systematic-debugginglisted

# Systematic Debugging Find the root cause before attempting a fix. A symptom patch without a causal explanation creates a second unknown. Read the complete failure and reproduce it with the smallest reliable loop. Trace the bad value or condition backward across boundaries, compare it with a working path, and inspect recent changes without assuming they are causal. For flakiness, identify nondeterministic input, timing, shared state, or resource contention instead of retrying until green. Treat the execution environment as a suspect. When a sandbox, permission layer, or harness restriction can explain the failure, re-run the probe outside that restriction before declaring a tool, service, or dependency broken. State one evidence-backed hypothesis and test the cheapest decisive prediction while changing one variable. A failed hypothesis is evidence; update the model before trying another. After the cause is confirmed, write and run a failing regression test at a stable boundary before changing production code. Make the smallest cause-level fix, then run the regression, relevant checks, and the original failure path. When a deterministic local test is impossible, agree on a substitute oracle and record the environment, correlation key, pre-change failure, post-change result, and monitoring window. After three failed fixes on one approach, stop, report the evidence and remaining uncertainty, and reconsider the design.