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.
