feat(balance): add migration v9 schema (5 tables, 7 indexes, seed)

Adds the SQL foundation for the Bilan (balance sheet) feature:

- 5 new tables: balance_categories, balance_accounts, balance_snapshots,
  balance_snapshot_lines, balance_account_transfers
- 7 indexes (category, active partial, snapshot, accounts x2, transaction,
  snapshot_date)
- Seed of 7 standard categories (5 simple + 2 priced) marked is_seed=1
- CHECK(currency = 'CAD') on balance_accounts (MVP — v2 lifts the constraint
  with a multi-currency rate table)
- CHECK kind invariants on balance_snapshot_lines (quantity/unit_price both
  NULL OR both NOT NULL)
- FK transaction_id ON DELETE RESTRICT to preserve reproducibility of
  Modified Dietz returns calculated on past periods

Migration v9 is added inline to the lib.rs Vec<Migration> via a new
constant database::BALANCE_SCHEMA backed by balance_schema.sql. The
schema is mirrored in consolidated_schema.sql so brand-new profiles
get the feature preinstalled without replaying v9.

13 new co-located rusqlite tests validate the migration on a fresh
in-memory DB: schema applies cleanly, 7 categories seeded with correct
kinds, CHECK rejects invalid currency/kind/direction, UNIQUE rejects
duplicate snapshot_date / (snapshot_id,account_id) / (transaction_id,
account_id), FK CASCADE on snapshot delete, FK RESTRICT on transaction
delete and on category with linked accounts, seed idempotent on replay.

