(
+  accountId: number,
+  transactionId: number,
+  direction: BalanceTransferDirection,
+  notes?: string | null
+): Promise<number> {
+  const dir = normalizeDirection(direction);
+  const trimmedNotes = notes ? notes.trim() || null : null;
+  const db = await getDb();
+  // Guard duplicate link with a SELECT — keeps the error typed instead of a
+  // raw "UNIQUE constraint failed" string.
+  const existing = await db.select<{ id: number }[]>(
+    `SELECT id FROM balance_account_transfers
+      WHERE account_id = $1 AND transaction_id = $2`,
+    [accountId, transactionId]
+  );
+  if (existing.length > 0) {
+    throw new BalanceServiceError(
+      "transfer_already_linked",
+      `Transaction ${transactionId} is already linked to account ${accountId}`
+    );
+  }
+  const result = await db.execute(
+    `INSERT INTO balance_account_transfers (account_id, transaction_id, direction, notes)
+     VALUES ($1, $2, $3, $4)`,
+    [accountId, transactionId, dir, trimmedNotes]
+  );
+  return result.lastInsertId as number;
+}
+
+/**
+ * Unlink a transaction from an account. Throws `transfer_not_linked` if the
+ * pair isn't in the table — keeps callers from silently no-op'ing on a stale
+ * UI state.
+ */
+export async function unlinkTransfer(
+  accountId: number,
+  transactionId: number
+): Promise<void> {
+  const db = await getDb();
+  const result = await db.execute(
+    `DELETE FROM balance_account_transfers
+      WHERE account_id = $1 AND transaction_id = $2`,
+    [accountId, transactionId]
+  );
+  if (result.rowsAffected === 0) {
+    throw new BalanceServiceError(
+      "transfer_not_linked",
+      `No transfer linked transaction ${transactionId} to account ${accountId}`
+    );
+  }
+}
+
+/**
+ * List every linked transfer for `accountId`, joined with the transaction
+ * table for date/description/amount. Optional `dateRange` (ISO YYYY-MM-DD,
+ * inclusive both sides) filters by `transactions.date`.
+ */
+export async function listAccountTransfers(
+  accountId: number,
+  dateRange?: { from?: string; to?: string }
+): Promise<BalanceAccountTransferWithTransaction[]> {
+  const params: unknown[] = [accountId];
+  const conditions: string[] = ["bat.account_id = $1"];
+  if (dateRange?.from) {
+    conditions.push(`t.date >= $${params.length + 1}`);
+    params.push(normalizeSnapshotDate(dateRange.from));
+  }
+  if (dateRange?.to) {
+    conditions.push(`t.date <= $${params.length + 1}`);
+    params.push(normalizeSnapshotDate(dateRange.to));
+  }
+  const where = `WHERE ${conditions.join(" AND ")}`;
+  const db = await getDb();
+  return db.select<BalanceAccountTransferWithTransaction[]>(
+    `SELECT bat.id AS id,
+            bat.account_id AS account_id,
+            bat.transaction_id AS transaction_id,
+            bat.direction AS direction,
+            bat.notes AS notes,
+            bat.created_at AS created_at,
+            t.date AS transaction_date,
+            t.description AS transaction_description,
+            t.amount AS transaction_amount,
+            a.name AS account_name
+       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}
+       ORDER BY t.date DESC, bat.id DESC`,
+    params
+  );
+}
+
+/**
+ * Returns the set of `transaction_id`s currently linked to ANY balance
+ * account. Used by the transactions table to render the transfer icon
+ * without an N+1 query — the caller receives the full set once per render
+ * and does an in-memory `.has(id)` lookup. Cheap on real-world scales
+ * (typically < 1000 linked transfers per profile).
+ */
+export async function listLinkedTransactionIds(): Promise<Set<number>> {
+  const db = await getDb();
+  const rows = await db.select<{ transaction_id: number }[]>(
+    `SELECT DISTINCT transaction_id FROM balance_account_transfers`
+  );
+  return new Set(rows.map((r) => r.transaction_id));
+}
+
+/**
+ * Returns transfer info keyed by `transaction_id` for tooltip rendering in
+ * the transactions table. Each transaction maps to an array because a
+ * single transaction *could* be linked to several accounts in principle
+ * (the UNIQUE is on the pair, not on transaction alone).
+ */
+export interface LinkedTransferTooltipRow {
+  transaction_id: number;
+  account_id: number;
+  account_name: string;
+  direction: BalanceTransferDirection;
+}
+
+export async function listAllLinkedTransfersForTooltip(): Promise<
+  Map<number, LinkedTransferTooltipRow[]>
+> {
+  const db = await getDb();
+  const rows = await db.select<LinkedTransferTooltipRow[]>(
+    `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
+       ORDER BY bat.transaction_id`
+  );
+  const map = new Map<number, LinkedTransferTooltipRow[]>();
+  for (const r of rows) {
+    const list = map.get(r.transaction_id) ?? [];
+    list.push(r);
+    map.set(r.transaction_id, list);
+  }
+  return map;
+}
+
+/**
+ * Detect whether the SQL error returned by `tauri-plugin-sql` is a FK
+ * RESTRICT violation from `balance_account_transfers.transaction_id`. The
+ * plugin surfaces the SQLite error message verbatim, so we match on the
+ * string. Used by `transactionService.deleteTransaction` to surface a
+ * clean i18n error instead of leaking the raw SQL.
+ */
+export function isLinkedTransactionFkError(error: unknown): boolean {
+  const msg = error instanceof Error ? error.message : String(error ?? "");
+  // SQLite FK error messages look like:
+  //   "FOREIGN KEY constraint failed"
+  // or
+  //   "code: 787, message: FOREIGN KEY constraint failed"
+  // Both contain the canonical "FOREIGN KEY constraint failed" substring.
+  return /FOREIGN KEY constraint failed/i.test(msg);
+}
+

