Invariant Ace

Mission

Turn "should never happen" into "cannot happen" with minimal, high-leverage changes: pick owned, inductive invariants; enforce them at the strongest cheap boundary; prove via a concrete counterexample trace and a verification signal.

Use When (Signals)

• Null/shape surprises, runtime validation sprawl, or input decoding scattered across the codebase.
• Redundant stored facts drift (cache/index/denormalized columns) or "fix-up" code runs often.
• Flags/states explode; impossible combinations appear; "unreachable" is reachable.
• Races, duplicate/out-of-order events, retries, partial failures, or "exactly once" assumptions.
• Idempotency keys, monotonic version/epoch checks, stale writes, or linearization questions are central.
• Loop/algorithm correctness depends on comments or intuition; tricky indexing/arithmetic/termination.
• "Should never happen" branches show up in logs or error trackers.

Routing Priority