Refs #138

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

src-tauri/src/database/balance_schema.sql

@@ -0,0 +1,153 @@
+-- Balance sheet schema (Bilan) — Migration v9
+-- Created: 2026-04-25
+-- Issue: #138 (Bilan #1a — Schema migration + balance.service skeleton + AccountsPage)
+--
+-- Adds 5 tables, 7 indexes, and seeds 7 standard categories (5 simple + 2 priced).
+-- Conventions aligned with consolidated_schema.sql:
+--   - INTEGER PRIMARY KEY AUTOINCREMENT
+--   - REAL for monetary amounts (matches transactions.amount)
+--   - snake_case
+--   - FK with explicit ON DELETE policies
+--   - is_* INTEGER NOT NULL DEFAULT for booleans
+--   - DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP for timestamps
+--
+-- MVP constraints (decisions-log + spec-decisions-bilan.md):
+--   - balance_accounts.currency hardcoded to 'CAD' via CHECK — v2 will lift this
+--   - balance_account_transfers.transaction_id ON DELETE RESTRICT (preserves
+--     reproducibility of Modified Dietz returns calculated on past periods)
+--   - balance_snapshot_lines kind invariants: (quantity, unit_price) both NULL
+--     (simple kind) OR both NOT NULL (priced kind)
+
+
+-- =========================================================================
+-- balance_categories — taxonomy of asset types
+-- =========================================================================
+-- Seeded with 7 standard categories (is_seed = 1). Users can add custom
+-- categories with their own kind ('simple' or 'priced'). Seeded categories
+-- can be renamed but never deleted.
+CREATE TABLE IF NOT EXISTS balance_categories (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    key TEXT NOT NULL UNIQUE,                    -- 'cash', 'tfsa', 'rrsp', 'fund', 'stock', 'crypto', 'other'
+    i18n_key TEXT NOT NULL,                      -- 'balance.category.cash', etc.
+    kind TEXT NOT NULL CHECK(kind IN ('simple','priced')),
+    sort_order INTEGER NOT NULL DEFAULT 0,
+    is_active INTEGER NOT NULL DEFAULT 1,
+    is_seed INTEGER NOT NULL DEFAULT 0
+);
+
+
+-- =========================================================================
+-- balance_accounts — user's specific holdings
+-- =========================================================================
+-- A "TFSA at Wealthsimple", a "BTC in Ledger", etc.
+-- For priced categories, `symbol` identifies the security/coin.
+-- For simple categories, `symbol` is NULL.
+-- MVP: currency hardcoded to 'CAD' — v2 lifts the CHECK and adds a rate table.
+CREATE TABLE IF NOT EXISTS balance_accounts (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    balance_category_id INTEGER NOT NULL,
+    name TEXT NOT NULL,
+    symbol TEXT,
+    currency TEXT NOT NULL DEFAULT 'CAD' CHECK(currency = 'CAD'),
+    notes TEXT,
+    is_active INTEGER NOT NULL DEFAULT 1,
+    archived_at DATETIME,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    FOREIGN KEY (balance_category_id) REFERENCES balance_categories(id) ON DELETE RESTRICT
+);
+
+
+-- =========================================================================
+-- balance_snapshots — point-in-time captures
+-- =========================================================================
+-- One snapshot per `snapshot_date` (UNIQUE). Editing a snapshot = updating
+-- its lines, not creating a duplicate.
+CREATE TABLE IF NOT EXISTS balance_snapshots (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    snapshot_date DATE NOT NULL UNIQUE,
+    notes TEXT,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+
+-- =========================================================================
+-- balance_snapshot_lines — one row per (snapshot, account)
+-- =========================================================================
+-- Storage shape:
+--   - simple kind: value is set, quantity/unit_price are NULL
+--   - priced kind: quantity + unit_price are set, value = quantity * unit_price
+-- Stored denormalized (value always set, even for priced rows) so reports
+-- are reproducible without re-fetching prices and the user can override a
+-- fetched price.
+-- The CHECK enforces kind invariants at SQL level for direct-write safety.
+CREATE TABLE IF NOT EXISTS balance_snapshot_lines (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    snapshot_id INTEGER NOT NULL,
+    account_id INTEGER NOT NULL,
+    quantity REAL,
+    unit_price REAL,
+    value REAL NOT NULL,
+    price_source TEXT,                           -- 'manual' | 'maximus-api' | NULL for simple
+    price_fetched_at DATETIME,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    FOREIGN KEY (snapshot_id) REFERENCES balance_snapshots(id) ON DELETE CASCADE,
+    FOREIGN KEY (account_id) REFERENCES balance_accounts(id) ON DELETE RESTRICT,
+    UNIQUE(snapshot_id, account_id),
+    CHECK (
+        (quantity IS NULL AND unit_price IS NULL)
+        OR (quantity IS NOT NULL AND unit_price IS NOT NULL)
+    )
+);
+
+
+-- =========================================================================
+-- balance_account_transfers — links transactions to accounts (capital flows)
+-- =========================================================================
+-- Used by the Modified Dietz return calculator (Issue #142 / Bilan #4) to
+-- separate contributions from gains. Direction follows the account's
+-- perspective: 'in' = capital added (deposit/buy), 'out' = capital removed
+-- (withdrawal/sell). The amount is taken from the linked transaction (no
+-- duplication).
+--
+-- transaction_id ON DELETE RESTRICT: preserves reproducibility of past
+-- Modified Dietz returns. The UI must force unlink before allowing the
+-- transaction to be deleted.
+CREATE TABLE IF NOT EXISTS balance_account_transfers (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    account_id INTEGER NOT NULL,
+    transaction_id INTEGER NOT NULL,
+    direction TEXT NOT NULL CHECK(direction IN ('in','out')),
+    notes TEXT,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    FOREIGN KEY (account_id) REFERENCES balance_accounts(id) ON DELETE CASCADE,
+    FOREIGN KEY (transaction_id) REFERENCES transactions(id) ON DELETE RESTRICT,
+    UNIQUE(transaction_id, account_id)
+);
+
+
+-- =========================================================================
+-- Indexes (7 total)
+-- =========================================================================
+CREATE INDEX IF NOT EXISTS idx_balance_accounts_category ON balance_accounts(balance_category_id);
+CREATE INDEX IF NOT EXISTS idx_balance_accounts_active ON balance_accounts(is_active) WHERE is_active = 1;
+CREATE INDEX IF NOT EXISTS idx_balance_snapshot_lines_snapshot ON balance_snapshot_lines(snapshot_id);
+CREATE INDEX IF NOT EXISTS idx_balance_snapshot_lines_account ON balance_snapshot_lines(account_id);
+CREATE INDEX IF NOT EXISTS idx_balance_account_transfers_account ON balance_account_transfers(account_id);
+CREATE INDEX IF NOT EXISTS idx_balance_account_transfers_transaction ON balance_account_transfers(transaction_id);
+CREATE INDEX IF NOT EXISTS idx_balance_snapshots_date ON balance_snapshots(snapshot_date);
+
+
+-- =========================================================================
+-- Seed (7 standard categories — idempotent via INSERT OR IGNORE on `key`)
+-- =========================================================================
+INSERT OR IGNORE INTO balance_categories (key, i18n_key, kind, sort_order, is_seed) VALUES
+    ('cash',   'balance.category.cash',   'simple', 10, 1),
+    ('tfsa',   'balance.category.tfsa',   'simple', 20, 1),
+    ('rrsp',   'balance.category.rrsp',   'simple', 30, 1),
+    ('fund',   'balance.category.fund',   'simple', 40, 1),
+    ('other',  'balance.category.other',  'simple', 50, 1),
+    ('stock',  'balance.category.stock',  'priced', 60, 1),
+    ('crypto', 'balance.category.crypto', 'priced', 70, 1);