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(
+  // 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;

src/shared/types/index.ts

@@ -630,3 +630,57 @@ export interface BalanceSnapshotLine {
   created_at: string;
   updated_at: string;
 }
+
+// Account transfers — added Issue #142 (Bilan #4). Links a transaction to a
+// balance account so the Modified Dietz return calculator can separate
+// contributions from gains. Direction follows the account's perspective:
+//   'in'  = capital added (deposit / buy)
+//   'out' = capital removed (withdrawal / sell)
+// `transaction_id` ON DELETE RESTRICT — preserves reproducibility of past
+// returns, the UI must force the user to unlink before deleting the
+// underlying transaction.
+export type BalanceTransferDirection = "in" | "out";
+
+export interface BalanceAccountTransfer {
+  id: number;
+  account_id: number;
+  transaction_id: number;
+  direction: BalanceTransferDirection;
+  notes: string | null;
+  created_at: string;
+}
+
+/** Joined view used by LinkTransfersModal + transaction icon lookup. */
+export interface BalanceAccountTransferWithTransaction
+  extends BalanceAccountTransfer {
+  transaction_date: string;
+  transaction_description: string;
+  transaction_amount: number;
+  account_name: string;
+}
+
+/**
+ * Modified Dietz return for one account over a period.
+ * Mirrors the Rust struct in `src-tauri/src/commands/return_calculator.rs`.
+ *
+ *   - `value_start` / `value_end`: latest snapshot value ≤ each endpoint, or
+ *     null when no snapshot exists.
+ *   - `net_contributions`: signed sum of cash flows in the period.
+ *   - `return_pct`: Modified Dietz return (0.05 = +5%); null if either
+ *     endpoint is missing or denominator is non-positive.
+ *   - `annualized_pct`: `(1 + R)^(365/T) - 1`; null for zero-length periods
+ *     or whenever `return_pct` is null.
+ *   - `is_partial`: true when one endpoint snapshot is missing.
+ *   - `has_no_transfers_warning`: true when no transfers were tagged in the
+ *     period — return collapses to simple `(V_end - V_start) / V_start` and
+ *     the UI surfaces a warning so the user can verify nothing was forgotten.
+ */
+export interface AccountReturn {
+  value_start: number | null;
+  value_end: number | null;
+  net_contributions: number;
+  return_pct: number | null;
+  annualized_pct: number | null;
+  is_partial: boolean;
+  has_no_transfers_warning: boolean;
+}