## Summary
- Replace `subMonths()` with `subMonthsNoOverflow()` across controllers,
commands, and tests to prevent date overflow on months with 31 days
- On Jan 31, `subMonths(2)` overflows: Nov 31 doesn't exist → Carbon
rolls forward to Dec 1, producing wrong date ranges and off-by-one month
counts
## Root cause
Carbon's `subMonths()` allows day overflow. When the target month has
fewer days than the source date, it rolls into the next month. For
example:
- `2026-01-31 subMonths(2)` → Nov 31 → **2025-12-01** (expected Nov 30)
- `2026-01-31 subMonths(11)` → Feb 31 → **2025-03-03** (expected Feb 28)
`subMonthsNoOverflow()` clamps to the last valid day of the target month
instead.
## Files changed
- `app/Http/Controllers/Api/CashflowAnalyticsController.php` — cashflow
trend start date calculation
- `app/Console/Commands/ResetDemoAccountCommand.php` — balance history
date generation (was causing duplicate `balance_date` entries)
- `tests/Feature/AccountControllerTest.php` — balance evolution `from`
param
- `tests/Feature/CashflowAnalyticsTest.php` — transaction date
generation in loop
- `tests/Feature/DashboardAnalyticsTest.php` — net worth evolution
`from` param
## Test plan
- [x] `account balance evolution returns data` — expects 3 months, was
getting 2
- [x] `cashflow trend returns monthly data` — expects 3 months, was
getting 2
- [x] `cashflow trend defaults to 12 months` — expects 12 months, was
getting 11
- [x] `net worth evolution returns monthly data points` — expects 3
months, was getting 2
- [x] `demo:reset creates demo user` — was throwing
UniqueConstraintViolation on duplicate balance dates
cc666a3111