src-tauri/src/database/consolidated_schema.sql

@@ -181,6 +181,95 @@ CREATE INDEX IF NOT EXISTS idx_budget_entries_period ON budget_entries(year, mon
 CREATE INDEX IF NOT EXISTS idx_adjustment_entries_adjustment ON adjustment_entries(adjustment_id);
 CREATE INDEX IF NOT EXISTS idx_imported_files_source ON imported_files(source_id);
 
+-- ============================================================================
+-- Balance sheet (Bilan) — Migration v9 mirror for new profiles
+-- ============================================================================
+-- 5 tables + 7 indexes + seeded categories. Kept in sync with
+-- `balance_schema.sql` (the source of truth applied by Migration v9 in lib.rs).
+-- New profiles created from this consolidated schema get the balance feature
+-- preinstalled without needing to replay v9 separately.
+
+CREATE TABLE IF NOT EXISTS balance_categories (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    key TEXT NOT NULL UNIQUE,
+    i18n_key TEXT NOT NULL,
+    kind TEXT NOT NULL CHECK(kind IN ('simple','priced')),
+    sort_order INTEGER NOT NULL DEFAULT 0,
+    is_active INTEGER NOT NULL DEFAULT 1,
+    is_seed INTEGER NOT NULL DEFAULT 0
+);
+
+CREATE TABLE IF NOT EXISTS balance_accounts (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    balance_category_id INTEGER NOT NULL,
+    name TEXT NOT NULL,
+    symbol TEXT,
+    currency TEXT NOT NULL DEFAULT 'CAD' CHECK(currency = 'CAD'),
+    notes TEXT,
+    is_active INTEGER NOT NULL DEFAULT 1,
+    archived_at DATETIME,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    FOREIGN KEY (balance_category_id) REFERENCES balance_categories(id) ON DELETE RESTRICT
+);
+
+CREATE TABLE IF NOT EXISTS balance_snapshots (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    snapshot_date DATE NOT NULL UNIQUE,
+    notes TEXT,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE TABLE IF NOT EXISTS balance_snapshot_lines (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    snapshot_id INTEGER NOT NULL,
+    account_id INTEGER NOT NULL,
+    quantity REAL,
+    unit_price REAL,
+    value REAL NOT NULL,
+    price_source TEXT,
+    price_fetched_at DATETIME,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    FOREIGN KEY (snapshot_id) REFERENCES balance_snapshots(id) ON DELETE CASCADE,
+    FOREIGN KEY (account_id) REFERENCES balance_accounts(id) ON DELETE RESTRICT,
+    UNIQUE(snapshot_id, account_id),
+    CHECK (
+        (quantity IS NULL AND unit_price IS NULL)
+        OR (quantity IS NOT NULL AND unit_price IS NOT NULL)
+    )
+);
+
+CREATE TABLE IF NOT EXISTS balance_account_transfers (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    account_id INTEGER NOT NULL,
+    transaction_id INTEGER NOT NULL,
+    direction TEXT NOT NULL CHECK(direction IN ('in','out')),
+    notes TEXT,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    FOREIGN KEY (account_id) REFERENCES balance_accounts(id) ON DELETE CASCADE,
+    FOREIGN KEY (transaction_id) REFERENCES transactions(id) ON DELETE RESTRICT,
+    UNIQUE(transaction_id, account_id)
+);
+
+CREATE INDEX IF NOT EXISTS idx_balance_accounts_category ON balance_accounts(balance_category_id);
+CREATE INDEX IF NOT EXISTS idx_balance_accounts_active ON balance_accounts(is_active) WHERE is_active = 1;
+CREATE INDEX IF NOT EXISTS idx_balance_snapshot_lines_snapshot ON balance_snapshot_lines(snapshot_id);
+CREATE INDEX IF NOT EXISTS idx_balance_snapshot_lines_account ON balance_snapshot_lines(account_id);
+CREATE INDEX IF NOT EXISTS idx_balance_account_transfers_account ON balance_account_transfers(account_id);
+CREATE INDEX IF NOT EXISTS idx_balance_account_transfers_transaction ON balance_account_transfers(transaction_id);
+CREATE INDEX IF NOT EXISTS idx_balance_snapshots_date ON balance_snapshots(snapshot_date);
+
+INSERT OR IGNORE INTO balance_categories (key, i18n_key, kind, sort_order, is_seed) VALUES
+    ('cash',   'balance.category.cash',   'simple', 10, 1),
+    ('tfsa',   'balance.category.tfsa',   'simple', 20, 1),
+    ('rrsp',   'balance.category.rrsp',   'simple', 30, 1),
+    ('fund',   'balance.category.fund',   'simple', 40, 1),
+    ('other',  'balance.category.other',  'simple', 50, 1),
+    ('stock',  'balance.category.stock',  'priced', 60, 1),
+    ('crypto', 'balance.category.crypto', 'priced', 70, 1);
+
 -- Default preferences (new profiles ship with the v1 IPC taxonomy)
 INSERT OR IGNORE INTO user_preferences (key, value) VALUES ('language', 'fr');
 INSERT OR IGNORE INTO user_preferences (key, value) VALUES ('theme', 'light');

