## Why
### Problem
The Indexa Capital dashboard shows +€11,339.01 profit for the Index
funds account, but our app shows +€9,680.43 — a €1,658.58 discrepancy.
The invested amount (and therefore the profit) is wrong.
### Root Cause
`calculateInvestedAmount()` used `instruments_cost + cash_amount` to
determine how much was invested. However, `instruments_cost` is the
**cost basis of currently held fund shares**, not the actual money
deposited. When Indexa rebalances portfolios, they sell shares
(realizing gains) and buy new ones at a higher cost basis. This inflates
`instruments_cost` over time without any new deposits, making the
"invested" figure too high and profit too low.
## What
### Changes
- Use `net_amounts` from the Indexa Capital API response instead of
`instruments_cost + cash_amount`
- `net_amounts` is an object keyed by date (`YYYYMMDD` format), where
each value is the cumulative net investment (inflows - outflows -
tax_outflows), matching Indexa Capital's own "investment" figure
- Keep `total_amount - return` as a fallback when `net_amounts` is
unavailable
- Return `null` when neither data source is available
### Concrete numbers (Index funds account, 2026-02-24)
| | Old (wrong) | New (correct) |
|---|---|---|
| Invested | €48,081.67 | €46,423.09 |
| Profit | €9,680.43 | €11,339.01 |
## Verification
### Tests
- Updated `stores invested_amount from net_amounts data` — verifies
invested_amount is sourced from `net_amounts`, not `instruments_cost +
cash_amount`
- Updated `stores null invested_amount when net_amounts is missing` —
verifies graceful null when API lacks `net_amounts`
- Updated `falls back to total_amount minus return when net_amounts is
missing` — verifies fallback path
- All 11 balance sync tests pass, all 23 SyncBankingConnectionJob tests
pass
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