28 Safe Refactor Stack – The Grimoire of Software Magic Words

29.1 Related Runes

1172 invariant - A law that must remain true while the rest of the system is allowed to move. If you cannot say the invariant, you probably do not yet understand the change.
1152 contract test - A promise checked at the seam between systems. Use it when mocks are too flattering and end-to-end tests are too blunt.
1088 diff {Forge} - A visible account of what changed between one state and another. Good diffs make review local; bad diffs turn truth into fog.
1430 backward-compatible - New versions do not casually break old clients or data.
1445 deterministic - Given the same inputs, the same result should return. This is the antidote to drift, heisenbugs, and unreviewable behavior.

Safe Refactoring
Test Generation
Stack Grammar
Failure Modes
Canon Map | Step | Spell | Artifact | Advance when | | —- | —————– | —————————————– | ——————————————————— | | 1 | Freeze invariants | Behavior and data contracts | What must not change is named | | 2 | Characterize | Tests or characterization evidence | Current behavior is pinned | | 3 | Reshape | Structural patch | Structure improves without intentional behavior change | | 4 | Static verify | Type, lint, and architecture check output | Static checks pass | | 5 | Behavior verify | Characterization test output | Behavior evidence stays green | | 6 | Review | Human review notes | No leaky abstractions, drift, or renamed confusion remain |

{
  "steps": [
    3,
    4,
    5
  ],
  "until": "Desired structure is reached without invariant breakage"
}

Revert to the last green state and restate invariants more precisely.

It puts behavioral contracts in front of structural ambition.