src-tauri/src/database/mod.rs

@@ -1,3 +1,4 @@
 pub const SCHEMA: &str = include_str!("schema.sql");
 pub const SEED_CATEGORIES: &str = include_str!("seed_categories.sql");
 pub const CONSOLIDATED_SCHEMA: &str = include_str!("consolidated_schema.sql");
+pub const BALANCE_SCHEMA: &str = include_str!("balance_schema.sql");

src-tauri/src/lib.rs

@@ -95,6 +95,19 @@ pub fn run() {
             INSERT OR IGNORE INTO user_preferences (key, value) VALUES ('categories_schema_version', 'v2');",
             kind: MigrationKind::Up,
         },
+        // Migration v9 — Bilan (balance sheet) schema:
+        // 5 tables (balance_categories, balance_accounts, balance_snapshots,
+        // balance_snapshot_lines, balance_account_transfers) + 7 indexes +
+        // 7 seeded categories (5 simple + 2 priced).
+        // CHECK(currency = 'CAD') is hardcoded for the MVP (will be lifted in v2
+        // with a multi-currency rate table). FK transaction_id ON DELETE
+        // RESTRICT preserves reproducibility of Modified Dietz returns.
+        Migration {
+            version: 9,
+            description: "create balance schema",
+            sql: database::BALANCE_SCHEMA,
+            kind: MigrationKind::Up,
+        },
     ];
 
