deepen

# deepen — make modules deep **Behavior is sacred: tests green before AND after. Every change shrinks an interface or hides a decision — deepen, don't churn.** A **deep module** hides a lot behind a small interface; a **shallow** one's interface costs as much to use as writing the code yourself. Complexity = dependencies + obscurity, and it compounds. Deepen spends spare usage paying that down *before* it becomes a §B. Run it when the build is green & you have budget to drain — not under deadline. ## WHEN TO DEEPEN - Build is green, tests pass, & you have token budget spare. - A module's interface feels as complex as its implementation (shallow smell). - The same change keeps touching many files (change amplification). - User explicitly asks to improve design quality. ⊥ run mid-feature or under pressure. Deepen is the deliberate pass, not the reflex. ## FIVE STEPS ### 1. PICK THE SHALLOW Scan the modules the spec touches. Rank by shallowness — interface surface vs work done. Pick the **one** worst offender. Tells: - Pass-through method that only forwards to one other (shallow layer). - Caller must set 5 flags right to use it (config leakage). - Same abstraction repeated at two layers (no information hiding). - A `?` or §B that traces back to a confusing interface. One module per pass. Deepening is surgical, ⊥ a codebase sweep. ### 2. DIAGNOSE Name the design defect in caveman, citing file:line: > src/auth/token.go: 6-arg ctor leaks rotation policy to every caller. shallow. Complexity is real only if it shows: change amplification, high cognitive load, or an unknown-unknown (caller must know a hidden fact to call it right). ### 3. RESEARCH THE DEEPENING What does a deeper version look like? Pull a known pattern (hand to **research** for the external case → §R) or derive from the codebase's own better modules. Moves that deepen: - **Pull complexity down** — hide the hard part inside, give callers the simple path. - **Define errors out of existence** — design the interface so the edge can't occur. - **Information hiding** — one decision, one module; callers don't learn it. - **General-purpose interface** over a pile of special-case methods. ### 4. PROPOSE Draft the change as spec edits, not a silent rewrite: - New/simpler §I shape for the module. - §V that locks the deepened invariant so a future build can't re-shallow it. - §T refactor row(s), each citing the §V/§I it serves. Hand to **spec** to write. Show the before/after interface so the user sees the shrink. ### 5. VERIFY BEHAVIOR HELD Refactor ≠ rewrite. Full suite green before you start AND after. A deepening that changes behavior is a feature in disguise — stop, route through `/spec` + `/build`. New interface gets a test proving the old callers still work. ## WHEN TO STOP Done when the chosen module's interface is strictly smaller, its hidden decision no longer leaks, tests are green, and §I/§V record the new shape. One module deepened beats five churned. Budget left → pick the next shallowest, fresh pass. ## BOUNDARIES - ⊥ change behavior. Green before, green after. Pure structure. - ⊥ write SPEC.md. Propose §I/§V/§T; spec writes. - ⊥ deepen more than one module per pass. - ⊥ run under deadline or mid-feature. This is the spare-budget pass. - ⊥ add abstraction for single-use code. A deep module earns its hiding; a speculative one is just more surface.