backprop
Bug → spec protocol. When a bug is found or a test fails, trace the cause, decide whether a new §V invariant would catch recurrence, append to §B. This is the one non-obvious thing SDD does that plan-then-execute doesn't. Triggers on test failure, bug report, post-mortem, or explicit user ask.
Install
With your agent
Install OMGSkills skill "juliusbrussee/cavekit:backprop" into this agent's normal skills directory: call the OMGSkills MCP get_install_plan tool for your agent and run the script it returns (it installs only the pinned commit and verifies SKILL.md), and stop if MCP or the pin is unavailable. Do not overwrite or change existing skills without asking me.
Manual command
git clone https://github.com/JuliusBrussee/cavekit /tmp/cavekit && ln -s /tmp/cavekit/skills/backprop ~/.claude/skills/backpropFrom README
backprop — bug → spec Plan-then-execute fixes the code & forgets. SDD fixes the code AND edits spec so recurrence is impossible. That edit is backprop. WHEN TO BACKPROP Test failed at /build verification. User reports bug. Post-mortem after production incident. /check flags VIOLATE with root cause found. SIX STEPS TRACE Read failure output / bug report. Find exact file:line of wrong behavior. Name root cause in one caveman sentence. ANALYZE Ask three questions: Would a new §V invariant catch this class of bug? (most common: yes) Is §I wrong — did spec claim shape the code cannot deliver? (sometimes) Is §T wrong — did we build the wrong thing? (rare but real) PROPOSE Draft the spec change. Never skip §B; §V/§I/§T are case-by-case. Template: Example: GENERATE TEST New invariant without test = lie. Add failing test first. Name test so it cites the invariant: TestV7RefundIdempotent. VERIFY Fix code. Run test. Must pass. Run full suite. Must not regress.