     tauri::Builder::default()
@@ -240,3 +253,443 @@ fn extract_query_param(url: &str, key: &str) -> Option<String> {
     }
     None
 }
+
+// =============================================================================
+// Tests for migration v9 — balance schema
+// -----------------------------------------------------------------------------
+// These tests apply `database::BALANCE_SCHEMA` (the SQL embedded in the v9
+// migration) on a fresh in-memory SQLite database and assert that:
+//   - the schema applies cleanly (all 5 tables + 7 indexes created)
+//   - the 7 seed categories are present (5 simple + 2 priced) with is_seed = 1
+//   - CHECK constraints reject invalid kind / direction / currency / kind invariants
+//   - UNIQUE constraints enforce snapshot_date / (snapshot_id,account_id) /
+//     (transaction_id,account_id) / category key
+//   - FK ON DELETE policies behave as expected (CASCADE on snapshot, RESTRICT
+//     on transaction_id and on category with linked accounts)
+//
+// rusqlite (0.32, bundled) is already a runtime dependency — no extra dev-dep
+// required. The migration v9 SQL is the source of truth; v1-v8 are not
+// required here because v9 is additive and only references the existing
+// `transactions` table for the FK on balance_account_transfers — we mirror
+// that with a minimal `transactions` table for the integration scenarios.
+#[cfg(test)]
+mod tests {
+    use rusqlite::Connection;
+
+    /// Apply the v9 schema on a fresh in-memory DB. Includes a minimal
+    /// `transactions` table because balance_account_transfers references it.
+    fn fresh_db() -> Connection {
+        let conn = Connection::open_in_memory().expect("open in-memory db");
+        // FKs must be enabled per-connection in SQLite.
+        conn.execute("PRAGMA foreign_keys = ON;", [])
+            .expect("enable FKs");
+        // Minimal transactions table mirroring the relevant columns the FK
+        // references (id is the only column we need at the SQL level).
+        conn.execute_batch(
+            "CREATE TABLE transactions (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                date DATE NOT NULL,
+                description TEXT NOT NULL,
+                amount REAL NOT NULL
+            );",
+        )
+        .expect("create stub transactions table");
+        conn.execute_batch(crate::database::BALANCE_SCHEMA)
+            .expect("apply BALANCE_SCHEMA");
+        conn
+    }
+
+    #[test]
+    fn migration_v9_applies_cleanly() {
+        let conn = fresh_db();
+        // 5 expected tables
+        let tables: Vec<String> = conn
+            .prepare(
+                "SELECT name FROM sqlite_master WHERE type='table' AND name LIKE 'balance_%' ORDER BY name",
+            )
+            .unwrap()
+            .query_map([], |row| row.get::<_, String>(0))
+            .unwrap()
+            .map(|r| r.unwrap())
+            .collect();
+        assert_eq!(
+            tables,
+            vec![
+                "balance_account_transfers",
+                "balance_accounts",
+                "balance_categories",
+                "balance_snapshot_lines",
+                "balance_snapshots",
+            ]
+        );
+        // 7 expected indexes
+        let index_count: i64 = conn
+            .query_row(
+                "SELECT COUNT(*) FROM sqlite_master WHERE type='index' AND name LIKE 'idx_balance_%'",
+                [],
+                |row| row.get(0),
+            )
+            .unwrap();
+        assert_eq!(index_count, 7);
+    }
+
+    #[test]
+    fn migration_v9_seeds_7_categories() {
+        let conn = fresh_db();
+        let count: i64 = conn
+            .query_row(
+                "SELECT COUNT(*) FROM balance_categories WHERE is_seed = 1",
+                [],
+                |row| row.get(0),
+            )
+            .unwrap();
+        assert_eq!(count, 7);
+
+        let simple_count: i64 = conn
+            .query_row(
+                "SELECT COUNT(*) FROM balance_categories WHERE kind = 'simple' AND is_seed = 1",
+                [],
+                |row| row.get(0),
+            )
+            .unwrap();
+        assert_eq!(simple_count, 5);
+
