Add start_date to financing plans and protect paid paychecks from refresh

- Migration 004: adds start_date column to financing_plans (DEFAULT CURRENT_DATE)
- generatePaychecks: skips financing plans whose start_date is after the target month
- buildVirtualPaychecks: same start_date guard for virtual previews (already applied)
- generatePaychecks upsert: preserves gross/net when paycheck has any paid bills
- financing.js POST/PUT: accept and store start_date
- Financing.jsx: add Start Date field to create/edit form (defaults to today)
- CLAUDE.md: document start_date guard and paid-paycheck refresh protection

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -61,8 +61,8 @@ The default route `/` renders the paycheck-centric main view (`client/src/pages/
 
 **Variable amount bills:** Bills with `variable_amount = true` require the amount to be entered each month in the paycheck view (stored as `amount_override` on `paycheck_bills`). The bill's `amount` field serves as an optional typical/estimated value.
 
-**Lazy paycheck generation:** `GET /api/paychecks` returns virtual (unsaved) data with `id: null` when no DB record exists for the month. Paychecks are only persisted when the first interaction occurs (bill toggle, expense add, etc.). The "↺ Refresh amounts" button on the paycheck view re-runs `POST /api/paychecks/generate` to sync gross/net from current Settings. Individual paycheck gross/net can also be edited inline via the pencil icon.
+**Lazy paycheck generation:** `GET /api/paychecks` returns virtual (unsaved) data with `id: null` when no DB record exists for the month. Paychecks are only persisted when the first interaction occurs (bill toggle, expense add, etc.). The "↺ Refresh amounts" button on the paycheck view re-runs `POST /api/paychecks/generate` to sync gross/net from current Settings — but gross/net are never overwritten when the paycheck already has any paid bills, preserving historical income values. Individual paycheck gross/net can also be edited inline via the pencil icon.
 
-**Financing:** `GET/POST /api/financing`, `PUT/DELETE /api/financing/:id`, `PATCH /api/financing-payments/:id/paid`. Plans track a total amount and payoff due date. Payment per period is auto-calculated as `(remaining balance) / (remaining periods)`. Split plans (`assigned_paycheck = null`) divide each period's payment across both paychecks. Plans auto-close when fully paid. Financing payments are included in the paycheck remaining balance.
+**Financing:** `GET/POST /api/financing`, `PUT/DELETE /api/financing/:id`, `PATCH /api/financing-payments/:id/paid`. Plans track a total amount, payoff due date, and `start_date`. Payment per period is auto-calculated as `(remaining balance) / (remaining periods)`. Split plans (`assigned_paycheck = null`) divide each period's payment across both paychecks. Plans auto-close when fully paid. Financing payments are included in the paycheck remaining balance. `start_date` prevents a plan from appearing on paycheck months before it was created — both virtual previews and `generate` respect this guard.
 
 **Migrations:** SQL files in `db/migrations/` are applied in filename order on server startup. Add new migrations as `00N_description.sql` — they run once and are tracked in the `migrations` table.

client/src/pages/Financing.jsx

@@ -20,10 +20,13 @@ function ProgressBar({ paid, total }) {
   );
 }
 
+const TODAY = new Date().toISOString().slice(0, 10);
+
 const EMPTY_FORM = {
   name: '',
   total_amount: '',
   due_date: '',
+  start_date: TODAY,
   assigned_paycheck: 'both',
 };
 
@@ -111,6 +114,7 @@ export default function Financing() {
       name: plan.name,
       total_amount: plan.total_amount,
       due_date: plan.due_date,
+      start_date: plan.start_date || TODAY,
       assigned_paycheck: plan.assigned_paycheck == null ? 'both' : String(plan.assigned_paycheck),
     });
     setFormError(null);
@@ -138,6 +142,7 @@ export default function Financing() {
         name: form.name,
         total_amount: parseFloat(form.total_amount),
         due_date: form.due_date,
+        start_date: form.start_date || TODAY,
         assigned_paycheck: form.assigned_paycheck === 'both' ? null : parseInt(form.assigned_paycheck, 10),
       };
       const url = editingId ? `/api/financing/${editingId}` : '/api/financing';
@@ -204,6 +209,11 @@ export default function Financing() {
                 <input name="due_date" type="date" value={form.due_date}
                   onChange={handleChange} required className="form-input" />
               </div>
+              <div className="form-group">
+                <label className="form-label">Start Date</label>
+                <input name="start_date" type="date" value={form.start_date}
+                  onChange={handleChange} required className="form-input" />
+              </div>
               <div className="form-group" style={{ gridColumn: '1 / -1' }}>
                 <label className="form-label">Assign to paycheck</label>
                 <select name="assigned_paycheck" value={form.assigned_paycheck}

