Duong Labs https://duonglabs.com/blog Short technical notes from Duong Labs: what broke, what fixed it, and when the fix is worth the trouble. en Sun, 06 Sep 2026 07:01:08 +0000 Regression-testing an agent whose output is never the same twice https://duonglabs.com/blog/agent-regression-testing https://duonglabs.com/blog/agent-regression-testing Sat, 05 Sep 2026 09:00:00 +0000 String diffs don't work on free-text output. Freeze the traces, assert on behaviour instead of text, and run the suite after every prompt or model change. Two ways usage-based AI billing quietly loses money https://duonglabs.com/blog/ai-usage-billing https://duonglabs.com/blog/ai-usage-billing Sat, 05 Sep 2026 09:00:00 +0000 Charge after the stream using the provider's real token counts, and let a unique key on the ledger reject Stripe's duplicate webhooks.