+        let priced_count: i64 = conn
+            .query_row(
+                "SELECT COUNT(*) FROM balance_categories WHERE kind = 'priced' AND is_seed = 1",
+                [],
+                |row| row.get(0),
+            )
+            .unwrap();
+        assert_eq!(priced_count, 2);
+
+        // Seeded keys are stable
+        let stock_kind: String = conn
+            .query_row(
+                "SELECT kind FROM balance_categories WHERE key = 'stock'",
+                [],
+                |row| row.get(0),
+            )
+            .unwrap();
+        assert_eq!(stock_kind, "priced");
+    }
+
+    #[test]
+    fn migration_v9_rejects_non_cad_currency() {
+        let conn = fresh_db();
+        // 'cash' category exists from seed; try to insert a non-CAD account.
+        let result = conn.execute(
+            "INSERT INTO balance_accounts (balance_category_id, name, currency)
+             VALUES ((SELECT id FROM balance_categories WHERE key='cash'), 'USD account', 'USD')",
+            [],
+        );
+        assert!(
+            result.is_err(),
+            "CHECK(currency='CAD') should reject 'USD'"
+        );
+        let err_msg = result.unwrap_err().to_string();
+        assert!(err_msg.to_lowercase().contains("check"));
+    }
+
+    #[test]
+    fn migration_v9_accepts_default_cad_currency() {
+        let conn = fresh_db();
+        let inserted = conn
+            .execute(
+                "INSERT INTO balance_accounts (balance_category_id, name)
+                 VALUES ((SELECT id FROM balance_categories WHERE key='cash'), 'Encaisse')",
+                [],
+            )
+            .expect("CAD default insert should succeed");
+        assert_eq!(inserted, 1);
+    }
+
+    #[test]
+    fn migration_v9_rejects_invalid_kind() {
+        let conn = fresh_db();
+        let result = conn.execute(
+            "INSERT INTO balance_categories (key, i18n_key, kind) VALUES ('bogus', 'x.bogus', 'unknown')",
+            [],
+        );
+        assert!(result.is_err(), "kind CHECK should reject 'unknown'");
+    }
+
+    #[test]
+    fn migration_v9_unique_snapshot_date() {
+        let conn = fresh_db();
+        conn.execute(
+            "INSERT INTO balance_snapshots (snapshot_date) VALUES ('2026-04-25')",
+            [],
+        )
+        .unwrap();
+        let result = conn.execute(
+            "INSERT INTO balance_snapshots (snapshot_date) VALUES ('2026-04-25')",
+            [],
+        );
+        assert!(result.is_err(), "UNIQUE(snapshot_date) should reject dup");
+    }
+
+    #[test]
+    fn migration_v9_kind_invariants_check() {
+        let conn = fresh_db();
+        // Setup: a snapshot + an account
+        conn.execute(
+            "INSERT INTO balance_snapshots (snapshot_date) VALUES ('2026-04-25')",
+            [],
+        )
+        .unwrap();
+        conn.execute(
+            "INSERT INTO balance_accounts (balance_category_id, name)
+             VALUES ((SELECT id FROM balance_categories WHERE key='cash'), 'Encaisse')",
+            [],
+        )
+        .unwrap();
+        let snap_id: i64 = conn
+            .query_row("SELECT id FROM balance_snapshots LIMIT 1", [], |r| r.get(0))
+            .unwrap();
+        let acct_id: i64 = conn
+            .query_row("SELECT id FROM balance_accounts LIMIT 1", [], |r| r.get(0))
+            .unwrap();
+
+        // OK: simple kind (quantity + unit_price both NULL)
+        conn.execute(
+            "INSERT INTO balance_snapshot_lines (snapshot_id, account_id, value)
+             VALUES (?1, ?2, 1234.56)",
+            rusqlite::params![snap_id, acct_id],
+        )
+        .expect("simple kind row (qty/price both NULL) should be accepted");
+
+        // OK: priced kind (both set) — needs second account on a priced category
+        conn.execute(
+            "INSERT INTO balance_accounts (balance_category_id, name, symbol)
+             VALUES ((SELECT id FROM balance_categories WHERE key='stock'), 'AAPL', 'AAPL')",
+            [],
+        )
+        .unwrap();
+        let acct2_id: i64 = conn
+            .query_row(
+                "SELECT id FROM balance_accounts WHERE name='AAPL'",
+                [],
+                |r| r.get(0),
+            )