server/src/routes/financing.js

@@ -86,7 +86,7 @@ router.get('/financing', async (req, res) => {
 
 // POST /api/financing
 router.post('/financing', async (req, res) => {
-  const { name, total_amount, due_date, assigned_paycheck } = req.body;
+  const { name, total_amount, due_date, assigned_paycheck, start_date } = req.body;
   if (!name || !total_amount || !due_date) {
     return res.status(400).json({ error: 'name, total_amount, and due_date are required' });
   }
@@ -96,9 +96,9 @@ router.post('/financing', async (req, res) => {
 
   try {
     const { rows } = await pool.query(
-      `INSERT INTO financing_plans (name, total_amount, due_date, assigned_paycheck)
+      `INSERT INTO financing_plans (name, total_amount, due_date, assigned_paycheck, start_date)
-       VALUES ($1, $2, $3, $4) RETURNING *`,
+       VALUES ($1, $2, $3, $4, $5) RETURNING *`,
-      [name.trim(), parseFloat(total_amount), due_date, assigned_paycheck ?? null]
+      [name.trim(), parseFloat(total_amount), due_date, assigned_paycheck ?? null, start_date || new Date().toISOString().slice(0, 10)]
     );
     res.status(201).json(await enrichPlan(pool, rows[0]));
   } catch (err) {
@@ -136,16 +136,16 @@ router.get('/financing/:id', async (req, res) => {
 
 // PUT /api/financing/:id
 router.put('/financing/:id', async (req, res) => {
-  const { name, total_amount, due_date, assigned_paycheck } = req.body;
+  const { name, total_amount, due_date, assigned_paycheck, start_date } = req.body;
   if (!name || !total_amount || !due_date) {
     return res.status(400).json({ error: 'name, total_amount, and due_date are required' });
   }
 
   try {
     const { rows } = await pool.query(
-      `UPDATE financing_plans SET name=$1, total_amount=$2, due_date=$3, assigned_paycheck=$4
+      `UPDATE financing_plans SET name=$1, total_amount=$2, due_date=$3, assigned_paycheck=$4, start_date=$5
-       WHERE id=$5 RETURNING *`,
+       WHERE id=$6 RETURNING *`,
-      [name.trim(), parseFloat(total_amount), due_date, assigned_paycheck ?? null, req.params.id]
+      [name.trim(), parseFloat(total_amount), due_date, assigned_paycheck ?? null, start_date || new Date().toISOString().slice(0, 10), req.params.id]
     );
     if (!rows.length) return res.status(404).json({ error: 'Not found' });
     res.json(await enrichPlan(pool, rows[0]));

server/src/routes/paychecks.js

@@ -96,6 +96,12 @@ async function buildVirtualPaychecks(year, month) {
   const client = await pool.connect();
   try {
     for (const plan of activePlans.rows) {
+      // Skip plans that haven't started yet for this period
+      const start = new Date(plan.start_date);
+      const planStartYear  = start.getFullYear();
+      const planStartMonth = start.getMonth() + 1;
+      if (year * 12 + month < planStartYear * 12 + planStartMonth) continue;
+
       const amount = await calcPaymentAmount(client, plan, year, month);
       if (amount <= 0) continue;
 
@@ -155,8 +161,20 @@ async function generatePaychecks(year, month) {
          VALUES ($1, $2, $3, $4, $5, $6)
          ON CONFLICT (period_year, period_month, paycheck_number)
          DO UPDATE SET pay_date = EXCLUDED.pay_date,
-                       gross = EXCLUDED.gross,
+                       gross = CASE
-                       net = EXCLUDED.net
+                         WHEN EXISTS (
+                           SELECT 1 FROM paycheck_bills pb
+                           WHERE pb.paycheck_id = paychecks.id AND pb.paid = TRUE
+                         ) THEN paychecks.gross
+                         ELSE EXCLUDED.gross
+                       END,
+                       net = CASE
+                         WHEN EXISTS (
+                           SELECT 1 FROM paycheck_bills pb
+                           WHERE pb.paycheck_id = paychecks.id AND pb.paid = TRUE
+                         ) THEN paychecks.net
+                         ELSE EXCLUDED.net
+                       END
          RETURNING id`,
         [year, month, num, payDate, gross || 0, net || 0]
       );
@@ -183,6 +201,12 @@ async function generatePaychecks(year, month) {
       `SELECT * FROM financing_plans WHERE active = TRUE ORDER BY due_date ASC`
     );
     for (const plan of activePlans.rows) {
+      // Skip plans that haven't started yet for this period
+      const start = new Date(plan.start_date);
+      const planStartYear  = start.getFullYear();
+      const planStartMonth = start.getMonth() + 1;
+      if (year * 12 + month < planStartYear * 12 + planStartMonth) continue;
+
       // Determine which paycheck(s) this plan applies to
       const targets = plan.assigned_paycheck == null ? [1, 2] : [plan.assigned_paycheck];
       for (const pcNum of targets) {