Shouldn't it be possible to encapsulate something like this with SQLite and produce an accounting engine that can guarantee consistent numbers and generate key numbers (trial balance, P&L, gearing, ...) ?
Indeed! https://www.gnucash.org/
> that can guarantee consistent numbers
It was consistent, and now it's transparent and user-friendly.
> and generate key numbers
Yes, hledger generates useful reports including trial balance, p&l
With ledger/hledger, I've never felt unsure about the change I'm making, and if something wipes out records I'll notice it before committing.
You express it exactly, I felt the same way with Gnucash, Quicken, and all the other non-plain-text accounting apps I tried. Finance was stressful enough without also worrying about messed-up data. That was perhaps the biggest motivation to switch to Ledger, when I found it.
Later, I often could not figure out how to make Ledger do something I knew it could do, and I often was surprised by a crash or wrong behaviour when it saw some new combination of features and data that hadn't been tested or implemented yet. This was a big motivation to write hledger.