+            .unwrap();
+        conn.execute(
+            "INSERT INTO balance_snapshot_lines (snapshot_id, account_id, quantity, unit_price, value)
+             VALUES (?1, ?2, 10.0, 200.0, 2000.0)",
+            rusqlite::params![snap_id, acct2_id],
+        )
+        .expect("priced kind row (both set) should be accepted");
+
+        // KO: only quantity set, unit_price NULL → CHECK violation
+        let bad = conn.execute(
+            "INSERT INTO balance_snapshot_lines (snapshot_id, account_id, quantity, value)
+             VALUES (?1, ?2, 10.0, 0.0)",
+            rusqlite::params![snap_id, acct_id],
+        );
+        assert!(
+            bad.is_err(),
+            "kind invariants CHECK should reject (qty set, price NULL)"
+        );
+
+        // KO: only unit_price set, quantity NULL → CHECK violation
+        let bad2 = conn.execute(
+            "INSERT INTO balance_snapshot_lines (snapshot_id, account_id, unit_price, value)
+             VALUES (?1, ?2, 200.0, 0.0)",
+            rusqlite::params![snap_id, acct_id],
+        );
+        assert!(
+            bad2.is_err(),
+            "kind invariants CHECK should reject (price set, qty NULL)"
+        );
+    }
+
+    #[test]
+    fn migration_v9_unique_snapshot_account_pair() {
+        let conn = fresh_db();
+        conn.execute(
+            "INSERT INTO balance_snapshots (snapshot_date) VALUES ('2026-04-25')",
+            [],
+        )
+        .unwrap();
+        conn.execute(
+            "INSERT INTO balance_accounts (balance_category_id, name)
+             VALUES ((SELECT id FROM balance_categories WHERE key='cash'), 'Encaisse')",
+            [],
+        )
+        .unwrap();
+        let snap_id: i64 = conn
+            .query_row("SELECT id FROM balance_snapshots LIMIT 1", [], |r| r.get(0))
+            .unwrap();
+        let acct_id: i64 = conn
+            .query_row("SELECT id FROM balance_accounts LIMIT 1", [], |r| r.get(0))
+            .unwrap();
+        conn.execute(
+            "INSERT INTO balance_snapshot_lines (snapshot_id, account_id, value)
+             VALUES (?1, ?2, 100.0)",
+            rusqlite::params![snap_id, acct_id],
+        )
+        .unwrap();
+        let dup = conn.execute(
+            "INSERT INTO balance_snapshot_lines (snapshot_id, account_id, value)
+             VALUES (?1, ?2, 200.0)",
+            rusqlite::params![snap_id, acct_id],
+        );
+        assert!(dup.is_err(), "UNIQUE(snapshot_id, account_id) should reject dup");
+    }
+
+    #[test]
+    fn migration_v9_fk_cascade_on_snapshot_delete() {
+        let conn = fresh_db();
+        conn.execute(
+            "INSERT INTO balance_snapshots (snapshot_date) VALUES ('2026-04-25')",
+            [],
+        )
+        .unwrap();
+        conn.execute(
+            "INSERT INTO balance_accounts (balance_category_id, name)
+             VALUES ((SELECT id FROM balance_categories WHERE key='cash'), 'Encaisse')",
+            [],
+        )
+        .unwrap();
+        let snap_id: i64 = conn
+            .query_row("SELECT id FROM balance_snapshots LIMIT 1", [], |r| r.get(0))
+            .unwrap();
+        let acct_id: i64 = conn
+            .query_row("SELECT id FROM balance_accounts LIMIT 1", [], |r| r.get(0))
+            .unwrap();
+        conn.execute(
+            "INSERT INTO balance_snapshot_lines (snapshot_id, account_id, value)
+             VALUES (?1, ?2, 100.0)",
+            rusqlite::params![snap_id, acct_id],
+        )
+        .unwrap();
+        conn.execute(
+            "DELETE FROM balance_snapshots WHERE id = ?1",
+            rusqlite::params![snap_id],
+        )
+        .expect("delete snapshot should cascade");
+        let remaining: i64 = conn
+            .query_row("SELECT COUNT(*) FROM balance_snapshot_lines", [], |r| r.get(0))
+            .unwrap();
+        assert_eq!(remaining, 0, "snapshot delete should cascade lines");
+    }
+
+    #[test]
+    fn migration_v9_fk_restrict_on_transaction_delete() {
+        let conn = fresh_db();
+        conn.execute(
+            "INSERT INTO balance_accounts (balance_category_id, name)
+             VALUES ((SELECT id FROM balance_categories WHERE key='cash'), 'Encaisse')",
