bug: App crashes when budget has empty capacities array

[moltboie]

Bug Description

The app crashes with TypeError: Cannot read properties of undefined (reading 'month') when a budget, section, or category exists with an empty capacities array.

Error location: LabeledBar/index.tsx:40 — barData.getActiveCapacity(date) returns undefined when capacities is empty.

Root Cause

Two issues combine:

1. Subclass constructors wipe the default capacity

BudgetFamily constructor correctly adds a fallback capacity when capacities is empty:

// BudgetFamily constructor
assign(this, init);
this.fromJSON();
if (!this.capacities.length) this.capacities = [new Capacity()]; // ✅ Adds default

But all three subclasses (Budget, Section, Category) re-assign from init after calling super():

// Budget/Section/Category constructor
super(init);           // ✅ BudgetFamily adds default capacity
assign(this, init);    // ❌ Overwrites capacities with the original [] from init
this.fromJSON();       // Maps over empty array → still empty

The second assign(this, init) overwrites the default capacity added by the parent constructor.

2. Server creates budgets with empty capacities

createBudget in budgets.ts uses data.capacities || [] — creating budgets with no capacities in the database.

Reproduction

1. The DB currently has two budgets with capacities: []:
   • 86a6f730-5a72-4ec6-9415-6446a18d87d8 (New Budget)
   • 540b7170-5c5b-42b0-941a-f1d814db116b (New Budget)
2. Loading the app (budgets page) crashes immediately

Proposed Fix

Client: In getActiveCapacity, return a default new Capacity() when capacities is empty (defensive), and fix the subclass constructors to not re-assign capacities from init (root cause).

Server: createBudget should provide a default capacity when none is specified.

Data cleanup: Update the two existing budgets with empty capacities:

UPDATE budgets SET capacities = '[{"month": 0, "capacity_id": "default"}]' WHERE capacities = '[]';

Impact

• Severity: High — crashes the entire app (error boundary catches but no recovery)
• Scope: Affects any user who creates a budget without immediately configuring a capacity
• Persistence: IndexedDB caches the broken data, so clearing browser state also fails until IDB is manually wiped