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

1. TRACE

Read failure output / bug report. Find exact file:line of wrong behavior. Name root cause in one caveman sentence.