+            [],
+        )
+        .unwrap();
+        conn.execute(
+            "INSERT INTO transactions (date, description, amount) VALUES ('2026-04-25', 'Deposit', 1000.0)",
+            [],
+        )
+        .unwrap();
+        let acct_id: i64 = conn
+            .query_row("SELECT id FROM balance_accounts LIMIT 1", [], |r| r.get(0))
+            .unwrap();
+        let tx_id: i64 = conn
+            .query_row("SELECT id FROM transactions LIMIT 1", [], |r| r.get(0))
+            .unwrap();
+        conn.execute(
+            "INSERT INTO balance_account_transfers (account_id, transaction_id, direction)
+             VALUES (?1, ?2, 'in')",
+            rusqlite::params![acct_id, tx_id],
+        )
+        .unwrap();
+
+        // Attempting to delete the linked transaction must be rejected (RESTRICT)
+        let result = conn.execute("DELETE FROM transactions WHERE id = ?1", rusqlite::params![tx_id]);
+        assert!(
+            result.is_err(),
+            "FK RESTRICT should block deleting linked transaction"
+        );
+
+        // Once the transfer is removed, deletion is allowed again
+        conn.execute(
+            "DELETE FROM balance_account_transfers WHERE transaction_id = ?1",
+            rusqlite::params![tx_id],
+        )
+        .unwrap();
+        conn.execute("DELETE FROM transactions WHERE id = ?1", rusqlite::params![tx_id])
+            .expect("after unlink, transaction can be deleted");
+    }
+
+    #[test]
+    fn migration_v9_fk_restrict_on_category_with_accounts() {
+        let conn = fresh_db();
+        conn.execute(
+            "INSERT INTO balance_accounts (balance_category_id, name)
+             VALUES ((SELECT id FROM balance_categories WHERE key='cash'), 'Encaisse')",
+            [],
+        )
+        .unwrap();
+        // Try to delete the seeded 'cash' category while an account references it
+        let result = conn.execute(
+            "DELETE FROM balance_categories WHERE key = 'cash'",
+            [],
+        );
+        assert!(
+            result.is_err(),
+            "FK RESTRICT should block deleting category with linked accounts"
+        );
+    }
+
+    #[test]
+    fn migration_v9_unique_transaction_account_transfer() {
+        let conn = fresh_db();
+        conn.execute(
+            "INSERT INTO balance_accounts (balance_category_id, name)
+             VALUES ((SELECT id FROM balance_categories WHERE key='cash'), 'Encaisse')",
+            [],
+        )
+        .unwrap();
+        conn.execute(
+            "INSERT INTO transactions (date, description, amount) VALUES ('2026-04-25', 'Deposit', 1000.0)",
+            [],
+        )
+        .unwrap();
+        let acct_id: i64 = conn
+            .query_row("SELECT id FROM balance_accounts LIMIT 1", [], |r| r.get(0))
+            .unwrap();
+        let tx_id: i64 = conn
+            .query_row("SELECT id FROM transactions LIMIT 1", [], |r| r.get(0))
+            .unwrap();
+        conn.execute(
+            "INSERT INTO balance_account_transfers (account_id, transaction_id, direction)
+             VALUES (?1, ?2, 'in')",
+            rusqlite::params![acct_id, tx_id],
+        )
+        .unwrap();
+        let dup = conn.execute(
+            "INSERT INTO balance_account_transfers (account_id, transaction_id, direction)
+             VALUES (?1, ?2, 'out')",
+            rusqlite::params![acct_id, tx_id],
+        );
+        assert!(
+            dup.is_err(),
+            "UNIQUE(transaction_id, account_id) should reject dup"
+        );
+    }
+
+    #[test]
+    fn migration_v9_seed_idempotent_on_replay() {
+        // The migration uses `INSERT OR IGNORE` keyed by `key`, so applying
+        // the schema twice on the same DB must not duplicate seeded rows.
+        let conn = fresh_db();
+        conn.execute_batch(crate::database::BALANCE_SCHEMA)
+            .expect("apply BALANCE_SCHEMA twice");
+        let count: i64 = conn
+            .query_row(
+                "SELECT COUNT(*) FROM balance_categories WHERE is_seed = 1",
+                [],
+                |row| row.get(0),
+            )
+            .unwrap();
+        assert_eq!(count, 7, "seed must remain idempotent on replay");
+    }
+}
+